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) providing iron powder, 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) providing phosphoric acid to react 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.

Description

Technical Field

[0001] The present invention relates to a preparation method, particularly to a preparation method of an iron 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 energy sources, chemical batteries are the technologies actively researched and developed in the industry. With the continuous investment in research and development by 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, etc.

[0003] Among them, the lithium iron phosphate (LiFePO 4 , abbreviated as LFP) composite material battery is 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 it has no explosion risk and has 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 it 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, so it 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 iron phosphate (FePO 4 ), lithium hydroxide (LiOH), and lithium carbonate (Li 2 CO 3 ). Among them, the morphology of the iron phosphate precursor before reacting with lithium hydroxide (LiOH) and lithium carbonate (Li 2 CO 3 ) has a greater impact on the production efficiency of the final lithium iron phosphate compound. Since the iron phosphate precursor is mainly prepared by reacting iron with phosphoric acid, the reaction process needs to consider the reaction rate, exothermic effect, and the difficulty of process operation, and the conversion rate of the obtained iron phosphate precursor seriously affects the product quality.

[0005] In view of this, how to provide a preparation method of an iron 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 at present. Summary of the Invention

[0006] The main purpose of this case is to provide a preparation method for 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 purpose of this case is to provide a preparation method for iron phosphate precursor for batteries. By controlling the specifications of raw material iron powder, the preparation reaction of iron phosphate precursor is optimized to avoid the too-fast reaction rate that increases the difficulty of process operation. On the other hand, in the secondary reaction of phosphoric acid, deionized water, and iron powder, phosphoric acid is added dropwise to the iron powder aqueous solution mixed with iron powder and water, avoiding the too-fast reaction rate between phosphoric acid and iron powder, which causes the aqueous solution to heat up too fast and too high, affecting the product quality of iron phosphate precursor. In addition, when the iron powder reactant has not completely reacted, the amorphous iron phosphate coating attached to the surface of the iron powder reactant can be removed by cooperating with the grinding process, enabling the iron powder reactant to come into contact with phosphoric acid again and fully react, so as to effectively reduce the waste of raw materials and comprehensively improve the conversion rate of iron phosphate precursor.

[0008] Another purpose of this case is to provide a preparation method for iron phosphate precursor for batteries. By adopting the dropwise addition method in the secondary reaction of phosphoric acid, deionized water, and iron powder, a relatively gentle reaction rate enables phosphoric acid and iron powder to fully react, so as to effectively reduce the waste of raw materials and comprehensively improve product quality. Moreover, a large amount of hydrogen gas will not be generated at one time during the reaction between phosphoric acid and iron powder, and the safety is better. In addition, adopting the dropwise addition method can also avoid the violent hydration reaction during the reaction, which causes the raw materials to become viscous and results in poor operability. Combining with the preparation method of iron phosphate precursor to further form a battery composite material can greatly 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 purpose, a broader implementation aspect of this case is to provide a preparation method for iron phosphate precursor for batteries, including the steps of: (a) providing an 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) providing a phosphoric acid, reacting 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 an embodiment, the iron powder has 700 cm 2from / g to 1300 cm 2 The BET surface area within the range of / 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 a 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, mixing iron powder with deionized water to form an iron powder aqueous solution; (b12) in a second temperature environment, adding phosphoric acid in a first quantitative amount at a titration rate to react with the iron powder aqueous solution, and after reaching the second temperature, cooling to a third temperature and maintaining for a first time; and (b13) cooling to a fourth temperature and adding phosphoric acid having a second quantitative amount, and continuously reacting the phosphoric acid with the iron powder aqueous solution for a second time to generate a first product.

[0015] In one embodiment, the weight ratio of the first quantitative amount to the second quantitative amount is greater than 2.5.

[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 Celsius, and the fourth temperature is below 35 °C.

[0017] In one embodiment, the phosphoric acid has a concentration of 85 wt.%, and the titration rate range is 10 ml / min to 40 ml / min.

[0018] In one embodiment, the first time is at least 3 hours, and the second time is between 5 hours and 9 hours.

[0019] In one embodiment, step (b) further includes the steps of: (b21) performing a first grinding to make the D99 particle size of the first product less than a first length; and (b22) continuously reacting for a third time.

[0020] In one embodiment, the first length is less than 100 μm, and the range of the third time is between 6 hours and 12 hours.

[0021] In one embodiment, step (b) further includes the steps of: (b31) adding a carbon source and a metal compound to react with the first product to form a precursor solution, and performing a second grinding; and (b32) when the particle D70 particle size in the precursor solution is less than a second length during the second grinding, performing a spray drying operation on the precursor solution.

[0022] In one embodiment, the spray drying operation is implemented by 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.

[0023] In one embodiment, the second length ranges between 1 μm and 10 μm.

[0024] In one embodiment, the rotation speed ranges of the first grinding and the second grinding are from 450 revolutions per minute to 650 revolutions per minute.

[0025] In one embodiment, the 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.

[0026] 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).

[0027] 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

[0028] Figure 1 It is a flowchart of the preparation method of the iron phosphate precursor for batteries of the preferred embodiment of this case.

[0029] Figure 2 It is a detailed flowchart of the preparation method of the iron phosphate precursor for batteries of this case.

[0030] Figure 3 It discloses the titration device used in the preparation method of the iron phosphate precursor for batteries of this case.

[0031] Figure 4 It is another detailed flowchart of the preparation method of the iron phosphate precursor for batteries of this case.

[0032] Figure 5It is a detailed flowchart of a method for preparing a lithium iron phosphate precursor for a battery combined with a battery composite material in this case.

[0033] Figure 6 It is another detailed flowchart of a method for preparing a lithium iron phosphate precursor for a battery combined with a battery composite material in this case. Specific embodiments

[0034] Some exemplary embodiments that embody 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 variations in different aspects, all of which do not depart from the scope of this case, and the descriptions and drawings therein are essentially for illustrative purposes and not 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 in which the above-mentioned first feature and the above-mentioned second feature are in direct contact, and also includes embodiments in which 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 symbols and / or labels may be used in different embodiments of this disclosure. These repetitions are for the purpose of simplicity 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 of 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 may be referred to as the second component, and similarly, the second component may 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 herein 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 ordinary rounding principles. Ranges can be expressed in this document as from one endpoint to the other or between two endpoints. All ranges disclosed herein include the endpoints unless otherwise specified.

[0035] Please refer to Figure 1 , which is a flowchart of a method for preparing a lithium iron phosphate precursor for a battery in a preferred embodiment of this case. AsFigure 1 As shown, the method for preparing the battery composite material in this case includes the following steps: First, as shown in step S100, iron powder is provided. The chemical formula of the 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 an overly fast reaction rate, which may increase the process operation difficulty or cause safety problems. 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 and a fine powder with iron powder ≤ 45 μm accounting for 10% to 30% of the total weight of the iron powder can be obtained 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 fine powder with 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 a coarse powder range and a fine powder range by screening, for example. Hereinafter, the first particle size range and the second particle size range are respectively described by the coarse powder obtained by sieving less than 212 μm and greater than 45 μm and the fine powder ≤ 45 μm, but this case is not limited thereto.

[0036] Secondly, as shown in step S200, phosphoric acid is provided. The chemical formula of the phosphoric acid is H 3 PO 4 , and the phosphoric acid is reacted with the iron powder 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.

[0037] Then, as shown in step S300, the first product is calcined in an air or oxygen atmosphere to produce 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, the present case is not limited thereto.

[0038] Please refer to Figure 2 and in conjunction with Figure 1 , where Figure 2 is a detailed flowchart of one of the methods for preparing the iron phosphate precursor for the battery in this case. As Figure 1 and Figure 2 shown, the detailed process of step S200 of the method for preparing the iron phosphate precursor for the battery in this case includes the steps: As shown in step S201, in a first temperature environment, for example, in an environment preheated to 35°C to 45°C, iron powder is mixed with deionized water to form an iron powder aqueous solution. In one embodiment, an environment preheated to 42°C is preferred, but not limited thereto. Then, as shown in step S202, in a second temperature environment, a first quantitative amount of phosphoric acid is added dropwise to the iron powder aqueous solution for reaction at a titration rate, and after reaching the second temperature, it is cooled to a third temperature and maintained for a first time. According to the concept of this case, other compounds that release phosphate ions in the aqueous solution after mixing can also be used for titrating the iron powder aqueous solution, and the present case is not limited thereto. In this embodiment, phosphoric acid has a concentration of 85 wt.%, and the titration rate range is 10 ml / min to 40 ml / min. In other embodiments, the phosphoric acid concentration is not limited to 85 wt.%, and the titration rate can vary according to mass production requirements, and the present case is not limited thereto. Additionally, the second temperature can be 60°C or below, preferably 60°C, and the third temperature can be 50°C or below, preferably 35°C. As for the first time, it is at least 3 hours, preferably 3 hours.

[0039] In one embodiment, the preferred step S202 is: controlling the titration rate of 85 wt.% phosphoric acid added to the iron powder aqueous solution to be completed within a titration time of 1 hour to 3 hours. The titration and digestion of the iron powder aqueous solution with phosphoric acid can be adjusted according to the reaction temperature, pH value, or gelling state. Reacting the iron powder aqueous solution with a first quantitative amount of phosphoric acid by titration, and cooling it after the reaction temperature reaches 60°C. After the first quantitative amount of phosphoric acid titration is completed or the peptization is completed, it is cooled to 35°C and held at that temperature for 3 hours, but not limited thereto. Then, as shown in step S203, it is cooled to a fourth temperature, and a second quantitative amount of phosphoric acid is added, and the phosphoric acid and the iron powder aqueous solution continue to react for a second time to produce the first product.

[0040] It should be noted that the device used for operating the titration of the iron powder aqueous solution with the first quantitative amount of phosphoric acid needs to consider both safety and operability to avoid generating a large amount of hydrogen gas at one time.Figure 3 Disclosed is a titration device used in the preparation method of the iron phosphate precursor for the battery in this case. As shown in the figure, the titration device 1 includes a tank body 10, a stirring module 20, and two feeding modules 30. The tank body 10 is, for example, a reaction tank with a water jacket for temperature control, configured to provide a space for accommodating the iron powder aqueous solution L and carry out the titration reaction. A baffle 11 is provided on the inner peripheral wall of the tank body 10 to cooperate with the stirring operation of the stirring module 20 to uniformly mix the reactants. Phosphoric acid T is titrated into the iron powder aqueous solution L through the two feeding modules 30. The feeding module 30 is composed of a feeding pipe 31 and a peristaltic pump 32. The feeding pipe 31 is, for example, fixed to the baffle 11 and communicated to the bottom layer of the tank body 10. Driven by the peristaltic pump 32, phosphoric acid T can be introduced into the iron powder aqueous solution L from the bottom layer of the tank body 10 at a stable titration rate. In one embodiment, the titration of the iron powder aqueous solution L with the first quantitative phosphoric acid T can be completed within 1 hour, with only bubbles appearing throughout the process and no gelling phenomenon, and the operability is significantly improved. Of course, the number and setting method of the feeding module 30 can be adjusted according to actual application requirements, and this case is not limited thereto.

[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 below 30 °C, preferably 30 °C, the second time is 5 to 9 hours, and the weight ratio of the first quantitative to the second quantitative is greater than 2.5. For example, the weight ratio of the first quantitative to the second quantitative is 3, that is, the first quantitative is 75% and the second quantitative is 25%. Of course, this case is not limited thereto.

[0042] Please refer to Figure 4 and cooperate with Figure 1 where Figure 4 is another detailed flowchart of the preparation method of the iron phosphate precursor for the battery in this case. As shown in Figure 1 and Figure 4 shown, the detailed process of step S200 in the preparation method of the iron phosphate precursor for the battery in this case further includes the steps: as shown in step S211, after the aforementioned reaction lasts for 5 to 9 hours, a first grinding is carried out to make the particle D99 diameter of the first product less than a first length. Then, as shown in step S212, the reaction is continued for a third time to promote the reaction and make the reaction between phosphoric acid and iron powder more complete. In this embodiment, the iron powder has a specific specification. Although the powdered metal has the characteristic of a fast reaction rate, it is also easy to form a barrier on the powder surface due to the too fast reaction rate. In this embodiment, when the iron powder has not completely reacted with phosphoric acid, by appropriately removing the amorphous iron phosphate coating attached to the surface of the iron powder through the grinding action, the iron powder reactant can be made to contact phosphoric acid again, making the overall reaction more complete. Of course, in other embodiments, the action of the first grinding in step S211 can also be omitted, and this case is not limited thereto.

[0043] In this embodiment, the first length is less than 100 μm, and the range of the third time is between 6 hours and 12 hours. In this embodiment, the first grinding is performed, for example, at the first rotation speed, and the first rotation speed is 450 revolutions per minute to 650 revolutions per minute (450 rpm to 650 rpm), and preferably 550 revolutions per minute (550 rpm). 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 be further applied to the preparation of the battery composite material. Figure 5 It is a detailed flowchart of one of the preparation methods of the iron phosphate precursor for the battery in this case combined with the battery composite material.

[0045] Figure 6 It is another detailed flowchart of the preparation method of the iron phosphate precursor for the battery in this case combined with the battery composite material. 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 after the above-mentioned phosphoric acid solution and iron powder fully react, so that the carbon source, metal compound and the first product generate a precursor solution, and a second grinding is performed. In this embodiment, the carbon source is, for example, saccharides, organic compounds, polymers or macromolecular materials. In some embodiments, the saccharides can be, for example but not limited to, fructose, sucrose, lactose, galactose, etc., and the macromolecular materials can be, for example but not limited to, polyvinylpyrrolidone (PVP, chemical formula (C 6 H 9 NO) n ). In this embodiment, the metal compound can be lithium carbonate (chemical formula 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 thereto.

[0046] Thereafter, as shown in step S222, when the D70 particle size of the particles in the precursor solution is less than a second length during the second grinding, a spray drying operation is performed on the precursor solution. In this embodiment, the rotation speed range of the second grinding can be the same as that of the aforementioned first grinding, between 450 and 650 revolutions per minute. The second length ranges from 1 μm to 10 μm. In this embodiment, the spray drying operation is implemented 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 ranges from 300 Hz to 400 Hz, but it is not limited thereto. In this embodiment, the addition of the carbon source is mainly used to block the growth of grains and avoid excessive melting. The dispersant used in the conventional spray drying operation is a dispersant containing metal ions, and in this case, the carbon source is used to replace the conventional dispersant. Since the carbon source is an organic compound, in addition to serving as an auxiliary function of the dispersant, it can be removed by subsequent calcination in air or oxygen, without residual other metal cations, which can further improve the purity of the product. Of course, this case is not limited thereto.

[0047] As shown in step S301, the metal compound and the iron phosphate precursor after spray drying are calcined at a high temperature. In this embodiment, the metal compound and the iron phosphate precursor after spray drying are placed in an air or oxygen atmosphere, first held at 325 °C for 0.5 hours, then held at 550 °C for 0.5 hours and held 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 2 O 5 , MgO, etc. can also be added in step S221, and then a LiFePO 4 material containing metal oxides can be obtained. The LiFePO 4 material containing metal oxides can be called "nano metal oxide co-crystallized lithium iron phosphate compound (LFP-NCO)".

[0048] It can be seen that in the secondary reaction of phosphoric acid, deionized water and iron powder in this case, phosphoric acid is added to the iron powder aqueous solution mixed with iron powder and water by titration to avoid too fast reaction rate between phosphoric acid and iron powder, resulting in too fast and too high temperature rise of the aqueous solution and affecting the product quality of the iron phosphate precursor. At the same time, the rate of hydrogen generation and the occurrence of hydration reaction can be slowed down, which improves both safety and the operability of raw materials. On the other hand, by further forming a battery composite material in combination with the preparation method of the iron phosphate precursor, the grinding time required can be significantly shortened, thereby reducing the unit time and cost. At the same time, it is also possible to combine the above-mentioned many parameter changes to reduce the pH value sensitivity of the process, avoid raw material viscosity and pipeline blockage, and stably control the process temperature, thereby reducing the operation difficulty of the process and the production line.

[0049] The following will use exemplary embodiments to assist in explaining the preparation method of the iron phosphate precursor for batteries in this case.

[0050] Demonstration Example 1

[0051] First, 9000 ml of deionized water and 2476 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 iron powder is mixed with deionized water to form an iron powder aqueous solution, and the iron powder aqueous solution is heated to an environment of 42 °C. Phosphoric acid with a first quantitative amount of 3760 grams (purity above 85%) is added to the iron powder aqueous solution at a titration rate of 37 ml / min for reaction. The reaction reaches 60 °C in about 54 minutes. When the reaction temperature reaches 60 °C or above, cooling is carried out to avoid too fast reaction and incomplete reaction of the iron powder with phosphoric acid. After the first quantitative amount of phosphoric acid is titrated within 1 hour and the peptization is completed, it can be cooled to 35 °C. Then, a second quantitative amount of 1467 grams of phosphoric acid can be directly added, stirred and left standing for 24 hours to allow the iron powder and phosphoric acid in the aqueous solution to fully react to form the first product. The aqueous solution containing the first product is spray-dried and then calcined at a temperature range of 610 °C to 670 °C for at least one hour to obtain the iron phosphate precursor, FePO 4 .

[0052] Demonstration Example 2

[0053] First, 9000 ml of deionized water and 2476 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 3The 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 iron powder is mixed with deionized water to form an iron powder aqueous solution, and the iron powder aqueous solution is heated to an environment of 42°C. Phosphoric acid (with a purity of over 85%) with a first quantitative amount of 3760 grams is added to the iron powder aqueous solution at a titration rate of 12.4 ml / min for reaction. The highest temperature of 56.9°C is reached in about 146 minutes. After the first quantitative amount of phosphoric acid is titrated within 3 hours, the temperature can be lowered to 35°C. Then, the second quantitative amount of 1467 grams of phosphoric acid can be directly added, stirred, and left standing for 24 hours to allow the iron powder and phosphoric acid in the aqueous solution to fully react to form the first product. The aqueous solution containing the first product is spray-dried and then calcined at a temperature range of 610°C to 670°C for at least one hour to obtain the iron phosphate precursor, FePO 4 。

[0054] Comparative Example 1

[0055] First, 9000 ml of deionized water and 2476 grams of iron powder (with a purity of over 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 iron powder is mixed with deionized water to form an iron powder aqueous solution, and the iron powder aqueous solution is heated to an environment of 42°C. A first quantitative amount of 3760 grams of phosphoric acid (with a purity of over 85%) is added to the iron powder aqueous solution at one time for reaction. The reaction reaches 60°C in about 9 minutes. When the reaction temperature reaches 60°C or above, the temperature is lowered to avoid the reaction being too fast and the iron powder not fully reacting with the phosphoric acid. After peptization is completed, the temperature can be lowered to 35°C. Then, the second quantitative amount of 1467 grams of phosphoric acid can be directly added, stirred, and left standing for 24 hours to allow the iron powder and phosphoric acid in the aqueous solution to fully react to form the first product. The aqueous solution containing the first product is spray-dried and then calcined at a temperature range of 610°C to 670°C for at least one hour to obtain the iron phosphate precursor, FePO 4 。

[0056] In the heating reaction after the first quantitative amount of phosphoric acid is added to the iron powder aqueous solution, it takes about 9 minutes for Comparative Example 1 to reach 60°C. It takes about 54 minutes for Example 1 to reach 60°C. It takes about 146 minutes for Example 2 to reach the highest temperature of 56.9°C. In other words, in the reaction of titrating the iron powder aqueous solution with the first quantitative amount of phosphoric acid, the time required to reach 60°C (or the highest temperature) is negatively correlated with the titration rate.

[0057] In this embodiment, after the titration of the first quantitative phosphoric acid in Demonstration Example 1 was completed within 1 hour for the iron powder aqueous solution, the pH value rose back to a relatively high value, indicating that the consumption of the first quantitative phosphoric acid in Example 1 was relatively complete. After adding the second quantitative phosphoric acid, the pH value changed in the same way, and the rise of the pH value in Demonstration Example 1 was better than that in Demonstration Example 2. In other embodiments, the stability of the pH value is not limited to being controlled by the titration rate. Of course, the phosphoric acid titration rate and the total titration duration can be adjusted according to actual application requirements and are related to the titration device.

[0058] As can be seen from the above, in the preparation method of the iron phosphate precursor for the battery in this case, by controlling the specifications of the raw material iron powder, the phosphoric acid can be added to the iron powder aqueous solution mixed with iron powder and water in a safe manner by titration. The titration time is controlled to be completed within 1 hour, and the reaction between phosphoric acid and iron powder can be realized at an optimized reaction rate, achieving the purposes of improving product quality and reducing raw material, time costs, and the difficulty of process operation. Furthermore, the amorphous iron phosphate formed by the iron phosphate precursor can be ground with a carbon source as a dispersant to adjust the viscosity and reduce the difficulty of process operation. Through the secondary reaction of phosphoric acid, deionized water, and iron powder, the phosphoric acid and iron powder can react fully. Once combined with the preparation method of the iron phosphate precursor to further form a battery composite material, the grinding time required can be significantly shortened, thereby reducing the unit time and cost. At the same time, the sensitivity of the process pH value can be reduced, the adhesion of raw materials and pipeline blockage can be avoided, and the process temperature can be stably controlled by combining the above-mentioned parameter changes, 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.

[0059] In summary, the present case provides a method for preparing iron phosphate precursor for batteries to improve product quality and reduce raw material, time costs, and the difficulty of process operation. By controlling the specifications of the raw iron powder, the preparation reaction of the iron phosphate precursor is optimized to avoid an overly fast reaction rate that would increase the difficulty of process operation. On the other hand, in the secondary reaction of phosphoric acid, deionized water, and iron powder, the phosphoric acid is added dropwise to the iron powder aqueous solution formed by mixing iron powder and water, avoiding an overly fast reaction rate between the phosphoric acid and the iron powder, which would cause the aqueous solution to heat up too quickly and too high, affecting the product quality of the iron phosphate precursor and rapidly generating a large amount of hydrogen, resulting in poor safety. In addition, in the case where the iron powder reactant has not fully reacted, the amorphous iron phosphate coating attached to the surface of the iron powder reactant can also be removed by cooperating with a grinding process, enabling the iron powder reactant to come into contact with the phosphoric acid again and react fully, effectively reducing waste of raw materials and comprehensively improving the conversion rate of the iron phosphate precursor. Moreover, through the secondary reaction of phosphoric acid, deionized water, and iron powder, the phosphoric acid and the iron powder can react fully, effectively reducing 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 significantly shorten the grinding time required, thereby reducing the unit time and cost. At the same time, it can also reduce the sensitivity of the process pH value, avoid raw material viscosity and pipeline blockage, and stably control the process temperature, thereby reducing the operation difficulty of the process and the production line.

[0060] 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, all such modifications do not depart from the scope as claimed in the appended patent application.

[0061] Symbol Explanation

[0062] 1: Titration device

[0063] 10: Tank

[0064] 11: Baffle

[0065] 20: Stirring module

[0066] 30: Feeding module

[0067] 31: Feeding pipe

[0068] 32: Peristaltic pump

[0069] L: Iron powder aqueous solution

[0070] T: Phosphoric acid

[0071] 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 an 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) providing phosphoric acid to react 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) mixing the iron powder with deionized water in a first temperature environment to form an iron powder aqueous solution; (b12) adding a first amount of phosphoric acid to the iron powder aqueous solution at a titration rate in a second temperature environment to react, and after reaching the second temperature, cooling to a third temperature and maintaining it for a first time; and (b13) cooling the mixture to a fourth temperature, adding a second amount of phosphoric acid, and allowing the phosphoric acid and the iron powder aqueous solution 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 greater than 2.

5.

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 35°C. 9 . The method for preparing an iron phosphate precursor for a battery as claimed in claim 6 , wherein the phosphoric acid has a concentration of 85 wt %, and the titration rate ranges from 10 ml / min to 40 ml / min. 10 . 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.

11. 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: (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. 12 . The method for preparing an iron phosphate precursor for a battery as claimed in claim 11 , wherein the first length is less than 100 μm, and the third time ranges from 6 hours to 12 hours.

13. The method for preparing an iron phosphate precursor for a battery as claimed in claim 11, 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.

14. The method for preparing an iron phosphate precursor for a battery as claimed in claim 13, 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. 15 . The method for preparing an iron phosphate precursor for a battery as claimed in claim 13 , wherein the second length range is between 1 μm and 10 μm. 16 . The method for preparing an iron phosphate precursor for a battery as claimed in claim 13 , wherein the rotation speed of the first grinding and the second grinding ranges from 450 to 650 revolutions per minute.

17. The method for preparing an iron phosphate precursor for a battery as claimed in claim 13, wherein the metal compound and the iron phosphate precursor form an iron phosphate precursor composite material in 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.

18. The method for preparing an iron phosphate precursor for a battery as claimed in claim 17, 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).

19. The method for preparing an iron phosphate precursor for a battery as claimed in claim 17, 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.

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