Preparation method of iron phosphate material, iron phosphate material, positive plate and battery

Abstract

The invention provides a preparation method of an iron phosphate material, the iron phosphate material, a positive plate and a battery, and the method comprises the following steps: carrying out slurrying treatment on a first mixed solution containing amorphous iron phosphate, phosphoric acid and water to obtain slurried slurry; the pH value of the first mixed solution is 0.5-1; carrying out primary aging treatment on the pulpified slurry, and carrying out first solid-liquid separation to obtain a first solid product; carrying out secondary aging treatment on a second mixed solution containing the first solid product, phosphoric acid and water, and carrying out secondary solid-liquid separation to obtain a second solid product; the pH value of the second mixed solution is 2.0-2.5; and roasting the second solid product to obtain the iron phosphate material. Slurrying is performed in a high-acid-content atmosphere with the pH value being 0.5-1, so that particles are refined, and the particles are kept uniform; in the primary aging process, primary aging is carried out under the high acid content of 0.5-1, fine iron phosphate crystal nucleuses are generated, and the particle size can be reduced and the particle size uniformity can be kept.

Description

Technical Field

[0001] This invention relates to the field of batteries, and more particularly to a method for preparing iron phosphate material, as well as the iron phosphate material, positive electrode sheet, and battery. Background Technology

[0002] With the widespread application of lithium iron phosphate cathode materials in energy storage and power batteries, improving the energy density and cycle stability of lithium iron phosphate has become a key research focus.

[0003] The performance of lithium iron phosphate (LFP) materials is mainly affected by factors such as particle size, particle distribution, and iron-to-phosphorus ratio. With the increasing demand for LFP materials with higher compaction density and higher charge / discharge capacity, higher requirements are being placed on the properties of LFP. Small-particle, narrow-distribution LFP materials have significant advantages in improving capacity and cycle stability. Small particles increase the battery surface area, promoting rapid lithium-ion insertion and extraction, thereby improving charge / discharge efficiency. Narrow distribution helps maintain particle uniformity, avoiding capacity degradation and battery performance instability caused by excessively large or unevenly distributed particles.

[0004] Therefore, optimizing the preparation process of iron phosphate and preparing iron phosphate materials with narrow distribution and small particles is an urgent problem to be solved. Summary of the Invention

[0005] This invention provides a method for preparing iron phosphate material, which optimizes the preparation process of iron phosphate to obtain iron phosphate material with narrow distribution and small particles.

[0006] In a first aspect, this application provides a method for preparing an iron phosphate material, the method comprising the following steps:

[0007] A first mixture comprising amorphous iron phosphate, phosphoric acid, and water is subjected to a slurry treatment to obtain a slurry; wherein the pH of the first mixture is 0.5-1;

[0008] The slurry is subjected to an aging process, followed by a first solid-liquid separation to obtain a first solid product.

[0009] The second mixture, comprising the first solid product, phosphoric acid, and water, is subjected to a second aging treatment, followed by a second solid-liquid separation to obtain the second solid product; wherein the pH of the second mixture is 2.0-2.5.

[0010] The second solid product is calcined to obtain the iron phosphate material.

[0011] Furthermore, the solid content of the slurry is 7-25%.

[0012] Furthermore, the solid content of the second mixture is 2-7%.

[0013] Furthermore, the pulping treatment time is 2-6 hours, and / or the pulping treatment temperature is ≤50℃.

[0014] Furthermore, the temperature of the first aging treatment is 91-95℃; and / or the time of the first aging treatment is 0.5-1h.

[0015] Furthermore, the temperature of the secondary aging treatment is 95-98℃; and / or the time of the secondary aging treatment is 2-6 hours.

[0016] Furthermore, the preparation method further includes: washing the second solid product until the conductivity of the washing liquid after washing is less than or equal to 1000 μs / cm, and then subjecting the second solid product to the calcination treatment.

[0017] And / or, the calcination temperature is 600-800℃, and the calcination time is 1-3h.

[0018] Furthermore, the preparation process of the amorphous iron phosphate includes:

[0019] A third mixture comprising an iron source, a phosphorus source, and an oxidant is reacted to obtain the amorphous iron phosphate; wherein the reaction temperature is 50-60℃ and the reaction time is 10-30 min.

[0020] Secondly, this application provides an iron phosphate material, which is prepared according to the preparation method described in any one of the first aspects.

[0021] Furthermore, the particle size of the iron phosphate material is 30–90 nm.

[0022] Thirdly, this application provides a method for preparing lithium iron phosphate, the method comprising:

[0023] Lithium iron phosphate is prepared by sintering a mixture of the iron phosphate material described in the second aspect and a lithium source.

[0024] Fourthly, this application provides a lithium iron phosphate cathode material, wherein the lithium iron phosphate cathode material comprises lithium iron phosphate formed by sintering a mixture of the iron phosphate material described in the second aspect and a lithium source.

[0025] Fifthly, this application provides a positive electrode sheet, including the lithium iron phosphate positive electrode material described in the fourth aspect.

[0026] Sixthly, this application provides a battery including the positive electrode sheet described in the fifth aspect.

[0027] This application provides a method for preparing ferric phosphate material, comprising the following steps: a first mixture comprising amorphous ferric phosphate, phosphoric acid, and water is subjected to slurry treatment to obtain a slurry; wherein the pH of the first mixture is 0.5-1; the slurry is subjected to a first aging treatment, followed by a first solid-liquid separation to obtain a first solid product; a second mixture comprising the first solid product, phosphoric acid, and water is subjected to a second aging treatment, followed by a second solid-liquid separation to obtain a second solid product; wherein the pH of the second mixture is 2.0-2.5; the second solid product is calcined to obtain the ferric phosphate material. Maintaining the pH of the first mixture at 0.5-1 and performing slurrying under a high acidity atmosphere refines the ferric phosphate particles, facilitating aging, crystallization, and dispersion, and maintaining particle uniformity. Maintaining the same pH as the slurrying during the first aging, and performing aging under high acidity, generates more fine ferric phosphate crystal nuclei, which helps reduce particle size and maintain particle size uniformity. Attached Figure Description

[0028] Figure 1 A process flow diagram of the preparation method of the iron phosphate material provided in this application;

[0029] Figure 2 SEM image of the iron phosphate material of Example 1 provided in this application;

[0030] Figure 3 SEM image of the iron phosphate material of Comparative Example 1 provided in this application. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0032] Traditional processes for preparing iron phosphate are not conducive to obtaining iron phosphate with narrow distribution and small particles, which can affect battery performance. Therefore, there is an urgent need for a preparation process for iron phosphate materials with narrow distribution and small particles.

[0033] In view of this, this application lowers the pH of the mixed solution before pulping amorphous ferric phosphate to 0.5-1, and refines the pulping particles under a high-acid atmosphere, facilitating aging, crystallization, and dispersion, and maintaining particle uniformity. The aging process after pulping is divided into two steps: primary aging and secondary aging. The first aging is controlled at a low pH to maintain uniform small particles; the second aging is carried out under acidic conditions to increase the pH, accelerate crystallization, and form narrowly distributed, small-particle ferric phosphate.

[0034] Figure 1 The process flow diagram for the preparation method of the iron phosphate material provided in this application is as follows: Figure 1 As shown, the preparation method includes the following steps:

[0035] S1. A first mixture comprising amorphous iron phosphate, phosphoric acid and water is subjected to a pulping treatment to obtain a pulped slurry; wherein the pH of the first mixture is 0.5-1.

[0036] S2. The pulped slurry is aged once, and then subjected to the first solid-liquid separation to obtain the first solid product.

[0037] S3. The second mixture, which includes the first solid product, phosphoric acid, and water, is subjected to a second aging treatment, followed by a second solid-liquid separation to obtain the second solid product; wherein the pH of the second mixture is 2.0-2.5.

[0038] S4. The second solid product is calcined to obtain iron phosphate material.

[0039] In step S1, the preparation method of amorphous iron phosphate is not limited. It can be prepared by iron source and phosphorus source, or it can be purchased from the market.

[0040] The first mixture uses water as a solvent, and the amorphous iron phosphate is partially dissolved in water, resulting in the presence of amorphous iron phosphate particles in the mixture. Phosphoric acid is used as the acid source to adjust the pH in the first mixture, thus avoiding the introduction of additional impurities.

[0041] The first mixture undergoes a slurry treatment, which can be achieved through stirring and / or ultrasonic vibration. During the slurry treatment, an equilibrium is reached between the dissolution and precipitation of ferric phosphate in the mixture, resulting in the amorphous ferric phosphate particles becoming smaller.

[0042] The pH of the first mixture is 0.5-1. In a highly acidic environment, the solubility of amorphous iron phosphate particles increases, allowing more iron phosphate particles to precipitate from the first mixture, thereby reducing the size of the iron phosphate particles while maintaining particle size uniformity. Specifically, the pH of the first mixture can be 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, or any combination of two of these values.

[0043] In step S2, the high-acid slurry is aged once. Compared with the low-acid slurry, more iron phosphate is dissolved in the water, and more fine iron phosphate crystals can be generated during aging.

[0044] In step S3, the pH of the second mixture is adjusted to 2.0-2.5 using phosphoric acid before a second aging process. During this second aging process, the relatively higher pH accelerates the crystal transformation of ferric phosphate, allowing it to grow on the basis of the fine ferric phosphate crystal nuclei generated in S2, ultimately yielding the second solid product. Specifically, the pH value of the second mixture can be 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, or any combination of two of these values.

[0045] In step S4, during the calcination process, the iron phosphate crystals of the second solid product are subjected to high temperature, causing the atoms inside the crystals to rearrange and form a more regular and compact lattice structure. In addition, the fine crystals fuse together, changing the size and shape of the iron phosphate particles.

[0046] The above preparation method, using an acid level of pH 0.5-1 for pulping, can reduce the size and uniformity of iron phosphate particles. A single aging treatment under the same acid level can generate fine iron phosphate crystal nuclei, thereby reducing the particle size after secondary aging, and ultimately reducing the particle size of the iron phosphate material obtained after calcination.

[0047] In some embodiments, the pulping temperature is ≤50°C, for example, 5°C, 10°C, 20°C, 30°C, 40°C, 50°C, or any combination of two of the above values. The pulping temperature is controlled at 50°C or below to ensure that aging and crystallization do not occur during the pulping process.

[0048] In some embodiments, the pulping treatment time is 2-6 hours, for example, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, or any combination thereof. A pulping treatment time greater than 2 hours ensures sufficient dispersion and reaction of the amorphous iron phosphate particles, preventing uneven particle distribution in the slurry. A pulping treatment time less than 6 hours avoids particle agglomeration caused by excessively long pulping times, maintaining the slurry's fluidity and uniform particle distribution. Therefore, controlling the pulping treatment time to 2-6 hours can reduce particle agglomeration.

[0049] In some embodiments, the stirring speed during the slurry treatment is 20-45 Hz, such as 20 Hz, 30 Hz, 40 Hz, 45 Hz, or any combination thereof. Stirring at a speed of 20-45 Hz allows the amorphous ferric phosphate to fully contact the water, resulting in a dissolution and precipitation reaction, which helps disperse the particles and reduces particle agglomeration.

[0050] In some embodiments, the temperature for the primary aging process is 91-95°C, for example, 91°C, 92°C.

[0051] ℃, 93℃, 94℃, 95℃, or any combination of two of the above. Preliminary aging treatment is carried out in the temperature range of 91-95℃ to control the relatively slow growth rate of crystals and avoid the formation of large or inhomogeneous crystals.

[0052] In some embodiments, the aging time for a single aging process is 0.5-1 hour, for example, 0.5 hours, 0.6 hours, 0.7 hours, 0.8 hours, 0.9 hours, 1.0 hour, or any combination thereof. Performing an aging process within a short time of 0.5-1 hour ensures that fine and uniform iron phosphate grains are obtained in a single aging process.

[0053] In some embodiments, the secondary aging treatment temperature is 95-98°C, such as 95°C, 96°C, 7°C, 98°C, or any combination thereof. Temperatures between 95-98°C help accelerate crystal growth and optimize crystal size.

[0054] In some embodiments, the secondary aging process takes 2-6 hours, for example, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, or any combination thereof. A secondary aging time of 2 to 6 hours is sufficient to allow the reaction to proceed fully, resulting in adequate crystal growth and optimization.

[0055] In some embodiments, the heating rate to the temperature of the first aging treatment is 3°C / min to 6°C / min.

[0056] In some embodiments, the heating rate to the secondary aging treatment temperature is 3°C / min-6°C / min.

[0057] In some embodiments, the solids content of the slurry is 7%-25%, for example 7%, 10%, 15%, 20%, 25%, or any combination thereof. A higher slurry solids content of 7%-25% can reduce the amount of acid used. A higher slurry solids content of 7-25% also results in more crystal nuclei being generated during a single aging process, which is beneficial for forming more uniform and refined iron phosphate crystals.

[0058] In some embodiments, the solid content of the second mixture is 2%-7%, for example, 2%, 4%, 6%, 7%, or any combination thereof. During secondary aging, the solid content is reduced and maintained at 2-7%, which is beneficial for crystal growth on the initial crystal nuclei and for maintaining the uniformity of crystal size.

[0059] In some embodiments, after obtaining the second solid, the second solid product is first washed until the conductivity of the washing liquid is less than or equal to 1000 μs / cm, and then the second solid product is calcined. A conductivity of less than or equal to 1000 μs / cm after washing indicates that residual water-soluble impurities in the second solid have been removed, improving the purity of the iron phosphate material obtained by subsequent calcination.

[0060] Specifically, the calcination temperature is 600-800℃, such as 600℃, 700℃, 800℃, or any combination thereof. A calcination temperature between 600-800℃ promotes crystal recombination and optimization, resulting in a more stable and uniform crystal structure.

[0061] Specifically, the calcination time is 1-3 hours, such as 1 hour, 2 hours, 3 hours, or any combination thereof. A calcination time of 1-3 hours ensures that the reactants react fully at high temperatures and avoids excessive particle size caused by over-sintering.

[0062] In some embodiments, the second solid product is dried prior to calcination at a temperature of 90-120°C, such as 90°C, 100°C, 110°C, 120°C, or any combination thereof. The drying time is 6-18 hours, such as 6 hours, 10 hours, 14 hours, 18 hours, or any combination thereof. This drying process effectively removes moisture and volatile impurities, improves the reactivity and purity of the material, and ensures the uniformity and stability of the subsequent calcination process.

[0063] In some embodiments, a first solid product is obtained after a first solid-liquid separation. The first solid product is then washed until the pH of the washing solution is 2.0-2.5. This washing process removes water-soluble impurities and reduces the acidity of the first solid product.

[0064] In some embodiments, the preparation process of amorphous iron phosphate includes:

[0065] A third mixture containing an iron source, a phosphorus source, and an oxidant is reacted to obtain amorphous iron phosphate.

[0066] The reaction temperature is 50-60℃, for example, 50℃, 53℃, 56℃, 60℃, or any combination thereof. The reaction time is 10-30 minutes, for example, 10 minutes, 15 minutes, 20 minutes, 30 minutes, or any combination thereof. A temperature of 50-60℃ combined with a reaction time of 10-30 minutes helps to avoid crystallization and maintain the amorphous state.

[0067] The iron source provides iron ions, such as ferrous sulfate, ferric chloride, and ferric nitrate. Phosphoric acid provides phosphate ions, such as phosphoric acid and phosphates. The oxidizing agent is used to control the oxidation state of iron and maintain the ferric ion in the trivalent state, such as hydrogen peroxide.

[0068] In one specific implementation, ferrous salts are dissolved in pure water to form a solution a with a certain iron ion concentration; phosphate salts are dissolved in pure water, ammonia is added to adjust the pH, and then a certain amount of hydrogen peroxide is added to form a solution b with a certain phosphorus content. Solution a is used as the bottom liquid in a reaction vessel, heated to a certain temperature, and a certain amount of solution b is fed into the reaction vessel at a certain flow rate. The amount of solution b is calculated based on the amount of solution a. After feeding is completed, the temperature is maintained for a certain period of time to form the first slurry A. The first slurry A is filtered and washed until a certain conductivity is achieved to obtain amorphous ferric sulfate.

[0069] In solution a, the iron ion concentration is 6 ± 0.5%, and in solution b, the phosphorus content is 5 ± 0.5%, with a pH of 6-7. The amount of hydrogen peroxide used, expressed as hydrogen, is 1.2 times the molar amount of phosphorus in solution b.

[0070] The ratio of solution a to solution b is 1.05-1.10, the molar ratio of iron ions to phosphorus is 1.05-1.10, the reaction temperature is 50-60℃, the addition rate of solution b is 1kg / min, and the reaction is kept at this temperature for 15min.

[0071] The first slurry A is filtered and washed until the conductivity of the washing liquid is ≤2500μs / cm.

[0072] This application also provides an iron phosphate material, which is prepared according to any of the preparation methods described in the above embodiments.

[0073] The particle size of iron phosphate material is 30–90 nm. For example, 30 nm, 40 nm, 60 nm, 70 nm, 80 nm, 90 nm, or any combination of the above.

[0074] This application also provides a method for preparing lithium iron phosphate, the method comprising:

[0075] Lithium iron phosphate was prepared by sintering the mixture of the above-mentioned iron phosphate material and lithium source.

[0076] Specifically, the iron phosphate material, lithium salt (e.g., lithium carbonate or lithium hydroxide), and additives (e.g., conductive agents) are ball-milled. The mixture is then placed in a furnace for high-temperature sintering at a temperature between 600°C and 800°C.

[0077] This application also provides a lithium iron phosphate cathode material, which is lithium iron phosphate formed by sintering a mixture including the above-mentioned iron phosphate material and a lithium source.

[0078] In some embodiments, the lithium iron phosphate obtained by sintering the mixture of the above-mentioned iron phosphate material and lithium source can be subjected to surface modification or coating treatment.

[0079] This application also provides a positive electrode sheet, comprising the aforementioned lithium iron phosphate positive electrode material.

[0080] The positive electrode sheet of this application specifically includes a positive current collector and a positive active layer formed of lithium iron phosphate material disposed on the surface of the positive current collector.

[0081] In the specific preparation of the positive electrode sheet, for example, lithium iron phosphate, a conductive agent, and a binder can be dispersed in an appropriate amount of N-methylpyrrolidone (NMP) solvent, and thoroughly stirred to form a uniform positive electrode slurry. The positive electrode slurry is then uniformly coated onto the positive electrode current collector, and after drying, rolling, and slitting, the positive electrode sheet is obtained. In one specific embodiment, the positive electrode active layer comprises, by weight percentage, 70-99 wt% positive electrode active material, 0.5-15 wt% conductive agent, and 0.5-15 wt% binder; more specifically, it comprises 80-98 wt% positive electrode active material, 1-10 wt% conductive agent, and 1-10 wt% binder.

[0082] The positive current collector can be made of at least one of aluminum foil or nickel foil; the conductive agent can be selected from at least one of carbon black, acetylene black, graphene, Ketjen black, and carbon fiber; and the binder can be selected from at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, polyethylene, polypropylene, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, ethylene oxide-containing polymers, polyvinylpyrrolidone, and polyurethane.

[0083] This application also provides a battery including the above-described positive electrode.

[0084] It is conceivable that, in addition to the aforementioned positive electrode, the lithium-ion battery of the present invention also includes a negative electrode, an electrolyte, and a separator.

[0085] This application does not strictly limit the negative electrode active material in the negative electrode sheet. It can be at least one of the negative electrode active materials commonly used in lithium-ion batteries, such as graphite, hard carbon, soft carbon, mesophase carbon microspheres, silicon-based negative electrode materials (mainly including silicon suboxide and silicon-carbon negative electrode), and tin-based negative electrode materials (mainly including tin and tin alloy).

[0086] This application does not strictly limit the choice of electrolyte, which may include one or more solvents commonly used in lithium-ion battery electrolytes, as well as lithium salts commonly used in lithium-ion electrolytes. For example, the solvent may be ethylene carbonate, propylene carbonate, butene carbonate, fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), diethyl carbonate (DEC), difluoroethylene carbonate (DFEC), dipropyl carbonate, methyl ethyl carbonate (EMC), ethyl acetate, ethyl propionate, propyl acetate, propyl propionate, sulfolane, γ-butyrolactone, etc.; the lithium salt may be one or more of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

[0087] This application does not strictly limit the choice of separator material. It can be one of the separator materials commonly used in lithium-ion batteries, such as polypropylene separator (PP), polyethylene separator (PE), polypropylene / polyethylene double-layer composite membrane (PP / PE), polyimide electrospun separator (PI), polypropylene / polyethylene / polypropylene triple-layer composite membrane (PP / PE / PP), cellulose nonwoven separator, and separator with ceramic coating.

[0088] In the preparation of lithium-ion batteries, the positive electrode, separator, and negative electrode are wound or stacked to obtain a bare cell, which is then packaged into a pre-stamped aluminum-plastic film bag. After the packaged battery is dried at 85°C, the electrolyte is injected into the dried battery. The battery undergoes resting, formation, and secondary sealing to complete the preparation of the lithium-ion battery.

[0089] The present invention will be further described below through specific embodiments.

[0090] Example 1

[0091] The preparation method of the iron phosphate material in this embodiment includes the following steps:

[0092] 1) Preparation of reaction solution: Dissolve 10.21 kg of refined ferrous sulfate in 20.49 kg of pure water to obtain solution a with a ferrous ion content of 6.7%; add 4.06 kg of monoammonium phosphate to 13.78 kg of pure water, add 1.65 kg of 28% ammonia water to adjust the pH to 6.4, add 2.4 kg of 30% hydrogen peroxide, and stir to obtain solution b with a phosphorus content of 5.0%.

[0093] 2) Use the solution a obtained in step 1) as the bottom liquid of the reactor, heat it to 55°C, and start feeding solution b at a flow rate of 1 kg / min. After all the above solution b has been transferred, continue to keep it warm for 15 min to form the first slurry A.

[0094] 3) Filter and wash the slurry A obtained in step 2) until the conductivity of the final wash water is ≤2500μs / cm, and obtain 16kg of the first filter cake X.

[0095] 4) Add 16 kg of the first filter cake X obtained in step 3) into an aging kettle containing 21.8 kg of pure water and disperse it. Add 5.3 kg of 85% phosphoric acid and adjust the pH to 0.6 to form a second slurry B (i.e. the first mixture) with a solid content of 15%. Slurry it at 25°C and 25 Hz for 3 hours to obtain the slurry.

[0096] 5) After the pulping in step 4) is completed, the pulped slurry is heated to 93°C to start aging. After keeping it warm for 30 minutes, the filtration is started. The mother liquor from the filtration is collected separately to adjust the pH of the second filter cake pulping in step 6). It is washed with pure water until the pH of the final wash water is 2.3, and 16 kg of the second filter cake Y (i.e. the first solid) is obtained.

[0097] 6) Add 16 kg of the second filter cake Y (i.e., the first solid) obtained in step 5) to an aging kettle containing 144 kg of pure water and disperse to form a slurry with a solid content of 4%. At the same time, add 300 g of the mother liquor obtained in step 5) and adjust the pH to 2.1 to obtain the second mixture. Continue to heat to 97°C and keep warm for 2 hours to obtain the third slurry C.

[0098] 7) Filter and wash the third slurry C obtained in step 6) until the conductivity of the final wash water is ≤1000μs / cm to obtain filter cake Z (i.e., the second solid).

[0099] 8) After drying the filter cake Z obtained in step 7) at 105℃ for 12 hours, it is calcined in a muffle furnace at 700℃ for 2 hours and then mechanically crushed to obtain small-particle high-iron-phosphorus ratio iron phosphate material.

[0100] Example 2

[0101] The preparation steps of the iron phosphate material in this embodiment are basically the same as those in Example 1, except that the pH of the first mixture is adjusted to 0.5 by using phosphoric acid.

[0102] Example 3

[0103] The preparation steps of the iron phosphate material in this embodiment are basically the same as those in Example 1, except that the pH of the first mixture is adjusted to 0.8 by using phosphoric acid.

[0104] Example 4

[0105] The preparation steps of the iron phosphate material in this embodiment are basically the same as those in Example 1, except that the pH of the first mixture is adjusted to 1.0 by using phosphoric acid.

[0106] Example 5

[0107] The preparation steps of the iron phosphate material in this embodiment are basically the same as those in Example 1, except that the pH of the second mixture is adjusted to 2.0.

[0108] Example 6

[0109] The preparation steps of the iron phosphate material in this embodiment are basically the same as those in Example 1, except that the pH of the second mixture is adjusted to 2.3.

[0110] Example 7

[0111] The preparation steps of the iron phosphate material in this embodiment are basically the same as those in Example 1, except that the pH of the second mixture is adjusted to 2.5.

[0112] Example 8

[0113] The preparation steps of the iron phosphate material in this embodiment are basically the same as those in Example 1. The difference is that the amount of water in the first mixture is increased, the solid content of the slurry is adjusted to 7%, and the pH of the first mixture is the same as that in Example 1 by adjusting the amount of phosphoric acid.

[0114] Example 9

[0115] The preparation steps of the iron phosphate material in this embodiment are basically the same as those in Example 1. The difference is that the amount of water in the first mixture is reduced, the solid content of the slurry is adjusted to 25%, and the pH of the first mixture is the same as that in Example 1 by adjusting the amount of phosphoric acid.

[0116] Example 10

[0117] The preparation steps of the iron phosphate material in this embodiment are basically the same as those in Example 1. The difference is that the amount of water in the first mixture is increased, the solid content of the slurry is adjusted to 5%, and the pH of the first mixture is the same as that in Example 1 by adjusting the amount of phosphoric acid.

[0118] Example 11

[0119] The preparation steps of the iron phosphate material in this embodiment are basically the same as those in Example 1. The difference is that the amount of water in the second mixture is increased, the solid content of the second mixture is adjusted to 2%, and the pH of the first mixture is made the same as that in Example 1 by adjusting the amount of phosphoric acid.

[0120] Example 12

[0121] The preparation steps of the iron phosphate material in this embodiment are basically the same as those in Example 1. The difference is that the amount of water in the second mixture is reduced, the solid content of the second mixture is adjusted to 7%, and the pH of the first mixture is made the same as that in Example 1 by adjusting the amount of phosphoric acid.

[0122] Example 13

[0123] The preparation steps of the iron phosphate material in this embodiment are basically the same as those in Example 1, except that the primary aging temperature is 91°C.

[0124] Example 14

[0125] The preparation steps of the iron phosphate material in this embodiment are basically the same as those in Example 1, except that the aging temperature is 95°C.

[0126] Example 15

[0127] The preparation steps of the iron phosphate material in this embodiment are basically the same as those in Example 1, except that the aging temperature is 98°C.

[0128] Example 16

[0129] The preparation steps of the iron phosphate material in this embodiment are basically the same as those in Example 1, except that the aging time for one treatment is 0.75 hours.

[0130] Example 17

[0131] The preparation steps of the iron phosphate material in this embodiment are basically the same as those in Example 1, except that the aging time is 1 hour.

[0132] Example 18

[0133] The preparation steps of the iron phosphate material in this embodiment are basically the same as those in Example 1, except that the secondary aging temperature is 95°C.

[0134] Example 19

[0135] The preparation steps of the iron phosphate material in this embodiment are basically the same as those in Example 1, except that the secondary aging time is 6 hours.

[0136] Example 20

[0137] The preparation steps of the iron phosphate material in this embodiment are basically the same as those in Example 1, except that the slurry treatment time is 2 hours.

[0138] Example 21

[0139] The preparation steps of the iron phosphate material in this embodiment are basically the same as those in Example 1, except that the slurry treatment time is 6 hours.

[0140] Example 22

[0141] The preparation steps of the iron phosphate material in this embodiment are basically the same as those in Example 1, except that the slurry treatment time is 8 hours.

[0142] Example 23

[0143] The preparation steps of the iron phosphate material in this embodiment are basically the same as those in Example 1, except that the slurry treatment temperature is 60°C.

[0144] Example 24

[0145] The preparation steps of the iron phosphate material in this embodiment are basically the same as those in Example 1, except that the slurry treatment temperature is 0°C.

[0146] Example 25

[0147] The preparation steps of the iron phosphate material in this embodiment are basically the same as those in Example 1, except that the slurry treatment temperature is 50°C.

[0148] Example 26

[0149] The preparation steps of the iron phosphate material in this embodiment are basically the same as those in Example 1, except that the calcination temperature in step 8 is 600°C.

[0150] Example 27

[0151] The preparation steps of the iron phosphate material in this embodiment are basically the same as those in Example 1, except that the calcination temperature in step 8 is 800°C.

[0152] Example 28

[0153] The preparation steps of the iron phosphate material in this embodiment are basically the same as those in Example 1, except that the calcination time in step 8 is 1 hour.

[0154] Example 29

[0155] The preparation steps of the iron phosphate material in this embodiment are basically the same as those in Example 1, except that the calcination time in step 8 is 3 hours.

[0156] Comparative Example 1

[0157] The preparation steps of the iron phosphate material in this comparative example are basically the same as those in Example 1, except that the pH of the first mixture is 1.5.

[0158] Comparative Example 2

[0159] The preparation steps of the iron phosphate material in this comparative example are basically the same as those in Example 1, except that the pH of the first mixture is 2.5.

[0160] Comparative Example 3

[0161] The preparation steps of the iron phosphate material in this comparative example include:

[0162] 1) Preparation of reaction solution: Dissolve 10.21 kg of refined ferrous sulfate in 20.49 kg of pure water to obtain solution a with a ferrous ion content of 6.7%; add 4.06 kg of monoammonium phosphate to 13.78 kg of pure water, add 1.65 kg of 28% ammonia water to adjust the pH to 6.4, add 2.4 kg of 30% hydrogen peroxide, and stir to obtain solution b with a phosphorus content of 5.0%.

[0163] 2) Use the solution a obtained in step 1) as the bottom liquid of the reactor, heat it to 55°C, and start feeding solution b at a flow rate of 1 kg / min. After all the above solution b has been transferred, continue to keep it warm for 15 min to form the first slurry A.

[0164] 3) Filter and wash the slurry A obtained in step 2) until the conductivity of the final wash water is ≤2500μs / cm, and obtain 16kg of the first filter cake X.

[0165] 4) Add 16 kg of the first filter cake X obtained in step 3) into an aging kettle containing 21.8 kg of pure water and disperse it. Add 5.3 kg of 85% phosphoric acid and adjust the pH to 0.6 to form a second slurry B (i.e. the first mixture) with a solid content of 15%. Slurry it at 25°C and 25 Hz for 3 hours to obtain the slurry.

[0166] 5) The pulping material from step 4) is subjected to vacuum filtration. The mother liquor from the vacuum filtration is collected separately to adjust the pH of the second filter cake pulping in step 6). The pulp is washed with pure water until the pH of the final wash water is 2.3, and 16 kg of the second filter cake Y is obtained.

[0167] 6) Add 16 kg of the second filter cake Y obtained in step 5) to an aging kettle containing 144 kg of pure water and disperse to form a slurry with a solid content of 4%. At the same time, add 300 g of the mother liquor obtained in step 5) and adjust the pH to 2.1 to obtain the second mixture. Continue to heat to 97°C and keep warm for 2 hours to obtain the third slurry C.

[0168] 7) Filter and wash the third slurry C obtained in step 6) until the conductivity of the final wash water is ≤1000μs / cm to obtain filter cake Z.

[0169] 8) After drying the filter cake Z obtained in step 7) at 105℃ for 12 hours, it is calcined in a muffle furnace at 700℃ for 2 hours and then mechanically crushed to obtain small-particle high-iron-phosphorus ratio iron phosphate material.

[0170] Test case

[0171] Particle size testing of iron phosphate materials: The iron phosphate materials obtained in each example and comparative example were subjected to SEM testing, and the particle size distribution of iron phosphate particles in the SEM images was statistically analyzed. Specifically, the samples to be tested were placed in a Hitachi IM4000 ion mill and subjected to ion beam milling at an accelerating voltage of 6000V for 1.5-2 hours to obtain particle cross-sections with clear boundaries. A Hitachi SU8600 field emission scanning electron microscope was used to observe the samples and acquire particle morphology images at an accelerating voltage of 3000V. The obtained SEM images were statistically analyzed using image analysis software to obtain the particle size distribution range of iron phosphate particles.

[0172] Figure 2 The image shows an SEM image of the iron phosphate material from Example 1 of this application. The iron phosphate particles in the image have a size of 40nm-80nm. Figure 3 The image provided in this application is a SEM image of the iron phosphate material from Comparative Example 1. Figure 3 The size of the ferric phosphate particles is larger than that of the ferric phosphate particles in Example 1, with a size range of 50-200 nm.

[0173] The particle size distribution of the iron phosphate materials in each embodiment and comparative example is detailed in Table 1.

[0174] Table 1. Particle size data of iron phosphate materials in each embodiment and comparative example

[0175]

[0176]

[0177]

[0178]

[0179] As can be seen from the data in Table 1 above, in Examples 1-29, the pH of the first mixture was maintained in the range of 0.5-1, and the pulping and primary aging were carried out in a high acid atmosphere. Compared with the low acid atmosphere of Comparative Examples 1 and 2, the particle size of iron phosphate was reduced, and the particle size was more concentrated and the distribution range was narrower.

[0180] Compared with Comparative Example 3, the addition of a high-acidity primary aging step in Example 1 can reduce the particle size of ferric phosphate.

[0181] Test case

[0182] Lithium iron phosphate / carbon composite materials were prepared using the iron phosphate powders from the various examples and comparative examples. 50.2 g of lithium carbonate, 200 g of the iron phosphate powders from the above examples or comparative examples, 19.2 g of glucose, 7.2 g of PEG6000, and 1.0 g of titanium dioxide were weighed out sequentially at a molar ratio of Li / Fe = 1.02 and added to 500 ml of water for dispersion. The mixture was then transferred to a grinder and ground at 1500 r / min until the slurry particle size D50 ≤ 500 nm was reached. This slurry was then spray-dried. After drying, the material was crushed, and the crushed material was sintered in a tube furnace under nitrogen atmosphere at 720°C for 10 hours. After the tube furnace cooled naturally to room temperature, the sintered material was pulverized and sieved through a 200-mesh sieve to obtain the lithium iron phosphate / carbon composite material.

[0183] After the lithium iron phosphate / carbon composite materials of the examples and comparative examples were respectively fabricated as positive electrode sheets, they were assembled with negative electrode sheets, electrolytes, and separators according to the following method to obtain coin cells. The method includes:

[0184] Battery assembly and electrochemical performance testing: 1) Grind and mix 1.6g of the above-mentioned lithium iron phosphate / carbon composite cathode material and 0.2g of acetylene black; 2) Dissolve 0.2g of polyvinylidene fluoride in 4ml of N-methyl-pyrrolidone, then slowly add the mixture of LiFePO4 and acetylene black, stir evenly, coat it on a 20μm thick aluminum foil, and dry it in a forced-air drying oven at 80℃ for 12h. Cut the dried electrode into small round pieces with a diameter of 12mm (containing about 6mg of active material) as the cathode, with a compaction density of 2.35±0.05. 3) Assemble CR2016 coin cells in an argon-filled glove box using a lithium metal sheet as the counter electrode, an ND525 separator as the separator, and 1mol / L LiPF6 / EC+DMC (volume ratio 1:1:1) as the electrolyte. The battery's charge and discharge performance was tested using a BTS-5V / 5mA battery testing system, with a voltage range of 3.65-2.5V.

[0185] Capacity retention test: At 25℃, charge at a constant current rate of 1C to 4.50V, then charge at a constant voltage rate of 0.05C to 4.50V, and then discharge at a discharge rate of 1C to 3.0V. Repeat this charge-discharge cycle 500 times. Measure the discharge capacity Q1 at the first cycle and the discharge capacity Q at the 500th cycle. 500 Capacity retention rate Q = Q 500 / Q1*100%. See Table 2 for detailed test results.

[0186] For specific capacity testing, a 2.0-3.75V / 20202915-T-610 coin cell tester was used to conduct a discharge test at a 1C discharge rate to obtain the battery capacity. The specific capacity (mAh / g) was then divided by the mass of the positive electrode material.

[0187] Table 2. Battery Performance

[0188]

[0189]

[0190] Compared to Comparative Examples 1-3, the iron phosphate particles in Examples 1-29 have smaller particle sizes and narrower particle size distributions, resulting in better specific capacity and cycle performance of the prepared batteries.

[0191] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing an iron phosphate material, characterized in that, The preparation method includes the following steps: A first mixture comprising amorphous iron phosphate, phosphoric acid, and water is subjected to a slurry treatment to obtain a slurry; wherein the pH of the first mixture is 0.5-1; The slurry is subjected to an aging process, followed by a first solid-liquid separation to obtain a first solid product. The second mixture, comprising the first solid product, phosphoric acid, and water, is subjected to a second aging treatment, followed by a second solid-liquid separation to obtain the second solid product; wherein the pH of the second mixture is 2.0-2.

5. The second solid product is calcined to obtain the iron phosphate material.

2. The method for preparing iron phosphate material according to claim 1, characterized in that, The solids content of the slurry is 7-25%; and / or the solids content of the second mixture is 2-7%.

3. The method for preparing the iron phosphate material according to claim 1 or 2, characterized in that, The pulping process takes 2-6 hours and / or the pulping temperature is ≤50℃.

4. The method for preparing the iron phosphate material according to claim 1 or 2, characterized in that, The temperature of the first aging treatment is 91-95℃; and / or the time of the first aging treatment is 0.5-1h; And / or, the temperature of the secondary aging treatment is 95-98℃; and / or, the time of the secondary aging treatment is 2-6h.

5. The method for preparing the iron phosphate material according to claim 1 or 2, characterized in that, The preparation method further includes: washing the second solid product until the conductivity of the washing liquid after washing is less than or equal to 1000 μs / cm, and then subjecting the second solid product to the calcination treatment; and / or, the calcination treatment temperature is 600-800℃, and the calcination treatment time is 1-3h. And / or, the preparation process of the amorphous iron phosphate includes: A third mixture comprising an iron source, a phosphorus source, and an oxidant is reacted to obtain the amorphous iron phosphate; wherein the reaction temperature is 50-60℃ and the reaction time is 10-30 min.

6. A type of iron phosphate material, characterized in that, The iron phosphate material is prepared according to the preparation method described in any one of claims 1-5.

7. The iron phosphate material according to claim 6, characterized in that, The particle size of the iron phosphate material is 30–90 nm.

8. A lithium iron phosphate cathode material, characterized in that, The lithium iron phosphate cathode material includes lithium iron phosphate formed by sintering a mixture of the iron phosphate material as described in claim 6 or 7 and a lithium source.

9. A positive electrode plate, characterized in that, Including the lithium iron phosphate cathode material as described in claim 8.

10. A battery, characterized in that, Includes the positive electrode sheet as described in claim 9.

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