Lithium iron phosphate material and preparation method thereof

Abstract

The present application relates to a lithium iron phosphate material and a preparation method thereof. The preparation method of the lithium iron phosphate material comprises the following steps: calcining ferrophosphorus slag to obtain a calcined material; dissolving the calcined material in an acid solution to obtain a ferrophosphorus mixture; mixing the ferrophosphorus mixture, an acid-base regulator, a stabilizer, and a ferrophosphorus compensator to obtain a precursor slurry; subjecting the precursor slurry to an aging treatment, a washing treatment, and a first drying treatment to obtain a precursor; mixing the precursor, a lithium source, and an organic carbon source, and performing a grinding treatment, a second drying treatment, and a sintering treatment to obtain a lithium iron phosphate material; the stabilizer comprises a dopant and a polyol grafted onto the dopant; the precursor has a flaky structure, the flaky layer thickness is 0.02 μm to 0.2 μm, and the specific surface area is 7 m 2 / g~17m 2 / g, and the tap density is 0.9g / cm 3 ~1.6g / cm 3 The lithium iron phosphate material has the advantages of high discharge specific capacity, high initial charge and discharge efficiency, and good rate performance.

Description

Technical Field

[0001] The present application relates to the technical field of battery materials, and in particular to a lithium iron phosphate material and a preparation method thereof. Background Art

[0002] With the depletion of traditional fossil fuels and the rapid development of new energy materials, the widespread adoption of electric vehicles has become a reality. Developing power batteries with higher efficiency, higher energy density, and lower cost has become a key focus and research direction in the electric vehicle industry. Currently, pressure to reduce power battery costs is increasing. Lithium iron phosphate batteries, thanks to their advantages such as high safety, long cycle life, relatively low cost, and good thermal stability, are gradually surpassing ternary batteries in production and installed capacity, and are showing a rapid growth trend. At the same time, the recycling of used lithium iron phosphate batteries has become an urgent issue.

[0003] Traditionally, recycling methods for spent lithium iron phosphate (LFP) have focused on selective lithium extraction, separating the high-value lithium element from the cathode material. However, this process produces a large amount of ferrophosphorus slag. This slag is high in impurities, making it difficult to recycle and producing LFP materials with stable and excellent electrochemical properties. Summary of the Invention

[0004] Based on this, it is necessary to provide a lithium iron phosphate material and a preparation method thereof to solve the problem that the impurity content of ferrophosphorus slag is high, the recycling is difficult, and it is difficult to prepare a lithium iron phosphate material with stable and excellent electrochemical properties.

[0005] The above-mentioned purpose of this application is achieved through the following technical solutions:

[0006] In a first aspect of the present application, a method for preparing a lithium iron phosphate material is provided, comprising the following steps:

[0007] calcining the ferrophosphorus slag to obtain a calcined material;

[0008] dissolving the calcined material in an acid solution to obtain a phosphorus-iron mixed solution;

[0009] Mixing the ferrophosphorus mixture, an acid-base regulator, a stabilizer, and a ferrophosphorus compensator to obtain a precursor slurry;

[0010] Performing an aging treatment, a washing treatment, and a first drying treatment on the precursor slurry to obtain a precursor;

[0011] The precursor, the lithium source and the organic carbon source are mixed, and subjected to grinding, a second drying and sintering treatment to obtain a lithium iron phosphate material;

[0012] Wherein, the stabilizer includes a dopant and a polyol;

[0013] The precursor has a flaky structure, the thickness of the flaky structure is 0.02 μm to 0.2 μm, and the specific surface area of ​​the precursor is 7 m 2 / g~17m 2 / g, and the tap density of the precursor is 0.9g / cm 3 ~1.6g / cm 3 , the D50 particle size of the precursor is 6 μm~16 μm.

[0014] In one embodiment, the preparation method of the stabilizer comprises the following steps:

[0015] The dopant and the polyol are mixed and ball milled to obtain the stabilizer.

[0016] In one embodiment, the dopant includes one or more of titanium dioxide, strontium oxide, ammonium metavanadate, chromium nitrate, barium nitrate, barium carbonate, aluminum oxide, aluminum nitrate, nickel oxide, magnesium oxide, and magnesium carbonate.

[0017] In one embodiment, the polyol includes one or more of ethylene glycol, propylene glycol, butylene glycol, hexylene glycol, neopentyl glycol, pentaerythritol, trihydroxymethylpropane and glycerol.

[0018] In one embodiment, the mass ratio of the dopant to the polyol is (0.2-1.5):1.

[0019] In one embodiment, the mass ratio of the doping element in the dopant to the iron element in the ferrophosphorus mixture is (0.01-0.5):100.

[0020] In one embodiment, the ball milling conditions include: ball milling time of 0.1h~5h, ball milling speed of 200rpm~800rpm, material-ball ratio of (0.1~0.8):1, and ball milling medium is zirconia ceramic ball.

[0021] In one embodiment, mixing the ferrophosphorus mixture, the acid-base regulator, the stabilizer and the ferrophosphorus compensator comprises the following steps:

[0022] Mixing the ferrophosphorus mixture and the acid-base regulator to obtain a first slurry with a pH of 1.5 to 3.0;

[0023] mixing the first slurry and the stabilizer, stirring and reacting them to obtain a second slurry;

[0024] The second slurry and the ferrophosphorus compensator are mixed so that the molar ratio of the iron element to the phosphorus element in the precursor slurry is (0.95-1.02):1.

[0025] In one embodiment, the acid-base regulator includes one or more of ammonia water, hydrogen peroxide, ammonium carbonate and ammonium bicarbonate.

[0026] In one embodiment, the stirring reaction temperature is 30°C to 70°C.

[0027] In one embodiment, the stirring reaction time is 0.5h~2h.

[0028] In one embodiment, the temperature for mixing the second slurry and the ferrophosphorus compensator is 50° C. to 105° C.

[0029] In one embodiment, the phosphorus-iron compensator includes one or more of phosphoric acid, ammonium dihydrogen phosphate, diammonium phosphate, triammonium phosphate, iron powder, iron oxide, iron hydroxide and iron oxyhydroxide.

[0030] In one embodiment, the calcination treatment includes a fluidized bed calcination treatment, the calcination temperature is 300° C. to 550° C., and the calcination time is 2 h to 8 h.

[0031] In one embodiment, the acid in the acid solution includes one or more of hydrochloric acid, sulfuric acid, nitric acid and phosphoric acid.

[0032] In one embodiment, the concentration of the acid in the acid solution is 0.5 mol / L to 5 mol / L.

[0033] In one embodiment, the temperature of the acid solution is 50°C~95°C.

[0034] In one embodiment, the molar ratio of the acid ions in the acid solution to the iron ions in the ferrophosphorus mixture is (1.2-3.6):1.

[0035] In one embodiment, the lithium source includes one or more of lithium carbonate, lithium hydroxide, lithium oxalate, lithium acetate and lithium nitrate.

[0036] In one embodiment, the molar ratio of the lithium element in the lithium source to the phosphorus element in the precursor is (0.97-1.05):1.

[0037] In one embodiment, the organic carbon source comprises one or more of starch, cellulose, sucrose, glucose, citric acid, chitin, Tween, polyvinyl alcohol, polyethylene glycol, polyacrylic acid and polyvinyl pyrrolidone.

[0038] In one embodiment, the mass ratio of the organic carbon source to the precursor is (3-20):100.

[0039] In one embodiment, the sintering process comprises the following steps:

[0040] In a protective atmosphere, keep warm at 650℃~830℃ for 4h~18h.

[0041] In a second aspect of the present application, a lithium iron phosphate material is provided, which is prepared using the above-mentioned method for preparing the lithium iron phosphate material.

[0042] This application has at least the following beneficial effects:

[0043] The present application utilizes the ferrophosphorus slag after lithium extraction from waste lithium iron phosphate batteries as raw material, firstly removes carbon impurities and other impurities that are easily oxidized and decomposed into volatile gases at high temperatures through roasting treatment, and then uses acid solution to fully leach the phosphorus and iron elements to obtain a ferrophosphorus mixed solution. In the slurry adjustment process, an acid-base regulator is used to control the pH value of the reaction system, a stabilizer composed of a dopant and a polyol grafted on the dopant is used to achieve the regulation of the precursor morphology, and a ferrophosphorus compensator is used to control the phosphorus-iron ratio of the precursor, and then the precursor is obtained through aging, washing and drying. The precursor presents a flaky structure with the characteristics of regular morphology, large specific surface area and high tap density, which is conducive to the release and insertion of lithium ions, so that the lithium iron phosphate material prepared from the precursor has the advantages of high discharge specific capacity, good rate performance and high first charge and discharge efficiency. The preparation method of lithium iron phosphate material provided in the present application effectively solves the problems of high impurity content and difficulty in recycling of ferrophosphorus slag, and prepares lithium iron phosphate material with stable and excellent electrochemical properties, thereby further expanding the lithium battery recycling and recycling industry and having high economic and environmental benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] In order to more clearly illustrate the technical solutions in the embodiments of the present application and to more fully understand the present application and its beneficial effects, the following is a brief introduction to the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present application. Those skilled in the art can also derive other drawings based on these drawings without inventive effort.

[0045] Figure 1 Schematic diagram of a process for preparing a lithium iron phosphate material in one embodiment;

[0046] Figure 2 This is the SEM image of the precursor prepared in Example 3;

[0047] Figure 3 This is an SEM image of the lithium iron phosphate material prepared in Example 3;

[0048] Figure 4 This is the XRD pattern of the lithium iron phosphate material prepared in Example 3. DETAILED DESCRIPTION

[0049] To facilitate understanding of the present application, the present application will be further described in detail below with reference to specific embodiments. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to provide a more thorough and comprehensive understanding of the disclosure of the present application.

[0050] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application pertains. The terms used herein in the specification of this application are for the purpose of describing specific embodiments only and are not intended to limit this application.

[0051] In this application, the meaning of "and / or" includes any and all combinations of one or more related listed items. "At least one" means more than one, such as one, two and more than two. "Multiple" or "several" means at least two, such as two, three, etc., and "multi-layer" means at least two layers, such as two layers, three layers, etc., unless otherwise clearly and specifically defined. In the description of this application, "several" means at least one, such as one, two, etc., unless otherwise clearly and specifically defined.

[0052] When a numerical range is disclosed in this application, the range is considered continuous and includes the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Further, when a range refers to an integer, every integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe a feature or characteristic, the ranges can be combined. In other words, unless otherwise indicated, all ranges disclosed in this application should be understood to include any and all subranges subsumed therein.

[0053] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0054] In this application, “above” or “below” includes the number itself. For example, “1 below” includes 1.

[0055] Unless otherwise specified, the temperature parameters in this application allow for both constant temperature treatment and temperature fluctuations within a certain temperature range. It should be understood that the constant temperature treatment allows for temperature fluctuations within the accuracy range of instrument control. Fluctuations within ranges such as ±5°C, ±4°C, ±3°C, ±2°C, and ±1°C are permitted.

[0056] In this application, room temperature refers to indoor temperature, normal temperature or general temperature. Generally speaking, the range of room temperature can be any one of the following temperature intervals: 23℃±2℃, 25℃±5℃ or 20℃±5℃.

[0057] the term

[0058] Unless otherwise specified or incompatible therewith, terms and phrases used in this application shall have the following meanings:

[0059] Particle size: For spherical particles, particle size refers to the diameter of the spherical particle. For non-spherical particles, such as those with an olivine morphology, particle size generally refers to the equivalent particle size of the non-spherical particle (often referred to as particle size). The particle size measured by a laser particle size analyzer is the equivalent particle diameter. The equivalent particle size refers to the diameter of a spherical particle representing the actual particle diameter when a physical property of the particle is the same or similar to that of a homogeneous spherical particle. Unless otherwise specified or in conflict, particle size in this application refers to the equivalent particle size.

[0060] Particle size distribution parameters: In a particle size distribution curve, the particle size at which the cumulative particle size distribution percentage reaches N% is called the DN particle size, indicating that particles smaller than this particle size account for N% of all particles, where N = 0-100. When N = 100, the D100 particle size represents the particle size at which the cumulative particle size distribution percentage reaches 100%. When N = 50, the D50 particle size represents the particle size at which the cumulative particle size distribution percentage reaches 50%, representing the median particle size or median diameter, indicating that particles smaller than this particle size each account for 50%. For example, a D50 particle size of 1 mm means that particles smaller than 1 mm and particles larger than 1 mm each account for 50% of all particles.

[0061] Span: Also known as span, it is calculated as: Span = (D90 - D10) ÷ D50. The smaller the span, the more concentrated the particle size distribution; the larger the span, the greater the size variation and the more dispersed the distribution.

[0062] In a first aspect, the present application provides a method for preparing a lithium iron phosphate material, which is used to solve the problem that the impurity content of ferrophosphorus slag is high, the recycling is difficult, and it is difficult to prepare a lithium iron phosphate material with stable and excellent electrochemical properties.

[0063] See Figure 1, which is a flow chart of a method for preparing lithium iron phosphate material in one embodiment. Figure 1 As shown, the preparation method of lithium iron phosphate material includes the following steps:

[0064] S1: calcining ferrophosphorus slag to obtain calcined material;

[0065] S2: dissolving the calcined material in an acid solution to obtain a phosphorus-iron mixed solution;

[0066] S3: mixing the ferrophosphorus mixture, the acid-base regulator, the stabilizer and the ferrophosphorus compensator to obtain a precursor slurry;

[0067] S4: performing an aging treatment, a washing treatment, and a first drying treatment on the precursor slurry to obtain a precursor;

[0068] S5: mixing the precursor, the lithium source and the organic carbon source, performing a grinding process, a second drying process and a sintering process to obtain a lithium iron phosphate material;

[0069] The stabilizer includes a dopant and a polyol grafted onto the dopant;

[0070] The precursor has a flaky structure with a thickness of 0.02μm~0.2μm and a specific surface area of ​​7m 2 / g~17m 2 / g, and the tap density of the precursor is 0.9g / cm 3 ~1.6g / cm 3 , the D50 particle size of the precursor is 6μm~16μm.

[0071] The present application utilizes the ferrophosphorus slag after lithium extraction from waste lithium iron phosphate batteries as raw material, firstly removes carbon impurities and other impurities that are easily oxidized and decomposed into volatile gases at high temperatures through roasting treatment, and then uses acid solution to fully leach the phosphorus and iron elements to obtain a ferrophosphorus mixed solution. In the slurry adjustment process, an acid-base regulator is used to control the pH value of the reaction system, a stabilizer composed of a dopant and a polyol grafted on the dopant is used to achieve the regulation of the precursor morphology, and a ferrophosphorus compensator is used to control the phosphorus-iron ratio of the precursor, and then the precursor is obtained through aging, washing and drying. The precursor presents a flaky structure with the characteristics of regular morphology, large specific surface area and high tap density, which is conducive to the release and insertion of lithium ions, so that the lithium iron phosphate material prepared from the precursor has the advantages of high discharge specific capacity, good rate performance and high first charge and discharge efficiency. The preparation method of lithium iron phosphate material provided in the present application effectively solves the problems of high impurity content and difficulty in recycling of ferrophosphorus slag, and prepares lithium iron phosphate material with stable and excellent electrochemical properties, thereby further expanding the lithium battery recycling and recycling industry and having high economic and environmental benefits.

[0072] The following is a detailed description of the preparation method of lithium iron phosphate material in a step-by-step manner.

[0073] S1: calcining the ferrophosphorus slag to obtain a calcined material.

[0074] Ferrophosphorus slag is the solid residue left after pulverization and selective lithium extraction from spent lithium iron phosphate batteries. Its primary components are iron phosphate, carbon, and small amounts of metallic impurities (such as nickel, copper, or aluminum). It appears as a dark gray solid or semi-solid. In some specific examples, ferrophosphorus slag contains the following elements by mass: 28% to 32% iron, 17% to 19% phosphorus, and 0.5% to 3% carbon.

[0075] Optionally, the calcination process comprises a fluidized bed calcination process.

[0076] It can be understood that fluidized bed roasting is a process in which the material is placed in a fluidized gas for heating and roasting. It has the characteristics of high heat and mass transfer efficiency and high temperature uniformity. It can quickly and fully remove carbon and other impurities that are easily decomposed into volatile gases at high temperatures, and ensure the stable quality of the roasted material.

[0077] Optionally, the calcination temperature is 300°C to 550°C, and the calcination time is 2 hours to 8 hours. As an example, the calcination temperature includes but is not limited to 300°C, 320°C, 340°C, 360°C, 380°C, 400°C, 420°C, 440°C, 460°C, 480°C, 500°C, 520°C, 540°C, or 550°C, and may further be 400°C to 500°C; the calcination time includes but is not limited to 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, or 8 hours, and may further be 3 hours to 5 hours.

[0078] S2: dissolving the calcined material in acid solution to obtain a phosphorus-iron mixed solution.

[0079] Optionally, the process of dissolving the roasting material in the acid solution is carried out under stirring conditions.

[0080] Optionally, the acid in the acid solution includes one or more of sulfuric acid (H2SO4), nitric acid (HNO3) and phosphoric acid (H3PO4), and may further be sulfuric acid (H2SO4) or phosphoric acid (H3PO4).

[0081] Optionally, the concentration of the acid in the acid solution is 0.5mol / L~5mol / L, including but not limited to 0.5mol / L, 1mol / L, 1.5mol / L, 2mol / L, 2.5mol / L, 3mol / L, 3.5mol / L, 4mol / L, 4.5mol / L or 5mol / L, and can further be 1mol / L~2mol / L.

[0082] Optionally, the temperature of the acid solution is 50°C to 95°C, including but not limited to 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C or 95°C, and can further be 55°C to 65°C.

[0083] Optionally, the molar ratio of the acid ions in the acid solution to the iron ions in the ferrophosphorus mixture is (1.2~3.6):1, including but not limited to 1.2:1, 1.4:1, 1.6:1, 1.8:1, 2.0:1, 2.2:1, 2.4:1, 2.6:1, 2.8:1, 3.0:1, 3.2:1, 3.4:1 or 3.6:1, and can further be (1.2~2.0):1.

[0084] By regulating the type, concentration, temperature and molar ratio of acid ions to iron ions, the roasted material can be quickly dissolved and phosphorus and iron elements can be fully leached to obtain a phosphorus-iron mixed solution.

[0085] S3: mixing the ferrophosphorus mixture, the acid-base regulator, the stabilizer and the ferrophosphorus compensator to obtain a precursor slurry.

[0086] Optionally, in step S3, mixing the ferrophosphorus mixed solution, the acid-base regulator, the stabilizer and the ferrophosphorus compensator comprises the following steps:

[0087] S31: mixing the phosphorus-iron mixed solution and the acid-base regulator to obtain a first slurry with a pH of 1.5 to 3.0;

[0088] S32: mixing the first slurry and the stabilizer, stirring and reacting to obtain a second slurry;

[0089] S33: Mixing the second slurry and the phosphorus-iron compensator to make the molar ratio of the iron element to the phosphorus element in the precursor slurry be (0.95-1.02):1.

[0090] As an example, the pH value of the first slurry includes but is not limited to 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9 or 3.0, and can further be 1.5~2.0.

[0091] Optionally, the acid-base regulator includes one or more of ammonia water, hydrogen peroxide, ammonium carbonate, and ammonium bicarbonate, and further includes one or more of ammonia water and hydrogen peroxide, wherein the mass fraction of ammonia water is 25% to 28% and the mass fraction of hydrogen peroxide is 20% to 30%.

[0092] Optionally, the preparation method of the stabilizer includes the following steps: mixing a dopant and a polyol, and performing ball milling to obtain the stabilizer.

[0093] Optionally, the dopant includes one or more of titanium dioxide, strontium oxide, ammonium metavanadate, chromium nitrate, barium nitrate, barium carbonate, aluminum oxide, aluminum nitrate, nickel oxide, magnesium oxide and magnesium carbonate, and can further be selected from one or more of titanium dioxide, strontium oxide and ammonium metavanadate.

[0094] It is understood that the dopant can be selected from compounds that do not contain bound water, such as anhydrous ammonium metavanadate, or compounds that contain bound water, such as chromium nitrate nonahydrate.

[0095] Optionally, the polyol includes one or more of ethylene glycol, propylene glycol, butanediol, hexanediol, neopentyl glycol, pentaerythritol, trihydroxymethylpropane and glycerol, and may further be one or more of hexanediol, neopentyl glycol and pentaerythritol.

[0096] Optionally, the mass ratio of the dopant to the polyol is (0.2~1.5):1, including but not limited to 0.2:1, 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1 or 1.5:1, and can further be (0.5~0.8):1.

[0097] Optionally, the mass ratio of the doping element in the dopant to the iron element in the ferrophosphorus mixture is (0.01~0.5):100, including but not limited to 0.01:100, 0.05:100, 0.1:100, 0.15:100, 0.2:100, 0.25:100, 0.3:100, 0.35:100, 0.4:100, 0.45:100 or 0.5:100, and can further be (0.2~0.3):100.

[0098] Optionally, the ball milling conditions include: a ball milling time of 0.1 h to 5 h, a ball milling speed of 200 rpm to 800 rpm, a material-to-ball ratio of (0.1 to 0.8):1, and a ball milling medium of zirconia ceramic balls.

[0099] As an example, the ball milling time includes but is not limited to 0.1h, 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h or 5h, and may further be 1h to 2h. The ball milling speed includes but is not limited to 200rpm, 250rpm, 300rpm, 400rpm, 450rpm, 500rpm, 550rpm, 600rpm, 650rpm, 700rpm, 750rpm or 800rpm, and may further be 400rpm to 500rpm. The ball-to-material ratio includes but is not limited to 0.1:1, 0.2:1, 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.7:1 or 0.8:1, and may further be (0.4 to 0.6):1.

[0100] Ball milling can produce a mechanical-chemical activation effect, which on the one hand reduces the particle size of the dopant, and on the other hand increases the active sites on the surface of the dopant, promoting the grafting and coating of the polyol on the surface of the dopant, which is beneficial for the stabilizer to be evenly dispersed in the first slurry, making the material sedimentation stable while playing a decisive inducing role in the final precursor morphology, inducing the precursor to form a dense lamellar structure, and is beneficial for refining the particle size of the precursor during the drying and dehydration process.

[0101] Optionally, the stirring reaction temperature is 30°C to 70°C, including but not limited to 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C or 70°C, and can further be 50°C to 60°C.

[0102] It is understood that before the stirring reaction, the temperature of the first slurry is controlled at 30°C to 70°C, and the temperature of the subsequent process of adding the stabilizer and the process of stirring the reaction are both controlled at 30°C to 70°C.

[0103] Optionally, the stirring reaction time is 0.5 h to 2 h, including but not limited to 0.5 h, 0.8 h, 1 h, 1.2 h, 1.5 h, 1.8 h or 2 h, and can further be 1 h to 2 h.

[0104] Optionally, the temperature of mixing the second slurry and the ferrophosphorus compensator is 50°C~105°C, including but not limited to 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, 100°C or 105°C, and can be further optionally 70°C~80°C.

[0105] Optionally, the phosphorus-iron compensating agent includes one or more of phosphoric acid, ammonium dihydrogen phosphate, diammonium phosphate, triammonium phosphate, iron powder, iron oxide, iron hydroxide and iron oxyhydroxide.

[0106] It is understood that the phosphorus-iron compensator includes two types: phosphorus compensator and iron compensator. The phosphorus compensator or the iron compensator can be selectively added according to the molar ratio of the iron element to the phosphorus element in the second slurry, so that the molar ratio of the iron element to the phosphorus element in the precursor slurry is (0.95~1.02): 1. As an example, the molar ratio of the iron element to the phosphorus element in the precursor slurry includes but is not limited to 0.95:1, 0.96:1, 0.97:1, 0.98:1, 0.99:1, 1:1, 1.01:1 or 1.02:1, and can further be (0.96~0.98):1.

[0107] S4: performing an aging treatment, a washing treatment, and a first drying treatment on the precursor slurry to obtain a precursor;

[0108] Optionally, the temperature of the aging reaction is 50°C~105°C, including but not limited to 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, 100°C or 105°C, and can further be 70°C~80°C.

[0109] Optionally, the aging reaction time is 2 h to 5 h, including but not limited to 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h or 5 h, and further optionally 2 h to 3 h.

[0110] Optionally, the washing treatment includes the following steps: washing the aged material obtained by the aging reaction with water for multiple times so that the iron content in the washing clear liquid is ≤4 mg / L and the phosphorus content is ≤200 mg / L.

[0111] Optionally, the temperature of the first drying treatment is 400°C to 800°C, including but not limited to 400°C, 450°C, 500°C, 550°C, 600°C, 650°C, 700°C, 750°C or 800°C, and can further be 550°C to 700°C.

[0112] Optionally, the time of the first drying treatment is 2 hours to 8 hours, including but not limited to 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours or 8 hours, and can further be 4 hours to 6 hours.

[0113] Optionally, the D50 particle size of the precursor is 6 μm to 16 μm, including but not limited to 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm or 16 μm, and can further be 10 μm to 15 μm.

[0114] Optionally, the precursor has a flaky structure, and the flaky structure is stacked to form a dense structure, wherein the flaky structure has a flaky layer thickness of 0.02 μm to 0.2 μm, including but not limited to 0.02 μm, 0.03 μm, 0.04 μm, 0.06 μm, 0.08 μm, 0.1 μm, 0.12 μm, 0.14 μm, 0.16 μm, 0.18 μm or 0.2 μm, and can be further optionally 0.05 μm to 0.09 μm.

[0115] Optionally, the specific surface area of ​​the precursor is 7m 2 / g~17m 2 / g, including but not limited to 7m 2 / g、8m 2 / g、9m 2 / g、10m 2 / g、11m 2 / g、12m 2 / g、13m 2 / g、14m 2 / g、15m 2 / g、16m 2 / g or 17m 2 / g, further optional 10.7m 2 / g~13.1m 2 / g.

[0116] Optionally, the tap density of the precursor is 0.9 g / cm 3 ~1.6g / cm 3 , including but not limited to 0.9g / cm 3 , 1g / cm 3 , 1.1g / cm 3 , 1.2g / cm 3 , 1.3g / cm 3 , 1.4g / cm 3 , 1.5g / cm 3 or 1.6 g / cm 3 , further optional 1.28g / cm 3 ~1.41g / cm 3 .

[0117] S5: mixing the precursor, the lithium source and the organic carbon source, performing a grinding process, a second drying process and a sintering process to obtain a lithium iron phosphate material;

[0118] Optionally, the lithium source includes one or more of lithium carbonate, lithium hydroxide, lithium oxalate, lithium acetate and lithium nitrate, and may further be lithium carbonate.

[0119] Optionally, the molar ratio of the lithium element in the lithium source to the phosphorus element in the precursor is (0.97~1.05):1, including but not limited to 0.97:1, 0.98:1, 0.99:1, 1:1, 1.01:1, 1.02:1, 1.03:1, 1.04:1 or 1.05:1, and can further be (0.99~1.02):1.

[0120] Optionally, the organic carbon source includes one or more of starch, cellulose, sucrose, glucose, citric acid, chitin, Tween, polyvinyl alcohol, polyethylene glycol, polyacrylic acid and polyvinyl pyrrolidone, and can further be one or more of sucrose, glucose, polyethylene glycol and polyacrylic acid.

[0121] It is understood that the organic carbon source can be selected from compounds that do not contain bound water, such as anhydrous glucose and anhydrous citric acid, or compounds that contain bound water, such as monohydrated glucose and monohydrated citric acid.

[0122] Optionally, the mass ratio of the organic carbon source to the precursor is (3-20):100, including but not limited to 3:100, 4:100, 6:100, 8:100, 10:100, 12:100, 14:100, 16:100, 18:100 or 20:100, and can further be (7-10):100.

[0123] Optionally, the grinding process includes the following steps: mixing the precursor, the lithium source and the organic carbon source, and then adding water to obtain a mixture with a solid content of ≤60%; wet grinding the mixture to obtain a grinding material with a D50 particle size of 150nm~800nm.

[0124] As an example, water can be one or more of tap water, distilled water, reverse osmosis water, deionized water, pure water and ultrapure water; the solid content of the mixture includes but is not limited to 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55% or 60%, and can be further selected as 40%~50%; the D50 particle size of the grinding material includes but is not limited to 150nm, 200nm, 250nm, 300nm, 350nm, 400nm, 450nm, 500nm, 550nm, 600nm, 650nm, 700nm, 750nm or 800nm, and can be further selected as 400nm~600nm.

[0125] Optionally, the second drying treatment includes the following steps: drying with a spray dryer at an air inlet temperature of 200°C to 300°C and an air outlet temperature of 90°C to 110°C to obtain a dried material with a moisture content of ≤5%.

[0126] Optionally, the sintering process includes the following steps: in a protective atmosphere, holding at 650°C to 830°C for 4 to 18 hours. As an example, the protective atmosphere includes one or more of nitrogen, helium, neon, argon, and xenon, and nitrogen can be further selected. The temperature of the sintering process includes, but is not limited to, 650°C, 660°C, 680°C, 700°C, 720°C, 740°C, 760°C, 780°C, 800°C, 810°C, or 830°C, and can further be 700°C to 800°C. The holding time of the sintering process includes, but is not limited to, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 15 hours, 16 hours, 17 hours, or 18 hours, and can further be 6 hours to 10 hours.

[0127] Optionally, after the sintering treatment, the method further comprises the following steps: performing air flow crushing treatment on the sintered material obtained by the sintering treatment to obtain a lithium iron phosphate material with a D50 particle size of 0.5 μm to 2.0 μm.

[0128] As an example, the D50 particle size of the lithium iron phosphate material includes but is not limited to 0.5 μm, 0.6 μm, 0.8 μm, 1 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm or 2.0 μm, and can be further optionally 0.8 μm to 1.7 μm.

[0129] In a second aspect of the present application, a lithium iron phosphate material is provided, which is prepared using the above-mentioned method for preparing the lithium iron phosphate material.

[0130] Optionally, the 0.1C discharge specific capacity of the lithium iron phosphate material is ≥159.2 mAh / g.

[0131] Optionally, the 0.1C first charge and discharge efficiency of the lithium iron phosphate material is ≥98%.

[0132] Optionally, the 10C discharge specific capacity of the lithium iron phosphate material is ≥123.6 mAh / g.

[0133] Optionally, the 10C / 0.1C rate of the lithium iron phosphate material is ≥77%.

[0134] The following is further described in conjunction with specific examples and comparative examples. Unless otherwise specified, the raw materials involved in the following specific examples and comparative examples can all be sourced from commercial sources. The instruments used can all be sourced from commercial sources unless otherwise specified. The processes involved can all be selected by those skilled in the art unless otherwise specified. Among them, ferrophosphorus slag is the solid waste residue after powdering and selective lithium extraction of waste lithium iron phosphate batteries.

[0135] Example 1

[0136] The preparation method of the lithium iron phosphate material of this embodiment comprises the following steps:

[0137] (1) The ferrophosphorus slag was calcined in a fluidized bed in an air atmosphere at a temperature of 450°C for 4 hours to obtain a calcined material.

[0138] (2) In a reactor, the roasted material is dissolved in a sulfuric acid solution by continuous stirring to obtain a phosphorus-iron mixture; wherein the concentration of the sulfuric acid solution is 1.5 mol / L, the initial temperature is 60°C, and the molar ratio of sulfate ion to iron in the phosphorus-iron mixture is (1.80-1.85):1.

[0139] (3) Under stirring conditions, an acid-base regulator is added to the ferrophosphorus mixture to obtain a first slurry; the temperature of the first slurry is controlled to 52°C, a stabilizer is added, and the mixture is stirred for 1 hour to obtain a second slurry; the second slurry is preheated to 70°C, and a ferrophosphorus compensator is added dropwise to obtain a precursor slurry.

[0140] The acid-base regulator is 26 wt % ammonia water, and the pH value of the first slurry is controlled to be 1.8.

[0141] The preparation method of the stabilizer comprises: mixing a dopant and a polyol, and ball milling for 2 hours at a rotation speed of 450 rpm, a material-to-ball ratio of 0.5:1, and a ball milling medium of zirconia ceramic balls to obtain the stabilizer; wherein the dopant is titanium dioxide, the polyol is neopentyl glycol, the mass ratio of the two is 0.6:1, and the molar ratio of the titanium element in the titanium dioxide to the iron element in the ferrophosphorus mixture is 0.26:100.

[0142] The phosphorus-iron compensator is phosphoric acid, and the molar ratio of the iron element to the phosphorus element in the precursor slurry is controlled to be 0.97:1.

[0143] (4) The precursor slurry was further aged at 70°C for 3 hours to obtain an aged material; the aged material was washed with pure water for 4 times, and the iron content in the clear liquid of the last washing was 3.62 mg / L and the phosphorus content was 123.56 mg / L to obtain a washed material; the washed material was transferred to a rotary kiln and dried and dehydrated at 550°C for 6 hours to obtain the desired precursor, which had a flaky structure, and the average thickness of the flaky structure was 0.06 μm, and the specific surface area was 10.7 m 2 / g, and the tap density is 1.36g / cm 3 , D50 particle size is 12.4μm.

[0144] (5) Mixing the precursor, lithium source, organic carbon source and pure water to obtain a mixture with a solid content of about 40%; performing wet grinding to obtain a grinding material with a D50 particle size of 454 nm; spray drying the grinding material to obtain a dry material with a moisture content of 3.4%; heating to 775°C in a pure nitrogen atmosphere and keeping the temperature for 8.5 h, and cooling to obtain a sintered material; and air-flow milling the sintered material to obtain a lithium iron phosphate material with a D50 particle size of 1.03 μm.

[0145] The lithium source is lithium carbonate, and the molar ratio of the lithium element in the lithium source to the phosphorus element in the precursor is 1.02:1.

[0146] The organic carbon sources are sucrose and polyacrylic acid, and the mass ratio of sucrose, polyacrylic acid and precursor is 7.2:5.3:100.

[0147] Example 2

[0148] The preparation method of the lithium iron phosphate material of this embodiment comprises the following steps:

[0149] (1) The ferrophosphorus slag was calcined in a fluidized bed in an air atmosphere at a temperature of 550°C for 3 h to obtain a calcined material.

[0150] (2) In a reactor, the roasted material is dissolved in a sulfuric acid solution by continuous stirring to obtain a phosphorus-iron mixture; wherein the concentration of the sulfuric acid solution is 1.8 mol / L, the initial temperature is 65°C, and the molar ratio of sulfate ion to iron in the phosphorus-iron mixture is (1.80-1.85):1.

[0151] (3) Under stirring conditions, an acid-base regulator is added to the ferrophosphorus mixture to obtain a first slurry; the temperature of the first slurry is controlled to 58°C, a stabilizer is added, and the mixture is stirred for 1.5 hours to obtain a second slurry; the second slurry is preheated to 75°C, and a ferrophosphorus compensator is added dropwise to obtain a precursor slurry.

[0152] The acid-base regulator is 26 wt % ammonia water, and the pH value of the first slurry is controlled to be 2.0.

[0153] The preparation method of the stabilizer comprises: mixing a dopant and a polyol, and ball milling for 2 hours at a rotation speed of 450 rpm, a material-to-ball ratio of 0.6:1, and a ball milling medium of zirconia ceramic balls to obtain the stabilizer; wherein the dopant is ammonium metavanadate, the polyol is hexanediol, the mass ratio of the two is 0.8:1, and the molar ratio of the vanadium element in the ammonium metavanadate to the iron element in the ferrophosphorus mixture is 0.25:100.

[0154] The phosphorus-iron compensator is phosphoric acid, and the molar ratio of the iron element to the phosphorus element in the precursor slurry is controlled to be 0.98:1.

[0155] (4) The precursor slurry was further aged at 75°C for 3 hours to obtain an aged material; the aged material was washed with pure water for 4 times, and the iron content in the clear liquid of the last washing was 2.92 mg / L and the phosphorus content was 163.96 mg / L to obtain a washed material; the washed material was transferred to a rotary kiln and dried and dehydrated at 600°C for 4 hours to obtain the desired precursor, which had a flaky structure, and the average thickness of the flaky structure was 0.05 μm, and the specific surface area was 12.2 m 2 / g, and the tap density is 1.33g / cm 3 , particle size D50 is 11.3μm.

[0156] (5) Mixing the precursor, lithium source, organic carbon source and pure water to obtain a mixture with a solid content of about 45%; wet grinding to obtain a grinding material with a D50 particle size of 485 nm; spray drying the grinding material to obtain a dry material with a moisture content of 2.8%; heating to 768°C in a pure nitrogen atmosphere and keeping the temperature for 9 hours, cooling to obtain a sintered material; and air-flow milling the sintered material to obtain a lithium iron phosphate material with a D50 particle size of 1.22 μm.

[0157] The lithium source is lithium carbonate, and the molar ratio of the lithium element in the lithium source to the phosphorus element in the precursor is 1.015:1.

[0158] The organic carbon sources are anhydrous glucose and Tween, and the mass ratio of anhydrous glucose, Tween and precursor is 9.2:1.6:100.

[0159] Example 3

[0160] The preparation method of the lithium iron phosphate material of this embodiment comprises the following steps:

[0161] (1) The ferrophosphorus slag was calcined in a fluidized bed in an air atmosphere at a temperature of 500°C for 3 hours to obtain a calcined material.

[0162] (2) In a reactor, the roasted material is dissolved in a sulfuric acid solution by continuous stirring to obtain a phosphorus-iron mixture; wherein the concentration of the sulfuric acid solution is 1.8 mol / L, the initial temperature is 65°C, and the molar ratio of sulfate ion to iron in the phosphorus-iron mixture is (1.9-2.0):1.

[0163] (3) Under stirring conditions, an acid-base regulator is added to the ferrophosphorus mixture to obtain a first slurry; the temperature of the first slurry is controlled to 54°C, a stabilizer is added, and the mixture is stirred for 2 hours to obtain a second slurry; the second slurry is preheated to 72°C, and a ferrophosphorus compensator is added dropwise to obtain a precursor slurry.

[0164] The acid-base regulator is 26 wt % ammonia water and 25 wt % hydrogen peroxide, with a volume ratio of 1:1, and the pH value of the first slurry is controlled to be 2.0.

[0165] The preparation method of the stabilizer comprises: mixing a dopant and a polyol, and ball milling for 2 hours at a rotation speed of 500 rpm, a material-to-ball ratio of 0.4:1, and zirconia ceramic balls as the ball milling medium to obtain a first stabilizer and a second stabilizer. In the first stabilizer, the dopant is ammonium metavanadate, the polyol is hexylene glycol, the mass ratio of the two is 0.8:1, and the molar ratio of the vanadium element in the ammonium metavanadate to the iron element in the ferrophosphorus mixture is 0.22:100. In the second stabilizer, the dopant is titanium dioxide, the polyol is neopentyl glycol, the mass ratio of the two is 0.6:1, and the molar ratio of the titanium element in the titanium dioxide to the iron element in the ferrophosphorus mixture is 0.15:100.

[0166] The phosphorus-iron compensator is phosphoric acid, and the molar ratio of the iron element to the phosphorus element in the precursor slurry is controlled to be 0.98:1.

[0167] (4) The precursor slurry was further aged at 72°C for 3 h to obtain an aged material; the aged material was washed 5 times with pure water, and the iron content in the clear liquid of the last washing was 2.22 mg / L and the phosphorus content was 93.54 mg / L to obtain a washed material; the washed material was transferred to a rotary kiln and dried and dehydrated at 700°C for 4 h to obtain the desired precursor, which had a flaky structure, and the average thickness of the flaky structure was 0.07 μm, and the specific surface area was 13.1 m 2 / g, and the tap density is 1.41g / cm 3 , particle size D50 is 10.4μm.

[0168] (5) Mixing the precursor, lithium source, organic carbon source and pure water to obtain a mixture with a solid content of about 45%; performing wet grinding to obtain a grinding material with a D50 particle size of 515 nm; spray drying the grinding material to obtain a dry material with a moisture content of 3.3%; heating to 770°C in a pure nitrogen atmosphere and keeping the temperature for 8 hours, and cooling to obtain a sintered material; and air-flow milling the sintered material to obtain a lithium iron phosphate material with a D50 particle size of 1.09 μm.

[0169] The lithium source is lithium carbonate, and the molar ratio of the lithium element in the lithium source to the phosphorus element in the precursor is 1.006:1.

[0170] The organic carbon sources are anhydrous glucose and polyvinyl alcohol, and the mass ratio of anhydrous glucose, polyvinyl alcohol and precursor is 8.5:5.3:100.

[0171] Example 4

[0172] The preparation method of the lithium iron phosphate material of this embodiment comprises the following steps:

[0173] (1) The ferrophosphorus slag was calcined in a fluidized bed in an air atmosphere at a temperature of 500°C for 3 hours to obtain a calcined material.

[0174] (2) In a reactor, the roasted material is dissolved in a phosphoric acid solution by continuous stirring to obtain a phosphorus-iron mixture; wherein the concentration of the phosphoric acid solution is 2 mol / L, the initial temperature is 55°C, and the molar ratio of the phosphate ion to the iron element in the phosphorus-iron mixture is (1.2-1.4):1.

[0175] (3) Under stirring conditions, an acid-base regulator is added to the ferrophosphorus mixture to obtain a first slurry; the temperature of the first slurry is controlled to 58°C, a stabilizer is added, and the mixture is stirred for 2 hours to obtain a second slurry; the second slurry is preheated to 70°C, and a ferrophosphorus compensator is added to obtain a precursor slurry.

[0176] The acid-base regulator is 26 wt % ammonia water and 25 wt % hydrogen peroxide, with a volume ratio of 1:1, and the pH value of the first slurry is controlled to be 1.6.

[0177] The preparation method of the stabilizer comprises: mixing a dopant and a polyol, and ball milling for 1 hour at a rotation speed of 500 rpm, a material-to-ball ratio of 0.4:1, and a ball milling medium of zirconia ceramic balls to obtain the stabilizer; wherein the dopant is strontium oxide, the polyol is pentaerythritol, the mass ratio of the two is 0.5:1, and the molar ratio of the vanadium element in the strontium oxide to the iron element in the ferrophosphorus mixture is 0.23:100.

[0178] The ferrophosphorus compensator is iron powder, and the molar ratio of the iron element to the phosphorus element in the precursor slurry is controlled to be 0.985:1.

[0179] (4) The precursor slurry was further aged at 70°C for 2.5 hours to obtain an aged material; the aged material was washed with pure water for 4 times, and the iron content in the clear liquid of the last washing was 3.47 mg / L and the phosphorus content was 183.92 mg / L to obtain a washed material; the washed material was transferred to a rotary kiln and dried and dehydrated at 700°C for 4 hours to obtain the desired precursor, which had a flaky structure, and the average thickness of the flaky structure was 0.06 μm, and the specific surface area was 12.6 m 2 / g, and the tap density is 1.29g / cm 3 , particle size D50 is 11.9μm.

[0180] (5) Mixing the precursor, lithium source, organic carbon source and pure water to obtain a mixture with a solid content of about 40%; performing wet grinding to obtain a grinding material with a D50 particle size of 418 nm; spray drying the grinding material to obtain a dry material with a moisture content of 3.5%; heating to 770°C in a pure nitrogen atmosphere and keeping the temperature for 8 hours, and cooling to obtain a sintered material; and air-flow milling the sintered material to obtain a lithium iron phosphate material with a D50 particle size of 0.95 μm.

[0181] The lithium source is lithium carbonate, and the molar ratio of the lithium element of the lithium source to the phosphorus element of the precursor is 0.996:1.

[0182] The organic carbon sources are sucrose and polyacrylic acid, and the mass ratio of sucrose, polyacrylic acid and precursor is 7.3:6.6:100.

[0183] Example 5

[0184] This embodiment is basically the same as embodiment 4, except that the fluidized bed calcination in step (1) is replaced by conventional calcination. The preparation method of the lithium iron phosphate material in this embodiment includes the following steps:

[0185] 1) The ferrophosphorus slag is conventionally roasted in an air atmosphere at a temperature of 500°C for 3 hours to obtain a roasted material.

[0186] (2) In a reactor, the roasted material is dissolved in a phosphoric acid solution by continuous stirring to obtain a phosphorus-iron mixture; wherein the concentration of the phosphoric acid solution is 2 mol / L, the initial temperature is 55°C, and the molar ratio of the phosphate ion to the iron element in the phosphorus-iron mixture is (1.2-1.4):1.

[0187] (3) Under stirring conditions, an acid-base regulator is added to the ferrophosphorus mixture to obtain a first slurry; the temperature of the first slurry is controlled to 58°C, a stabilizer is added, and the mixture is stirred for 2 hours to obtain a second slurry; the second slurry is preheated to 70°C, and a ferrophosphorus compensator is added to obtain a precursor slurry.

[0188] The acid-base regulator is 26 wt % ammonia water and 25 wt % hydrogen peroxide, with a volume ratio of 1:1, and the pH value of the first slurry is controlled to be 1.6.

[0189] The preparation method of the stabilizer comprises: mixing a dopant and a polyol, and ball milling for 1 hour at a rotation speed of 500 rpm, a material-to-ball ratio of 0.4:1, and a ball milling medium of zirconia ceramic balls to obtain the stabilizer; wherein the dopant is strontium oxide, the polyol is pentaerythritol, the mass ratio of the two is 0.5:1, and the molar ratio of the vanadium element in the strontium oxide to the iron element in the ferrophosphorus mixture is 0.23:100.

[0190] The ferrophosphorus compensator is iron powder, and the molar ratio of the iron element to the phosphorus element in the precursor slurry is controlled to be 0.985:1.

[0191] (4) The precursor slurry was further aged at 70°C for 2.5 hours to obtain an aged material; the aged material was washed with pure water for 4 times, and the iron content in the clear liquid of the last washing was 3.68 mg / L and the phosphorus content was 193.32 mg / L to obtain a washed material; the washed material was transferred to a rotary kiln and dried and dehydrated at 700°C for 4 hours to obtain the desired precursor, which had a flaky structure, and the average thickness of the flaky structure was 0.09 μm, and the specific surface area was 11.6 m 2 / g, and the tap density is 1.28g / cm 3 , particle size D50 is 14.7μm.

[0192] (5) Mixing the precursor, lithium source, organic carbon source and pure water to obtain a mixture with a solid content of about 40%; performing wet grinding to obtain a grinding material with a D50 particle size of 424 nm; spray drying the grinding material to obtain a dry material with a moisture content of 3.7%; heating to 770°C in a pure nitrogen atmosphere and keeping the temperature for 8 hours, and cooling to obtain a sintered material; and air-flow milling the sintered material to obtain a lithium iron phosphate material with a D50 particle size of 0.99 μm.

[0193] The lithium source is lithium carbonate, and the molar ratio of the lithium element of the lithium source to the phosphorus element of the precursor is 0.996:1.

[0194] The organic carbon sources are sucrose and polyacrylic acid, and the mass ratio of sucrose, polyacrylic acid and precursor is 7.3:6.6:100.

[0195] Comparative Example 1

[0196] The preparation method of the lithium iron phosphate material of this embodiment comprises the following steps:

[0197] (1) The ferrophosphorus slag is calcined in an air atmosphere at a temperature of 500°C for 3 hours to obtain a calcined material.

[0198] (2) In a reactor, the roasted material is dissolved in a phosphoric acid solution by continuous stirring to obtain a phosphorus-iron mixture; wherein the concentration of the phosphoric acid solution is 2 mol / L, the initial temperature is 55°C, and the molar ratio of the phosphate ion to the iron element in the phosphorus-iron mixture is (1.2-1.4):1.

[0199] (3) Under stirring conditions, an acid-base regulator is added to the ferrophosphorus mixture to obtain a first slurry; the temperature of the first slurry is controlled to 58°C, no stabilizer is added, and the reaction is stirred for 2 hours to obtain a second slurry; the first slurry is preheated to 70°C, and a ferrophosphorus compensator is added dropwise to obtain a precursor slurry.

[0200] The acid-base regulator is 26 wt % ammonia water and 25 wt % hydrogen peroxide, with a volume ratio of 1:1, and the pH value of the first slurry is controlled to be 1.6.

[0201] The ferrophosphorus compensator is iron powder, and the molar ratio of the iron element to the phosphorus element in the precursor slurry is controlled to be 0.985:1.

[0202] (4) The precursor slurry was further aged at 70°C for 2.5 hours to obtain an aged material; the aged material was washed with pure water for 4 times, and the iron content in the clear liquid of the last washing was 5.46 mg / L and the phosphorus content was 282.34 mg / L to obtain a washed material; the washed material was transferred to a rotary kiln and dried and dehydrated at 700°C for 4 hours to obtain the desired precursor, which showed a loose flaky structure with many fragmented points and a specific surface area of ​​9.6 m 2 / g, and the tap density is 1.12g / cm 3 , particle size D50 is 18.8μm.

[0203] (5) Mixing the precursor, lithium source, organic carbon source and pure water to obtain a mixture with a solid content of about 40%; wet grinding to obtain a grinding material with a D50 particle size of 423 nm; spray drying the grinding material to obtain a dry material with a moisture content of 3.7%; heating to 770°C in a pure nitrogen atmosphere and keeping the temperature for 8 hours, cooling to obtain a sintered material; air flow crushing the sintered material to obtain a lithium iron phosphate material with a D50 particle size of 1.13 μm.

[0204] The lithium source is lithium carbonate, and the molar ratio of the lithium element of the lithium source to the phosphorus element of the precursor is 0.996:1.

[0205] The organic carbon sources are sucrose and polyacrylic acid, and the mass ratio of sucrose, polyacrylic acid and precursor is 7.3:6.6:100.

[0206] Comparative Example 2

[0207] This comparative example is basically the same as Example 4, except that: in step (3), the stabilizer does not contain pentaerythrodiol, but only contains dopant strontium oxide, and the strontium oxide is ball-milled for 1 hour under the same conditions.

[0208] Comparative Example 3

[0209] This comparative example is basically the same as Example 4, except that: the stabilizer in step (3) does not contain the dopant strontium oxide, but only pentaerythritol, and the pentaerythritol is ball-milled for 1 hour under the same conditions.

[0210] Comparative Example 4

[0211] This comparative example is basically the same as Example 4, except that the stabilizer in step (3) is replaced by a mixture of strontium oxide and pentaerythritol, and ball milling is not performed.

[0212] Test Case

[0213] (1) Test method

[0214] 1. Scanning electron microscope (SEM) test: The sample is fixed with conductive glue or tape, the instrument uses an accelerating voltage of 5kV, and the test is observed in a vacuum state. The results are shown in Figure 2~Figure 3 , and observed the structural parameters of the sample (sheet thickness, D10 particle size, D50 particle size and D90 particle size), and calculated the diameter distance based on (D90-D10) / D50. The results are shown in Table 1 and Table 2. Among them, Figure 2 This is the SEM image of the precursor prepared in Example 3. Figure 3 This is the SEM image of the lithium iron phosphate material prepared in Example 3.

[0215] 2. X-ray powder diffraction (XRD) test: the test scanning speed is 5° / min, the angle range is 5°~90°, and the results are shown in Figure 4 .

[0216] 3. Specific surface area (BET) test: The adsorption gas is nitrogen, and the degassing condition is 200℃ for 2h.

[0217] 4. Tap density: Weigh 50 g of sample, put it into a 100 mL graduated cylinder, place the graduated cylinder on a vibration device, and vibrate it 3000 times.

[0218] 5. Electrochemical Performance Testing: Lithium iron phosphate (LiFePO4), conductive agent SP, and binder PVDF were weighed in a mass ratio of 90:5:5. NMP was added and ball-milled for 4 hours to create a slurry. The slurry was coated on an aluminum foil surface and dried at 120°C. The process was then roller-pressed, sheeted, and assembled. The negative electrode consisted of a lithium sheet, the electrolyte was a 1 mol / L LiPF6 solution, and the solvent was a 1:1 volume ratio of ethylene carbonate (EC) and diethyl carbonate (DEC). A polypropylene microporous membrane served as the separator. Coin-type cells were assembled and tested using a battery testing system at room temperature over a voltage range of 2.0–3.80 V. Similar commercially available products were assembled and tested identically. The battery's 0.1C initial discharge specific capacity, 0.1C initial charge / discharge efficiency, 10C initial discharge specific capacity, and 10C / 0.1C rate were recorded. The results are shown in Table 2.

[0219] Depend on Figure 2 It can be seen that the precursor prepared in Example 3 has a flaky structure, and the flaky structures are stacked to form a dense structure, which is conducive to the preparation of lithium iron phosphate materials with stable performance.

[0220] Depend on Figure 3 It can be seen that the lithium iron phosphate material prepared in Example 3 has a spherical structure with relatively uniform particle size and high sphericity, and the carbon coating effect is good, which plays an important role in stabilizing the performance of the material.

[0221] Depend on Figure 4 It can be seen that the XRD curve of the lithium iron phosphate material prepared in Example 3 is consistent with the lithium iron phosphate standard card, with no impurity peaks and no impurity phases, indicating that the material is a lithium iron phosphate material with good crystallinity.

[0222] As shown in Table 1, the precursors prepared in Examples 1 to 5 all have a flaky and dense structure, with a flaky layer thickness of 0.05 μm to 0.09 μm, a D50 particle size of 10.4 μm to 14.7 μm, and a specific surface area of ​​10.7 m 2 / g~13.1m 2 / g, and the tap density is 1.28g / cm 3 ~1.41g / cm 3 Compared with Examples 1 to 5, the precursors prepared in Comparative Examples 1 to 4 exhibited a loose flaky structure with many fragmented points and a significantly lower tap density.

[0223] As shown in Table 2, the lithium iron phosphate materials prepared in Examples 1-5 all have spherical structures, with D50 particle sizes ranging from 0.95 μm to 1.22 μm and diameter spacings ranging from 2.03 to 2.48. Compared to Examples 1-5, the lithium iron phosphate materials prepared in Comparative Examples 1-4 have quasi-spherical structures with lower sphericity, significantly increased diameter spacing, and reduced particle size uniformity.

[0224] As can be seen from Table 3, after the lithium iron phosphate materials prepared in Examples 1 to 5 are used as the positive electrode material to be assembled into button batteries, the 0.1C discharge specific capacity of the battery can reach more than 159.2 mAh / g, the 0.1C first charge and discharge efficiency is stable at more than 98%, the 10C discharge specific capacity can reach more than 123.6 mAh / g, and the 10C / 0.1C rate is stable at more than 77%, which is significantly higher than that of Comparative Examples 1 to 4 and commercially available products.

[0225] Table 1. Precursor related parameters

[0226]

[0227] Table 2. Related parameters of lithium iron phosphate

[0228]

[0229] Table 3. Electrochemical properties of button cells

[0230]

[0231] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0232] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of protection of the present application. It should be noted that a person of ordinary skill in the art may make various modifications and improvements without departing from the spirit of the present application, and such modifications and improvements fall within the scope of protection of the present application. Therefore, the scope of protection of the present application shall be determined by the appended claims.

Claims

1. A method for preparing a lithium iron phosphate material, characterized in that: The following steps are involved: calcining the ferrophosphorus slag to obtain a calcined material; dissolving the calcined material in an acid solution to obtain a phosphorus-iron mixed solution; Mixing the ferrophosphorus mixture, an acid-base regulator, a stabilizer, and a ferrophosphorus compensator to obtain a precursor slurry; Performing an aging treatment, a washing treatment, and a first drying treatment on the precursor slurry to obtain a precursor; The precursor, the lithium source and the organic carbon source are mixed, and subjected to grinding, a second drying and sintering treatment to obtain a lithium iron phosphate material; Wherein, the stabilizer includes a dopant and a polyol grafted onto the dopant; The preparation method of the stabilizer comprises the following steps: mixing the dopant and the polyol, and performing ball milling to obtain the stabilizer; The dopant includes one or more of titanium dioxide, strontium oxide, ammonium metavanadate, chromium nitrate, barium nitrate, barium carbonate, aluminum oxide, aluminum nitrate, nickel oxide, magnesium oxide, and magnesium carbonate; The polyol includes one or more of ethylene glycol, propylene glycol, butylene glycol, hexylene glycol, neopentyl glycol, pentaerythritol, trihydroxymethylpropane and glycerol; The acid-base regulator includes one or more of ammonia water, hydrogen peroxide, ammonium carbonate and ammonium bicarbonate; The phosphorus-iron compensator includes one or more of phosphoric acid, ammonium dihydrogen phosphate, diammonium phosphate, triammonium phosphate, iron powder, iron oxide, iron hydroxide and iron oxyhydroxide; The precursor has a flaky structure, the thickness of the flaky structure is 0.02 μm to 0.2 μm, and the specific surface area of ​​the precursor is 7 m 2 / g~17m 2 / g, and the tap density of the precursor is 0.9g / cm 3 ~1.6g / cm 3 , the D50 particle size of the precursor is 6 μm~16 μm.

2. The method for preparing the lithium iron phosphate material according to claim 1, wherein: One or more of the following conditions are met: (1) The mass ratio of the dopant to the polyol is (0.2-1.5):1; (2) The mass ratio of the doping element in the dopant to the iron element in the ferrophosphorus mixture is (0.01-0.5):100; (3) The ball milling conditions include: ball milling time of 0.1h~5h, ball milling speed of 200rpm~800rpm, material-ball ratio of (0.1~0.8):1, and ball milling medium of zirconia ceramic balls.

3. The method for preparing the lithium iron phosphate material according to any one of claims 1 to 2, wherein: Mixing the ferrophosphorus mixed solution, the acid-base regulator, the stabilizer and the ferrophosphorus compensator comprises the following steps: Mixing the ferrophosphorus mixture and the acid-base regulator to obtain a first slurry with a pH of 1.5 to 3.0; mixing the first slurry and the stabilizer, stirring and reacting them to obtain a second slurry; The second slurry and the ferrophosphorus compensator are mixed so that the molar ratio of the iron element to the phosphorus element in the precursor slurry is (0.95-1.02):

1.

4. The method for preparing the lithium iron phosphate material according to claim 3, wherein: One or more of the following conditions are met: (1) The stirring reaction temperature is 30°C to 70°C; (2) The stirring reaction time is 0.5h~2h; (3) The temperature of mixing the second slurry and the ferrophosphorus compensator is 50°C to 105°C.

5. The method for preparing the lithium iron phosphate material according to claim 3, wherein: The calcination process includes a fluidized bed calcination process, the calcination temperature is 300° C. to 550° C., and the calcination time is 2 hours to 8 hours.

6. The method for preparing the lithium iron phosphate material according to claim 3, wherein: One or more of the following conditions are met: (1) The acid in the acid solution includes one or more of sulfuric acid, nitric acid and phosphoric acid; (2) The acid concentration in the acid solution is 0.5 mol / L to 5 mol / L; (3) The temperature of the acid solution is 50°C to 95°C; (4) The molar ratio of the acid radical ions in the acid solution to the iron ions in the ferrophosphorus mixture is (1.2-3.6):

1.

7. The method for preparing the lithium iron phosphate material according to any one of claims 1 to 2 and 4 to 6, characterized in that: One or more of the following conditions are met: (1) The lithium source includes one or more of lithium carbonate, lithium hydroxide, lithium oxalate, lithium acetate and lithium nitrate; (2) The molar ratio of the lithium element in the lithium source to the phosphorus element in the precursor is (0.97-1.05):1; (3) The organic carbon source includes one or more of starch, cellulose, sucrose, glucose, citric acid, chitin, Tween, polyvinyl alcohol, polyethylene glycol, polyacrylic acid and polyvinyl pyrrolidone; (4) The mass ratio of the organic carbon source to the precursor is (3-20):

100.

8. The method for preparing the lithium iron phosphate material according to claim 7, wherein: The sintering process comprises the following steps: In a protective atmosphere, keep warm at 650℃~830℃ for 4h~18h.

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