Anhydrous iron phosphate and preparation method therefor, positive electrode material and preparation method therefor, positive electrode sheet, and secondary battery

Abstract

Anhydrous iron phosphate and a preparation method therefor, a positive electrode material and a preparation method therefor, a positive electrode sheet, and a secondary battery. Among primary particles of the anhydrous iron phosphate, by weight percentage, the proportion of particles having a particle size greater than or equal to 0.01 μm and less than 0.1 μm is 10% to 30%, the proportion of particles having a particle size of 0.1 μm to 0.2 μm is 50% to 60%, the proportion of particles having a particle size greater than 0.2 μm and less than 0.4 μm is 15% to 30%, and the proportion of particles having a particle size of 0.4 μm to 0.6 μm is 0.2% to 10%. The present method is advantageous in that, by controlling particle size gradation, anhydrous iron phosphate having good dispersibility can be obtained; the anhydrous iron phosphate serves as a basis for preparing a high-compaction positive electrode material, thereby facilitating acquisition of a positive electrode material having high compaction density, good rate performance, and high charging and discharging efficiency.

Description

Anhydrous iron phosphate and its preparation method, cathode materials and their preparation methods, cathode plates, secondary batteries Technical Field

[0001] This application relates to the field of secondary battery technology, specifically to anhydrous iron phosphate and its preparation method, positive electrode material and its preparation method, positive electrode sheet, and secondary battery. Background Technology

[0002] Lithium iron phosphate is a cathode material with high specific capacity, high energy, environmental friendliness, and excellent safety performance. It has the characteristics of high theoretical specific capacity (2400mAh / g), low lithium intercalation potential (3.4V), wide operating voltage range (3.4V~4.4V), and good safety performance, and has good application prospects in electric vehicles and energy storage.

[0003] However, in many energy storage applications, the compaction density (or simply compaction) and charge / discharge efficiency (or simply energy efficiency) of lithium iron phosphate batteries still do not adequately meet user needs. Compaction density is a crucial parameter measuring the density of lithium iron phosphate electrode materials and is closely related to the electrode's volumetric energy density and cycle performance. Charge / discharge efficiency refers to the energy conversion efficiency of the battery during charging and discharging. High charge / discharge efficiency means less energy loss during charging and discharging, improving the battery's energy utilization and cycle life.

[0004] Increasing the compaction density of lithium iron phosphate is an effective way to increase driving range. However, in existing technologies, compaction density is generally increased by increasing the sintering temperature or reducing the amount of metal doping. Increasing the sintering temperature will lead to an excessive proportion of single-crystal lithium iron phosphate and increased polarization. Reducing the amount of doping will lead to a decrease in the lithium-ion diffusion rate, both of which will result in a decrease in charge and discharge efficiency.

[0005] Lithium iron phosphate is generally produced by sintering anhydrous iron phosphate with a lithium source. The performance of anhydrous iron phosphate has a significant impact on lithium iron phosphate. For example, if the particle size of anhydrous iron phosphate is too large, it will be difficult to dehydrate during rotary kiln sintering, resulting in low crystallinity of iron phosphate. This will cause crystal transformation and the production of impurity phases during the sintering process of lithium iron phosphate, leading to a decrease in the electrical performance of lithium iron phosphate. If the particle size is too small, it will cause primary particle agglomeration, reduce the efficiency of rinsing and impurity removal, and result in a high impurity content. A high proportion of small particles during sintering is not conducive to the preparation of high-compact products.

[0006] Therefore, there is still significant room for improvement in the charge-discharge efficiency of high-compact lithium iron phosphate (LFP) in existing technologies. However, research on the key raw material, anhydrous iron phosphate, mainly focuses on controlling the iron-to-phosphorus ratio and BET specific surface area. The electrical performance of LFP is improved primarily by increasing the iron-to-phosphorus ratio and decreasing the BET specific surface area. However, LFP prepared in this way tends to have small particles and elongated strip-like or sheet-like structures, failing to achieve good particle size distribution and resulting in low packing density. LFP prepared with high iron-to-phosphorus ratio iron phosphate generally has low compaction density. The strip-like and sheet-like iron phosphate is difficult to mill, resulting in irregular particles, poor carbon coating, high powder internal resistance, and unsatisfactory electrical performance. Anhydrous iron phosphate with a small BET specific surface area is mainly achieved by increasing the rotary kiln sintering temperature, which is difficult to mill, requires a high sintering temperature, and leads to poor discharge performance. Therefore, increasing the compaction density of currently prepared high-compact LFP always reduces discharge performance. Currently, there is no LFP material with both high compaction density and high charge-discharge efficiency. Summary of the Invention

[0007] In view of the technical problems existing in the background art, this application provides anhydrous iron phosphate and its preparation method, cathode material and its preparation method, cathode electrode sheet, and secondary battery, aiming to solve the technical problem that the particle size distribution of anhydrous iron phosphate in the prior art is not good, which leads to the inability of lithium iron phosphate cathode materials to achieve both high actual density and high charge and discharge efficiency.

[0008] In a first aspect, embodiments of this application provide anhydrous ferric phosphate, wherein, by weight percentage, the primary particles of the anhydrous ferric phosphate contain 10% to 30% particles with a diameter greater than or equal to 0.01 μm and less than 0.1 μm, 50% to 60% particles with a diameter of 0.1 μm to 0.2 μm, 15% to 30% particles with a diameter greater than 0.2 μm and less than 0.4 μm, and 0.2% to 10% particles with a diameter of 0.4 μm to 0.6 μm.

[0009] In the technical solution of this application embodiment, by controlling the particle size distribution within the above range, an anhydrous iron phosphate with good dispersibility is obtained. The anhydrous iron phosphate with a good particle size distribution becomes the basis for preparing high-compact cathode materials, ensuring that lithium iron phosphate grains grow normally under high doping conditions, which is beneficial to obtaining cathode materials with high compaction density, good rate performance, and high charging and discharging efficiency.

[0010] In some embodiments, the anhydrous ferric phosphate particles are spherical with a sphericity of 0.84–0.98; the tap density of the anhydrous ferric phosphate is 0.93 g / cm³. 3 ~1.13g / cm 3 The compacted density is 1.57 g / cm³. 3 ~1.61g / cm 3The iron-to-phosphorus ratio is (0.957~0.970):1.

[0011] In this embodiment, anhydrous iron phosphate has higher sphericity and higher tap density, indicating better particle packing density and reasonable particle size distribution. The lithium iron phosphate prepared as raw material also has a relatively higher compaction density. Combined with a suitable iron-phosphorus ratio, it is beneficial to further improve charging and discharging efficiency.

[0012] Secondly, embodiments of this application provide a method for preparing anhydrous ferric phosphate, comprising:

[0013] The ferrous source is mixed with the first dispersant to obtain the first raw material solution; the first phosphorus source is mixed with the second dispersant to obtain the second raw material solution.

[0014] The first raw material liquid, the second raw material liquid, and the first oxidant are mixed and subjected to a first reaction treatment to obtain a first mixture;

[0015] A second phosphorus source is added to the first mixture, followed by a second reaction treatment, and then a second oxidant is added to obtain a second mixture.

[0016] After adjusting the pH and temperature of the second mixture and undergoing a third reaction, anhydrous ferric phosphate is obtained.

[0017] The first dispersant includes a cationic monomer and a coupling agent, and the second dispersant includes anionic monomers and a chain transfer agent.

[0018] In the technical solution of this application embodiment, anhydrous iron phosphate is prepared by precipitation method. The surface tension of the solution is reduced and the reaction rate is increased by the surfactant-like effect of the polymer formed by the first dispersant and the second dispersant. At the same time, the dispersion and complexation effect of the polymer is used to regulate the crystal morphology. Combined with the stepwise addition of oxidant and phosphorus source to regulate the reaction process and control the iron-phosphorus ratio, the anhydrous iron phosphate prepared has higher sphericity, more reasonable particle size distribution, and a lower proportion of large particles. Under these conditions, the compaction density is significantly improved. The compaction density of lithium iron phosphate prepared by this anhydrous iron phosphate is significantly increased, and the charge-discharge rate performance is better.

[0019] In some embodiments, the cationic monomer comprises dimethyl diallyl ammonium chloride and / or acryloyloxyethyl trimethyl ammonium chloride; and / or, the coupling agent comprises vinyltrimethoxysilane and / or 3-(methacryloyloxy)propyltrimethoxysilane; when the cationic monomer comprises dimethyl diallyl ammonium chloride and acryloyloxyethyl trimethyl ammonium chloride, the mass ratio of dimethyl diallyl ammonium chloride to acryloyloxyethyl trimethyl ammonium chloride is 1:(2.5-3.5); and / or,

[0020] The anionic monomer includes one or more of methacrylic acid, itaconic acid, and fumaric acid; and / or, the chain transfer agent includes sodium hypophosphite and / or isopropanol; when the anionic monomer includes methacrylic acid and itaconic acid, the mass ratio of methacrylic acid to itaconic acid is 1:(2.5-3.5); when the anionic monomer includes methacrylic acid and fumaric acid, the mass ratio of methacrylic acid to fumaric acid is 1:(2.5-3.5); and / or, the molar ratio of cationic monomer to coupling agent is 100:(20-35); and / or, the molar ratio of anionic monomer to chain transfer agent is 100:(10-15).

[0021] In this embodiment, the aforementioned cationic and anionic monomers are more conducive to the smooth polymerization of the polymer with the assistance of coupling agents and chain transfer agents. This polymer is a surfactant-like agent; after initially exerting its dispersing ionic effect, the polymer formed by the cationic and anionic monomers continuously disperses the ferric phosphate crystal particles. Simultaneously, the polymer formed by the anionic and cationic monomers further reduces the surface tension of the solution, better promoting the spherical growth of ferric phosphate crystals and increasing the crystallinity of ferric phosphate crystals, thereby improving the tap density of the final anhydrous ferric phosphate.

[0022] In some embodiments, the molar ratio of iron in the ferrous source to the first dispersant is 1:(0.0125–0.0150); and / or, the molar ratio of iron in the ferrous source to phosphorus in the phosphorus source is 1:(0.9–1.1); and / or, the molar ratio of phosphorus in the phosphorus source to the second dispersant is 1:(0.0150–0.0170); and / or, the ferrous source is prepared by the following method: dissolving titanium dioxide byproduct containing ferrous sulfate in water by heating, adding 5%–15% ammonia water by mass for sedimentation, filtering, and retaining the filtrate to obtain the ferrous source; and / or, independently, the first phosphorus source and the second phosphorus source are prepared by the following method: dissolving monoammonium phosphate in phosphoric acid and water and filtering, adding 5%–15% ammonia water by mass to the filtrate to adjust the pH to 6–8.

[0023] In this embodiment, the above-mentioned ratio conditions are more conducive to the full precipitation of iron ions by phosphate ions, and further enhance the binding force between the positive charge of the cationic group from the cationic monomer and phosphate ions in the polymer formed by the anionic monomer and the cationic monomer, as well as the binding force between the anionic group from the anionic monomer and iron ions in the polymer formed by the anionic monomer and the cationic monomer, thereby promoting the spherical growth of particles and playing a better role in particle size control.

[0024] In some embodiments, the first oxidant includes hydrogen peroxide and / or sodium peroxide; and / or, the second oxidant includes hydrogen peroxide and / or sodium peroxide; and / or, the mass ratio of the first phosphorus source to the second phosphorus source is (15-25):(75-85); and / or, the molar ratio of the first oxidant to the iron element in the ferrous source is (0.6-1.1):1, and the molar ratio of the second oxidant to the iron element in the ferrous source is (2.1-2.8):1.

[0025] In this embodiment, the concentrations of the oxidant and reactants are used together to regulate the reaction rate within a more suitable range; the addition of the first phosphorus source and the second phosphorus source are controlled to control the stepwise feeding, thereby controlling the formation and growth of ferric phosphate, further improving the particle size distribution, and which is conducive to further improving the sphericity and dispersibility of anhydrous ferric phosphate.

[0026] In some embodiments, in the first reaction treatment, the temperature is 40°C to 60°C and the time is 0.5h to 1h; and / or, in the second reaction treatment, the temperature is 40°C to 60°C and the time is 5min to 10min.

[0027] In this embodiment, the precipitation rate and dispersion effect of ferric phosphate are better within the above-mentioned reaction temperature and time range, further improving the particle size distribution of anhydrous ferric phosphate particles.

[0028] In some embodiments, the step of adjusting the pH and temperature of the second mixture and obtaining anhydrous ferric phosphate after a third reaction includes: adjusting the temperature of the second mixture to 40°C to 60°C, controlling the pH of the second mixture to 0.9 to 1.5, raising the temperature to 90°C to 95°C and reacting until the pH value is 1.6 to 2.0 to obtain a third mixture; and sequentially subjecting the third mixture to pressure filtration, rinsing, flash evaporation, drying, pulverizing, and sieving to obtain anhydrous ferric phosphate.

[0029] In this embodiment, by adjusting the temperature and pH of the mixture within a suitable range, the stable precipitation of ferric phosphate is further controlled. Combined with pressure filtration, rinsing, flash evaporation, drying, pulverizing, and sieving, anhydrous ferric phosphate with high sphericity, good dispersibility, and good particle size distribution is prepared, making the preparation method more practical.

[0030] Thirdly, embodiments of this application provide a cathode material, the general formula of which is LiFe. 1-a-b-c Y a Ce b M c PO4@C, wherein M is one or more of tin, titanium, boron, and manganese, a is 0.007 to 0.013, b is 0.029 to 0.057, and c is 0.01 to 0.033; the mass fraction of C in the cathode material is 1.2% to 1.4%.

[0031] In this embodiment, the positive electrode material contains the above-mentioned anhydrous iron phosphate, and is modified by doping with three metal cations with different mechanisms and proportions to refine the grains. The cations combine with the phosphate ions in the anhydrous iron phosphate to reduce the grain coarsening effect of the phosphate ions, ensuring the normal growth of the grains under the initial structure of iron phosphate and high doping conditions. Therefore, it has the advantages of high compaction density, good rate performance, and high charging and discharging efficiency.

[0032] In some embodiments, the average primary particle size of the cathode material is 0.24 μm to 0.34 μm; wherein, in the cathode material, the fraction of particles with an average primary particle size greater than or equal to 1 μm is less than or equal to 3.20%, and the compaction density is 2.52 g / cm³. 3 ~2.64g / cm 3 .

[0033] In this embodiment, the raw material can be anhydrous iron phosphate with a variety of particle sizes, which can control the crystallization and growth process of lithium iron phosphate, further reduce the formation of large single crystals in high-compact lithium iron phosphate, and improve the compaction density and energy storage performance of the cathode material.

[0034] Fourthly, embodiments of this application provide a method for preparing a cathode material, comprising the following steps:

[0035] The anhydrous iron phosphate, lithium source, carbon source, complexing agent, and dopant described in this application are mixed with water to obtain a mixture.

[0036] The mixture is sintered under a protective atmosphere to obtain the cathode material;

[0037] The dopants include oxides of yttrium, oxides of cerium, and other oxides, including one or more oxides of tin, titanium, boron, and manganese.

[0038] In this embodiment, anhydrous iron phosphate with high crystallinity, low impurity content, and excellent particle size distribution is used as raw material. By controlling the crystallization and growth process of lithium iron phosphate, the generation of large single crystals in high-compact lithium iron phosphate is significantly reduced. During the crystallization and growth process of lithium iron phosphate, the complexing agent plays an inhibitory role before carbon coating, effectively avoiding the formation of crystal nuclei and reducing the generation of ineffective single crystals during the growth of lithium iron phosphate particles. On the one hand, this ensures the effective proportion of high-efficiency lithium iron phosphate and improves the compaction density of lithium iron phosphate; on the other hand, it ensures good carbon coating effect and low powder internal resistance and polarization of lithium iron phosphate, so that the cathode material has excellent charging performance, discharging performance and long-lasting cycle performance.

[0039] In some embodiments, the complexing agent includes glycerol and / or sodium gluconate; and / or, the dopant includes yttrium oxide, cerium oxide and other oxides, the other oxides including one or more of tin dioxide, titanium dioxide, boron trioxide and manganese carbonate; the mass ratio of yttrium oxide, cerium oxide and other oxides is 1:(2-3):(1-2); and / or, the mass ratio of anhydrous iron phosphate to the complexing agent is 1:(0.02-0.03); and / or, the mass ratio of anhydrous iron phosphate to the dopant is 1:(0.008-0.009); and / or, the molar ratio of anhydrous iron phosphate to the lithium source is 1:(1-1.05); and / or, the mass ratio of anhydrous iron phosphate to the carbon source is 1:(0.09-0.11).

[0040] In this embodiment, the aforementioned inhibitor binds to the active sites of the raw materials, reducing the formation of lithium iron phosphate single crystals and improving the battery performance of lithium iron phosphate. By controlling the raw material ratio within the above-mentioned range, raw material waste is reduced while achieving more complete synthesis of lithium iron phosphate, thereby further reducing the preparation cost while maintaining the excellent battery performance of lithium iron phosphate.

[0041] In some embodiments, the step of obtaining a cathode material by sintering the mixture under a protective atmosphere includes: grinding the mixture to obtain a ground material with a D50 particle size of 0.38 μm to 0.42 μm; spray drying the ground material to obtain a spray material with a D50 particle size of 3.4 μm to 6.7 μm; and sintering the spray material under a protective atmosphere to obtain the cathode material; the sintering temperature is 760℃ to 820℃ and the time is 10h to 18h.

[0042] In this embodiment, the anhydrous lithium iron phosphate exhibits high sphericity and good particle size distribution, resulting in smaller particle size in the products obtained through grinding and spray drying. By controlling the sintering temperature within a suitable range, the compaction density can be increased, thereby enhancing the lithium-ion diffusion rate. Furthermore, this leads to a smaller proportion of single-crystal lithium iron phosphate, less polarization, and improved lithium iron phosphate battery performance.

[0043] Fifthly, embodiments of this application provide a positive electrode sheet, including a positive current collector and a positive active layer disposed on at least one side of the positive current collector, the positive active layer including the aforementioned positive electrode material.

[0044] In this embodiment, the positive electrode sheet contains the aforementioned positive electrode material, thus possessing the advantages of good rate performance and high charging and discharging efficiency.

[0045] Sixthly, embodiments of this application provide a secondary battery, including the aforementioned positive electrode sheet.

[0046] In this embodiment, the secondary battery includes the aforementioned positive electrode plate, thus possessing the advantages of good rate performance and high charging and discharging efficiency.

[0047] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0048] To more clearly illustrate the technical solutions of this application, the accompanying drawings used in this application will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without any creative effort.

[0049] Figure 1 is a SEM image of the anhydrous ferric phosphate prepared in Example 5 of this application;

[0050] Figure 2 is a SEM image of the anhydrous ferric phosphate prepared in Comparative Example 5 of this application;

[0051] Figure 3 is a comparison of the XRD patterns of anhydrous ferric phosphate prepared in Example 5 and Comparative Example 5 of this application;

[0052] Figure 4 is a SEM particle size analysis diagram of the anhydrous iron phosphate prepared in Example 5 of this application;

[0053] Figure 5 shows the SEM particle size analysis of the anhydrous iron phosphate prepared in Comparative Example 5 of this application. Detailed Implementation

[0054] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0055] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0056] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0057] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0058] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0059] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0060] In the description of the embodiments of this application, unless otherwise specified, the solvents used in the raw material liquid, reaction liquid, solution, etc., are selected from at least one of deionized water, distilled water, pure water, and ultrapure water. Similarly, unless otherwise specified, in the description of the embodiments of this application, "water" is selected from at least one of deionized water, distilled water, pure water, and ultrapure water.

[0061] The main approach to increasing the compaction density of lithium iron phosphate (LFP) is to increase the milling particle size and thus the final particle size. However, these approaches all lead to a decrease in the battery performance of LFP, especially its charge and discharge performance. One feasible method is to reduce the BET specific surface area of ​​the key raw material, anhydrous iron phosphate. However, anhydrous iron phosphate with a small BET specific surface area is mainly achieved by increasing the rotary kiln sintering temperature. Milling is difficult, the sintering temperature is high, the discharge performance is poor, and the particle size distribution is not ideal. Therefore, the discharge performance of LFP prepared under high compaction density will decrease after the compaction density is increased.

[0062] This application provides anhydrous iron phosphate and its preparation method, a cathode material and its preparation method, a cathode electrode sheet, and a secondary battery. The anhydrous iron phosphate has a suitable particle size distribution, which can achieve close packing. Furthermore, it can be used as a key raw material for preparing cathode materials, improving their compaction density, charging performance, and discharging performance.

[0063] To address the technical problem of poor particle size distribution of anhydrous iron phosphate, which leads to the inability of lithium iron phosphate cathode materials to simultaneously achieve high compaction density and high charge-discharge efficiency, this application provides anhydrous iron phosphate and its preparation method, cathode material and its preparation method, cathode electrode sheet, and secondary battery. By controlling the anhydrous iron phosphate to have a suitable particle size distribution, it achieves close packing, further serving as a key raw material for preparing the cathode material. This improves the compaction density and charge-discharge performance of the cathode material, thereby enhancing the compaction density and charge-discharge performance of the cathode electrode sheet and secondary battery.

[0064] In a first aspect, embodiments of this application provide anhydrous ferric phosphate, wherein, by weight percentage, the primary particles of the anhydrous ferric phosphate contain 10% to 30% particles with a diameter greater than or equal to 0.01 μm and less than 0.1 μm, 50% to 60% particles with a diameter of 0.1 μm to 0.2 μm, 15% to 30% particles with a diameter greater than 0.2 μm and less than 0.4 μm, and 0.2% to 10% particles with a diameter of 0.4 μm to 0.6 μm.

[0065] Preferably, by weight percentage, in the primary particles of anhydrous ferric phosphate, the proportion of particles with a diameter greater than or equal to 0.01 μm and less than 0.1 μm is 13.27% to 22.45%, the proportion of particles with a diameter of 0.1 μm to 0.2 μm is 54.23% to 59.37%, the proportion of particles with a diameter greater than 0.2 μm and less than 0.4 μm is 17.98% to 26.76%, and the proportion of particles with a diameter of 0.4 μm to 0.6 μm is 0.3% to 7.46%.

[0066] More preferably, by weight percentage, in the primary particles of anhydrous ferric phosphate, the proportion of particles with a diameter greater than or equal to 0.01 μm and less than 0.1 μm is 15.04% to 21.03%, the proportion of particles with a diameter of 0.1 μm to 0.2 μm is 54.73% to 59.37%, the proportion of particles with a diameter greater than 0.2 μm and less than 0.4 μm is 17.98% to 25.76%, and the proportion of particles with a diameter of 0.4 μm to 0.6 μm is 1.49% to 6.68%.

[0067] Typical, but not limiting, percentage by weight of anhydrous ferric phosphate particles, the percentage of particles with a diameter greater than or equal to 0.01 μm and less than 0.1 μm is 10%, 15%, 20%, 25%, 30%, or any two of these values; the percentage of particles with a diameter of 0.1 μm to 0.2 μm is 50%, 52%, 55%, 58%, 60%, or any two of these values; the percentage of particles with a diameter greater than 0.2 μm and less than 0.4 μm is 15%, 18%, 20%, 22%, 25%, 28%, 30%, or any two of these values; and the percentage of particles with a diameter of 0.4 μm to 0.6 μm is 0.2%, 1%, 2%, 5%, 8%, 10%, or any two of these values.

[0068] By controlling the particle size distribution within the aforementioned range, a well-dispersed anhydrous iron phosphate is obtained, exhibiting a normally distributed particle size distribution. After sintering, the overall particle size increases, but the particle size distribution remains relatively good, ensuring a suitable ratio of large to small anhydrous iron phosphate particles. This reduces the proportion of coarse particles while achieving high compaction density and high discharge performance through the close packing of the anhydrous iron phosphate particles. The well-matched particle sizes of anhydrous iron phosphate form the basis for further preparation of high-compact-density lithium iron phosphate materials, ensuring normal grain growth of the prepared lithium iron phosphate under high doping conditions, resulting in a cathode material with high compaction density, good rate performance, and high charging and discharging efficiency.

[0069] Furthermore, in some embodiments, the anhydrous ferric phosphate particles are spherical in shape, with a sphericity of 0.84 to 0.98, preferably 0.96 to 0.98.

[0070] In some embodiments, the tap density of anhydrous ferric phosphate is 0.93 g / cm³. 3 ~1.13g / cm 3 The preferred value is 0.95 g / cm³. 3 ~1.06g / cm 3 .

[0071] In some embodiments, the compaction density is 1.57 g / cm³. 3 ~1.61g / cm 3 The preferred value is 1.58 g / cm³. 3 ~1.61g / cm 3 .

[0072] In some embodiments, the iron-to-phosphorus ratio is (0.957–0.970):1, preferably (0.963–0.966):1. Wherein, the iron-to-phosphorus ratio is the molar ratio of iron to phosphorus in anhydrous ferric phosphate.

[0073] In some embodiments, the BET specific surface area of ​​anhydrous ferric phosphate is 8 m². 2 / g~10.8m 2 / g, preferably 8.65m 2 / g~9.37m 2 / g.

[0074] Typically, but not exclusively, anhydrous ferric phosphate particles are spherical, with a sphericity ranging from 0.84, 0.85, 0.90, 0.95, 0.98, or any two of these values; the tap density of anhydrous ferric phosphate is 0.93 g / cm³. 3 0.95g / cm 3 1.00g / cm 3 1.05g / cm 3 1.10 g / cm 3 1.13 g / cm 3 The compacted density is 1.57 g / cm³, or a range of any two values ​​thereof. 3 1.58g / cm 3 1.59g / cm 3 1.60g / cm 3 1.61 g / cm 3 The iron-to-phosphorus ratio is 0.957:1, 0.960:1, 0.965:1, 0.970:1, or any two of these values ​​within a range. The BET specific surface area of ​​anhydrous ferric phosphate is 8 m². 2 / g, 8.5m 2 / g、9m 2 / g, 9.5m 2 / g, 10m 2 / g, 10.5m 2 / g, 10.8m 2 / g or a range of values ​​consisting of any two of its values.

[0075] In the technical solution of this application embodiment, anhydrous iron phosphate exhibits higher sphericity and higher tap density, indicating better particle packing density and reasonable particle size distribution. This results in a relatively higher compaction density for lithium iron phosphate. With better particle size distribution, the grinding time during lithium iron phosphate preparation can be further reduced, thereby lowering energy consumption and improving efficiency while maintaining lithium iron phosphate performance. A lower iron-to-phosphorus ratio also facilitates the generation of excess phosphate ions, allowing for further modification of lithium iron phosphate and improving its compaction density and charging / discharging efficiency.

[0076] Secondly, embodiments of this application provide a method for preparing anhydrous ferric phosphate, comprising:

[0077] The ferrous source is mixed with the first dispersant to obtain the first raw material solution; the first phosphorus source is mixed with the second dispersant to obtain the second raw material solution.

[0078] The first raw material liquid, the second raw material liquid, and the first oxidant are mixed and subjected to a first reaction treatment to obtain a first mixture;

[0079] A second phosphorus source is added to the first mixture, followed by a second reaction treatment, and then a second oxidant is added to obtain a second mixture.

[0080] After adjusting the pH and temperature of the second mixture and undergoing a third reaction, anhydrous ferric phosphate is obtained.

[0081] The first dispersant includes a cationic monomer and a coupling agent, and the second dispersant includes anionic monomers and a chain transfer agent.

[0082] The most important aspects of preparing anhydrous ferric phosphate via coprecipitation are controlling the iron-to-phosphorus ratio and the reaction process, followed by controlling particle size and morphology. This application utilizes the surfactant-like effect of the polymer formed by the first and second dispersants to reduce the surface tension of the reaction solvent and increase the reaction rate. Simultaneously, the dispersion and complexation effects of this polymer (e.g., the adsorption and binding of carboxyl groups in the polymer anions with ferrous ions) are used to regulate the crystal morphology. Furthermore, the stepwise addition of oxidant and phosphorus source is combined to regulate the reaction process and control the iron-to-phosphorus ratio. This results in anhydrous ferric phosphate with higher sphericity, more reasonable particle size distribution, and a significantly increased compaction density under conditions of lower large particle proportion. The resulting lithium iron phosphate prepared from this anhydrous ferric phosphate exhibits a significantly increased compaction density and better charge-discharge rate performance.

[0083] Specifically, this application uses a co-precipitation method to prepare ferric phosphate. Iron ions and phosphate ions undergo a precipitation reaction in a specific ratio. The cationic monomer is an organic compound containing both a cationic and carbon-carbon double bonds, and the anionic monomer is an organic compound containing both anionic and carbon-carbon double bonds. The cationic and anionic monomers undergo a polymerization reaction under the action of an oxidizing agent and a reducing agent (partially iron in the form of ferrous ions) to generate a polymer containing both anionic and cationic groups. The ionicly active portion exists during the ferric phosphate reaction, thus readily adsorbing the polymer. After adsorption onto the surface of the ferric phosphate particles, the polymer forms an adsorption layer, facilitating particle separation and dispersing. Simultaneously, the polymer's electrostatic adsorption on the surface of the ferric phosphate particles, occupying active sites, also restricts the growth of ferric phosphate, thereby inhibiting the growth of ferric phosphate crystals. Furthermore, the polymer is a surfactant-like agent, capable of reducing the surface tension of the solution and promoting the spherical growth of ferric phosphate particles to achieve the lowest surface energy, thereby controlling the reaction rate and particle morphology.

[0084] In summary, this application controls the formation and growth of ferric phosphate by stepwise feeding of phosphorus source combined with the complexing and dispersing effect of polymers formed by cationic and anionic monomers, thereby achieving particle size distribution and preparing anhydrous ferric phosphate with high sphericity, good dispersibility and good particle size distribution.

[0085] When preparing lithium iron phosphate cathode materials based on the anhydrous iron phosphate of this application, the anhydrous iron phosphate prepared by the aforementioned method exhibits better dispersibility, higher crystallinity, and better particle size distribution. Furthermore, the interpenetration and barrier stratification of the polymers formed by cationic and anionic monomers also contribute to improved rinsing efficiency. Combined with controlling the crystallization and growth of lithium iron phosphate during the preparation process, this significantly reduces the formation of large single crystals in high-compact lithium iron phosphate, ensuring the effective proportion of high-efficiency lithium iron phosphate and endowing it with excellent energy storage performance. Simultaneously, when the iron-to-phosphorus ratio of the aforementioned anhydrous iron phosphate is (0.957–0.970):1, excess phosphate ions can also modify lithium iron phosphate, ensuring normal grain growth of lithium iron phosphate under high doping conditions. This results in the preparation of cathode materials with high compaction density, good rate performance, and high charging and discharging efficiency.

[0086] Furthermore, in some embodiments, the cationic monomer includes dimethyl diallyl ammonium chloride and / or acryloyloxyethyl trimethyl ammonium chloride.

[0087] In some embodiments, when the cationic monomers include dimethyl diallyl ammonium chloride and acryloyloxyethyltrimethyl ammonium chloride, the mass ratio of dimethyl diallyl ammonium chloride to acryloyloxyethyltrimethyl ammonium chloride is 1:(2.5 to 3.5).

[0088] Typical, but not limiting, the cationic monomers include dimethyl diallyl ammonium chloride and acryloyloxyethyl trimethyl ammonium chloride, wherein the mass ratio of the two is 1:2.5, 1:2.8, 1:3.0, 1:3.2, 1:3.5 or any two of these values.

[0089] In some embodiments, the coupling agent includes vinyltrimethoxysilane and / or 3-(methacryloyloxy)propyltrimethoxysilane.

[0090] In some embodiments, the anionic monomer includes one or more of methacrylic acid, itaconic acid, and fumaric acid. When the anionic monomer includes methacrylic acid and itaconic acid, the mass ratio of methacrylic acid to itaconic acid is 1:(2.5 to 3.5). Alternatively, when the anionic monomer includes methacrylic acid and fumaric acid, the mass ratio of methacrylic acid to fumaric acid is 1:(2.5 to 3.5).

[0091] Typical, but not limiting, when the anionic monomers include methacrylic acid and itaconic acid, the mass ratio of the two is 1:2.5, 1:2.8, 1:3.0, 1:3.2, 1:3.5, or any two of these values; when the anionic monomers include methacrylic acid and fumaric acid, the mass ratio of the two is 1:2.5, 1:2.8, 1:3.0, 1:3.2, 1:3.5, or any two of these values.

[0092] In some embodiments, the chain transfer agent includes sodium hypophosphite and / or isopropanol.

[0093] In some embodiments, the molar ratio of cationic monomer to coupling agent is 100:(20-35).

[0094] In some embodiments, the molar ratio of anionic monomer to chain transfer agent is 100:(10-15).

[0095] Typical, but not limiting, molar ratios of cationic monomers to coupling agents are 100:20, 100:28, 100:30, 100:32, 100:35, or any two of these values; molar ratios of anionic monomers to chain transfer agents are 100:10, 100:11, 100:12, 100:13, 100:14, 100:15, or any two of these values.

[0096] In the technical solution of this application embodiment, the polymer formed by the cationic monomer in the first dispersant and the anionic monomer in the second dispersant polymerizes relatively rapidly under redox reaction conditions. This results in a problem where some polymer is partially encapsulated by newly generated ferric phosphate, causing the polymer to lose its surfactant-like properties. Polymers formed by anionic monomers and cationic monomers with different structures have different reactivity and reaction rates. Therefore, selecting multiple anionic monomers such as methacrylic acid, itaconic acid, and fumaric acid, or selecting dimethyl diallyl ammonium chloride and acryloyloxyethyl trimethyl ammonium chloride as cationic monomers, is beneficial because it allows the polymers formed by the polymerization of anionic and cationic monomers to adsorb onto the ferric phosphate surface at different rates, thereby improving the problem of being encapsulated by newly generated ferric phosphate due to the one-time formation of the polymer. For example, the carboxyl groups in the anionic monomer combine with cations such as ferrous and ferric ions, and the cations in the cationic monomer combine with anions such as phosphate groups, adsorbing onto the surface of the obtained ferric phosphate to form a coating layer, thereby dispersing the ferric phosphate particles and improving the dispersion effect through electrostatic complexation.

[0097] For example, dimethyl diallyl ammonium chloride has two double bonds and four methyl groups. In this cationic monomer, the steric hindrance of the methyl groups reduces the electrostatic interaction between the cation and free phosphate ions, slowing down the rate of polymer adsorption and burial, which is beneficial to improving the dispersion effect and ensuring the proportion of cations in the polymer. Similarly, the three methyl groups in acryloyloxyethyltrimethylammonium chloride also play a role in providing steric hindrance and promoting dispersion. After the chloride ions dissolve, the ammonium ions in the remaining structure are positively charged and have electrostatic repulsion with ferrous ions, ferric ions, and other ammonium ions, which is beneficial to retaining ammonium ions and thus promoting their long-term dispersion effect. The combined use of the above two is beneficial to improve the long-term dispersion of cations, control the polymerization efficiency, ensure the full progress of the polymerization reaction between anionic and cationic monomers, control the molecular weight of the polymer, and improve the problem that the polymer formed by anionic and cationic monomers is coated and buried by newly generated iron phosphate in the first mixture and / or the second mixture, thereby playing a good role in dispersing iron phosphate particles, maintaining the long-term stability of iron phosphate particles, and further promoting the uniform growth of iron phosphate particles.

[0098] For example, methacrylic acid is highly reactive. At high concentrations, it reacts rapidly with cationic monomers to form polymers with excessively large molecular weights, thus failing to exert its inhibitory effect. The inhibitory effect mainly refers to the inhibition effect of the anions in the polymer preventing the crystal nuclei from continuing to grow after the polymer adsorbs onto the surface of the iron phosphate crystal nuclei. However, when the polymer molecular weight is too large, it easily disperses the iron phosphate particles, making them easier to grow, thus weakening the inhibitory effect of the polymer. Itaconic acid and fumaric acid are both dicarboxylic acids, and their polymerization reaction with cationic monomers is relatively slow. Therefore, when itaconic acid or fumaric acid is used in combination with methacrylic acid, it is beneficial to control the reaction rate of the formation of polymers from anionic and cationic monomers and to regulate the polymer molecular structure. At the same time, the strong complexation between the carboxyl anion of methacrylic acid and the ferrous and ferric ions on the surface of the iron phosphate crystal nuclei (based on surface energy electrostatic adsorption) will cause its carboxyl anions to be adsorbed and consumed too quickly. The slow release of anions by itaconic acid or fumaric acid is beneficial for the sustained effect of the complexation. Combined with the surfactant-like effect formed by the above-mentioned cationic and anionic monomers to reduce the surface tension of the solution, they jointly control the structure of the iron phosphate precursor to tend to be spherical.

[0099] The aforementioned cationic and anionic monomers are more conducive to the smooth polymerization of the polymer with the assistance of coupling agents and chain transfer agents. This polymer is a surfactant-like substance. First, the polymer plays a role in dispersing ions. Specifically, after the first and second mixtures are mixed, some free ferrous ions, ferric ions, and phosphate ions combine with the carboxyl and amino groups in the cationic and anionic monomers through electrostatic interactions. This facilitates the uniform distribution of free ferrous and ferric ions, and they combine more easily with the polymerization of the anionic and cationic monomers, thus making it easier to control the primary particle size of the generated iron phosphate particles. Subsequently, the polymer formed by the cationic and anionic monomers continues to disperse the iron phosphate crystal particles. At the same time, the polymer formed by the anionic and cationic monomers further reduces the surface tension of the solution, thereby better promoting the spherical growth of iron phosphate crystals and improving the crystallinity of iron phosphate crystals, which is beneficial to improving the tap density and other properties of the final anhydrous iron phosphate.

[0100] Furthermore, in some embodiments, the molar ratio of iron in the ferrous source to the first dispersant is 1:(0.0125 to 0.0150).

[0101] In some embodiments, the molar ratio of iron in the ferrous source to phosphorus in the phosphorus source is 1:(0.9 to 1.1).

[0102] Typical, but not limiting, the molar ratio of iron in the ferrous source to the first dispersant is 1:0.0125, 1:0.0130, 1:0.0135, 1:0.0140, 1:0.0145, 1:0.0150, or any two of these values; the molar ratio of iron in the ferrous source to phosphorus in the phosphorus source is 1:0.9, 1:0.95, 1:1.0, 1:1.05, 1:1.1, or any two of these values.

[0103] In some embodiments, the molar ratio of phosphorus in the phosphorus source to the second dispersant is 1:(0.0150 to 0.0170).

[0104] Typical, but not limiting, the molar ratio of phosphorus in the phosphorus source to the second dispersant is 1:0.0150, 1:0.0155, 1:0.0160, 1:0.0165, 1:0.0170, or any two of these values.

[0105] In some embodiments, the ferrous source is prepared by the following method: titanium dioxide byproduct containing ferrous sulfate is mixed with water and heated to dissolve, 5% to 15% ammonia water is added for sedimentation, the filtrate is retained after filtration to obtain the ferrous source.

[0106] In some embodiments, the first phosphorus source and the second phosphorus source are prepared independently by dissolving monoammonium phosphate in phosphoric acid and water and filtering, and adding 5% to 15% ammonia water by mass to adjust the pH to 6 to 8.

[0107] In the technical solution of this application embodiment, ferric ions are formed by oxidizing ferrous ions with a first oxidant and / or a second oxidant. The conversion rate of the reaction is affected by factors such as reactant concentration, temperature, and surface tension. Therefore, the iron-to-phosphorus ratio of the obtained anhydrous ferric phosphate is less than 1. Under the above ratio conditions, it is more advantageous to use excess phosphate to completely precipitate ferric ions, and further enhance the binding force between the positive charge of the cationic group from the cationic monomer and the phosphate ion in the polymer formed by the anionic monomer and the cationic monomer, as well as the binding force between the anionic group from the anionic monomer and the ferric ion in the polymer formed by the anionic monomer and the cationic monomer, thereby promoting the spherical growth of particles and playing a better role in particle size control.

[0108] Furthermore, in some embodiments, the first oxidant includes hydrogen peroxide and / or sodium peroxide; preferably, the first oxidant is added in the form of a first oxidant solution, wherein the mass fraction of the first oxidant in the first oxidant solution is 20% to 30%.

[0109] In some embodiments, the second oxidant includes hydrogen peroxide and / or sodium peroxide; preferably, the second oxidant is added in the form of a second oxidant solution, wherein the mass fraction of the second oxidant in the second oxidant solution is 20% to 30%.

[0110] In some embodiments, the mass ratio of the first phosphorus source to the second phosphorus source is (15-25):(75-85).

[0111] Typical, but not limiting, mass ratios of the first phosphorus source to the second phosphorus source are 15:85, 18:82, 20:80, 22:78, 25:75, or any two of these values.

[0112] In some embodiments, the molar ratio of the first oxidant to the iron element in the ferrous source is (0.6–1.1):1, and the molar ratio of the second oxidant to the iron element in the ferrous source is (2.1–2.8):1.

[0113] Typically, but not limitingly, the molar ratio of iron in the ferrous source to the first oxidant is 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1.0, 1:1.1, or any two of these values; the molar ratio of iron in the ferrous source to the second oxidant is 1:2.1, 1:2.2, 1:2.5, 1:2.6, 1:2.8, or any two of these values.

[0114] In the technical solution of this application embodiment, the iron ion concentration is controlled by a first oxidant and / or a second oxidant, and the phosphate concentration is controlled by the addition of a phosphorus source. The reaction rate is controlled from two aspects: a faster reaction rate results in more crystal nuclei and smaller crystal size; a slower reaction results in larger crystal size, thus controlling the size of the iron phosphate crystal particles. The aforementioned oxidant, together with the reactant concentration, can regulate the reaction rate within a more suitable range. The stepwise feeding is controlled by adjusting the amount of the first and second phosphorus sources, thereby controlling the formation and growth of iron phosphate, further improving the particle size distribution, and contributing to the further improvement of the sphericity, dispersibility, and particle size distribution of anhydrous iron phosphate.

[0115] Furthermore, in some embodiments, in the first reaction treatment, the temperature is 40°C to 60°C and the time is 0.5h to 1h; and / or, in the second reaction treatment, the temperature is 40°C to 60°C and the time is 5min to 10min.

[0116] Typical, but not limiting, in the first reaction treatment, the temperature is 40°C, 45°C, 50°C, 55°C, 60°C or any two of these values, and the time is 0.5h, 0.6h, 0.7h, 0.8h, 0.9h, 1h or any two of these values.

[0117] Typical, but not limiting, the second reaction treatment involves a temperature of 40°C, 45°C, 50°C, 55°C, 60°C or any two of these values, and a time of 5 min, 6 min, 7 min, 8 min, 9 min, 10 min or any two of these values.

[0118] In the technical solution of this application embodiment, the control of the above-mentioned reaction temperature and time can promote the polymerization rate and degree of polymerization of cationic and anionic monomers, control the precipitation rate and dispersion effect of ferric phosphate, and further improve the particle size distribution of anhydrous ferric phosphate particles.

[0119] Further, in some embodiments, the step of adjusting the pH and temperature of the second mixture and obtaining anhydrous ferric phosphate after a third reaction includes: adjusting the temperature of the second mixture to 40°C–60°C, controlling the pH of the second mixture to 0.9–1.5, raising the temperature to 90°C–95°C and reacting until the pH value is 1.6–2.0 to obtain a third mixture; and sequentially subjecting the third mixture to pressure filtration, rinsing, flash evaporation, drying, pulverizing, and sieving to obtain anhydrous ferric phosphate. Preferably, raising the temperature to 90°C–95°C and reacting for 1.5–2.5 hours until the pH value is 1.6–2.0 to obtain the third mixture is beneficial for ensuring complete reaction of the materials.

[0120] Typically, but not limitingly, the temperature of the second mixture is adjusted to a range of 40°C, 45°C, 50°C, 55°C, 60°C or any two of these values, the pH of the second mixture is controlled to 0.9–1.5, and the temperature is increased to 90°C–95°C until the pH reaches 1.6–2.0, thus obtaining the third mixture.

[0121] In the technical solution of this application embodiment, by adjusting the temperature and pH value of the second mixture within a suitable range, the stable precipitation of ferric phosphate can be further controlled. Combined with pressure filtration, rinsing, flash evaporation, drying, pulverizing, and sieving, anhydrous ferric phosphate with high sphericity, good dispersibility, and good particle size distribution as described above is prepared, making the preparation method more practical.

[0122] In some embodiments, the pH value of the second mixture is obtained by testing the solution portion of the second mixture.

[0123] Thirdly, embodiments of this application provide a cathode material, the general formula of which is LiFe. 1-a-b-c Y a Ce b M c PO4@C, wherein M is one or more of tin, titanium, boron, and manganese, a is 0.007 to 0.013, b is 0.029 to 0.057, and c is 0.01 to 0.033; the mass fraction of C in the cathode material is 1.2% to 1.4%.

[0124] Typical, but not limiting, general formula for cathode materials is LiFe. 1-a-b-c Y a Ce b M c PO4@C, where a is a range of 0.007, 0.008, 0.009, 0.010, 0.011, 0.012, 0.013 or any two of these values; b is a range of 0.029, 0.030, 0.035, 0.040, 0.045, 0.050, 0.055, 0.057 or any two of these values; and c is a range of 0.016, 0.020, 0.025, 0.030, 0.033 or any two of these values. The mass percentage of C in the cathode material is 1.2%, 1.25%, 1.3%, 1.35%, 1.4% or any two of these values.

[0125] In some embodiments, a is preferably 0.008 to 0.012, b is preferably 0.03 to 0.052, and c is preferably 0.01 to 0.026.

[0126] In some embodiments, the mass fraction of C in the cathode material is preferably 1.28% to 1.34%.

[0127] In some embodiments, the chemical formula of the cathode material can be represented as: LiFe 0.912 Y 0.012 Sn 0.024 Ce 0.052 PO4@C, LiFe 0.910 Y 0.012 Ti 0.026 Ce 0.052 PO4@C, LiFe 0.94 Y 0.012 Ti 0.018 Ce 0.05 PO4@C, LiFe 0.943 Y 0.008 Ti 0.016 Ce 0.033 PO4@C, LiFe 0.936 Y 0.01 Mn 0.018 Ce 0.036 PO4@C, LiFe 0.94 Y 0.01 Ce 0.03 (PO4) 0.99 (BO3) 0.01 At least one of @C.

[0128] In the technical solution of this application embodiment, anhydrous iron phosphate with good particle size distribution (the anhydrous iron phosphate can be the anhydrous iron phosphate as described above or anhydrous iron phosphate prepared by the anhydrous iron phosphate preparation method described above) is used as the key synthesis raw material. Due to its reasonable particle size distribution, high tap density, high compaction density, and good particle packing density, the final prepared lithium iron phosphate has a relatively high compaction density. At the same time, three metal cations with different mechanisms of action and doping ratios are combined for doping modification. Among them, Y doping can inhibit particle growth and avoid excessive particle growth leading to deterioration of electrical performance; Ce has a high valence, and doping can significantly improve the lithium-ion conductivity; M (tin, titanium, boron, manganese) has a valence close to Fe, which is beneficial to further improve the stability of the doped cathode material. Meanwhile, the aforementioned metal cations can combine with phosphate ions in anhydrous iron phosphate, which can reduce the coarsening of phosphate grains, ensure the stability of the initial structure of iron phosphate, and allow for the normal growth of the cathode material grains under conditions of high metal element doping. This results in the cathode material having advantages such as high compaction density, good rate performance, and high charging and discharging efficiency.

[0129] Furthermore, in some embodiments, the average primary particle size of the cathode material is 0.24 μm to 0.34 μm; wherein, in the cathode material, the fraction of particles with an average primary particle size greater than or equal to 1 μm is less than or equal to 3.20%, and the compaction density is 2.52 g / cm³.3 ~2.64g / cm 3 Preferably, in the cathode material, the fraction of primary particles with a particle size of 200 nm or less is 32% to 67%. More preferably, the fraction of primary particles with an average particle size of 1 μm or greater is 0% to 3.12%; more preferably, the fraction of primary particles with an average particle size of 1 μm or greater is 0.93% to 3.12%.

[0130] Typical, but not limiting, primary particle sizes of cathode materials are 0.24 μm, 0.25 μm, 0.028 μm, 0.30 μm, 0.32 μm, 0.34 μm, or any two of these values.

[0131] Typical, but not limiting, cathode materials have a compaction density of 2.52 g / cm³. 3 2.55g / cm 3 2.58g / cm 3 2.60g / cm 3 2.62 g / cm 3 2.64 g / cm 3 Or a range of values ​​consisting of any two of its values.

[0132] In the technical solution of this application embodiment, the charging and discharging principle of lithium iron phosphate is that lithium ions are inserted and extracted under the action of voltage. The larger the lithium iron phosphate particles, the more difficult it is for lithium ions to be extracted and inserted, resulting in reduced charging and discharging performance. Spherical particles help to ensure the shortest movement path of lithium ions, reduce the obstacles to lithium ion insertion and extraction, and effectively improve charging and discharging performance. The raw material of the above-mentioned cathode material in this application is anhydrous iron phosphate with a variety of particle sizes, which is beneficial to controlling the crystallization and growth process of lithium iron phosphate, further reducing the formation of large single crystals in lithium iron phosphate, thereby giving the cathode material excellent compaction density and energy storage performance.

[0133] Fourthly, embodiments of this application provide a method for preparing a cathode material, comprising the following steps:

[0134] The anhydrous iron phosphate, lithium source, carbon source, complexing agent, and dopant described in this application are mixed with water to obtain a mixture.

[0135] The mixture is sintered under a protective atmosphere to obtain the cathode material;

[0136] The dopants include oxides of yttrium, oxides of cerium, and other oxides, including one or more oxides of tin, titanium, boron, and manganese.

[0137] In the technical solution of this application embodiment, the higher the sphericity of the anhydrous iron phosphate particles, the more the particle size distribution tends to be normal distribution, the higher the packing density, and the higher the compaction density. The process of preparing lithium iron phosphate is mainly to embed lithium ions and doping elements into iron phosphate through sintering treatment. Under high temperature conditions, iron phosphate particles will also grow. Therefore, the morphology and particle distribution of anhydrous iron phosphate directly determine the particle morphology and particle size distribution of lithium iron phosphate.

[0138] This application uses anhydrous iron phosphate (which can be the anhydrous iron phosphate as described above or anhydrous iron phosphate prepared by the aforementioned method) with high crystallinity, low impurity content, excellent particle size distribution, high sphericity, high bulk density, and high compaction density as raw material. By controlling the crystallization and growth process of lithium iron phosphate, the generation of large single crystals in high-compact lithium iron phosphate is significantly reduced. During the crystallization and growth process of lithium iron phosphate, the complexing agent plays an inhibitory role before carbon coating, effectively avoiding the generation of crystal nuclei and reducing the generation of ineffective single crystals during the growth of lithium iron phosphate particles. On the one hand, this ensures the effective proportion of high-efficiency lithium iron phosphate and improves the compaction density; on the other hand, it ensures good carbon coating effect and low powder internal resistance of lithium iron phosphate, reduces polarization, and thus exhibits excellent charging and discharging performance and long-lasting cycle performance.

[0139] Further, in some embodiments, the complexing agent includes glycerol and / or sodium gluconate; and / or, the dopant includes yttrium oxide, cerium oxide and other oxides, the other oxides including one or more of tin dioxide, titanium dioxide, boron trioxide and manganese carbonate; preferably, the mass ratio of yttrium oxide, cerium oxide and other oxides is 1:(2-3):(1-2); and / or, the mass ratio of anhydrous iron phosphate to the complexing agent is 1:(0.02-0.03); and / or, the mass ratio of anhydrous iron phosphate to the dopant is 1:(0.008-0.009); and / or, the molar ratio of anhydrous iron phosphate to the lithium source is 1:(1-1.05); and / or, the mass ratio of anhydrous iron phosphate to the carbon source is 1:(0.09-0.11).

[0140] Typical, but not limiting, mass ratios of yttrium oxide to cerium oxide are 1:2, 1:2.2, 1:2.5, 1:2.8, 1:3, or any two of these values; mass ratios of yttrium oxide to other oxides are 1:1, 1:1.2, 1:1.5, 1:1.8, 1:2, or any two of these values.

[0141] Typical, but not limiting, mass ratios of anhydrous ferric phosphate to complexing agent are 1:0.02, 1:0.022, 1:0.025, 1:0.028, 1:0.03, or any two of these values.

[0142] Typical, but not limiting, mass ratios of anhydrous iron phosphate to dopant are 1:0.008, 1:0.0082, 1:0.0085, 1:0.0088, 1:0.009, or any two of these values.

[0143] Typical, but not limiting, molar ratios of anhydrous iron phosphate to lithium source are 1:1, 1:1.01, 1:1.02, 1:1.03, 1:1.04, 1:1.05, or any two of these values.

[0144] Typical, but not limiting, mass ratios of anhydrous iron phosphate to carbon source are 1:0.09, 1:0.095, 1:0.10, 1:0.105, 1:0.11, or any two of these values.

[0145] In the technical solution of this application embodiment, glycerol or sodium gluconate is selected as the complexing agent. During the sintering process, it binds to the active sites of the raw materials through strong polarity, inhibiting crystal nucleus formation, reducing the generation of lithium iron phosphate single crystals, and improving the purity of lithium iron phosphate, thereby improving the electrical performance of the cathode material. By controlling the raw material ratio within the above range, the synthesis of lithium iron phosphate is more complete, thereby reducing raw material waste and further reducing the preparation cost while maintaining the excellent electrical performance of the cathode material.

[0146] Furthermore, in some embodiments, the step of obtaining the cathode material by sintering the mixture under a protective atmosphere includes: grinding the mixture to obtain a ground material with a D50 particle size of 0.38 μm to 0.42 μm; spray drying the ground material to obtain a spray material with a D50 particle size of 3.4 μm to 6.7 μm; and sintering the spray material under a protective atmosphere to obtain the cathode material. Preferably, the sintering temperature is 760°C to 820°C, and the time is 10 h to 18 h.

[0147] Typical, but not limiting, D50 particle sizes of abrasive materials are 0.38 μm, 0.39 μm, 0.40 μm, 0.41 μm, 0.42 μm or any two of these values; D50 particle sizes of sprayed materials are 3.4 μm, 3.5 μm, 4.0 μm, 4.5 μm, 5.0 μm, 5.5 μm, 6.0 μm, 6.5 μm, 6.7 μm or any two of these values.

[0148] Typical, but not limiting, sintering temperatures are 760°C, 770°C, 780°C, 790°C, 800°C, 810°C, 820°C or any two of these values, and sintering times are 10h, 12h, 15h, 16h, 18h or any two of these values.

[0149] In some embodiments, the protective atmosphere is achieved by a protective gas. The protective gas may be selected from at least one of nitrogen and argon.

[0150] In the technical solution of this application embodiment, anhydrous iron phosphate has high sphericity and good particle size distribution. The product particle size of the grinding and spray drying is small, which also helps to further reduce grinding and spray drying time. While ensuring the obtained lithium iron phosphate particle size and performance, it further reduces production energy consumption and improves production efficiency. By controlling the sintering temperature within a suitable range, on the one hand, the compaction density is increased, the lithium ion diffusion rate is increased, and on the other hand, the proportion of single-crystal lithium iron phosphate is smaller, the polarization is smaller, and the electrochemical performance of the cathode material is better.

[0151] Fifthly, embodiments of this application provide a positive electrode sheet, including a positive current collector and a positive active layer disposed on at least one side of the positive current collector, the positive active layer including the aforementioned positive electrode material.

[0152] In this embodiment, the positive electrode sheet contains the aforementioned positive electrode material, thus possessing the advantages of good rate performance and high charging and discharging efficiency.

[0153] Sixthly, embodiments of this application provide a secondary battery, including the aforementioned positive electrode sheet.

[0154] In this embodiment, the secondary battery includes the aforementioned positive electrode plate, thus possessing the advantages of good rate performance and high charging and discharging efficiency.

[0155] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0156] I. Preparation Method

[0157] Example 1

[0158] This embodiment provides a method for preparing anhydrous iron phosphate and a positive electrode material. The specific steps of the preparation method are as follows:

[0159] Step 1: 1) Mix the titanium dioxide byproduct containing ferrous sulfate with water and heat to dissolve. Add 5% ammonia water to precipitate, filter under pressure to remove impurities, and obtain a ferrous solution with a ferrous ion mass fraction of 1.5 mol / L and a pH value of 2.8.

[0160] 2) Phosphorus source preparation: Industrial monoammonium phosphate is dissolved in phosphoric acid and water, filtered, and then adjusted to neutral pH with 5% ammonia water to obtain a phosphorus source solution, in which PO4... 3- The content is 2 mol / L;

[0161] 3) Preparation of dispersant: Mix 0.010 mol dimethyl diallyl ammonium chloride and 0.0028 mol vinyltrimethoxysilane to prepare solution A, and mix 0.015 mol methacrylic acid and 0.0015 mol isopropanol to prepare solution B, and stir evenly;

[0162] 4) Using 1 mol of iron as a reference (i.e., using a solution containing 1 mol of ferrous ions as a reference, the same applies below), first mix the ferrous source and solution A and add them to the reaction vessel as the base material, then add a 1 mol phosphorus source solution (i.e., a solution containing 1 mol of PO4) 3- 15% of the phosphorus source solution (hereinafter the same) and solution B were mixed and slowly added dropwise with 20% of 3.2 mol hydrogen peroxide solution to carry out the synthesis reaction. After the addition was completed, the reaction was stirred at 50°C for half an hour. Then, the remaining phosphorus source was added at once, and the reaction was stirred at 50°C for another 5 minutes. The remaining hydrogen peroxide solution was then slowly added dropwise, keeping the reaction temperature below 60°C. After the addition was completed, the pH was adjusted to 1.2 with phosphoric acid. Then, the temperature was raised to 95°C and the reaction was stirred for another 2 hours until the pH reached 1.8. The mixture was then filtered, rinsed, flash-evaporated, dried, pulverized, and sieved to obtain anhydrous ferric phosphate.

[0163] Step 2: The anhydrous iron phosphate prepared in Step 1, lithium carbonate at 1.02 times the amount of anhydrous iron phosphate, yttrium oxide, tin dioxide, and cerium oxide at a mass ratio of 1:2:3 (0.86% of the mass of anhydrous iron phosphate), glycerol at a mass ratio of 1:4 (11.8% of the mass of anhydrous iron phosphate), and soluble starch are mixed with pure water to form a slurry with a solid content of 48.0%. The D50 particle size is adjusted to 0.38 μm by sand milling, and then spray-dried at a temperature above 215°C to control the D50 particle size to 3.4 μm. Then, the mixture is heated to 786°C at a rate of 5°C / min under a nitrogen protective atmosphere, held at this temperature for 12 hours, cooled to below 100°C by air cooling, and then pulverized to obtain the lithium iron phosphate cathode material.

[0164] Example 2

[0165] This embodiment provides a method for preparing anhydrous iron phosphate and a positive electrode material. The specific steps of the preparation method are as follows:

[0166] Step 1: 1) Mix the titanium dioxide byproduct containing ferrous sulfate with water and heat to dissolve. Add 5% ammonia water to precipitate, filter under pressure to remove impurities, and obtain a ferrous solution with a ferrous ion mass fraction of 2 mol / L and a pH value of 3.2.

[0167] 2) Phosphorus source preparation: Industrial monoammonium phosphate is dissolved in phosphoric acid and water, filtered, and then adjusted to neutral pH with 5% ammonia water to obtain a phosphorus source solution, in which PO4... 3- The content is 2 mol / L;

[0168] 3) Preparation of dispersant: Mix 0.012 mol of dimethyl diallyl ammonium chloride (1:3 mass ratio) with acryloyloxyethyl trimethyl ammonium chloride and 0.0028 mol of 3-(methacryloyloxy)propyltrimethoxysilane to prepare solution A; mix 0.015 mol of methacrylic acid (1:3 mass ratio) with fumaric acid and 0.0019 mol of sodium hypophosphite to prepare solution B; stir evenly.

[0169] 4) Using 1 mol of iron as a reference, first mix the ferrous source and solution A and add them to the reactor as the base material. Then mix 20% of the 1 mol phosphorus source solution with solution B and slowly add it dropwise along with 20% of the 3.2 mol hydrogen peroxide solution to carry out the synthesis reaction. After the addition is complete, stir the reaction at 50°C for half an hour. Then add the remaining phosphorus source all at once and continue stirring at 50°C for 5 minutes. Then slowly add the remaining hydrogen peroxide solution, keeping the reaction temperature below 60°C. After the addition is complete, adjust the pH value to 1.2 with phosphoric acid. Then raise the temperature to 95°C and continue stirring the reaction for 2 hours until the pH value is 1.8. Filter, rinse, flash evaporate, dry, pulverize, and sieve to obtain anhydrous ferric phosphate.

[0170] Step 2: The anhydrous iron phosphate prepared in Step 1, lithium carbonate at 1.02 times the amount of anhydrous iron phosphate, yttrium oxide, tin dioxide, and cerium oxide at a mass ratio of 1:2:3 (0.86% of the mass of anhydrous iron phosphate), glycerol at a mass ratio of 1:4 (11.8% of the mass of anhydrous iron phosphate), and soluble starch are mixed with pure water to form a slurry with a solid content of 48.0%. The D50 particle size is adjusted to 0.38 μm by sand milling, and then spray-dried at a temperature above 215°C to control the D50 particle size to 5 μm. Then, the mixture is heated to 786°C at a rate of 5°C / min under a nitrogen protective atmosphere, held at this temperature for 12 hours, cooled to below 100°C by air cooling, and then pulverized to obtain the lithium iron phosphate cathode material.

[0171] Example 3

[0172] This embodiment provides a method for preparing anhydrous iron phosphate and a positive electrode material. The specific steps of the preparation method are as follows:

[0173] Step 1: 1) Mix the titanium dioxide byproduct containing ferrous sulfate with water and heat to dissolve. Add 5% ammonia water to precipitate, filter under pressure to remove impurities, and obtain a ferrous solution with a ferrous ion mass fraction of 2 mol / L and a pH value of 3.0.

[0174] 2) Phosphorus source preparation: Industrial monoammonium phosphate is dissolved in phosphoric acid and water, filtered, and then adjusted to neutral pH with 5% ammonia water to obtain a phosphorus source solution, in which PO4... 3- The content is 2 mol / L;

[0175] 3) Preparation of dispersant: Mix 0.01 mol of dimethyl diallyl ammonium chloride (1:3 by mass ratio) with acryloyloxyethyl trimethyl ammonium chloride and 0.0031 mol of vinyltrimethoxysilane to prepare solution A; mix 0.014 mol of methacrylic acid (1:3 by mass ratio) with itaconic acid and 0.0017 mol of sodium hypophosphite to prepare solution B; stir evenly.

[0176] 4) Using 1 mol of iron as a reference, first mix the ferrous source and solution A and add them to the reactor as the base material. Then mix 25% of the 1 mol phosphorus source solution with solution B and slowly add it dropwise with 20% of the 3.4 mol hydrogen peroxide solution to carry out the synthesis reaction. After the addition is complete, stir the reaction at 50°C for half an hour. Then add the remaining phosphorus source all at once, continue stirring at 50°C for 5 minutes, and then slowly add the remaining hydrogen peroxide solution dropwise, keeping the reaction temperature below 60°C. After the addition is complete, adjust the pH value to 1.0 with phosphoric acid, and then raise the temperature to 95°C and continue stirring the reaction for 2 hours until the pH value is 1.8. The resulting third mixture is filtered, washed, flash evaporated, dried, pulverized, and sieved to obtain anhydrous ferric phosphate.

[0177] Step 2: The anhydrous iron phosphate prepared in Step 1, lithium carbonate at 1.02 times the amount of anhydrous iron phosphate, yttrium oxide, tin dioxide, and cerium oxide at a mass ratio of 1:2:3 (0.86% of the mass of anhydrous iron phosphate), glycerol at a mass ratio of 1:4 (11.8% of the mass of anhydrous iron phosphate), and soluble starch are mixed with pure water to form a slurry with a solid content of 48.0%. The D50 particle size is adjusted to 0.38 μm by sand milling, and then spray-dried at a temperature above 215°C to control the D50 particle size to 6.7 μm. Then, the mixture is heated to 786°C at a rate of 5°C / min under a nitrogen protective atmosphere, held at this temperature for 12 hours, cooled to below 100°C by air cooling, and then pulverized to obtain the lithium iron phosphate cathode material.

[0178] Example 4

[0179] This embodiment provides a method for preparing anhydrous iron phosphate and a positive electrode material. The specific steps of the preparation method are as follows:

[0180] Step 1: 1) Mix the titanium dioxide byproduct containing ferrous sulfate with water and heat to dissolve. Add 5% ammonia water to precipitate, filter under pressure to remove impurities, and obtain a ferrous solution with a ferrous ion mass fraction of 2 mol / L and a pH value of 3.0.

[0181] 2) Phosphorus source preparation: Industrial monoammonium phosphate is dissolved in phosphoric acid and water, filtered, and then adjusted to neutral pH with 5% ammonia water to obtain a phosphorus source solution, in which PO4... 3- The content is 2 mol / L;

[0182] 3) Preparation of dispersant: Mix 0.01 mol of dimethyl diallyl ammonium chloride (1:3 by mass ratio) with acryloyloxyethyl trimethyl ammonium chloride and 0.0031 mol of vinyltrimethoxysilane to prepare solution A; mix 0.014 mol of methacrylic acid (1:3 by mass ratio) with itaconic acid and 0.0017 mol of sodium hypophosphite to prepare solution B; stir evenly.

[0183] 4) Using 1 mol of iron as a reference, first mix the ferrous source and solution A and add them to the reactor as the base material. Then mix 25% of the 1 mol phosphorus source solution with solution B and slowly add it dropwise with 20% of the 3.4 mol hydrogen peroxide solution to carry out the synthesis reaction. After the addition is complete, stir the reaction at 50°C for half an hour. Then add the remaining phosphorus source all at once, continue stirring at 50°C for 5 minutes, and then slowly add the remaining hydrogen peroxide solution dropwise, keeping the reaction temperature below 60°C. After the addition is complete, adjust the pH value to 1.0 with phosphoric acid, then raise the temperature to 95°C and continue stirring the reaction for 2 hours until the pH value is 1.8. Filter, rinse, flash evaporate, dry, pulverize, and sieve to obtain anhydrous ferric phosphate.

[0184] Step 2: The anhydrous iron phosphate prepared in Step 1, lithium carbonate at 1.03 times the amount of anhydrous iron phosphate, yttrium oxide, titanium dioxide, and cerium oxide at a mass ratio of 1:2:3 (0.86% of the mass of anhydrous iron phosphate), glycerol and β-cyclodextrin at a mass ratio of 1:4 (11.8% of the mass of anhydrous iron phosphate), and pure water are added and stirred to form a slurry with a solid content of 48.0%. The D50 particle size is controlled to 0.40 μm by sand milling, and then spray-dried at a temperature above 215℃ to control the D50 particle size to 6.7 μm. Then, under a nitrogen protective atmosphere, the temperature is increased to 786℃ at a rate of 5℃ / min, held for 16 hours, cooled to below 100℃ by air cooling, and then pulverized to obtain the lithium iron phosphate cathode material.

[0185] Example 5

[0186] This embodiment provides a method for preparing anhydrous iron phosphate and a positive electrode material. The specific steps of the preparation method are as follows:

[0187] Step 1: 1) Mix the titanium dioxide byproduct containing ferrous sulfate with water and heat to dissolve. Add 5% ammonia water to precipitate, filter under pressure to remove impurities, and obtain a ferrous solution with a ferrous ion mass fraction of 2 mol / L and a pH value of 3.0.

[0188] 2) Phosphorus source preparation: Industrial monoammonium phosphate is dissolved in phosphoric acid and water, filtered, and then adjusted to neutral pH with 5% ammonia water to obtain a phosphorus source solution, in which PO4... 3- The content is 2 mol / L;

[0189] 3) Preparation of dispersant: Mix 0.01 mol of dimethyl diallyl ammonium chloride (1:3 by mass ratio) with acryloyloxyethyl trimethyl ammonium chloride and 0.0031 mol of vinyltrimethoxysilane to prepare solution A; mix 0.014 mol of methacrylic acid (1:3 by mass ratio) with itaconic acid and 0.0017 mol of sodium hypophosphite to prepare solution B; stir evenly.

[0190] 4) Using 1 mol of iron as a reference, first mix the ferrous source and solution A and add them to the reactor as the base material. Then mix 25% of the 1 mol phosphorus source solution with solution B and slowly add it dropwise with 20% of the 3.4 mol hydrogen peroxide solution to carry out the synthesis reaction. After the addition is complete, stir the reaction at 50°C for half an hour. Then add the remaining phosphorus source all at once, continue stirring at 50°C for 5 minutes, and then slowly add the remaining hydrogen peroxide solution dropwise, keeping the reaction temperature below 60°C. After the addition is complete, adjust the pH value to 1.0 with phosphoric acid, then raise the temperature to 95°C and continue stirring the reaction for 2 hours until the pH value is 1.8. Filter, rinse, flash evaporate, dry, pulverize, and sieve to obtain anhydrous ferric phosphate.

[0191] Step 2: The anhydrous iron phosphate prepared in Step 1, lithium carbonate at 1.03 times the amount of anhydrous iron phosphate, yttrium oxide, titanium dioxide, and cerium oxide at a mass ratio of 2:3:5 (0.83% of the mass of anhydrous iron phosphate), glycerol and β-cyclodextrin at a mass ratio of 1:4 (12.7% of the mass of anhydrous iron phosphate), and pure water are added and stirred to form a slurry with a solid content of 48.0%. The D50 particle size is controlled to 0.42 μm by sand milling, and then spray-dried at a temperature above 215℃ to control the D50 particle size to 4.5 μm. Then, under a nitrogen protective atmosphere, the temperature is increased to 788℃ at a rate of 5℃ / min, held for 14 hours, cooled to below 100℃ by air cooling, and then pulverized to obtain the lithium iron phosphate cathode material.

[0192] Example 6

[0193] This embodiment provides a method for preparing anhydrous iron phosphate and a positive electrode material. The specific steps of the preparation method are as follows:

[0194] Step 1: 1) Mix the titanium dioxide byproduct containing ferrous sulfate with water and heat to dissolve. Add 5% ammonia water to precipitate, filter under pressure to remove impurities, and obtain a ferrous solution with a ferrous ion mass fraction of 2 mol / L and a pH value of 3.0.

[0195] 2) Phosphorus source preparation: Industrial monoammonium phosphate is dissolved in phosphoric acid and water, filtered, and then adjusted to neutral pH with 5% ammonia water to obtain a phosphorus source solution, in which PO4... 3- The content is 2 mol / L;

[0196] 3) Preparation of dispersant: Mix 0.01 mol of dimethyl diallyl ammonium chloride (1:3 by mass ratio) with acryloyloxyethyl trimethyl ammonium chloride and 0.0031 mol of vinyltrimethoxysilane to prepare solution A; mix 0.014 mol of methacrylic acid (1:3 by mass ratio) with itaconic acid and 0.0017 mol of sodium hypophosphite to prepare solution B; stir evenly.

[0197] 4) Using 1 mol of iron as a reference, first mix the ferrous source and solution A and add them to the reactor as the base material. Then mix 25% of the 1 mol phosphorus source solution with solution B and slowly add it dropwise with 20% of the 3.4 mol hydrogen peroxide solution to carry out the synthesis reaction. After the addition is complete, stir the reaction at 50°C for half an hour. Then add the remaining phosphorus source all at once, continue stirring at 50°C for 5 minutes, and then slowly add the remaining hydrogen peroxide solution dropwise, keeping the reaction temperature below 60°C. After the addition is complete, adjust the pH value to 1.0 with phosphoric acid, then raise the temperature to 95°C and continue stirring the reaction for 2 hours until the pH value is 1.8. Filter, rinse, flash evaporate, dry, pulverize, and sieve to obtain anhydrous ferric phosphate.

[0198] Step 2: The anhydrous iron phosphate prepared in Step 1, lithium carbonate at 1.03 times the amount of anhydrous iron phosphate, yttrium oxide, titanium dioxide, and cerium oxide at a mass ratio of 2:3:5 (0.83% of the mass of anhydrous iron phosphate), glycerol and β-cyclodextrin at a mass ratio of 1:4 (13.2% of the mass of anhydrous iron phosphate), and pure water are added and stirred to form a slurry with a solid content of 48.0%. The D50 particle size is controlled to 0.40 μm by sand milling, and then spray-dried at a temperature above 215℃ to control the D50 particle size to 4.5 μm. Then, under a nitrogen protective atmosphere, the temperature is heated to 790℃ at a rate of 5℃ / min, held for 14 hours, cooled to below 100℃ by air cooling, and then pulverized to obtain the lithium iron phosphate cathode material.

[0199] Example 7

[0200] The difference from Example 5 is that in step one: 3) dispersant preparation, 0.0105 mol of dimethyl diallyl ammonium chloride in a mass ratio of 1:2.5, acryloyloxyethyl trimethyl ammonium chloride and 0.0021 mol of 3-(methacryloyloxy)propyltrimethoxysilane are mixed to prepare solution A, and 0.014 mol of methacrylic acid in a mass ratio of 1:2.5, itaconic acid and 0.0014 mol of sodium hypophosphite are mixed to prepare solution B, and stirred evenly.

[0201] Example 8

[0202] The difference from Example 5 is that in step one: 3) dispersant preparation, 0.011 mol of dimethyl diallyl ammonium chloride in a mass ratio of 1:3.5, acryloyloxyethyl trimethyl ammonium chloride and 0.0039 mol of vinyltrimethoxysilane are mixed to prepare solution A, and 0.0145 mol of methacrylic acid in a mass ratio of 1:3.5, fumaric acid and 0.0022 mol of isopropanol are mixed to prepare solution B, and stirred evenly.

[0203] Example 9

[0204] The difference from Example 5 is that step one:

[0205] 1) The titanium dioxide byproduct containing ferrous sulfate was mixed with water and heated to dissolve. Ammonia water with a mass fraction of 5% was added for precipitation, and the mixture was filtered to remove impurities, resulting in a ferrous solution with a ferrous ion mass fraction of 2 mol / L and a pH value of 3.0.

[0206] 2) Phosphorus source preparation: Industrial monoammonium phosphate is dissolved in phosphoric acid and water, filtered, and then adjusted to neutral pH with 5% ammonia water to obtain a phosphorus source solution, in which PO4... 3- The content is 2 mol / L;

[0207] 3) Preparation of dispersant: Mix 0.01 mol of dimethyl diallyl ammonium chloride (1:3 by mass ratio) with acryloyloxyethyl trimethyl ammonium chloride and 0.0031 mol of vinyltrimethoxysilane to prepare solution A; mix 0.014 mol of methacrylic acid (1:3 by mass ratio) with itaconic acid and 0.0017 mol of sodium hypophosphite to prepare solution B; stir evenly.

[0208] 4) Using 1 mol of iron as a reference, first mix the ferrous source and solution A and add them to the reactor as the base material. Then, mix 15% of the 1 mol phosphorus source solution with solution B and slowly add it dropwise with 18% of the 3.4 mol hydrogen peroxide solution to carry out the synthesis reaction. After the addition is complete, stir the reaction at 40°C for 1 hour. Then, add the remaining phosphorus source all at once and continue stirring at 40°C for 10 minutes. Then, slowly add the remaining hydrogen peroxide solution, keeping the reaction temperature below 40°C. After the addition is complete, adjust the pH value to 0.9 with phosphoric acid. Then, raise the temperature to 90°C and continue stirring the reaction for 2.5 hours until the pH value is 1.6. Filter, rinse, flash evaporate, dry, pulverize, and sieve to obtain anhydrous ferric phosphate.

[0209] Example 10

[0210] The difference from Example 5 is that step one:

[0211] 1) The titanium dioxide byproduct containing ferrous sulfate was mixed with water and heated to dissolve. Ammonia water with a mass fraction of 15% was added for precipitation, and the mixture was filtered to remove impurities, resulting in a ferrous solution with a ferrous ion mass fraction of 2 mol / L and a pH value of 3.0.

[0212] 2) Phosphorus source preparation: Industrial monoammonium phosphate is dissolved in phosphoric acid and water, filtered, and then adjusted to neutral pH with 15% ammonia solution to obtain a phosphorus source solution, in which PO4... 3- The content is 2 mol / L;

[0213] 3) Preparation of dispersant: Mix 0.01 mol of dimethyl diallyl ammonium chloride (1:3 by mass ratio) with acryloyloxyethyl trimethyl ammonium chloride and 0.0031 mol of vinyltrimethoxysilane to prepare solution A; mix 0.014 mol of methacrylic acid (1:3 by mass ratio) with itaconic acid and 0.0017 mol of sodium hypophosphite to prepare solution B; stir evenly.

[0214] 4) Using 1 mol of iron as a reference, first mix the ferrous source and solution A and add them to the reactor as the base material. Then, mix 25% of the 1 mol phosphorus source solution with solution B and slowly add it dropwise with 30% of the 3.4 mol hydrogen peroxide solution to carry out the synthesis reaction. After the addition is complete, stir the reaction at 60°C for half an hour. Then, add the remaining phosphorus source all at once and continue stirring at 60°C for 5 minutes. Then, slowly add the remaining hydrogen peroxide solution, keeping the reaction temperature below 60°C. After the addition is complete, adjust the pH value to 1.5 with phosphoric acid. Then, raise the temperature to 95°C and continue stirring the reaction for 1.5 hours until the pH value is 2.0. Filter, rinse, flash evaporate, dry, pulverize, and sieve to obtain anhydrous ferric phosphate.

[0215] Example 11

[0216] The difference from Example 5 is that step two:

[0217] The anhydrous iron phosphate prepared in step one, lithium carbonate (1 times the amount of anhydrous iron phosphate), yttrium oxide, titanium dioxide, and cerium oxide (0.8% of the mass of anhydrous iron phosphate in a mass ratio of 1:1:2), glycerol and β-cyclodextrin (11.3% of the mass of anhydrous iron phosphate in a mass ratio of 1:4), and pure water were added and stirred to form a slurry with a solid content of 48.0%. The D50 particle size was adjusted to 0.42 μm by sand milling and then spray-dried at a temperature above 215°C to control the D50 particle size to 4.5 μm. Then, the slurry was heated to 760°C at a rate of 5°C / min under a nitrogen protective atmosphere, held at that temperature for 18 hours, cooled to below 100°C by air cooling, and then pulverized to obtain the lithium iron phosphate cathode material.

[0218] Example 12

[0219] The difference from Example 5 is that step two:

[0220] The anhydrous iron phosphate prepared in step one, lithium carbonate (1.05 times the amount of anhydrous iron phosphate), yttrium oxide, manganese carbonate, and cerium oxide (0.9% of the mass of anhydrous iron phosphate, in a mass ratio of 1:2:3), sodium gluconate and β-cyclodextrin (13.6% of the mass of anhydrous iron phosphate, in a mass ratio of 1:4), and pure water were added and stirred to form a slurry with a solid content of 48.0%. The D50 particle size was adjusted to 0.42 μm by sand milling and then spray-dried at a temperature above 215°C to control the D50 particle size to 4.5 μm. Then, the slurry was heated to 820°C at a rate of 5°C / min under a nitrogen protective atmosphere, held at that temperature for 10 hours, cooled to below 100°C by air cooling, and then pulverized to obtain the lithium iron phosphate cathode material.

[0221] Example 13

[0222] The difference from Example 5 is that step two:

[0223] The anhydrous iron phosphate prepared in step one, lithium carbonate (1.03 times the amount of anhydrous iron phosphate), yttrium oxide, boron trioxide, and cerium oxide (0.83% of the mass of anhydrous iron phosphate, in a mass ratio of 1:1:3), glycerol and β-cyclodextrin (13.2% of the mass of anhydrous iron phosphate, in a mass ratio of 1:4), and pure water were added and stirred to form a slurry with a solid content of 48.0%. The D50 particle size was adjusted to 0.40 μm by sand milling and then spray-dried at a temperature above 215°C to control the D50 particle size to 4.5 μm. Then, the slurry was heated to 790°C at a rate of 5°C / min under a nitrogen protective atmosphere, held at that temperature for 14 h, cooled to below 100°C by air cooling, and pulverized to obtain the lithium iron phosphate cathode material.

[0224] Comparative Example 1

[0225] A comparative example provides a method for preparing anhydrous iron phosphate and a positive electrode material, which is obtained by the following method:

[0226] Step 1: 1) Mix the titanium dioxide byproduct containing ferrous sulfate with water and heat to dissolve. Add 5% ammonia water to precipitate, filter under pressure to remove impurities, and obtain a ferrous solution with a ferrous ion mass fraction of 1.5 mol / L and a pH value of 2.8.

[0227] 2) Phosphorus source preparation: Industrial monoammonium phosphate is dissolved in phosphoric acid and water, filtered, and then adjusted to neutral pH with 5% ammonia water to obtain a phosphorus source solution, in which PO4... 3- The content is 2 mol / L;

[0228] 3) Using 1 mol of iron as a reference, ferrous iron source was first added to the reactor as a base material. Then, phosphorus source solution and 3.2 mol of hydrogen peroxide solution were slowly added dropwise to carry out the synthesis reaction, ensuring that the addition was completed within 1 hour. The reaction temperature was kept below 60℃. After the addition was completed, the pH value was adjusted to 1.2 with phosphoric acid. Then, the temperature was raised to 95℃ and the reaction was stirred for 2 hours until the pH value was 1.8. The mixture was then filtered, rinsed, flash-evaporated, dried, pulverized, and sieved to obtain anhydrous ferric phosphate.

[0229] Step 2: The anhydrous iron phosphate prepared in Step 1, lithium carbonate at 1.02 times the amount of anhydrous iron phosphate, titanium dioxide at 0.86% of the mass of anhydrous iron phosphate, and glucose monohydrate at 11.8% of the mass of anhydrous iron phosphate are mixed with pure water to form a slurry with a solid content of 48.0%. The D50 particle size is adjusted to 0.38 μm by sand milling, and then spray-dried at a temperature above 215℃ to control the D50 particle size to 4.5 μm. Then, the temperature is raised to 786℃ at 5℃ / min under a nitrogen protective atmosphere, held for 12 hours, cooled to below 100℃ by air cooling, and then pulverized to obtain lithium iron phosphate cathode material.

[0230] Comparative Example 2

[0231] A comparative example provides a method for preparing anhydrous iron phosphate and a positive electrode material, which is obtained by the following method:

[0232] Step 1: 1) Mix the titanium dioxide byproduct containing ferrous sulfate with water and heat to dissolve. Add 5% ammonia water to precipitate, filter under pressure to remove impurities, and obtain a ferrous solution with a ferrous ion mass fraction of 2 mol / L and a pH value of 3.2.

[0233] 2) Phosphorus source preparation: Industrial monoammonium phosphate is dissolved in phosphoric acid and water, filtered, and then adjusted to neutral pH with 5% ammonia water to obtain a phosphorus source solution, in which PO4... 3- The content is 2 mol / L;

[0234] 3) Using 1 mol of iron as a reference, ferrous iron source was first added to the reactor as a base material. Then, 20% of 1 mol of phosphorus source solution and 20% of 3.2 mol of hydrogen peroxide solution were slowly added dropwise simultaneously to carry out the synthesis reaction. After the addition was completed, the reaction was stirred for half an hour. Then, the remaining phosphorus source was added all at once, and the reaction was stirred for another 5 minutes. The remaining hydrogen peroxide solution was then slowly added dropwise, keeping the reaction temperature below 60°C. After the addition was completed, the pH value was adjusted to 1.2 with phosphoric acid. Then, the temperature was raised to 95°C and the reaction was stirred for another 2 hours until the pH value reached 1.8. The mixture was then filtered, rinsed, flash-evaporated, dried, pulverized, and sieved to obtain anhydrous ferric phosphate.

[0235] Step 2: The anhydrous iron phosphate prepared in Step 1, lithium carbonate at 1.02 times the amount of anhydrous iron phosphate, titanium dioxide at 0.86% of the mass of anhydrous iron phosphate, and glucose monohydrate at 11.8% of the mass of anhydrous iron phosphate are mixed with pure water to form a slurry with a solid content of 48.0%. The D50 particle size is adjusted to 0.38 μm by sand milling, and then spray-dried at a temperature above 215℃ to control the D50 particle size to 4.5 μm. Then, the temperature is raised to 786℃ at 5℃ / min under a nitrogen protective atmosphere, held for 12 hours, cooled to below 100℃ by air cooling, and then pulverized to obtain lithium iron phosphate cathode material.

[0236] Comparative Example 3

[0237] A comparative example provides a method for preparing anhydrous iron phosphate and a positive electrode material, which is obtained by the following method:

[0238] Step 1: 1) Mix the titanium dioxide byproduct containing ferrous sulfate with water and heat to dissolve. Add 5% ammonia water to precipitate, filter under pressure to remove impurities, and obtain a ferrous solution with a ferrous ion mass fraction of 2 mol / L and a pH value of 3.0.

[0239] 2) Phosphorus source preparation: Industrial monoammonium phosphate is dissolved in phosphoric acid and water, filtered, and then adjusted to neutral pH with 5% ammonia water to obtain a phosphorus source solution, in which PO4... 3- The content is 2 mol / L;

[0240] 3) Using 1 mol of iron as a reference, ferrous iron source was first added to the reactor as a base material. Then, 25% of 1 mol of phosphorus source solution and 20% of 3.4 mol of hydrogen peroxide solution were slowly added dropwise simultaneously to carry out the synthesis reaction. After the addition was completed, the reaction was stirred for half an hour. Then, the remaining phosphorus source was added all at once, and the reaction was stirred for another 5 minutes. The remaining hydrogen peroxide solution was then slowly added dropwise, keeping the reaction temperature below 60°C. After the addition was completed, the pH value was adjusted to 1.0 with phosphoric acid. Then, the temperature was raised to 95°C and the reaction was stirred for another 2 hours until the pH value reached 1.8. The mixture was then filtered, rinsed, flash-evaporated, dried, pulverized, and sieved to obtain anhydrous ferric phosphate.

[0241] Step 2: The anhydrous iron phosphate prepared in Step 1, lithium carbonate at 1.02 times the amount of anhydrous iron phosphate, titanium dioxide at 0.86% of the mass of anhydrous iron phosphate, and glucose monohydrate at 11.8% of the mass of anhydrous iron phosphate are mixed with pure water to form a slurry with a solid content of 48.0%. The D50 particle size is adjusted to 0.38 μm by sand milling, and then spray-dried at a temperature above 215℃ to control the D50 particle size to 4.5 μm. Then, the temperature is raised to 786℃ at 5℃ / min under a nitrogen protective atmosphere, held for 12 hours, cooled to below 100℃ by air cooling, and then pulverized to obtain lithium iron phosphate cathode material.

[0242] Comparative Example 4

[0243] A comparative example provides a method for preparing anhydrous iron phosphate and a positive electrode material, which is obtained by the following method:

[0244] Step 1: 1) Mix the titanium dioxide byproduct containing ferrous sulfate with water and heat to dissolve. Add 5% ammonia water to precipitate, filter under pressure to remove impurities, and obtain a ferrous solution with a ferrous ion mass fraction of 2 mol / L and a pH value of 3.0.

[0245] 2) Phosphorus source preparation: Industrial monoammonium phosphate is dissolved in phosphoric acid and water, filtered, and then adjusted to neutral pH with 5% ammonia water to obtain a phosphorus source solution, in which PO4... 3- The content is 2 mol / L;

[0246] 3) Using 1 mol of iron as a reference, ferrous iron source was first added to the reactor as a base material. Then, 25% of 1 mol of phosphorus source solution and 20% of 3.4 mol of hydrogen peroxide solution were slowly added dropwise simultaneously to carry out the synthesis reaction. After the addition was completed, the reaction was stirred for half an hour. Then, the remaining phosphorus source was added all at once, and the reaction was stirred for another 5 minutes. The remaining hydrogen peroxide solution was then slowly added dropwise, keeping the reaction temperature below 60°C. After the addition was completed, the pH value was adjusted to 1.0 with phosphoric acid. Then, the temperature was raised to 95°C and the reaction was stirred for another 2 hours until the pH value reached 1.8. The mixture was then filtered, rinsed, flash-evaporated, dried, pulverized, and sieved to obtain anhydrous ferric phosphate.

[0247] Step 2: The anhydrous iron phosphate prepared in Step 1, lithium carbonate (1.03 times the amount of anhydrous iron phosphate), yttrium oxide (0.86% of the amount of anhydrous iron phosphate), titanium dioxide and cerium oxide (in a mass ratio of 1:2:3), glycerol (11.8% of the amount of anhydrous iron phosphate), and β-cyclodextrin (in a mass ratio of 1:4) are mixed with pure water to form a slurry with a solid content of 48.0%. The D50 particle size is adjusted to 0.40 μm by sand milling, and then spray-dried at a temperature above 215℃ to control the D50 particle size to 4.5 μm. Then, the mixture is heated to 786℃ at a rate of 5℃ / min under a nitrogen protective atmosphere, held at this temperature for 16 hours, cooled to below 100℃ by air cooling, and then pulverized to obtain the lithium iron phosphate cathode material.

[0248] Comparative Example 5

[0249] A comparative example provides a method for preparing anhydrous iron phosphate and a positive electrode material, which is obtained by the following method:

[0250] Step 1: 1) Mix the titanium dioxide byproduct containing ferrous sulfate with water and heat to dissolve. Add 5% ammonia water to precipitate, filter under pressure to remove impurities, and obtain a ferrous solution with a ferrous ion mass fraction of 2 mol / L and a pH value of 3.0.

[0251] 2) Phosphorus source preparation: Industrial monoammonium phosphate is dissolved in phosphoric acid and water, filtered, and then adjusted to neutral pH with 5% ammonia water to obtain a phosphorus source solution, in which PO4... 3- The content is 2 mol / L;

[0252] 3) Using 1 mol of iron as a reference, ferrous iron source was first added to the reactor as a base material. Then, 25% of 1 mol of phosphorus source solution and 20% of 3.4 mol of hydrogen peroxide solution were slowly added dropwise simultaneously to carry out the synthesis reaction. After the addition was completed, the reaction was stirred for half an hour. Then, the remaining phosphorus source was added all at once, and the reaction was stirred for another 5 minutes. The remaining hydrogen peroxide solution was then slowly added dropwise, keeping the reaction temperature below 60°C. After the addition was completed, the pH value was adjusted to 1.0 with phosphoric acid. Then, the temperature was raised to 95°C and the reaction was stirred for another 2 hours until the pH value reached 1.8. The mixture was then filtered, rinsed, flash-evaporated, dried, pulverized, and sieved to obtain anhydrous ferric phosphate.

[0253] Step 2: The anhydrous iron phosphate prepared in Step 1, lithium carbonate (1.03 times the amount of anhydrous iron phosphate), yttrium oxide (0.83% of the mass of anhydrous iron phosphate) in a mass ratio of 2:3:5, titanium dioxide and cerium oxide, glycerol (12.7% of the mass of anhydrous iron phosphate) in a mass ratio of 1:4, and β-cyclodextrin are mixed with pure water to form a slurry with a solid content of 48.0%. The D50 particle size is adjusted to 0.42 μm by sand milling, and then spray-dried at a temperature above 215℃ to control the D50 particle size to 4.5 μm. Then, the temperature is increased to 788℃ at 5℃ / min under a nitrogen protective atmosphere, held for 14 hours, cooled to below 100℃ by air cooling, and then pulverized to obtain the lithium iron phosphate cathode material.

[0254] Comparative Example 6

[0255] A comparative example provides a method for preparing anhydrous iron phosphate and a positive electrode material, which is obtained by the following method:

[0256] Step 1: 1) Mix the titanium dioxide byproduct containing ferrous sulfate with water and heat to dissolve. Add 5% ammonia water to precipitate, filter under pressure to remove impurities, and obtain a ferrous solution with a ferrous ion mass fraction of 2 mol / L and a pH value of 3.0.

[0257] 2) Phosphorus source preparation: Industrial monoammonium phosphate is dissolved in phosphoric acid and water, filtered, and then adjusted to neutral pH with 5% ammonia water to obtain a phosphorus source solution, in which PO4... 3- The content is 2 mol / L;

[0258] 3) Using 1 mol of iron as a reference, ferrous iron source was first added to the reactor as a base material. Then, 25% of 1 mol of phosphorus source solution and 20% of 3.4 mol of hydrogen peroxide solution were slowly added dropwise simultaneously to carry out the synthesis reaction. After the addition was completed, the reaction was stirred for half an hour. Then, the remaining phosphorus source was added all at once, and the reaction was stirred for another 5 minutes. The remaining hydrogen peroxide solution was then slowly added dropwise, keeping the reaction temperature below 60°C. After the addition was completed, the pH value was adjusted to 1.0 with phosphoric acid. Then, the temperature was raised to 95°C and the reaction was stirred for another 2 hours until the pH value reached 1.8. The mixture was then filtered, rinsed, flash-evaporated, dried, pulverized, and sieved to obtain anhydrous ferric phosphate.

[0259] Step 2: The anhydrous iron phosphate prepared in Step 1, lithium carbonate (1.03 times the amount of anhydrous iron phosphate), yttrium oxide (0.83% of the amount of anhydrous iron phosphate) in a mass ratio of 2:3:5, titanium dioxide and cerium oxide, glycerol (13.2% of the amount of anhydrous iron phosphate) in a mass ratio of 1:4, and β-cyclodextrin are mixed with pure water to form a slurry with a solid content of 48.0%. The D50 particle size is controlled to 0.40 μm by sand milling, and then spray-dried at a temperature above 215℃ to control the D50 particle size to 4.5 μm. Then, the temperature is increased to 790℃ at 5℃ / min under a nitrogen protective atmosphere, held for 14 hours, cooled to below 100℃ by air cooling, and then pulverized to obtain the lithium iron phosphate cathode material.

[0260] II. Testing Methods

[0261] 1. Property testing of anhydrous iron phosphate and cathode materials

[0262] 1) SEM test: Scanning electron microstructure analysis was performed using a JSM6390 scanning electron microscope, and the particle size and distribution were analyzed using Nano Measurer software.

[0263] 2) XRD testing: X-ray diffraction (XRD) analysis was used to determine the composition and content of phases in the sample. This experiment used an Empyrean rotating anode X-ray diffractometer from PANalytical, Netherlands.

[0264] 3) Sphericity: Based on the SEM image, the overall particles are distributed between ellipses and spheres, and the sphericity is calculated (the sphericity of a tetrahedron is 0.908, and the sphericity of a sphere is 1).

[0265] 4) Tap density: Tested using a tap density meter with 5000 vibrations.

[0266] 5) Compaction density test: The compaction density meter was used for the test. The test pressure was 3T and the compaction time was 30S.

[0267] 6) Iron-to-phosphorus ratio: The iron content is determined by the potassium dichromate method, and the phosphorus content is determined by the quinoline phosphomolybdate weighing method. The iron-to-phosphorus ratio is the molar ratio of iron to phosphorus.

[0268] 7) BET Specific Surface Area: A Micromeritics TriStar II 3020 surface area analyzer was used, with nitrogen as the adsorbate and helium or hydrogen as the carrier gas. The two gases were mixed in a certain proportion to reach a specified relative pressure, and then flowed through the solid material. By changing the mixing ratio of nitrogen and carrier gas, the adsorption amount at several nitrogen relative pressures could be measured, and the specific surface area could be calculated according to the BET specific surface area formula. A 2g sample was degassed and dried at 120℃ for 2 hours and then tested in a Dewar flask containing liquid nitrogen.

[0269] 8) Carbon content test: Infrared carbon-sulfur meter, model HCS-140, Shanghai Dekai Instrument Co., Ltd.

[0270] 2. Properties of secondary batteries

[0271] Lithium iron phosphate specific capacity testing: Blue electrode test. Using the prepared material as the positive electrode material, acetylene black as the conductive agent, and polytetrafluoroethylene as the binder, electrode sheets were fabricated at a mass ratio of 90:5:5. Lithium metal was used as the negative electrode, and CR2032 coin cells were assembled. 1C charge-discharge was tested at 2V–3.75V and 25±0.5℃, and 1P constant power charge-discharge was tested at 2.5V–3.75V and 25±0.5℃.

[0272] III. Analysis of Test Results for Each Embodiment and Comparative Example

[0273] The tap density of anhydrous iron phosphate and the compaction density of lithium iron phosphate prepared in the examples and comparative examples are shown in Tables 1 and 2, and the electrochemical performance test results are shown in Table 3.

[0274] Table 1

[0275] Table 2

[0276] Table 3

[0277] Comparing the data in Tables 1 and 2, it can be found that the sample prepared by forming a surfactant-like substance using anionic and cationic monomers has a higher compaction density. The sample prepared from this anhydrous iron phosphate has a higher compaction density, indicating that the addition of the first and second dispersants can effectively control the crystal morphology. The preparation method of this application can ensure that the prepared lithium iron phosphate has a more reasonable particle size distribution, which helps to prepare lithium iron phosphate cathode materials with high compaction density and good electrical performance.

[0278] Comparing the data in Table 3, it can be found that the lithium iron phosphate prepared in the examples and the comparative examples has similar 1C charging performance, but the discharge efficiency of the comparative example is significantly lower. The constant power charge and discharge performance of the comparative example 1P is significantly worse. Combining the lithium iron phosphate particle size distribution in Tables 1 and 2, it can be seen that the addition of the first dispersant and the second dispersant can effectively regulate the crystal morphology of anhydrous iron phosphate, thereby controlling the primary particle size distribution and morphology of lithium iron phosphate, and improving the carbon coating effect and electrochemical performance of lithium iron phosphate. Among them, the compaction density and electrochemical performance of Example 5 are the best, which is related to its better crystal morphology and primary particle size distribution.

[0279] The anhydrous iron phosphate obtained in Example 5 and Comparative Example 5 were observed for morphology. The SEM images (scanning electron microscope images) of the two are shown in Figure 1 and Figure 2, respectively. The XRD comparison image is shown in Figure 3. The upper half of the image in Figure 3 is a magnified view of the lower half to better compare the position and height of the diffraction peaks.

[0280] The SEM images and primary particle size distribution analysis of the lithium iron phosphate obtained in Example 5 and Comparative Example 5 are shown in Figures 4 and 5.

[0281] As shown in Figures 1 and 2, the anhydrous ferric phosphate prepared in Example 5 with the addition of the first and second dispersants exhibits higher sphericity, while the anhydrous ferric phosphate prepared in Comparative Example 5 tends to grow into elongated strips without the addition of any dispersant. Comparison of Tables 1 and 2 indicates that the anhydrous ferric phosphate prepared in the examples with the addition of the first and second dispersants has a smaller BET specific surface area and a higher compaction density.

[0282] The XRD comparison analysis in Figure 3 shows that the anhydrous iron phosphate prepared in Example 5 has stronger XRD diffraction peaks, while the anhydrous iron phosphate prepared in Comparative Example 5 has significantly left-biased XRD diffraction peaks and more impurity peaks. This indicates that the first and second dispersants are beneficial to promoting the formation of anhydrous iron phosphate and regulating the crystal growth morphology of anhydrous iron phosphate.

[0283] Comparison of SEM images and particle size distribution analysis in Figures 4 and 5 revealed that the lithium iron phosphate spheres prepared using anhydrous iron phosphate prepared with the addition of the first and second dispersants in the examples exhibited better morphology and a higher proportion of particles with a diameter within 200 nm. Correspondingly, the compaction density was higher in Tables 1 and 2. This indicates that the addition of the first and second dispersants can effectively regulate the morphology of anhydrous iron phosphate, thereby controlling the morphology and compaction density of lithium iron phosphate and improving its electrochemical performance.

[0284] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. Anhydrous ferric phosphate, characterized in that, By weight percentage, in the primary particles of the anhydrous ferric phosphate, the proportion of particles with a diameter greater than or equal to 0.01 μm and less than 0.1 μm is 10% to 30%, the proportion of particles with a diameter of 0.1 μm to 0.2 μm is 50% to 60%, the proportion of particles with a diameter greater than 0.2 μm and less than 0.4 μm is 15% to 30%, and the proportion of particles with a diameter of 0.4 μm to 0.6 μm is 0.2% to 10%.

2. The anhydrous ferric phosphate according to claim 1, characterized in that, The anhydrous ferric phosphate particles are nearly spherical with a sphericity of 0.84–0.98; the tap density of the anhydrous ferric phosphate is 0.93 g / cm³. 3 ~1.13g / cm 3 The compacted density is 1.57 g / cm³. 3 ~1.61g / cm 3 The iron-to-phosphorus ratio is (0.957~0.970):

1.

3. A method for preparing anhydrous ferric phosphate, characterized in that, include: The ferrous source is mixed with the first dispersant to obtain the first raw material liquid; The first phosphorus source is mixed with the second dispersant to obtain the second raw material solution; The first raw material liquid, the second raw material liquid, and the first oxidant are mixed and subjected to a first reaction treatment to obtain a first mixture; A second phosphorus source is added to the first mixture, followed by a second reaction treatment, and then a second oxidant is added to obtain a second mixture. The pH and temperature of the second mixture are adjusted, and after a third reaction, the anhydrous ferric phosphate is obtained. The first dispersant comprises a cationic monomer and a coupling agent, and the second dispersant comprises an anionic monomer and a chain transfer agent.

4. The method for preparing anhydrous ferric phosphate according to claim 3, characterized in that, The cationic monomers include dimethyl diallyl ammonium chloride and / or acryloyloxyethyltrimethylammonium chloride; And / or, the coupling agent comprises vinyltrimethoxysilane and / or 3-(methacryloyloxy)propyltrimethoxysilane; When the cationic monomer comprises dimethyl diallyl ammonium chloride and acryloyloxyethyltrimethyl ammonium chloride, the mass ratio of dimethyl diallyl ammonium chloride to acryloyloxyethyltrimethyl ammonium chloride is 1:(2.5-3.5). And / or, The anionic monomers include one or more of methacrylic acid, itaconic acid, and fumaric acid; And / or, the chain transfer agent comprises sodium hypophosphite and / or isopropanol; When the anionic monomer includes methacrylic acid and itaconic acid, the mass ratio of methacrylic acid to itaconic acid is 1:(2.5-3.5); when the anionic monomer includes methacrylic acid and fumaric acid, the mass ratio of methacrylic acid to fumaric acid is 1:(2.5-3.5). And / or, The molar ratio of the cationic monomer to the coupling agent is 100:(20-35); And / or, The molar ratio of the anionic monomer to the chain transfer agent is 100:(10-15).

5. The method for preparing anhydrous ferric phosphate according to claim 3 or 4, characterized in that, The molar ratio of iron in the ferrous source to the first dispersant is 1:(0.0125~0.0150); and / or, The molar ratio of iron in the ferrous source to phosphorus in the phosphorus source is 1:(0.9–1.1); and / or, The molar ratio of phosphorus in the phosphorus source to the second dispersant is 1:(0.0150~0.0170); And / or, the ferrous source is prepared by the following method: mixing titanium dioxide byproduct containing ferrous sulfate with water and heating to dissolve, adding ammonia water with a mass fraction of 5% to 15% for precipitation, filtering and retaining the filtrate to obtain the ferrous source; And / or, independently, the first phosphorus source and the second phosphorus source are prepared by the following method: dissolving monoammonium phosphate in phosphoric acid and water and filtering, and adding 5% to 15% ammonia water by mass to adjust the pH to 6 to 8.

6. The method for preparing anhydrous ferric phosphate according to any one of claims 3 to 5, characterized in that, The first oxidant includes hydrogen peroxide and / or sodium peroxide; and / or, The second oxidant includes hydrogen peroxide and / or sodium peroxide; and / or, The mass ratio of the first phosphorus source to the second phosphorus source is (15-25):(75-85); and / or, The molar ratio of iron in the ferrous source to the first oxidant is 1:(0.6-1.1); and / or, the molar ratio of iron in the ferrous source to the second oxidant is 1:(2.1-2.8).

7. The method for preparing anhydrous ferric phosphate according to any one of claims 3 to 6, characterized in that, In the first reaction treatment, the temperature is 40℃~60℃, and the time is 0.5h~1h; and / or, In the second reaction treatment, the temperature is 40℃~60℃ and the time is 5min~10min.

8. The method for preparing anhydrous ferric phosphate according to any one of claims 3 to 7, characterized in that, The steps of adjusting the pH and temperature of the second mixture and obtaining the anhydrous ferric phosphate after the third reaction include: Adjust the temperature of the second mixture to 40℃~60℃, control the pH value of the second mixture to 0.9~1.5, raise the temperature to 90℃~95℃ and react until the pH value is 1.6~2.0 to obtain the third mixture; The third mixture was subjected to pressure filtration, rinsing, flash evaporation, drying, pulverization, and sieving in sequence to obtain the anhydrous ferric phosphate.

9. A positive electrode material, characterized in that, The general formula of the cathode material is LiFe. 1-a-b-c Y a Ce b M c PO4@C, wherein M is one or more of tin, titanium, boron, and manganese, a is 0.007 to 0.013, b is 0.029 to 0.057, and c is 0.01 to 0.033; C accounts for 1.2% to 1.4% of the mass percentage of the cathode material.

10. The cathode material according to claim 9, characterized in that, The average particle size of the primary particles of the cathode material is 0.24 μm to 0.34 μm; In the cathode material, the fraction of particles with an average primary particle size greater than or equal to 1 μm is less than or equal to 3.20%, and the compaction density is 2.52 g / cm³. 3 ~2.64g / cm 3 .

11. A method for preparing a positive electrode material, characterized in that, Includes the following steps: The anhydrous iron phosphate, lithium source, carbon source, complexing agent, and dopant described in claim 1 or 2 are mixed with water to obtain a mixture. The mixture is sintered under a protective atmosphere to obtain the cathode material. The dopant includes yttrium oxide, cerium oxide, and other oxides, wherein the other oxides include one or more of tin oxide, titanium oxide, boron oxide, and manganese oxide.

12. The method for preparing the cathode material according to claim 11, characterized in that, The complexing agent includes glycerol and / or sodium gluconate; and / or, The dopant includes yttrium oxide, cerium oxide, and the other oxides, wherein the other oxides include one or more of tin dioxide, titanium dioxide, boron trioxide, and manganese carbonate; the mass ratio of yttrium oxide, cerium oxide, and the other oxides is 1:(2-3):(1-2); and / or, The mass ratio of anhydrous ferric phosphate to the complexing agent is 1:(0.02-0.03); and / or, the mass ratio of anhydrous ferric phosphate to the dopant is 1:(0.008-0.009); and / or, The molar ratio of the anhydrous iron phosphate to the lithium source is 1:(1 to 1.05); and / or the mass ratio of the anhydrous iron phosphate to the carbon source is 1:(0.09 to 0.11).

13. The method for preparing the cathode material according to claim 11 or 12, characterized in that, The step of obtaining the cathode material by sintering the mixture under a protective atmosphere includes: The mixture is ground to obtain ground material, the D50 particle size of which is 0.38μm to 0.42μm; The ground material is spray-dried to obtain a spray material with a D50 particle size of 3.4 μm to 6.7 μm. The sprayed material is sintered under the protective atmosphere to obtain the positive electrode material. The sintering temperature is 760℃~820℃, and the time is 10h~18h.

14. A positive electrode plate, characterized in that, It includes a positive current collector and a positive active layer disposed on at least one side of the positive current collector, wherein the positive active layer includes the positive electrode material as described in claim 9 or 10.

15. A secondary battery, characterized in that, Includes the positive electrode sheet as described in claim 14.

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