Iron phosphate material, and positive electrode material, preparation method therefor, and use thereof

Abstract

Provided in the present application are an iron phosphate material, and a positive electrode material, a preparation method therefor, and use thereof, belonging to the field of lithium ion batteries. The general formula of the iron phosphate material is Fe1-xMxPO4·2H2O, wherein M is selected from one or more of Mg and Ce, and 0.008 ≤ x ≤ 0.016. According to the iron phosphate material of the present application, an iron phosphate dihydrate material is doped with the M element to partially replace the iron element, thereby reducing the iron-to-phosphorus ratio of the iron phosphate material within an appropriate range, promoting the growth of iron phosphate material particles, helping to obtain an iron phosphate material having a uniform particle size, and facilitating the reduction in the content of magnetic foreign matter and the improvement of capacity in the prepared positive electrode material, thereby improving the electrochemical performance of the positive electrode material.

Description

Iron phosphate materials, cathode materials, their preparation methods and applications Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to an iron phosphate material, a cathode material, its preparation method, and its application. Background Technology

[0002] Lithium iron phosphate (LiFePO4) is an electrode material widely used in lithium-ion batteries. Currently, lithium iron phosphate materials are typically prepared using anhydrous iron phosphate as a precursor. In the preparation process, anhydrous iron phosphate, a lithium source, and a carbon source are mixed and then sintered to form the lithium iron phosphate material.

[0003] In traditional techniques for preparing lithium iron phosphate (LFP) using anhydrous iron phosphate, the particle size distribution of the anhydrous iron phosphate is difficult to control. This results in an excessive proportion of small-diameter particles and a significant number of large-diameter particles, leading to an uneven particle size distribution in the obtained LFP material. This makes it difficult to balance the compaction density with electrochemical properties such as discharge capacity and rate performance. Introducing dopants into the mixture of anhydrous iron phosphate, lithium source, and carbon source can improve the capacity of doped LFP materials. However, as the amount of dopant added increases, the capacity improvement effect is limited, and it also leads to decreased compaction density and increased magnetic foreign matter content. Again, it is difficult to balance the compaction density with electrochemical properties such as discharge capacity and rate performance.

[0004] Based on the above, further research is still needed on how to improve the performance of iron phosphate materials in order to improve the material properties of lithium iron phosphate materials and thus obtain lithium iron phosphate materials with improved electrochemical performance. Summary of the Invention

[0005] In view of the technical problems existing in the background art, this application provides an iron phosphate material, a cathode material, a preparation method thereof, and its application. The iron phosphate material of this application, by doping iron phosphate dihydrate, partially replaces iron, reducing the iron-to-phosphorus ratio of the iron phosphate material within an appropriate range, promoting the growth of iron phosphate particles, which is beneficial for obtaining iron phosphate material with uniform particle size. Furthermore, it helps to reduce the content of magnetic foreign matter and increase the capacity of the prepared cathode material, thereby improving the electrochemical performance of the cathode material.

[0006] In a first aspect, embodiments of this application provide an iron phosphate material, wherein the general formula of the iron phosphate material is Fe. 1-x M x PO4·2H2O, wherein M is selected from one or more of Mg and Ce, and 0.008≤x≤0.016.

[0007] In the technical solution of this application embodiment, the iron phosphate dihydrate material is doped with element M to partially replace the iron element, thereby reducing the iron-to-phosphorus ratio of the iron phosphate material within an appropriate range, promoting the growth of iron phosphate material particles, which is beneficial to obtaining iron phosphate material with uniform particle size, and also beneficial to reducing the content of magnetic foreign matter and increasing the capacity in the prepared cathode material, thereby improving the electrochemical performance of the cathode material.

[0008] In some embodiments, the average particle size of the primary particles of the iron phosphate material is 200 nm to 300 nm.

[0009] In this embodiment, within the range of the average particle size of the primary particles of the aforementioned iron phosphate material, the particle size of the iron phosphate material is more suitable, which is beneficial for the particle size and distribution of the cathode material prepared by the iron phosphate material to be more suitable, thereby obtaining a higher compaction density and taking into account the capacity improvement.

[0010] In some embodiments, in the primary particles of the iron phosphate material, the proportion of primary particles with a diameter less than 100 nm is 15.3% to 23.7%, the proportion of primary particles with a diameter between 100 nm and 400 nm is 63.3% to 73.6%, the proportion of primary particles with a diameter greater than 400 nm and less than or equal to 1000 nm is 9.6% to 17.5%, and the proportion of primary particles with a diameter greater than 1000 nm is 0.8% to 2.8%.

[0011] In this embodiment, the particle size distribution of the primary particles in the primary particles of the above-mentioned iron phosphate material is more suitable, which is conducive to a more uniform particle size distribution of the cathode material prepared by the iron phosphate material, thereby obtaining a higher compaction density and taking into account the capacity improvement.

[0012] In some embodiments, the iron-to-phosphorus ratio of the iron phosphate material is 0.964 to 0.981.

[0013] In this embodiment, within the range of the iron-phosphorus ratio of the aforementioned iron phosphate material, it is beneficial for the iron phosphate material particles to grow to a suitable size, thereby making the particle size and distribution of the cathode material prepared by the iron phosphate material more suitable, thus obtaining a higher compaction density while also improving capacity.

[0014] Secondly, embodiments of this application provide a cathode material, the general formula of which is LiFe. 1-y-z M y N z PO4@C, wherein M is selected from one or more of Mg and Ce, N is selected from one or more of Ti and Mn, 0.008≤y≤0.016, 0.001≤z≤0.03.

[0015] In the technical solution of this application embodiment, multi-level and multi-element doping of lithium iron phosphate material with M and N elements is beneficial to significantly improve the charging specific capacity and discharging specific capacity of the cathode material. At the same time, within the doping ratio range of the above-mentioned M element and the doping ratio range of N element, the cathode material is beneficial to have high charging specific capacity, high discharging specific capacity and good rate performance, etc., while having high compaction density.

[0016] In some embodiments, the average primary particle size of the cathode material is 340 nm to 415 nm.

[0017] In this embodiment, within the range of the average primary particle size of the above-mentioned cathode material, the particle size of the cathode material is more suitable, which is beneficial for the cathode material to have high charge specific capacity, high discharge specific capacity, and good rate performance, while having high compaction density.

[0018] In some embodiments, in the primary particles of the positive electrode material, the proportion of primary particles with a diameter less than 200 nm is 36.29% to 53.01%, the proportion of primary particles with a diameter between 200 nm and 400 nm is 34.02% to 44.30%, the proportion of primary particles with a diameter greater than 400 nm and less than or equal to 1000 nm is 8.05% to 17.48%, and the proportion of primary particles with a diameter greater than 1000 nm is 0.60% to 1.93%.

[0019] In this embodiment, within the range of the proportion of the primary particle size distribution of the above-mentioned cathode material, the particle size distribution of the cathode material is more suitable, which is beneficial for the cathode material to have high charge specific capacity, high discharge specific capacity, and good rate performance, while having high compaction density.

[0020] In some embodiments, the compaction density of the cathode material under a pressure of 3 kN is 2.57 g / cm³. 3 ~2.68g / cm 3 .

[0021] In this embodiment, the cathode material has a high compaction density, which is beneficial to improving the energy density of the cathode material, thereby improving the electrochemical performance of the cathode material.

[0022] In some embodiments, the resistivity of the positive electrode material powder is 8.6 Ω·cm to 14 Ω·cm.

[0023] In this embodiment, within the range of resistivity of the cathode material powder, the cathode material has a high electronic conductivity, which helps to fully utilize the electrochemical performance of the active materials in the cathode material, allowing more active materials to participate in the electrochemical reaction, thereby increasing the capacity of the secondary battery.

[0024] In some embodiments, the specific surface area of ​​the positive electrode material is 10 m². 2 / g~13m 2 / g.

[0025] In this embodiment, within the specific surface area range of the above-mentioned positive electrode material, it is beneficial to control the contact area with the electrolyte and the reactivity of the positive electrode material, thereby improving the electrochemical performance of the positive electrode material, such as the charging rate and discharging rate.

[0026] In some embodiments, the content of magnetic foreign matter in the positive electrode material is less than or equal to 0.10 ppm.

[0027] In this embodiment, within the range of magnetic foreign matter content of the aforementioned positive electrode material, it is beneficial to improve the safety and reliability of the secondary battery using the positive electrode material.

[0028] Thirdly, embodiments of this application provide a method for preparing a cathode material, comprising the following steps:

[0029] The first dopant source is mixed with a ferrous iron solution to form a mixture;

[0030] The mixture is combined with a first phosphorus source and a first oxidant, and then subjected to a first reaction treatment to obtain a first slurry;

[0031] The first slurry is mixed with the second phosphorus source and the second oxidant, and then subjected to a second reaction treatment to obtain the second slurry;

[0032] The second slurry undergoes a first solid-liquid separation process to obtain a first solid phase material;

[0033] The first solid material is mixed with phosphoric acid and aged to obtain the third slurry;

[0034] The third slurry undergoes a second solid-liquid separation process to obtain a second solid phase material;

[0035] The second solid material is subjected to crystallization treatment to obtain iron phosphate material;

[0036] The iron phosphate material, lithium source, second doping source, surfactant, carbon source and solvent are mixed to obtain a precursor slurry;

[0037] The precursor slurry is subjected to grinding and drying processes to obtain a precursor; and,

[0038] The precursor is sintered to obtain the cathode material;

[0039] Wherein, the first doping source contains a first doping element, which is selected from one or more of Mg and Ce, and the molar ratio of iron in the ferrous solution to the first doping element is (1-x):x, 0.008≤x≤0.016; the second doping source contains a second doping element, which is selected from one or more of Ti and Mn, and the molar ratio of iron in the iron phosphate material to the second doping element in the second doping source is (1-yz):z, 0.008≤y≤0.016, 0.001≤z≤0.03.

[0040] In the technical solution of this application embodiment, the preparation of the first solid phase material is carried out in two steps. During the first reaction treatment, some crystal nuclei are formed. During the second reaction treatment, the growth of the crystal nuclei formed during the first reaction treatment is promoted, thereby reducing the generation of small particles and making the obtained iron phosphate material have a uniform particle size distribution and appropriate particle size. In the process of preparing iron phosphate material, ferrous solution is mixed with the first doping source. The cations of the first doping element and ferrous ions co-precipitate to form a compound with internal doping, which facilitates the uniform doping and growth of iron phosphate material, thereby obtaining iron phosphate material with a more uniform particle size distribution and doped with the first element. By doping the dihydrate iron phosphate material with element M, the iron element is partially replaced, and the iron-phosphorus ratio of the iron phosphate material is reduced within an appropriate range, which promotes the growth of iron phosphate material particles and is beneficial to obtaining iron phosphate material with uniform particle size. It is also beneficial to reduce the content of magnetic foreign matter and increase the capacity in the prepared cathode material. To improve the electrochemical performance of the cathode material, a second doping element is added during the preparation of the precursor, and the molar ratio of iron in the iron phosphate material to the second doping element in the second doping source is controlled to be (1-yz):z, 0.008≤y≤0.016, 0.001≤z≤0.03. Through a two-step doping method, the cathode material achieves better rate performance under conditions of lower secondary doping amount. The preparation method of this application adds a surfactant during the grinding process to improve the dispersibility of the iron phosphate material, reduce the agglomeration of the iron phosphate material during grinding, and facilitate particle growth during sintering, thereby obtaining a cathode material with more uniform particle size distribution and more suitable particle size. The cathode material prepared by the cathode material preparation method of this application has high compaction density, high charge specific capacity, high discharge specific capacity, and good rate performance, among other electrochemical properties.

[0041] In some embodiments, the step of mixing the mixture with a first phosphorus source and a first oxidant, and then subjecting it to a first reaction treatment to obtain a first slurry includes:

[0042] The mixture is mixed with the first phosphorus source and the first oxidant at the first mixing temperature for the first mixing time, and then at the first reaction temperature for the first reaction time to obtain the first slurry;

[0043] Wherein, the first mixing temperature is 25℃~50℃, the first mixing time is 20min~40min, the first reaction time is 20min~40min, and the first reaction temperature is 50℃~70℃.

[0044] In this embodiment, within the range of the first mixing temperature, the first mixing time, the first reaction time, and the first reaction temperature, it is beneficial for the crystal nuclei to grow more completely, which in turn is beneficial for obtaining iron phosphate material with a more uniform particle size distribution and a more suitable particle size.

[0045] In some embodiments, the step of mixing the first slurry with a second phosphorus source and a second oxidant, and then subjecting it to a second reaction treatment to obtain a second slurry includes:

[0046] The mixture and the second phosphorus source are mixed at a second mixing temperature for a second mixing time to obtain a fourth slurry;

[0047] The fourth slurry and the second oxidant are mixed at a third mixing temperature for a third mixing time, and then at a second reaction temperature for a second reaction time to obtain the second slurry;

[0048] Wherein, the second mixing temperature is 45℃~60℃, the second mixing time is 3min~8min, the third mixing temperature is 50℃~60℃, the third mixing time is 10min~16min, the second reaction time is 50min~70min, and the second reaction temperature is 50℃~70℃;

[0049] The mass ratio of the first phosphorus source to the second phosphorus source is (45-60):(40-55), and the mass ratio of the first oxidant to the second oxidant is (70-85):(15-30).

[0050] In this embodiment, within the range of the above-mentioned reaction parameters, it is beneficial to promote the growth of crystal nuclei during the second reaction process, thereby obtaining iron phosphate material with more uniform particle size distribution and more suitable particle size.

[0051] In some embodiments, the step of mixing the first solid material with phosphoric acid and aging it to obtain the third slurry includes:

[0052] The first solid material is mixed with phosphoric acid to a pH of 1.2–1.7, and after aging at an aging temperature for a specified time, the third slurry is obtained.

[0053] The aging temperature is 75℃~95℃, the aging time is 1.5h~2.5h, and the pH value of the third slurry is 1.7~2.

[0054] In this embodiment, within the range of parameters of the above-mentioned aging treatment, it is beneficial to further uniform growth of particles, thereby obtaining iron phosphate material with more uniform particle size distribution and more suitable particle size.

[0055] In some embodiments, after the precursor slurry is milled, the D50 particle size of the solid particles in the precursor slurry is 0.2 μm to 0.5 μm.

[0056] In this embodiment, within the range of the D50 particle size of the solid particles in the precursor slurry, it is beneficial to prepare a cathode material with a more uniform particle size distribution and a more suitable particle size.

[0057] In some embodiments, the D50 particle size of the precursor is 3 μm to 6 μm.

[0058] In this embodiment, within the D50 particle size range of the aforementioned precursor, it is advantageous to prepare a cathode material with a more uniform particle size distribution and a more suitable particle size.

[0059] In some embodiments, the surfactant is selected from at least one of isooctanol polyoxyethylene polyoxypropylene ether-9 and polyethylene glycol; the mass of the surfactant is 0.02% to 0.1% of the mass of the iron phosphate material.

[0060] In this embodiment, within the range of the mass ratio of the surfactant to the mass of the iron phosphate material, it is beneficial to improve the dispersibility of the iron phosphate material particles, ensure uniform heating of the particles during sintering, and improve the consistency of particle growth, thereby preparing a cathode material with a more uniform particle size distribution and a more suitable particle size.

[0061] In some embodiments, the step of obtaining the cathode material by sintering the precursor includes:

[0062] The precursor is sintered at a first sintering temperature for a first sintering time to obtain a pre-sintered material; and,

[0063] The pre-sintered material is sintered at a second sintering temperature for a second sintering time to obtain the cathode material;

[0064] The first sintering temperature is 400℃~500℃, the first sintering time is 1h~6h, the second sintering temperature is 700℃~900℃, and the second sintering time is 4h~12h.

[0065] In this embodiment, within the parameter range of the above sintering treatment, it is beneficial to ensure sufficient dehydration time and uniform heating of the particles, so that the growth of the cathode material particles has better consistency, thereby preparing cathode materials with more uniform particle size distribution and more suitable particle size.

[0066] Fourthly, embodiments of this application provide an electrode sheet, the electrode sheet comprising a current collector and an electrode active layer disposed on the current collector, the electrode active layer comprising the positive electrode material described in any one of the above claims, or the electrode active layer comprising the positive electrode material prepared by any one of the above preparation methods.

[0067] In this embodiment, the active layer of the positive electrode sheet includes the aforementioned positive electrode material, thus exhibiting good electrochemical performance.

[0068] Fifthly, embodiments of this application provide a secondary battery, the secondary battery including a positive electrode and a negative electrode, the positive electrode including the aforementioned electrode.

[0069] In this embodiment, the secondary battery includes the aforementioned positive electrode, thus possessing comprehensively improved electrochemical performance, and can be well applied in multiple application scenarios.

[0070] 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, specific embodiments of this application are given below. Attached Figure Description

[0071] 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.

[0072] Figure 1 is a schematic diagram of the steps in a method for preparing a cathode material according to the present invention;

[0073] Figure 2 shows the scanning electron microscope (SEM) results of the iron phosphate material in Example 1 of the present invention;

[0074] Figure 3 shows the SEM results of the iron phosphate material in Comparative Example 2;

[0075] Figure 4 is a SEM image of the cathode material in Example 1 of the present invention;

[0076] Figure 5 is a particle size distribution diagram of the cathode material in Example 1 of the present invention;

[0077] Figure 6 shows the SEM results of the cathode material in Comparative Example 2;

[0078] Figure 7 shows the particle size distribution of the cathode material in Comparative Example 2. Detailed Implementation

[0079] 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.

[0080] 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.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] 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).

[0085] In the description of the embodiments of this application, unless otherwise specified, the solvent for solutions, mixtures, slurries, etc., is selected from at least one of distilled water, deionized water, pure water, and ultrapure water.

[0086] In the embodiments of this application, ppm represents the mass of the element to be measured as a percentage of the sample mass in parts per million.

[0087] In a first aspect, embodiments of this application provide an iron phosphate material, the general formula of which is Fe. 1-x M x PO4·2H2O, wherein M is selected from one or more of Mg and Ce, and 0.008≤x≤0.016.

[0088] In the technical solution of this application embodiment, the iron phosphate dihydrate material is doped with element M to partially replace the iron element, thereby reducing the iron-to-phosphorus ratio of the iron phosphate material within an appropriate range, promoting the growth of iron phosphate material particles, which is beneficial to obtaining iron phosphate material with uniform particle size, and also beneficial to reducing the content of magnetic foreign matter and increasing the capacity in the prepared cathode material, thereby improving the electrochemical performance of the cathode material.

[0089] In the technical solution of this application embodiment, the iron phosphate material is a doped iron phosphate dihydrate material. Compared with anhydrous iron phosphate, it is not only easier to achieve uniform doping during the synthesis process, but also easier to grow during sintering to prepare the cathode material. This is beneficial for obtaining a cathode material with a more suitable particle size, thereby improving the electrochemical performance of the cathode material while also taking into account its compaction density. Simultaneously, since the M element is used to replace part of the iron element, it is less likely to generate elemental iron, iron phosphide, or other magnetic substances during the sintering preparation of the cathode material, thus reducing the content of magnetic foreign matter in the cathode material prepared from the iron phosphate material.

[0090] Optionally, x = 0.008, 0.009, 0.01, 0.012, 0.0125, 0.013, 0.0135, 0.014, 0.0145, 0.015, 0.0155, or 0.016, or x can be within the range of any two of the above values. Preferably, 0.012 ≤ x ≤ 0.016.

[0091] In some embodiments, the average particle size of the primary particles of the iron phosphate material is 200 nm to 300 nm, preferably 240 nm to 300 nm.

[0092] In this embodiment, within the range of the average particle size of the primary particles of the aforementioned iron phosphate material, the particle size of the iron phosphate material is more suitable. This is beneficial for the cathode material prepared from the iron phosphate material to have a more suitable particle size and distribution, thereby achieving higher compaction density while also improving capacity. Optionally, the average particle size of the primary particles of the iron phosphate material is 200nm, 210nm, 220nm, 230nm, 240nm, 250nm, 260nm, 270nm, 280nm, 290nm, or 300nm, or the average particle size of the primary particles of the iron phosphate material can also be within the range between any two of the above particle sizes.

[0093] In some embodiments, the primary particle size in the primary particles of the iron phosphate material is between 10 nm and 2200 nm.

[0094] In this embodiment, within the range of primary particle size in the primary particles of the aforementioned iron phosphate material, the particle size of the iron phosphate material is more suitable. This is beneficial for the cathode material prepared from the iron phosphate material to have a more suitable particle size and distribution, thereby achieving higher compaction density while also improving capacity. Optionally, the primary particle size in the primary particles of the iron phosphate material is 10nm, 20nm, 50nm, 100nm, 200nm, 500nm, 1000nm, 1500nm, 2000nm, or 2200nm. Alternatively, the primary particle size in the primary particles of the iron phosphate material can also be within the range between any two of the above particle sizes.

[0095] In some embodiments, in the primary particles of the iron phosphate material, the proportion of primary particles with a diameter less than 100 nm is 15.3% to 23.7%, the proportion of primary particles with a diameter between 100 nm and 400 nm is 63.3% to 73.6%, the proportion of primary particles with a diameter greater than 400 nm and less than or equal to 1000 nm is 9.6% to 17.5%, and the proportion of primary particles with a diameter greater than 1000 nm is 0.8% to 2.8%.

[0096] In this embodiment, the particle size distribution of the primary particles in the above-mentioned iron phosphate material is more suitable. It controls both the proportion of primary particles with a primary particle size of less than 100 nm and the proportion of primary particles with a primary particle size of more than 1000 nm. This is beneficial to the more uniform particle size distribution of the cathode material prepared by the iron phosphate material, thereby obtaining a higher compaction density and taking into account the capacity improvement.

[0097] Optionally, in the primary particles of the iron phosphate material, the proportion of primary particles with a diameter less than 100 nm is 15.3%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, or 23.7%, or the proportion of primary particles with a diameter less than 100 nm can be within any two of the above percentages. Preferably, in the primary particles of the iron phosphate material, the proportion of primary particles with a diameter less than 100 nm is 16.4% to 22%.

[0098] Optionally, in the primary particles of the iron phosphate material, the proportion of primary particles with a diameter between 100 nm and 400 nm is 63.3%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, or 73.6%. Alternatively, the proportion of primary particles with a diameter between 100 nm and 400 nm in the primary particles of the iron phosphate material can also be within any two of the above percentages. Preferably, the proportion of primary particles with a diameter between 100 nm and 400 nm in the primary particles of the iron phosphate material is 63.3% to 67.7%.

[0099] Optionally, in the primary particles of the iron phosphate material, the proportion of primary particles with a diameter greater than 400 nm and less than or equal to 1000 nm is 9.6%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, or 17.5%. Alternatively, the proportion of primary particles with a diameter greater than 400 nm and less than or equal to 1000 nm in the primary particles of the iron phosphate material may also be within the range of any two of the above percentages.

[0100] Optionally, in the primary particles of the iron phosphate material, the proportion of primary particles with a diameter greater than 1000 nm is 0.8%, 1%, 1.5%, 2%, 2.5%, or 2.8%, or the proportion of primary particles with a diameter greater than 1000 nm can be within any two of the above percentages. Preferably, the proportion of primary particles with a diameter greater than 1000 nm is 0.8% to 2.38%.

[0101] In some embodiments, the iron-to-phosphorus ratio of the iron phosphate material is 0.964 to 0.981. That is, in the iron phosphate material, the molar ratio of iron to phosphorus is 0.964 to 0.981.

[0102] In this embodiment, within the aforementioned iron-to-phosphorus ratio range of the iron phosphate material, it is beneficial for the iron phosphate material particles to grow to a suitable size, thereby resulting in a more suitable particle size and distribution of the cathode material prepared from the iron phosphate material, thus achieving higher compaction density while also improving capacity. Optionally, the iron-to-phosphorus ratio of the iron phosphate material is 0.964, 0.965, 0.966, 0.967, 0.968, 0.969, 0.97, 0.971, 0.972, 0.973, 0.974, 0.975, 0.978, or 0.981, or the iron-to-phosphorus ratio of the iron phosphate material can also be within the range between any two of the aforementioned iron-to-phosphorus ratios.

[0103] Secondly, embodiments of this application provide a cathode material, the general formula of which is LiFe. 1-y-z M y N z PO4@C, wherein M is selected from one or more of Mg and Ce, N is selected from one or more of Ti and Mn, 0.008≤y≤0.016, 0.001≤z≤0.03.

[0104] In the technical solution of this application embodiment, multi-level and multi-element doping of lithium iron phosphate material with M and N elements is beneficial to significantly improve the charging specific capacity and discharging specific capacity of the cathode material. At the same time, within the doping ratio range of the above-mentioned M element and the doping ratio range of N element, the cathode material is beneficial to have high charging specific capacity, high discharging specific capacity and good rate performance, etc., while having high compaction density.

[0105] Optionally, y = 0.008, 0.009, 0.01, 0.012, 0.0125, 0.013, 0.0135, 0.014, 0.0145, 0.015, 0.0155, or 0.016, or y can be within the range of any two of the above values. Preferably, 0.012 ≤ y ≤ 0.016.

[0106] Optionally, z = 0.001, 0.002, 0.005, 0.008, 0.01, 0.014, 0.015, 0.016, 0.017, 0.018, 0.019, 0.02, 0.022, 0.025, 0.028, or 0.03, or z can be within the range of any two of the above values. Preferably, 0.01 ≤ z ≤ 0.03, more preferably, 0.02 ≤ z ≤ 0.025.

[0107] In some embodiments, the cathode material includes a core and a carbon coating layer covering the surface of the core, wherein the core can be of the general formula: LiFe 1-y-z My N z PO4 represents a compound in which M is selected from one or more of Mg and Ce, N is selected from one or more of Ti and Mn, and 0.008≤y≤0.016, 0.001≤z≤0.03. Preferably, 0.012≤y≤0.016. More preferably, 0.01≤z≤0.03, and even more preferably, 0.02≤z≤0.025.

[0108] In some embodiments, the mass fraction of the carbon coating layer of the cathode material is 1% to 1.2%, preferably 1.15% to 1.2%.

[0109] A lower carbon coating content reduces the inhibition of particle growth during the formation of cathode materials, which is conducive to obtaining cathode materials with more suitable particle size distribution. It also avoids the reduction in compaction density caused by excessive carbon elements, which is beneficial to improving the compaction density of cathode materials.

[0110] In some embodiments, the average primary particle size of the cathode material is 340 nm to 415 nm, preferably 345 nm to 410 nm.

[0111] In this embodiment, the particle size of the cathode material is more suitable within the range of the average primary particle size described above. This is beneficial for the cathode material to have high charge specific capacity, high discharge specific capacity, and good rate performance, while simultaneously possessing high compaction density. Optionally, the average primary particle size of the cathode material is 340nm, 350nm, 360nm, 370nm, 380nm, 390nm, 400nm, or 415nm, or the average primary particle size of the cathode material can be within the range of any two of the above particle sizes.

[0112] In some embodiments, in the primary particles of the cathode material, the proportion of primary particles with a diameter less than 200 nm is 36.29% to 53.01%, the proportion of primary particles with a diameter between 200 nm and 400 nm is 34.02% to 44.30%, the proportion of primary particles with a diameter greater than 400 nm and less than or equal to 1000 nm is 8.05% to 17.48%, and the proportion of primary particles with a diameter greater than 1000 nm is 0.60% to 1.93%.

[0113] In this embodiment, within the range of the proportion of the primary particle size distribution of the above-mentioned cathode material, the particle size distribution of the cathode material is more suitable, which is beneficial for the cathode material to have high charge specific capacity, high discharge specific capacity, and good rate performance, while having high compaction density.

[0114] Optionally, in the primary particles of the cathode material, the proportion of primary particles with a diameter less than 200 nm is 36.29%, 38%, 40%, 42%, 44%, 46%, 48%, 50%, 52%, or 53.01%, or the proportion of primary particles with a diameter less than 200 nm can be within any two of the above percentages. Preferably, in the primary particles of the cathode material, the proportion of primary particles with a diameter less than 200 nm is 45.88% to 53.01%.

[0115] Optionally, in the primary particles of the cathode material, the proportion of primary particles with a diameter between 200 nm and 400 nm is 34.02%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, or 44.30%. Alternatively, the proportion of primary particles with a diameter between 200 nm and 400 nm in the primary particles of the cathode material can also be within the range of any two of the above percentages. Preferably, the proportion of primary particles with a diameter between 200 nm and 400 nm in the primary particles of the cathode material is 34.02% to 40.27%.

[0116] Optionally, in the primary particles of the cathode material, the proportion of primary particles with a diameter greater than 400 nm and less than or equal to 1000 nm is 8.05%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, or 17.48%. Alternatively, the proportion of primary particles with a diameter greater than 400 nm and less than or equal to 1000 nm can also be within the range of any two of the above percentages. Preferably, in the primary particles of the cathode material, the proportion of primary particles with a diameter greater than 400 nm and less than or equal to 1000 nm is 8.05% to 15.09%.

[0117] Optionally, in the primary particles of the cathode material, the proportion of primary particles with a diameter greater than 1000 nm is 0.60%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.4%, 1.6%, 1.8%, or 1.93%, or the proportion of primary particles with a diameter greater than 1000 nm can be within any two of the above percentages. Preferably, in the primary particles of the cathode material, the proportion of primary particles with a diameter greater than 1000 nm is 0.60% to 1.70%.

[0118] In some embodiments, the compaction density of the cathode material under a pressure of 3 kN is 2.57 g / cm³. 3 ~2.68g / cm 3 The preferred value is 2.58 g / cm³. 3 ~2.68g / cm3 .

[0119] In this embodiment, the cathode material has a high compaction density, which is beneficial for improving the energy density of the cathode material, thereby enhancing its electrochemical performance. Optionally, the compaction density of the cathode material at a pressure of 3 kN is 2.57 g / cm³. 3 2.58g / cm 3 2.59g / cm 3 2.6g / cm 3 2.61 g / cm 3 2.62 g / cm 3 2.63 g / cm 3 2.64 g / cm 3 2.65g / cm 3 2.66 g / cm 3 2.67 g / cm 3 Or 2.68g / cm 3 Alternatively, the compaction density of the cathode material under 3kN pressure can also be within the range between any two of the above compaction densities.

[0120] In some embodiments, the resistivity of the positive electrode material powder is 8.6 Ω·cm to 14 Ω·cm, preferably 8.6 Ω·cm to 10.6 Ω·cm.

[0121] In this embodiment, the positive electrode material exhibits high electronic conductivity within the range of powder resistivity, which helps to fully utilize the electrochemical performance of the active materials in the positive electrode material, allowing more active materials to participate in the electrochemical reaction, thereby increasing the capacity of the secondary battery. Optionally, the powder resistivity of the positive electrode material is 8.6 Ω·cm, 8.8 Ω·cm, 9 Ω·cm, 9.2 Ω·cm, 9.4 Ω·cm, 9.6 Ω·cm, 9.8 Ω·cm, 10 Ω·cm, 11 Ω·cm, 12 Ω·cm, 13 Ω·cm, or 14 Ω·cm, or the powder resistivity of the positive electrode material can also be within the range of any two of the above powder resistivities.

[0122] In some embodiments, the specific surface area of ​​the cathode material is 10 m². 2 / g~13m 2 / g, preferably 11m 2 / g~12.7m 2 / g.

[0123] In this embodiment, within the specific surface area range of the aforementioned cathode material, it is beneficial to control the contact area with the electrolyte and the reactivity of the cathode material, thereby improving the electrochemical performance of the cathode material, such as charging rate and discharging rate. Optionally, the specific surface area of ​​the cathode material is 10 m² / g. 2 / g、11m 2 / g, 11.2m 2 / g, 11.4m 2 / g, 11.6m 2 / g, 11.8m 2 / g、12m 2 / g, 12.2m 2 / g, 12.4m 2 / g, 12.6m 2 / g, 12.8m 2 / g or 13m 2 / g, or the specific surface area of ​​the cathode material can be within the range of any two specific surface areas mentioned above.

[0124] In some embodiments, the content of magnetic foreign matter in the positive electrode material is less than or equal to 0.20 ppm, preferably 0.10 ppm.

[0125] In this embodiment, within the range of magnetic foreign matter content in the aforementioned positive electrode material, it is beneficial to improve the safety and reliability of the secondary battery using this positive electrode material. Optionally, the magnetic foreign matter content of the positive electrode material is 0, 0.02ppm, 0.04ppm, 0.06ppm, 0.08ppm, or 0.10ppm, or the magnetic foreign matter content of the positive electrode material can also be within the range of any two of the above contents.

[0126] In some embodiments, the static iron leaching amount of the positive electrode material is 0.95ppm to 4.88ppm, preferably 0.95ppm to 2.3ppm.

[0127] In this embodiment, within the range of static iron dissolution of the above-mentioned positive electrode material, it is beneficial to reduce the capacity decay of the positive electrode material and improve the service life of the secondary battery using the positive electrode material. Optionally, the static iron dissolution of the positive electrode material is 0.95ppm to 4.88ppm, or the static iron dissolution of the positive electrode material can also be within the range between any two of the above-mentioned static iron dissolution values.

[0128] In some embodiments, the 1C initial charge specific capacity (25°C, 2V~3.75V) of the cathode material is 148.02mAh / g~152.1mAh / g.

[0129] Preferably, the 1C initial charge specific capacity (25℃, 2V~3.75V) of the positive electrode material is 149.8mAh / g~152.1mAh / g.

[0130] In some embodiments, the 1C initial discharge specific capacity (25°C, 2V to 3.75V) of the cathode material is 138.7mAh / g to 142.38mAh / g.

[0131] Preferably, the 1C initial discharge specific capacity (25℃, 2V~3.75V) of the positive electrode material is 140.45mAh / g~142.38mAh / g.

[0132] In some embodiments, the 1C initial discharge efficiency (25°C, 2V to 3.75V) of the positive electrode material is 93.21% to 94.83%. Preferably, the 1C initial discharge efficiency (25°C, 2V to 3.75V) of the positive electrode material is 94.29% to 94.83%.

[0133] In some embodiments, the 5C initial charge specific capacity (25°C, 2V~3.75V) of the cathode material is 112.5mAh / g~121.5mAh / g. Preferably, the 5C initial charge specific capacity (25°C, 2V~3.75V) of the cathode material is 115.6mAh / g~121.5mAh / g.

[0134] In some embodiments, the 5C initial discharge specific capacity (25°C, 2V~3.75V) of the cathode material is 98.98mAh / g~

[0135] 112.37 mAh / g. Preferably, the 5C initial discharge specific capacity (25℃, 2V~3.75V) of the cathode material is 110.06 mAh / g~

[0136] 112.37mAh / g.

[0137] In some embodiments, the 5C initial discharge efficiency (25°C, 2V to 3.75V) of the positive electrode material is 87.98% to 97.89%. Preferably, the 5C initial discharge efficiency (25°C, 2V to 3.75V) of the positive electrode material is 94.99% to 97.89%.

[0138] Thirdly, embodiments of this application provide a method for preparing a cathode material, comprising the following steps:

[0139] The first dopant source is mixed with a ferrous iron solution to form a mixture;

[0140] The mixture is combined with a first phosphorus source and a first oxidant, and then subjected to a first reaction treatment to obtain a first slurry;

[0141] The first slurry is mixed with the second phosphorus source and the second oxidant, and then subjected to a second reaction treatment to obtain the second slurry;

[0142] The second slurry undergoes a first solid-liquid separation process to obtain the first solid phase material;

[0143] The first solid material is mixed with phosphoric acid and then aged to obtain the third slurry;

[0144] The third slurry undergoes a second solid-liquid separation process to obtain a second solid phase material;

[0145] The second solid material is crystallized to obtain iron phosphate material;

[0146] Iron phosphate material, lithium source, second doping source, surfactant, carbon source and solvent are mixed to obtain precursor slurry;

[0147] The precursor slurry is ground and dried to obtain the precursor; and,

[0148] The precursor is sintered to obtain the cathode material;

[0149] The first doping source contains a first doping element, which is selected from one or more of Mg and Ce. The molar ratio of iron in the ferrous solution to the first doping element is (1-x):x, 0.008≤x≤0.016. The second doping source contains a second doping element, which is selected from one or more of Ti and Mn. The molar ratio of iron in the iron phosphate material to the second doping element in the second doping source is (1-yz):z, 0.008≤y≤0.016, 0.001≤z≤0.03.

[0150] In the technical solution of this application embodiment, the preparation of the first solid phase material is carried out in two steps. During the first reaction treatment, some crystal nuclei are formed. During the second reaction treatment, the growth of the crystal nuclei formed during the first reaction treatment is promoted, thereby reducing the generation of small particles and making the obtained iron phosphate material have a uniform particle size distribution and appropriate particle size. In the process of preparing iron phosphate material, ferrous solution is mixed with the first doping source. The cations of the first doping element and ferrous ions co-precipitate to form a compound with internal doping, which facilitates the uniform doping and growth of iron phosphate material, thereby obtaining iron phosphate material with a more uniform particle size distribution and doped with the first element. By doping the dihydrate iron phosphate material with element M, the iron element is partially replaced, and the iron-phosphorus ratio of the iron phosphate material is reduced within an appropriate range, which promotes the growth of iron phosphate material particles and is beneficial to obtaining iron phosphate material with uniform particle size. It is also beneficial to reduce the content of magnetic foreign matter and increase the capacity in the prepared cathode material. To improve the electrochemical performance of the cathode material, a second doping element is added during the preparation of the precursor, and the molar ratio of iron in the iron phosphate material to the second doping element in the second doping source is controlled to be (1-yz):z, 0.008≤y≤0.016, 0.001≤z≤0.03. Through a two-step doping method, the cathode material achieves better rate performance under conditions of lower secondary doping amount. The preparation method of this application adds a surfactant during the grinding process to improve the dispersibility of the iron phosphate material, reduce the agglomeration of the iron phosphate material during grinding, and facilitate particle growth during sintering, thereby obtaining a cathode material with more uniform particle size distribution and more suitable particle size. The cathode material prepared by the cathode material preparation method of this application has high compaction density, high charge specific capacity, high discharge specific capacity, and good rate performance, among other electrochemical properties.

[0151] Alternatively, x = 0.008, 0.009, 0.010, 0.011, 0.012, 0.013, 0.014, 0.015, or 0.016, or x can be within the range of any two of the above values.

[0152] Alternatively, y = 0.008, 0.009, 0.010, 0.011, 0.012, 0.013, 0.014, 0.015, or 0.016, or y can be within the range of any two of the above values.

[0153] Alternatively, z = 0.001, 0.005, 0.01, 0.015, 0.02, 0.025 or 0.003, or z can be within the range of any two of the above values.

[0154] Preferably, 0.012 ≤ x ≤ 0.016.

[0155] Preferably, 0.012≤y≤0.016.

[0156] Preferably, 0.01≤z≤0.03, more preferably, 0.02≤z≤0.025.

[0157] In some embodiments, the iron phosphate material prepared in the method for preparing the cathode material provided in this application is the iron phosphate material as described above.

[0158] In some embodiments, the cathode material prepared by the method of this application is the cathode material as described above.

[0159] In some embodiments, the first dopant source includes at least one of magnesium sulfate heptahydrate and cerium nitrate.

[0160] In some embodiments, the first phosphorus source includes at least one of lithium dihydrogen phosphate and lithium monohydrogen phosphate.

[0161] In some embodiments, the first oxidant includes hydrogen peroxide, wherein the mass fraction of hydrogen peroxide in the hydrogen peroxide is 25% to 35%.

[0162] Optionally, the mass fraction of hydrogen peroxide in the hydrogen peroxide solution of the first oxidant is 25%, 27.5%, 30%, 32.5%, or 35%, or the mass fraction of hydrogen peroxide in the hydrogen peroxide solution of the first oxidant may be within the range of any two of the above mass fractions. Preferably, the mass fraction of hydrogen peroxide in the hydrogen peroxide solution of the first oxidant is 27.5% or 30%.

[0163] In some embodiments, the second phosphorus source includes at least one of lithium dihydrogen phosphate and lithium monohydrogen phosphate.

[0164] In some embodiments, the second oxidant includes hydrogen peroxide, wherein the mass fraction of hydrogen peroxide in the hydrogen peroxide is 25% to 35%.

[0165] Optionally, the mass fraction of hydrogen peroxide in the hydrogen peroxide solution of the second oxidant is 5%, 27.5%, 30%, 32.5%, or 35%, or the mass fraction of hydrogen peroxide in the hydrogen peroxide solution of the second oxidant can also be within the range of any two of the above mass fractions. Preferably, the mass fraction of hydrogen peroxide in the hydrogen peroxide solution of the second oxidant is 27.5% or 30%.

[0166] Using the first dopant source, first phosphorus source, first oxidant, second phosphorus source, and second oxidant reduces the introduction of impurities, which is beneficial for preparing high-purity iron phosphate materials, and thus for preparing high-purity cathode materials.

[0167] In some embodiments, the mass fraction of hydrogen peroxide in the hydrogen peroxide solution of the first oxidant can be the same as the mass fraction of hydrogen peroxide in the hydrogen peroxide solution of the second oxidant, so as to facilitate co-configuration, simplify the process, and reduce the preparation cost.

[0168] In some embodiments, the lithium source includes at least one of lithium carbonate, lithium hydroxide, lithium oxalate, and lithium acetate.

[0169] In some embodiments, the second doping source includes at least one of titanium dioxide and manganese carbonate.

[0170] In some embodiments, the carbon source includes at least one of glucose and sucrose.

[0171] Using the aforementioned lithium source, second doping source, and carbon source reduces the introduction of impurities, which is beneficial for preparing high-purity cathode materials.

[0172] In some embodiments, the drying process is spray drying.

[0173] In some embodiments, the inlet air temperature of the spray dryer is 150°C to 350°C, and the outlet air temperature of the spray dryer is 60°C to 110°C.

[0174] Optionally, the inlet air temperature for spray drying is 150℃, 180℃, 200℃, 220℃, 250℃, 280℃, 300℃, 320℃, or 350℃, or the inlet air temperature for spray drying may be within the range of any two of the above temperatures. Optionally, the outlet air temperature for spray drying is 60℃, 70℃, 80℃, 90℃, 100℃, or 110℃, or the outlet air temperature for spray drying may be within the range of any two of the above temperatures.

[0175] In some embodiments, the sintering process is performed in a protective gas atmosphere.

[0176] In some embodiments, the protective gas includes at least one of nitrogen and argon.

[0177] In some embodiments, the step of mixing the mixture with a first phosphorus source and a first oxidant, and then subjecting it to a first reaction treatment to obtain a first slurry includes:

[0178] After the mixture is mixed with the first phosphorus source and the first oxidant at the first mixing temperature for the first mixing time, and then at the first reaction temperature for the first reaction time, a first slurry is obtained.

[0179] The first mixing temperature is 25℃~50℃, the first mixing time is 20min~40min, the first reaction time is 20min~40min, and the first reaction temperature is 50℃~70℃.

[0180] In this embodiment, within the range of the first mixing temperature, the first mixing time, the first reaction time, and the first reaction temperature, it is beneficial for the crystal nuclei to grow more completely, which in turn is beneficial for obtaining iron phosphate material with a more uniform particle size distribution and a more suitable particle size.

[0181] Optionally, the first mixing temperature is 25°C, 30°C, 35°C, 40°C, 45°C or 50°C, or the first mixing temperature may be within the range of any two of the above temperatures.

[0182] Optionally, the first mixing time is 20 min, 25 min, 30 min, 35 min or 40 min, or the first mixing time may be within any two of the above times.

[0183] Optionally, the first reaction time is 20 min, 25 min, 30 min, 35 min or 40 min, or the first reaction time can be within any two of the above times.

[0184] Optionally, the first reaction temperature is 50°C, 55°C, 60°C, 65°C or 70°C, or the first reaction temperature may be within the range of any two of the above temperatures.

[0185] In some embodiments, the step of mixing the first slurry with a second phosphorus source and a second oxidant, and then subjecting the mixture to a second reaction treatment to obtain a second slurry includes:

[0186] After the mixture and the second phosphorus source are mixed at the second mixing temperature for the second mixing time, a fourth slurry is obtained;

[0187] The fourth slurry and the second oxidant are mixed at a third mixing temperature for a third mixing time, and then at a second reaction temperature for a second reaction time to obtain the second slurry;

[0188] The second mixing temperature is 45℃~60℃, the second mixing time is 3min~8min, the third mixing temperature is 50℃~60℃, the third mixing time is 10min~16min, the second reaction time is 50min~70min, and the second reaction temperature is 50℃~70℃.

[0189] The mass ratio of the first phosphorus source to the second phosphorus source is (45-60):(40-55), and the mass ratio of the first oxidant to the second oxidant is (70-85):(15-30).

[0190] In this embodiment, within the range of the above-mentioned reaction parameters, it is beneficial to promote the growth of crystal nuclei during the second reaction process, thereby obtaining iron phosphate material with more uniform particle size distribution and more suitable particle size.

[0191] Optionally, the second mixing temperature is 45°C, 50°C, 55°C or 60°C, or the second mixing temperature may be within the range of any two of the above temperatures.

[0192] Optionally, the second mixing time is 3 min, 4 min, 5 min, 6 min, 7 min or 8 min, or the second mixing time may be within the range of any two of the above times.

[0193] Optionally, the third mixing temperature is 50°C, 52°C, 54°C, 56°C, 58°C, or 60°C, or the third mixing time can be within the range of any two of the above temperatures.

[0194] Optionally, the third mixing time is 10 min, 11 min, 12 min, 13 min, 14 min, 15 min, or 16 min, or the third mixing time may be within the range of any two of the above times.

[0195] Optionally, the second reaction time is 50 min, 55 min, 60 min, 65 min or 70 min, or the second reaction time may be within any two of the above times.

[0196] Optionally, the second reaction temperature is 50°C, 52°C, 54°C, 56°C, 58°C, 60°C, 62°C, 64°C, 66°C, 68°C, or 70°C, or the second reaction temperature may be within any two of the above temperatures.

[0197] Optionally, the mass ratio of the first phosphorus source to the second phosphorus source is 45:55, 45:50, 45:45, 45:40, 50:40, 55:40 or 60:40, or the mass ratio of the first phosphorus source to the second phosphorus source may be within the range of any two of the above mass ratios.

[0198] Optionally, the mass ratio of the first oxidant to the second oxidant is 85:30, 80:30, 75:30, 70:30, 70:25, 70:20 or 70:15, or the mass ratio of the first oxidant to the second oxidant may be within the range of any two of the above mass ratios.

[0199] In some embodiments, the step of obtaining a first solid phase material by subjecting the second slurry to a first solid-liquid separation treatment includes:

[0200] The second slurry undergoes a first solid-liquid separation process to obtain the first solid material;

[0201] The first solid material is washed until the conductivity of the first washing liquid is less than or equal to 500 μS / cm, thus obtaining the first solid phase material.

[0202] In some embodiments, the first washing solution is selected from at least one of deionized water, secondary water, distilled water, pure water, or ultrapure water.

[0203] In some embodiments, the first solid-liquid separation can be performed by at least one of atmospheric pressure filtration, pressure filtration, vacuum filtration, centrifugation, etc.

[0204] In some embodiments, the step of mixing the first solid material with phosphoric acid and aging it to obtain the third slurry includes:

[0205] The first solid material is mixed with phosphoric acid to a pH of 1.2–1.7, and after aging at the aging temperature for the specified time, a third slurry is obtained.

[0206] The aging temperature is 75℃~95℃, the aging time is 1.5h~2.5h, and the pH value of the third slurry is 1.7~2.

[0207] In some embodiments, the concentration of phosphoric acid is 2.5 mol / L to 4.0 mol / L.

[0208] In this embodiment, within the range of parameters of the above-mentioned aging treatment, it is beneficial to further uniform growth of particles, thereby obtaining iron phosphate material with more uniform particle size distribution and more suitable particle size.

[0209] Optionally, the concentration of phosphoric acid is 2.5 mol / L, 2.75 mol / L, 3 mol / L, 3.25 mol / L, 3.5 mol / L, 3.75 mol / L, or 4.0 mol / L, or the concentration of phosphoric acid may be within any two of the above concentrations.

[0210] Optionally, the first solid material is mixed with phosphoric acid to a pH value of 1.5, 1.55, 1.6, 1.65 or 1.7, or the first solid material is mixed with phosphoric acid to a pH value within any two of the above pH ranges.

[0211] In some embodiments, the step of mixing the first solid material with phosphoric acid to a pH value of 1.2 to 1.7 and then aging it at an aging temperature for a specified time to obtain a third slurry includes:

[0212] The first solid material is mixed with water and then slurried to form a premixed slurry.

[0213] The premixed slurry is mixed with phosphoric acid to a pH of 1.2–1.7, and after aging at the aging temperature for the specified time, a third slurry is obtained.

[0214] In some embodiments, the water is selected from at least one of deionized water, recycled water, distilled water, pure water, or ultrapure water.

[0215] Optionally, the aging temperature is 75°C, 80°C, 85°C, 90°C or 95°C, or the aging temperature may be within any two of the above temperatures.

[0216] Optionally, the aging time is 1.5h, 1.8h, 2h, 2.2h or 2.5h, or the aging time can be within any two of the above times.

[0217] Optionally, the pH value of the third slurry is 1.7, 1.8, 1.9 or 2, or the pH value of the third slurry may be within the range of any two of the above pH values.

[0218] In some embodiments, after the precursor slurry is milled, the D50 particle size of the solid particles in the precursor slurry is 0.2 μm to 0.5 μm.

[0219] In this embodiment, within the range of the D50 particle size of the solid particles in the precursor slurry, it is beneficial to prepare a cathode material with a more uniform particle size distribution and a more suitable particle size. Optionally, after the precursor slurry is milled, the D50 particle size of the solid particles in the precursor slurry is 0.2μm, 0.25μm, 0.3μm, 0.35μm, 0.4μm, 0.45μm, or 0.5μm; or, after the precursor slurry is milled, the D50 particle size of the solid particles in the precursor slurry can also be within the range between any two of the above particle sizes.

[0220] In some embodiments, the D50 particle size of the precursor is 3 μm to 6 μm.

[0221] In this embodiment, within the aforementioned D50 particle size range of the precursor, it is advantageous to prepare a cathode material with a more uniform particle size distribution and a more suitable particle size. Optionally, the D50 particle size of the precursor is 3μm, 3.5μm, 4μm, 4.5μm, 5μm, 5.5μm, or 6μm, or the D50 particle size of the precursor can also be within the range between any two of the aforementioned particle sizes.

[0222] In some embodiments, the solid content of the precursor slurry is 40% to 55%, that is, the mass fraction of solid particles in the precursor slurry is 40% to 55%, preferably 45%, 46%, 47%, 48%, 49%, 50%, 52%, etc.

[0223] In some embodiments, the step of obtaining a second solid material by subjecting the third slurry to a second solid-liquid separation process includes:

[0224] The third slurry undergoes a second solid-liquid separation to obtain a second solid material.

[0225] In some embodiments, the second solid-liquid separation can be performed by at least one of atmospheric pressure filtration, pressure filtration, vacuum filtration, centrifugation, etc.

[0226] In some embodiments, the step of obtaining iron phosphate material by crystallization treatment of the second solid material includes:

[0227] The second solid phase material was subjected to flash evaporation to obtain iron phosphate material.

[0228] In some embodiments, the surfactant is selected from at least one of isooctanol polyoxyethylene polyoxypropylene ether-9 and polyethylene glycol; the mass of the surfactant is 0.02% to 0.1% of the mass of the iron phosphate material.

[0229] In this embodiment, within the range of the mass ratio of the surfactant to the mass of the iron phosphate material, it is beneficial to improve the dispersibility of the iron phosphate material particles, ensure uniform heating of the particles during sintering, and enhance the consistency of particle growth, thereby preparing a cathode material with a more uniform particle size distribution and a more suitable particle size. Optionally, the mass of the surfactant is 0.02%, 0.04%, 0.06%, 0.08%, or 0.1% of the mass of the iron phosphate material, or the mass ratio of the surfactant to the mass of the iron phosphate material can also be within any two of the above percentages.

[0230] In some embodiments, the step of sintering the precursor to obtain the cathode material includes:

[0231] After the precursor is sintered at a first sintering temperature for a first sintering time, a pre-sintered material is obtained; and,

[0232] The pre-sintered material is sintered at a second sintering temperature for a second sintering time to obtain the cathode material;

[0233] The first sintering temperature is 400℃~500℃, the first sintering time is 1h~6h, the second sintering temperature is 700℃~900℃, and the second sintering time is 4h~12h.

[0234] In this embodiment, within the parameter range of the above sintering treatment, it is beneficial to ensure sufficient dehydration time and uniform heating of the particles, so that the growth of the cathode material particles has better consistency, thereby preparing cathode materials with more uniform particle size distribution and more suitable particle size.

[0235] Optionally, the first sintering temperature is 400℃, 420℃, 440℃, 460℃, 480℃ or 500℃, or the first sintering temperature may be within the range of any two of the above temperatures.

[0236] Optionally, the first sintering time is 1h, 2h, 3h, 4h, 5h or 6h, or the first sintering time can be within any two of the above times.

[0237] Optionally, the second sintering temperature is 700°C, 750°C, 800°C, 850°C or 900°C, or the second sintering temperature may be within the range of any two of the above temperatures.

[0238] Optionally, the second sintering time is 4h, 6h, 8h, 10h or 12h, or the second sintering time may be within the range of any two of the above times.

[0239] Fourthly, embodiments of this application provide an electrode sheet, which includes a current collector and an electrode active layer disposed on the current collector. The electrode active layer includes a positive electrode material of any one of the above-mentioned methods, or the electrode active layer includes a positive electrode material prepared by any one of the above-mentioned methods.

[0240] In this embodiment, the active layer of the positive electrode sheet includes the aforementioned positive electrode material, thus exhibiting good electrochemical performance.

[0241] Fifthly, embodiments of this application provide a secondary battery, which includes a positive electrode and a negative electrode, wherein the positive electrode includes the aforementioned electrode.

[0242] In this embodiment, the secondary battery includes the aforementioned positive electrode, thus possessing comprehensively improved electrochemical performance, and can be well applied in multiple application scenarios.

[0243] Sixthly, embodiments of this application provide an electrical device.

[0244] The electrical devices provided in this application embodiment can be, but are not limited to, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, etc. Among them, electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc., and spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.

[0245] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0246] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0247] 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.

[0248] I. Preparation Method

[0249] Example 1

[0250] Methods for preparing cathode materials:

[0251] (1) Heat and dissolve the titanium dioxide byproduct containing ferrous sulfate, add 5% (by mass fraction) of liquid alkali for precipitation, filter under pressure to remove impurities, and obtain a ferrous solution with a ferrous ion concentration of 1.5 mol / L and a pH value of 2.8.

[0252] (2) Industrial monoammonium phosphate is dissolved in phosphoric acid and water, filtered, and then ammonia is added to adjust the pH to neutral to obtain PO4. 3- A phosphorus source solution with a concentration of 2 mol / L;

[0253] (3) Using 1 mol of iron as a base, first add ferrous solution to the reactor as a base material, then add 0.012 mol of magnesium sulfate heptahydrate and stir to dissolve. Then, add 50% of the phosphorus source (50% of the total molar amount of phosphorus when it is 1 mol) and 70% of the 30% hydrogen peroxide solution (i.e., the molar amount of hydrogen peroxide is 0.35 mol) dropwise over 30 minutes to carry out the synthesis reaction at a temperature of 35°C. After the addition is complete, stir the reaction at 60°C for 30 minutes. Next, add the remaining phosphorus source (1 mol of total molar amount of phosphorus) all at once at 52°C. After stirring the remaining 50% for 5 minutes, the remaining 30% (30% by mass) of hydrogen peroxide solution (i.e., 0.15 mol of hydrogen peroxide) was slowly added dropwise over 13 minutes at 55°C. The reaction temperature was maintained at 60°C, and the mixture was stirred for 1 hour. Afterward, the mixture was filtered, rinsed until the conductivity of the first washing liquid was ≤500 μS / cm, and then pulped. Phosphoric acid was added to adjust the pH to 1.4. The temperature was then raised to 80°C, and the mixture was stirred at a constant speed for 2 hours until the pH reached 1.8. After a second filtration, the mixture was flash-evaporated to obtain the iron phosphate material. The chemical formula of the iron phosphate material is Fe. 0.988 Mg 0.012 PO4·2H2O, with an iron-to-phosphorus ratio of 0.966.

[0254] (4) A precursor slurry with a solid content of 48.0% was prepared by mixing iron phosphate material, lithium carbonate (1.04 times the amount of iron in the iron phosphate material), titanium dioxide (0.47% of the mass of iron phosphate material), glucose monohydrate (6.9% of the mass of iron phosphate material), isooctanol polyoxyethylene polyoxypropylene ether-9 (0.06% of the mass of iron phosphate material), and pure water. The D50 particle size of the solid particles in the precursor slurry was adjusted to 0.36 μm by sand milling. The precursor was obtained by spray drying at an inlet air temperature of 250℃ and an outlet air temperature of 85℃. The D50 particle size of the precursor was controlled to be 4.5 μm. Then, the temperature was increased to 450℃ at 2℃ / min under a nitrogen protective atmosphere and held for 2 h. Then, the temperature was increased to 783℃ at 5℃ / min and held for 8 h. Finally, the temperature was cooled to below 100℃ by water and air cooling and then removed from the furnace and pulverized to obtain the cathode material.

[0255] In this embodiment, the chemical formula of the positive electrode material is LiFe. 0.966 Ti 0.022 Mg 0.012 PO4@C.

[0256] Example 2

[0257] Methods for preparing cathode materials:

[0258] The preparation method of the positive electrode material in Example 2 is the same or similar to that in Example 1, except that: in step (3) of this example, based on 1 mol of iron, ferrous iron solution is first added to the reaction vessel as the base material, and then 0.016 mol of magnesium sulfate heptahydrate is added and stirred to dissolve. 60% of the phosphorus source (60% when the total molar amount of phosphorus is 1 mol) and 75% of the 30% hydrogen peroxide solution (i.e., the molar amount of hydrogen peroxide is 0.375 mol) are added dropwise over 20 minutes to carry out the synthesis reaction. The dropwise temperature is 25°C. After the dropwise addition is completed, the reaction is stirred at 50°C for 20 minutes. Then, the reaction is carried out at 45°C. Next, the remaining phosphorus source (40% remaining when the total molar amount of phosphorus is 1 mol) is added and stirred for 3 minutes. Then, the remaining hydrogen peroxide solution (i.e., 0.125 mol of hydrogen peroxide) is slowly added dropwise over 10 minutes at 50°C, maintaining the reaction temperature below 50°C. After stirring for 50 minutes, the mixture is filtered under pressure and rinsed until the conductivity of the first washing liquid is ≤500 μS / cm. The mixture is then pulped, and phosphoric acid is added to adjust the pH to 1.2. Subsequently, the temperature is raised to 75°C and the mixture is stirred at a constant speed for 1.5 hours until the pH reaches 1.7. After a second filtration under pressure, the mixture is flash-evaporated to obtain the iron phosphate material. The chemical formula of the iron phosphate material is Fe. 0.984 Mg 0.016 PO4·2H2O, with an iron-to-phosphorus ratio of 0.964.

[0259] In this embodiment, the chemical formula of the positive electrode material is LiFe. 0.962 Ti 0.022 Mg 0.016 PO4@C.

[0260] Example 3

[0261] Methods for preparing cathode materials:

[0262] The preparation method of the positive electrode material in Example 3 is the same or similar to that in Example 1, except that: in step (3) of this example, based on 1 mol of iron, ferrous solution is first added to the reaction vessel as a base material, and then 0.014 mol of magnesium sulfate heptahydrate is added and stirred to dissolve. Then, 45% of the phosphorus source (45% when the total molar amount of phosphorus is 1 mol) and 85% of the hydrogen peroxide solution (i.e., the molar amount of hydrogen peroxide is 0.425 mol) are added dropwise over 40 min to carry out the synthesis reaction. The dropwise temperature is 50°C. After the dropwise addition is completed, the reaction is stirred at 70°C for 40 min. Then, the reaction is carried out at 60°C once. The remaining phosphorus source (55% of the total phosphorus molar amount when the total molar amount of phosphorus is 1 mol) was added and stirred for 8 min. Then, the remaining hydrogen peroxide solution (i.e., 0.075 mol of hydrogen peroxide molar amount) was slowly added dropwise over 16 min at 60 °C. The reaction temperature was maintained at 70 °C, and the reaction was stirred for 70 min. After that, the mixture was filtered by pressure, and washed until the conductivity of the first washing liquid was ≤500 μS / cm. The mixture was then slurried, and phosphoric acid was added to adjust the pH to 1.7. The temperature was then raised to 95 °C and stirred at a constant speed for 2.5 h until the pH reached 2. After a second pressure filtration, the mixture was flash-evaporated to obtain the iron phosphate material. The chemical formula of the iron phosphate material is Fe. 0.986 Mg 0.014 PO4·2H2O, with an iron-to-phosphorus ratio of 0.968.

[0263] In this embodiment, the chemical formula of the positive electrode material is LiFe. 0.964 Ti 0.022 Mg 0.014 PO4@C.

[0264] Example 4

[0265] Methods for preparing cathode materials:

[0266] The preparation method of the positive electrode material in Example 4 is the same or similar to that in Example 1, except that: in step (3) of this example, based on 1 mol of iron, ferrous solution is first added to the reaction vessel as a base material, and then 0.014 mol of cerium nitrate is added and stirred to dissolve. Then, 55% of the phosphorus source (55% when the total molar amount of phosphorus is 1 mol) and 75% of the hydrogen peroxide solution (i.e., the molar amount of hydrogen peroxide is 0.375 mol) are added dropwise over 30 minutes to carry out the synthesis reaction. The dropwise temperature is 35°C. After the dropwise addition is completed, the reaction is stirred at 60°C for 30 minutes. Then, the reaction is carried out at 52°C. The remaining phosphorus source (45% remaining when the total molar amount of phosphorus is 1 mol) is added in a single batch and stirred for 5 min. Then, the remaining hydrogen peroxide solution (i.e., 0.125 mol of hydrogen peroxide) is slowly added dropwise over 13 min at 55 °C. The reaction temperature is maintained at 60 °C, and the mixture is stirred for 1 h. After stirring, the mixture is filtered, rinsed until the conductivity of the first washing liquid is ≤500 μS / cm, and then pulped. Phosphoric acid is added to adjust the pH to 1.6. The temperature is then raised to 85 °C, and the mixture is stirred at a constant speed for 2 h until the pH reaches 1.8. After a second filtration, the mixture is flash-evaporated to obtain the iron phosphate material. The chemical formula of the iron phosphate material is Fe. 0.986 Ce 0.014 PO4·2H2O, with an iron-to-phosphorus ratio of 0.967.

[0267] In this embodiment, the chemical formula of the positive electrode material is LiFe. 0.964 Ti 0.022 Ce 0.014 PO4@C.

[0268] Example 5

[0269] Methods for preparing cathode materials:

[0270] The preparation method of the positive electrode material in Example 5 is the same as or similar to that in Example 4, except that in step (4) of this example, lithium carbonate (the amount of lithium is 1.04 times the amount of iron in the iron phosphate material), titanium dioxide (0.53% of the mass of the iron phosphate material), glucose monohydrate (6.9% of the mass of the iron phosphate material), isooctanol polyoxyethylene polyoxypropylene ether-9 (0.08% of the mass of the iron phosphate material), and pure water are stirred and mixed to form a solid content of 48.0%. The precursor slurry was controlled to have a D50 particle size of 0.2 μm by sand milling, and then spray-dried at an inlet air temperature of 150℃ and an outlet air temperature of 60℃ to obtain the precursor, with the D50 particle size of the precursor controlled to be 3 μm. Then, it was heated to 400℃ at a rate of 2℃ / min under a nitrogen protective atmosphere and held for 6 h, then heated to 700℃ at a rate of 5℃ / min and held for 12 h, and then cooled to below 100℃ by water and air cooling before being removed from the furnace and pulverized to obtain the cathode material.

[0271] In this embodiment, the chemical formula of the positive electrode material is LiFe. 0.961 Ti 0.025 Ce 0.014 PO4@C.

[0272] Example 6

[0273] Methods for preparing cathode materials:

[0274] The preparation method of the positive electrode material in Example 6 is the same as or similar to that in Example 4, except that in step (4) of this example, lithium carbonate (the amount of lithium is 1.04 times the amount of iron in the iron phosphate material), manganese carbonate (0.53% of the mass of the iron phosphate material), glucose monohydrate (7.1% of the mass of the iron phosphate material), isooctanol polyoxyethylene polyoxypropylene ether-9 (0.02% of the mass of the iron phosphate material), and pure water are stirred and mixed to form a solid content of 48.0%. The precursor slurry was controlled to have a D50 particle size of 0.5 μm by sand milling, and then spray-dried at an inlet air temperature of 350℃ and an outlet air temperature of 110℃ to obtain the precursor, with the D50 particle size of the precursor controlled to be 6 μm. Then, it was heated to 500℃ at a rate of 2℃ / min under a nitrogen protective atmosphere and held for 1 hour. Then, it was heated to 900℃ at a rate of 5℃ / min and held for 4 hours. Finally, it was cooled to below 100℃ by water and air cooling and then removed from the furnace and pulverized to obtain the cathode material.

[0275] In this embodiment, the chemical formula of the positive electrode material is LiFe. 0.968 Mn 0.018 Ce 0.014 PO4@C.

[0276] Example 7

[0277] Methods for preparing cathode materials:

[0278] The preparation method of the positive electrode material in Example 7 is the same or similar to that in Example 4. The difference is that in step (4) of this example, titanium dioxide and manganese carbonate with a mass ratio of 3:1 are used to replace titanium dioxide, and the total mass is 0.54% of the mass of iron phosphate material, and the mass of glucose monohydrate is 7.1% of the mass of iron phosphate material; the temperature is increased to 400°C at 2°C / min under nitrogen protection atmosphere, and held for 2 hours, and then increased to 785°C at 5°C / min and held for 8 hours.

[0279] cathode materials

[0280] In this embodiment, the chemical formula of the positive electrode material is LiFe. 0.969 Ti 0.017 Mn 0.0005 Ce 0.014 PO4@C.

[0281] Example 8

[0282] Methods for preparing cathode materials:

[0283] The preparation method of the cathode material in Example 8 is the same as or similar to that in Example 4, except that the mass of titanium dioxide in this example is 0.24% of the mass of iron phosphate material.

[0284] In this embodiment, the chemical formula of the positive electrode material is LiFe. 0.976 Ti 0.01 Ce 0.014 PO4@C.

[0285] Example 9

[0286] Methods for preparing cathode materials:

[0287] The preparation method of the cathode material in Example 9 is the same as or similar to that in Example 4, except that the mass of titanium dioxide in this example is 0.63% of the mass of iron phosphate material.

[0288] In this embodiment, the chemical formula of the positive electrode material is LiFe. 0.956 Ti 0.03 Ce 0.014 PO4@C.

[0289] Example 10

[0290] Methods for preparing cathode materials:

[0291] The preparation method of the positive electrode material in Example 10 is the same as or similar to that in Example 1, except that in step (3) of this example, 0.01 mol of magnesium sulfate heptahydrate is added, and the chemical formula of the iron phosphate material is Fe. 0.99 Mg 0.01 PO4·2H2O, with an iron-to-phosphorus ratio of 0.978.

[0292] In this embodiment, the chemical formula of the positive electrode material is LiFe. 0.968 Ti 0.022 Mg 0.01 PO4@C.

[0293] Example 11

[0294] Methods for preparing cathode materials:

[0295] The preparation method of the positive electrode material in Example 11 is the same as or similar to that in Example 1, except that in step (3) of Example 11, 0.008 mol of magnesium sulfate heptahydrate is added, and the chemical formula of the iron phosphate material is Fe. 0.992 Mg 0.008PO4·2H2O, with an iron-to-phosphorus ratio of 0.981.

[0296] In this embodiment, the chemical formula of the positive electrode material is LiFe. 0.970 Ti 0.022 Mg 0.008 PO4@C.

[0297] Example 12

[0298] Methods for preparing cathode materials:

[0299] The preparation method of the positive electrode material in Example 12 is the same as or similar to that in Example 4, except that in step (4) of this example, lithium carbonate (1.04 times the amount of iron in the iron phosphate material), titanium dioxide (0.47% of the mass of the iron phosphate material), glucose monohydrate (6.9% of the mass of the iron phosphate material), and polyethylene glycol (0.1% of the mass of the iron phosphate material) are mixed with pure water to form a precursor slurry with a solid content of 55.0%. After controlling the particle size of solid particles D50 in the precursor slurry to 0.24 μm by sand milling, the precursor was spray-dried at an inlet air temperature of 250℃ and an outlet air temperature of 85℃ to obtain the precursor, and the precursor D50 particle size was controlled to be 4.5 μm. Then, the precursor was heated to 400℃ at a rate of 2℃ / min under a nitrogen protective atmosphere and held for 4 hours. Then, it was heated to 850℃ at a rate of 5℃ / min and held for 5 hours. Finally, it was cooled to below 100℃ by water cooling and air cooling and then removed from the furnace and pulverized to obtain the cathode material.

[0300] In this embodiment, the chemical formula of the positive electrode material is LiFe. 0.964 Ti 0.022 Ce 0.014 PO4@C.

[0301] Comparative Example 1

[0302] The preparation method of the cathode material in Comparative Example 1 is the same as or similar to that in Example 1, except that in step (4) of Comparative Example 1, titanium dioxide and dispersant are not added, and the chemical formula of the iron phosphate material is Fe. 0.988 Mg 0.012 PO4·2H2O, with an iron-to-phosphorus ratio of 0.966.

[0303] The chemical formula of the cathode material in Comparative Example 1 is LiFe. 0.988 Mg 0.012 PO4@C.

[0304] Comparative Example 2

[0305] Methods for preparing cathode materials:

[0306] The preparation method of the positive electrode material in Comparative Example 2 is the same or similar to that in Example 1. The difference is that in step (3) of Comparative Example 2, magnesium sulfate heptahydrate is not added, the chemical formula of the iron phosphate material is FePO4·2H2O, and the iron-to-phosphorus ratio is 0.974.

[0307] The chemical formula of the cathode material in Comparative Example 2 is LiFe. 0.978 Ti 0.022 PO4@C.

[0308] Comparative Example 3

[0309] Methods for preparing cathode materials:

[0310] The preparation method of the cathode material in Comparative Example 3 is the same as or similar to that in Example 1, except that in step (3) of Comparative Example 3, the ferric phosphate material obtained by flash evaporation is replaced by anhydrous ferric phosphate obtained by drying in a rotary kiln. The chemical formula of anhydrous ferric phosphate is Fe. 0.988 Mg 0.012 PO4.

[0311] The chemical formula of the cathode material in Comparative Example 3 is LiFe. 0.966 Ti 0.022 Mg 0.012 PO4@C.

[0312] II. Testing Methods

[0313] The elemental content of the cathode materials prepared in Examples 1-12 and Comparative Examples 1-3 was tested. The elemental composition was detected by ICP-OES; the free lithium content was determined by potentiometric titration; and the carbon content was tested using a carbon-sulfur analyzer. The test results are shown in Table 1 below.

[0314] Table 1

[0315] The properties of the iron phosphate materials and cathode materials prepared in Examples 1-12 and Comparative Examples 1-3 were tested. Powder resistivity was measured using the four-probe method at a pressure of 8 MPa; compaction density was measured under a pressure of 3 tons; specific surface area was determined using the gas adsorption BET method; and particle size was determined by SEM imaging and then analyzed using a Nano Measurer. 1.2.5 Statistical analysis; Magnetic foreign matter content: Weigh 100g of material and pour it into a capped plastic bottle. Add 1000g of pure water, then add an 8000GS magnetic magnet. Protect the magnet with PTFE. Tighten the cap, place the plastic bottle horizontally, and rotate it at 10-20 rpm for 30-45 minutes. Stop rotating and remove the magnetic magnet. Add 1000g of pure water to the plastic bottle, tighten the cap, place the bottle horizontally, and rotate it at 10-20 rpm for 5-10 minutes. Stop rotating and remove the magnetic magnet. Dissolve the magnet in aqua regia, measure the solution using ICP, bring the volume to a final volume, and measure the nickel, chromium, copper, zinc, and iron content. Calculate the total mass of nickel, chromium, copper, zinc, and iron, and divide by the weight of the material to obtain the magnetic foreign matter content of the material.

[0316] The test results of the iron phosphate material are shown in Table 2 below:

[0317] Table 2

[0318] The test results of the cathode material are shown in Tables 3 and 4 below:

[0319] Table 3

[0320] Table 4

[0321] The positive electrode materials prepared in Examples 1-12 and Comparative Examples 1-3 were mixed with conductive carbon black and PVDF binder at a mass ratio of 90:5:5 and coated onto a 12μm thick aluminum foil. The electrode was then dried in an oven at 110℃ for 10 hours. The dried electrode was then cut into 15mm diameter positive electrode discs and compacted to a density of 2.5g / cm³. 3 The cells were rolled and assembled in a glove box manufactured by Wig Gas Purification Technology (Suzhou) Co., Ltd., using a 16mm diameter lithium sheet as the counter electrode and 1M LiPF6 dissolved in EC:EMC:DEC in a volume ratio of 1:1:1. The resulting coin cell half-cells were then subjected to rate performance testing.

[0322] The battery performance testing system (model: CT3002A) from Wuhan Landian Electronics Technology Co., Ltd. was used. The test temperature was 25℃, and the voltage range was 2V~3.75V. Tests were conducted at 1C and 5C rates, and the test results are shown in Table 5 below.

[0323] Table 5

[0324] III. Analysis of Test Results for Each Embodiment and Comparative Example

[0325] As shown in Tables 1 to 5, the compaction density of the cathode materials provided in each embodiment of this application is 2.57 g / ml to 2.68 g / ml. The 1C first discharge efficiency (2V to 3.75V) tested in each embodiment is 93.21% to 94.83%, and the 5C first discharge efficiency (2V to 3.75V) is 87.98% to 97.89%. In each embodiment, iron phosphate dihydrate doped with element M is used as a precursor. Through two-step doping, the particle size distribution of the iron phosphate material and the cathode material can be controlled, thereby obtaining cathode materials with high compaction density and rate performance.

[0326] Compared to the cathode material obtained in the examples, the cathode material in Comparative Example 1 has poor growth uniformity and poor particle size distribution uniformity, resulting in lower compaction density and poorer rate performance of the cathode material obtained in Comparative Example 1.

[0327] In Comparative Example 2, without the addition of the first doping source, the iron-to-phosphorus ratio of the iron phosphate material was 0.974, resulting in poor control over the uniform growth of the iron phosphate material particles. Consequently, the cathode material obtained in Comparative Example 2 had poorer uniformity in particle size distribution, lower compaction density, and poorer rate performance compared to the cathode material obtained in the example.

[0328] Compared to the cathode material obtained in the examples, the anhydrous iron phosphate prepared by rotary kiln drying in Comparative Example 3 has poor particle size distribution uniformity, which in turn leads to poor particle size distribution uniformity and a higher content of magnetic foreign matter in the cathode material obtained in Comparative Example 3. The cathode material obtained in Comparative Example 3 has a lower compaction density and poorer rate performance.

[0329] Comparing Figures 2 and 3, it can be seen that doping significantly improved the morphology of the precursor during its preparation. In Example 1 of this application, a spherical and columnar combined ferric phosphate material was prepared by doping with element M, while in Comparative Example 2, no ferric phosphate dihydrate was doped, resulting only in a single plate-like morphology of ferric phosphate. Comparing Figures 4 to 7, it can be seen that compared to the cathode material obtained in Comparative Example 2, the cathode material prepared in Example 1 of this application has a more concentrated primary particle size distribution, with fewer particles having a primary particle size greater than 1000 nm, thus exhibiting superior electrochemical performance.

[0330] Compared to other embodiments, the Ti doping amount in Embodiment 8 is relatively small, resulting in a higher compaction density of the prepared cathode material, but a poorer rate performance. In Embodiment 9, the Ti doping amount is relatively large, resulting in a cathode material with better rate performance, but a lower compaction density. Comparing Embodiments 8, 9, and other embodiments, it can be seen that controlling the concentration of Ti in the cathode material to 0.02 ≤ z ≤ 0.025 is beneficial for obtaining a cathode material with a more balanced compaction density and rate performance.

[0331] Compared to other embodiments, in Embodiment 12, the sintering temperature during the preparation of the cathode material is higher at 850°C. The higher temperature leads to an increase in side reactions, which in turn promotes the formation of magnetic foreign matter such as iron phosphide, resulting in a higher content of magnetic foreign matter in the cathode material obtained in Embodiment 12.

[0332] 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. A ferric phosphate material, characterized in that, The general formula of the iron phosphate material is Fe. 1-x M x PO4·2H2O, wherein M is selected from one or more of Mg and Ce, and 0.008≤x≤0.

016.

2. The iron phosphate material according to claim 1, characterized in that, The average particle size of the primary particles of the iron phosphate material is 200 nm to 300 nm; and / or, In the primary particles of the iron phosphate material, the proportion of primary particles with a diameter less than 100 nm is 15.3% to 23.7%, the proportion of primary particles with a diameter between 100 nm and 400 nm is 63.3% to 73.6%, the proportion of primary particles with a diameter greater than 400 nm and less than or equal to 1000 nm is 9.6% to 17.5%, and the proportion of primary particles with a diameter greater than 1000 nm is 0.8% to 2.8%.

3. The iron phosphate material according to any one of claims 1 to 2, characterized in that, The iron-to-phosphorus ratio of the iron phosphate material is 0.964 to 0.

981.

4. A positive electrode material, characterized in that, The general formula of the cathode material is LiFe. 1-y-z M y N z PO4@C, wherein M is selected from one or more of Mg and Ce, N is selected from one or more of Ti and Mn, 0.008≤y≤0.016, 0.001≤z≤0.

03.

5. The positive electrode material according to claim 4, characterized in that, The average primary particle size of the cathode material is 340 nm to 415 nm; and / or, In the primary particles of the cathode material, the proportion of primary particles with a diameter less than 200 nm is 36.29% to 53.01%, the proportion of primary particles with a diameter between 200 nm and 400 nm is 34.02% to 44.30%, the proportion of primary particles with a diameter greater than 400 nm and less than or equal to 1000 nm is 8.05% to 17.48%, and the proportion of primary particles with a diameter greater than 1000 nm is 0.60% to 1.93%.

6. The cathode material according to any one of claims 4 to 5, characterized in that, The compaction density of the cathode material under 3kN pressure is 2.57 g / cm³. 3 ~2.68g / cm 3 ; and / or, The resistivity of the positive electrode material powder is 8.6 Ω·cm to 14 Ω·cm; and / or, The specific surface area of ​​the cathode material is 10m². 2 / g~13m 2 / g; and / or, The magnetic foreign matter content of the positive electrode material is less than or equal to 0.10 ppm.

7. A method for preparing a positive electrode material, characterized in that, Includes the following steps: The first dopant source is mixed with a ferrous iron solution to form a mixture; The mixture is combined with a first phosphorus source and a first oxidant, and then subjected to a first reaction treatment to obtain a first slurry; The first slurry is mixed with the second phosphorus source and the second oxidant, and then subjected to a second reaction treatment to obtain the second slurry; The second slurry undergoes a first solid-liquid separation process to obtain a first solid phase material; The first solid material is mixed with phosphoric acid and aged to obtain the third slurry; The third slurry undergoes a second solid-liquid separation process to obtain a second solid phase material; The second solid material is subjected to crystallization treatment to obtain iron phosphate material; The iron phosphate material, lithium source, second doping source, surfactant, carbon source and solvent are mixed to obtain a precursor slurry; The precursor slurry is subjected to grinding and drying processes to obtain the precursor. as well as, The precursor is sintered to obtain the cathode material; Wherein, the first doping source contains a first doping element, which is selected from one or more of Mg and Ce, and the molar ratio of iron in the ferrous solution to the first doping element is (1-x):x, 0.008≤x≤0.016; the second doping source contains a second doping element, which is selected from one or more of Ti and Mn, and the molar ratio of iron in the iron phosphate material to the second doping element in the second doping source is (1-yz):z, 0.008≤y≤0.016, 0.001≤z≤0.

03.

8. The method for preparing the cathode material according to claim 7, characterized in that, The step of mixing the mixture with a first phosphorus source and a first oxidant, and then subjecting it to a first reaction treatment to obtain a first slurry includes: The mixture is mixed with the first phosphorus source and the first oxidant at the first mixing temperature for the first mixing time, and then at the first reaction temperature for the first reaction time to obtain the first slurry; Wherein, the first mixing temperature is 25℃~50℃, the first mixing time is 20min~40min, the first reaction time is 20min~40min, and the first reaction temperature is 50℃~70℃.

9. The method for preparing the cathode material according to claim 7, characterized in that, The step of mixing the first slurry with the second phosphorus source and the second oxidant, and then subjecting it to a second reaction treatment to obtain the second slurry includes: The mixture and the second phosphorus source are mixed at a second mixing temperature for a second mixing time to obtain a fourth slurry; The fourth slurry and the second oxidant are mixed at a third mixing temperature for a third mixing time, and then at a second reaction temperature for a second reaction time to obtain the second slurry; Wherein, the second mixing temperature is 45℃~60℃, the second mixing time is 3min~8min, the third mixing temperature is 50℃~60℃, the third mixing time is 10min~16min, the second reaction time is 50min~70min, and the second reaction temperature is 50℃~70℃; The mass ratio of the first phosphorus source to the second phosphorus source is (45-60):(40-55), and the mass ratio of the first oxidant to the second oxidant is (70-85):(15-30).

10. The method for preparing the cathode material according to claim 7, characterized in that, The steps of mixing the first solid material with phosphoric acid and aging it to obtain the third slurry include: The first solid material is mixed with phosphoric acid to a pH of 1.2–1.7, and after aging at an aging temperature for a specified time, the third slurry is obtained. The aging temperature is 75℃~95℃, the aging time is 1.5h~2.5h, and the pH value of the third slurry is 1.7~2.

11. The method for preparing the cathode material according to claim 7, characterized in that, After the precursor slurry is milled, the D50 particle size of the solid particles in the precursor slurry is 0.2 μm to 0.5 μm; and / or, The precursor has a D50 particle size of 3 μm to 6 μm; and / or, The surfactant is selected from at least one of isooctanol polyoxyethylene polyoxypropylene ether-9 and polyethylene glycol; the mass of the surfactant is 0.02% to 0.1% of the mass of the iron phosphate material.

12. The method for preparing the cathode material according to claim 7, characterized in that, The step of obtaining the cathode material by sintering the precursor includes: The precursor is sintered at a first sintering temperature for a first sintering time to obtain a pre-sintered material; and, The pre-sintered material is sintered at a second sintering temperature for a second sintering time to obtain the cathode material; The first sintering temperature is 400℃~500℃, the first sintering time is 1h~6h, the second sintering temperature is 700℃~900℃, and the second sintering time is 4h~12h.

13. An electrode sheet, characterized in that, The electrode sheet includes a current collector and an electrode active layer disposed on the current collector. The electrode active layer includes the positive electrode material as described in any one of claims 4 to 6, or the electrode active layer includes the positive electrode material prepared by the preparation method as described in any one of claims 7 to 12.

14. A secondary battery, characterized in that, The secondary battery includes a positive electrode and a negative electrode, wherein the positive electrode includes the electrode as described in claim 13.

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