Iron phosphate material, positive electrode material and preparation method and application thereof

Abstract

The invention provides an iron phosphate material, a positive electrode material and a preparation method and application thereof, and belongs to the field of lithium ion batteries, the general formula of the iron phosphate material is Fe < 1-x > MxPO4. 2H2O, M is selected from one or more of Mg and Ce, and x is greater than or equal to 0.008 and less than or equal to 0.016. According to the iron phosphate material disclosed by the embodiment of the invention, the iron element is partially replaced by doping the iron phosphate dihydrate material through the element M, so that the iron-phosphorus ratio of the iron phosphate material is reduced in a proper range, the growth of iron phosphate material particles is promoted, and the iron phosphate material with uniform particle size is favorably obtained; and reduction of the content of magnetic foreign matters in the prepared positive electrode material and improvement of the capacity are facilitated, so that the electrochemical performance of the positive electrode material is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and particularly relates to a ferric phosphate material, a cathode material, a preparation method thereof and an application thereof. Background Art

[0002] Lithium iron phosphate (LiFePO4) is an electrode material widely used in lithium-ion batteries. Currently, ferric phosphate anhydrous materials are usually used as precursors for preparing lithium iron phosphate. In the preparation process, after mixing ferric phosphate anhydrous, a lithium source and a carbon source and then performing a sintering treatment, a lithium iron phosphate material can be formed.

[0003] When preparing lithium iron phosphate using ferric phosphate anhydrous in traditional technologies, it is difficult to control the particle size distribution of ferric phosphate anhydrous. The proportion of small particle size particles is too large, and there are also many large particle size particles, resulting in uneven particle size distribution of the obtained lithium iron phosphate material, and it is difficult to balance the tap density, discharge capacity, rate performance and other electrochemical properties of the lithium iron phosphate material. Even when a dopant is introduced during the mixing of ferric phosphate anhydrous, a lithium source and a carbon source to obtain a doped lithium iron phosphate material, which is beneficial to improving its capacity, with the increase of the addition amount of the doping element, the effect of improving the capacity of the lithium iron phosphate material is limited, and there are problems of reducing the tap density and increasing the content of magnetic foreign matters, and it is also difficult to balance the tap density, discharge capacity, rate performance and other electrochemical properties of the lithium iron phosphate material.

[0004] Based on the above situation, it is still necessary to further study how to improve the performance of ferric phosphate materials to improve the material properties of lithium iron phosphate materials so as to obtain lithium iron phosphate materials with improved electrochemical properties. Summary of the Invention

[0005] In view of the technical problems existing in the background art, the present application provides a ferric phosphate material, a cathode material, a preparation method thereof and an application thereof. The ferric phosphate material of the present application is doped with a dihydrate ferric phosphate material, partially replacing iron elements, reducing the iron-to-phosphorus ratio of the ferric phosphate material within an appropriate range, promoting the growth of ferric phosphate material particles, being beneficial to obtaining ferric phosphate materials with uniform particle sizes, and being beneficial to reducing the content of magnetic foreign matters and improving the capacity in the prepared cathode material, thereby improving the electrochemical properties of the cathode material.

[0006] In a first aspect, an embodiment of the present application provides a ferric phosphate material, and the general formula of the ferric 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 the embodiment of the present application, the iron phosphate dihydrate material is doped with element M to partially replace the iron element, reducing the iron-to-phosphorus ratio of the iron phosphate material within an appropriate range, promoting the growth of the iron phosphate material particles, facilitating the acquisition of iron phosphate material with uniform particle size, and being conducive to reducing the content of magnetic foreign substances and improving the capacity in the prepared cathode material, thereby enhancing 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 above iron phosphate material, the particle size of the iron phosphate material is more suitable, which is conducive to the particle size and distribution of the cathode material prepared from the iron phosphate material being more suitable, thereby obtaining a higher tap density and taking into account the improvement of the capacity.

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

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

[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-to-phosphorus ratio of the above iron phosphate material, it is conducive to the growth of the iron phosphate material particles to a suitable size, thereby being conducive to the particle size and distribution of the cathode material prepared from the iron phosphate material being more suitable, thereby obtaining a higher tap density and taking into account the improvement of the capacity.

[0014] In a second aspect, the embodiment of the present application provides a cathode material, and the general formula of the cathode material is LiFe 1-y- z M y N z PO4@C, where 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, and 0.001 ≤ z ≤ 0.03.

[0015] In the technical solution of the embodiment of the present application, the lithium iron phosphate material is doped with element M and element N at multiple levels and multiple elements, which is beneficial to significantly improve the charge specific capacity and discharge specific capacity of the positive electrode material; at the same time, within the doping proportion range of the above-mentioned element M and within the doping proportion range of element N, it is beneficial for the positive electrode material to have high charge specific capacity, high discharge specific capacity, and good rate performance and other electrochemical performances while having a high tap density.

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

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

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

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

[0020] In some embodiments, the tap density of the positive electrode material under a pressure of 3 kN is 2.57 g / cm 3 ~2.68 g / cm 3 。

[0021] In this embodiment, the above-mentioned positive electrode material has a high tap density, which is beneficial to improve the energy density of the positive electrode material, thereby improving the electrochemical performance of the positive electrode material.

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

[0023] In this embodiment, within the range of the powder resistivity of the positive electrode material, the positive electrode material has a relatively high electronic conductivity, which helps to fully exert the electrochemical performance of the active material in the positive electrode material, enabling more active material 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 m 2 / g to 13 m 2 / g.

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

[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 the content of magnetic foreign matter in the positive electrode material described above, it is beneficial to improve the safety and reliability of the secondary battery using this positive electrode material.

[0028] In a third aspect, an embodiment of the present application provides a method for preparing a positive electrode material, including the following steps:

[0029] Mix the first doping source with the ferrous solution to form a mixed solution;

[0030] Mix the mixed solution with the first phosphorus source and the first oxidant, and after the first reaction treatment, obtain a first slurry;

[0031] Mix the first slurry with the second phosphorus source and the second oxidant, and after the second reaction treatment, obtain a second slurry;

[0032] Perform the first solid-liquid separation treatment on the second slurry to obtain a first solid-phase material;

[0033] Mix the first solid-phase material with phosphoric acid, and after aging treatment, obtain a third slurry;

[0034] Perform the second solid-liquid separation treatment on the third slurry to obtain a second solid-phase material;

[0035] Perform crystallization treatment on the second solid-phase material to obtain a ferric phosphate material;

[0036] Mix the ferric phosphate material, a lithium source, a second doping source, a surfactant, a carbon source, and a solvent to obtain a precursor slurry;

[0037] Perform grinding treatment and drying treatment on the precursor slurry to obtain a precursor; and,

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

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

[0040] In the technical solution of the embodiment of the present application, the preparation of the first solid-phase material is carried out in two steps. During the first reaction treatment, part of the crystal nuclei are formed. During the second reaction treatment, the crystal nuclei formed during the first reaction treatment are promoted to grow, thereby reducing the generation of small particles, making the particle size distribution of the obtained iron phosphate material uniform and the particle size appropriate; during the preparation of the iron phosphate material, the ferrous solution is mixed with the first doping source, and the cations of the first doping element and ferrous ions co-precipitate to form a compound with internal doping, which is convenient for the uniform doping and growth of the iron phosphate material, thereby obtaining an iron phosphate material with a more uniform particle size distribution and doped with the first element; by doping the iron phosphate dihydrate material with element M, partially replacing the iron element, the iron-phosphorus ratio of the iron phosphate material is reduced within an appropriate range, promoting the growth of the iron phosphate material particles, being beneficial to obtaining an iron phosphate material with a uniform particle size, and being beneficial to reducing the content of magnetic foreign substances and improving the capacity in the prepared cathode material, thereby improving the electrochemical performance of the cathode material; during the preparation of the precursor, the second doping element is doped, and the molar ratio of the iron element in the iron phosphate material to the second doping element in the second doping source is controlled to be (1 - y - z):z, where 0.008 ≤ y ≤ 0.016 and 0.001 ≤ z ≤ 0.03. By means of two-step doping, under the condition of a relatively low secondary doping amount, the cathode material obtains better rate performance; in the preparation method of the present application, a surfactant is added during the grinding process to improve the dispersibility of the iron phosphate material, reduce the agglomeration of the iron phosphate material generated during the grinding process, be beneficial to the growth of particles during the sintering treatment, thereby obtaining a cathode material with a more uniform particle size distribution and a more suitable particle size; the cathode material prepared by the preparation method of the cathode material in the embodiment of the present application has electrochemical properties such as a relatively high tap density, a relatively high charge specific capacity, a relatively high discharge specific capacity, and good rate performance.

[0041] In some embodiments, the step of mixing the mixed solution with the first phosphorus source and the first oxidant and performing the first reaction treatment to obtain the first slurry includes:

[0042] After the mixed solution, the first phosphorus source, and the first oxidant are mixed at the first mixing temperature for the first mixing time, and then reacted at the first reaction temperature for the first reaction time, the first slurry is obtained.

[0043] Among them, the first mixing temperature is 25°C to 50°C, the first mixing time is 20 min to 40 min, the first reaction time is 20 min to 40 min, and the first reaction temperature is 50°C to 70°C.

[0044] In this embodiment, within the ranges of the above first mixing temperature, first mixing time, first reaction time, and first reaction temperature, it is beneficial for the crystal nuclei to grow more completely, and thus it is beneficial to obtain a more uniform particle size distribution and a more suitable particle size of the iron phosphate material.

[0045] In some embodiments, the steps of mixing the first slurry with the second phosphorus source and the second oxidant and performing a second reaction treatment to obtain a second slurry include:

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

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

[0048] Among them, the second mixing temperature is 45°C to 60°C, the second mixing time is 3 min to 8 min, the third mixing temperature is 50°C to 60°C, the third mixing time is 10 min to 16 min, the second reaction time is 50 min to 70 min, and the second reaction temperature is 50°C to 70°C;

[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 ranges of the above reaction parameters, it is beneficial to promote the growth of crystal nuclei during the second reaction treatment, and thus a more uniform particle size distribution and a more suitable particle size of the iron phosphate material can be obtained.

[0051] In some embodiments, the steps of mixing the first solid-phase material with phosphoric acid and performing an aging treatment to obtain a third slurry include:

[0052] The first solid-phase material and phosphoric acid are mixed to a pH value of 1.2 to 1.7, and after aging at the aging temperature for the aging time, the third slurry is obtained;

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

[0054] In this embodiment, within the ranges of the parameters of the above aging treatment, it is beneficial to the further uniform growth of particles, and thus a lithium iron phosphate material with a more uniform particle size distribution and a more suitable particle size can be obtained.

[0055] In some embodiments, after the precursor slurry is subjected to sanding treatment, 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 above 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 range of the D50 particle size of the above precursor, it is beneficial 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 isooctyl alcohol polyoxyethylene polyoxypropylene ether-9 and polyethylene glycol; the mass of the surfactant is 0.02% to 0.1% of the mass of the lithium iron phosphate material.

[0060] In this embodiment, within the range of the proportion of the mass of the above surfactant in the mass of the lithium iron phosphate material, it is beneficial to improve the dispersibility of the lithium iron phosphate material particles, ensure uniform heating of the particles during the sintering process, enhance the consistency of particle growth, and thus prepare a cathode material with a relatively uniform particle size distribution and a more suitable particle size.

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

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

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

[0064] Wherein, the first sintering temperature is 400°C to 500°C, the first sintering time is 1 h to 6 h, the second sintering temperature is 700°C to 900°C, and the second sintering time is 4 h to 12 h.

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

[0066] Fourthly, an electrode sheet provided by an embodiment of the present application includes a current collector and an electrode active layer provided on the current collector. The electrode active layer includes the positive electrode material described in any one of the above, or the electrode active layer includes the positive electrode material prepared by the preparation method described in any one of the above.

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

[0068] Fifthly, a secondary battery provided by an embodiment of the present application includes a positive electrode sheet and a negative electrode sheet, and the positive electrode sheet includes the above electrode sheet.

[0069] In this embodiment, the secondary battery includes the above positive electrode sheet, and thus has comprehensively improved electrochemical performance, and can thus be well applied to multiple usage scenarios.

[0070] The above description is only an overview of the technical solution of the present application. In order to be able to understand the technical means of the present application more clearly, it can be implemented according to the content of the specification. And in order to make the above and other purposes, features and advantages of the present application more obvious and understandable, the specific embodiments of the present application are specifically given below. BRIEF DESCRIPTION OF THE DRAWINGS

[0071] In order to more clearly illustrate the technical solution of the present application, the drawings used in the present application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained according to these drawings without creative efforts.

[0072] Figure 1 It is a schematic diagram of the steps of a method for preparing a positive electrode material of the present invention;

[0073] Figure 2 It is a scanning electron microscope (SEM) result diagram of the iron phosphate material in Example 1 of the present invention;

[0074] Figure 3 It is the SEM result diagram of the iron phosphate material in Comparative Example 2;

[0075] Figure 4 It is the SEM result diagram of the positive electrode material in Example 1 of the present invention;

[0076] Figure 5 It is the particle size distribution diagram of the positive electrode material in Embodiment 1 of the present invention;

[0077] Figure 6 It is the SEM result diagram of the positive electrode material in Comparative Example 2;

[0078] Figure 7 It is the particle size distribution diagram of the positive electrode material in Comparative Example 2. Specific Embodiments

[0079] Next, embodiments of the technical solution of the present application will be described in detail with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application, so they are only examples and cannot be used to limit the protection scope of the present application.

[0080] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification and claims of this application and the above 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 only used to distinguish different objects and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity, specific order or primary-secondary relationship of the indicated technical features. In the description of the embodiments of this application, the meaning of "a plurality" is more than two, unless otherwise clearly and specifically defined.

[0082] Referring to "embodiment" herein means that the specific features, structures or characteristics described in connection with the embodiment may be included in at least one embodiment of this application. The phrase appears in various positions in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art explicitly and implicitly understand that the embodiments described herein may be combined with other embodiments.

[0083] In the description of the embodiments of this application, the term "and / or" is only a description of the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B may represent: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this article generally represents an "or" relationship between the associated objects before and after.

[0084] In the description of the embodiments of this application, the term "a plurality" refers to more than two (including two). Similarly, "a plurality of groups" refers to more than two groups (including two groups), and "a plurality of pieces" refers to more than two pieces (including two pieces).

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

[0086] In the examples of the present application, ppm represents the ratio of the mass of the element to be measured to parts per million of the mass of the sample.

[0087] In the first aspect, the present invention provides an iron phosphate material, 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.

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

[0089] In the technical solution of the embodiment of the present application, the iron phosphate material is a doped dihydrate iron phosphate material. Compared with anhydrous iron phosphate, it is not only easier to achieve uniform doping during the synthesis process, but also easier to grow when sintering to prepare the positive electrode material, which is conducive to obtaining a positive electrode material with a more suitable particle size, thereby improving the electrochemical performance of the positive electrode material while taking into account the compaction density of the positive electrode material. At the same time, since the M element is used to replace part of the iron element, it is not easy to generate magnetic substances such as iron element and iron phosphide when sintering to prepare the positive electrode material, thereby reducing the content of magnetic foreign matter in the positive electrode 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 may be in the range between 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 above-mentioned iron phosphate material, the particle size of the iron phosphate material is more suitable, which is beneficial to the particle size and distribution of the cathode material prepared from the iron phosphate material to be more suitable, so as to obtain a higher tap density while taking into account the improvement of 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, in the primary particles of the iron phosphate material, the primary particle size is between 10nm and 2200nm.

[0094] In this embodiment, within the range of the primary particle size in the primary particles of the above-mentioned iron phosphate material, the particle size of the iron phosphate material is more suitable, which is beneficial to the particle size and distribution of the cathode material prepared from the iron phosphate material to be more suitable, so as to obtain a higher tap density while taking into account the improvement of capacity. Optionally, in the primary particles of the iron phosphate material, the primary particle size is 10nm, 20nm, 50nm, 100nm, 200nm, 500nm, 1000nm, 1500nm, 2000nm or 2200nm, or in the primary particles of the iron phosphate material, the primary particle size 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 the number of primary particles with a primary particle size less than 100nm is 15.3% - 23.7%, the proportion of the number of primary particles with a primary particle size between 100nm and 400nm is 63.3% - 73.6%, the proportion of the number of primary particles with a primary particle size greater than 400nm and less than or equal to 1000nm is 9.6% - 17.5%, and the proportion of the number of primary particles with a primary particle size greater than 1000nm is 0.8% - 2.8%.

[0096] In this embodiment, the particle size distribution of the primary particles of the above-mentioned iron phosphate material is more suitable, which not only controls the proportion of primary particles with a primary particle size less than 100nm, but also controls the proportion of primary particles with a primary particle size greater than 1000nm, which is beneficial to the particle size distribution of the cathode material prepared from the iron phosphate material to be more uniform, so as to obtain a higher tap density while taking into account the improvement of capacity.

[0097] Optionally, in the primary particles of the iron phosphate material, the proportion of the number of primary particle sizes less than 100 nm is 15.3%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23% or 23.7%. Alternatively, in the primary particles of the iron phosphate material, the proportion of the number of primary particle sizes less than 100 nm can also be within the range between any two of the above percentages. Preferably, in the primary particles of the iron phosphate material, the proportion of the number of primary particle sizes less than 100 nm is 16.4% - 22%.

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

[0099] Optionally, in the primary particles of the iron phosphate material, the proportion of the number of primary particle sizes 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, in the primary particles of the iron phosphate material, the proportion of the number of primary particle sizes greater than 400 nm and less than or equal to 1000 nm can also be within the range between any two of the above percentages.

[0100] Optionally, in the primary particles of the iron phosphate material, the proportion of the number of primary particle sizes greater than 1000 nm is 0.8%, 1%, 1.5%, 2%, 2.5% or 2.8%. Alternatively, in the primary particles of the iron phosphate material, the proportion of the number of primary particle sizes greater than 1000 nm can also be within the range between any two of the above percentages. Preferably, the proportion of the number of primary particle sizes greater than 1000 nm is 0.8% - 2.38%.

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

[0102] In this embodiment, within the range of the iron-to-phosphorus ratio of the above-mentioned iron phosphate material, it is beneficial for the growth of the iron phosphate material particles to an appropriate size, thereby facilitating the particle size and distribution of the positive electrode material prepared from the iron phosphate material to be more suitable, so as to obtain a higher tap density and take into account the improvement of 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 above iron-to-phosphorus ratios.

[0103] In a second aspect, an embodiment of the present application provides a positive electrode material, and the general formula of the positive electrode material is LiFe 1-y- z M y N z PO4@C, where 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, and 0.001 ≤ z ≤ 0.03.

[0104] In the technical solution of the embodiment of the present application, multi-level and multi-element doping of M element and N element on the lithium iron phosphate material is beneficial to significantly improve the charge specific capacity and discharge specific capacity of the positive electrode material; at the same time, within the above-mentioned doping ratio range of M element and the doping ratio range of N element, it is beneficial for the positive electrode material to have higher charge specific capacity, higher discharge specific capacity, and better rate performance and other electrochemical performances while having a higher tap 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 also be within the range between 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 also be within the range between any two of the above values. Preferably, 0.01 ≤ z ≤ 0.03, and more preferably, 0.02 ≤ z ≤ 0.025.

[0107] In some embodiments, the positive electrode material includes a core and a carbon coating layer coated on the surface of the core, where the core can be represented by the general formula: LiFe 1-y-zM y N z PO4 represents, where 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, and 0.001 ≤ z ≤ 0.03. Preferably, 0.012 ≤ y ≤ 0.016. Preferably, 0.01 ≤ z ≤ 0.03, and more preferably, 0.02 ≤ z ≤ 0.025.

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

[0109] A lower carbon coating layer content reduces the inhibition of particle growth during the formation of the positive electrode material, which is beneficial to obtaining a positive electrode material with a more suitable particle size distribution, and avoids the decrease in tap density caused by excessive carbon elements, which is beneficial to improving the tap density of the positive electrode material.

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

[0111] In this embodiment, within the range of the average primary particle size of the above positive electrode material, the particle size of the positive electrode material is more suitable, which is beneficial to the positive electrode material having higher electrochemical properties such as a higher charge specific capacity, a higher discharge specific capacity, and better rate performance while having a higher tap density. Optionally, the average primary particle size of the positive electrode material is 340 nm, 350 nm, 360 nm, 370 nm, 380 nm, 390 nm, 400 nm or 415 nm, or the average primary particle size of the positive electrode material can also be within the range between any two of the above particle sizes.

[0112] In some embodiments, in the primary particles of the positive electrode material, the proportion of the number of primary particle sizes less than 200 nm is 36.29% - 53.01%, the proportion of the number of primary particle sizes between 200 nm and 400 nm is 34.02% - 44.30%, the proportion of the number of primary particle sizes greater than 400 nm and less than or equal to 1000 nm is 8.05% - 17.48%, and the proportion of the number of primary particle sizes greater than 1000 nm is 0.60% - 1.93%.

[0113] In this embodiment, within the range of the proportion of the particle size distribution of the primary particles of the above positive electrode material, the particle size distribution of the positive electrode material is more suitable, which is beneficial to the positive electrode material having higher electrochemical properties such as a higher charge specific capacity, a higher discharge specific capacity, and better rate performance while having a higher tap density.

[0114] Optionally, in the primary particles of the positive electrode material, the proportion of the number of primary particle sizes less than 200 nm is 36.29%, 38%, 40%, 42%, 44%, 46%, 48%, 50%, 52% or 53.01%, or, in the primary particles of the positive electrode material, the proportion of the number of primary particle sizes less than 200 nm can also be within the range between any two of the above percentages. Preferably, in the primary particles of the positive electrode material, the proportion of the number of primary particle sizes less than 200 nm is 45.88% - 53.01%.

[0115] Optionally, in the primary particles of the positive electrode material, the proportion of the number of primary particle sizes between 200 nm and 400 nm is 34.02%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44% or 44.30%, or, in the primary particles of the positive electrode material, the proportion of the number of primary particle sizes between 200 nm and 400 nm can also be within the range between any two of the above percentages. Preferably, in the primary particles of the positive electrode material, the proportion of the number of primary particle sizes between 200 nm and 400 nm is 34.02% - 40.27%.

[0116] Optionally, in the primary particles of the positive electrode material, the proportion of the number of primary particle sizes 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%, or, in the primary particles of the positive electrode material, the proportion of the number of primary particle sizes greater than 400 nm and less than or equal to 1000 nm can also be within the range between any two of the above percentages. Preferably, in the primary particles of the positive electrode material, the proportion of the number of primary particle sizes greater than 400 nm and less than or equal to 1000 nm is 8.05% - 15.09%.

[0117] Optionally, in the primary particles of the positive electrode material, the proportion of the number of primary particle sizes 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, in the primary particles of the positive electrode material, the proportion of the number of primary particle sizes greater than 1000 nm can also be within the range between any two of the above percentages. Preferably, in the primary particles of the positive electrode material, the proportion of the number of primary particle sizes greater than 1000 nm is 0.60% - 1.70%.

[0118] In some embodiments, the tap density of the positive electrode material under a pressure of 3 kN is 2.57 g / cm 3 ~2.68 g / cm 3 , preferably 2.58 g / cm 3 ~2.68 g / cm3 。

[0119] In this embodiment, the above-mentioned positive electrode material has a high tap density, which is beneficial to improving the energy density of the positive electrode material, thereby enhancing the electrochemical performance of the positive electrode material. Optionally, the tap density of the positive electrode material under a pressure of 3 kN is 2.57 g / cm 3 、2.58 g / cm 3 、2.59 g / cm 3 、2.6 g / cm 3 、2.61 g / cm 3 、2.62 g / cm 3 、2.63 g / cm 3 、2.64 g / cm 3 、2.65 g / cm 3 、2.66 g / cm 3 、2.67 g / cm 3 or 2.68 g / cm 3 , or the tap density of the positive electrode material under a pressure of 3 kN can also be within the range between any two of the above tap densities.

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

[0121] In this embodiment, within the range of the powder resistivity of the positive electrode material, the positive electrode material has a high electronic conductivity, which helps to fully exert the electrochemical performance of the active substances in the positive electrode material, enables more active substances to participate in the electrochemical reaction, and thus improves 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 between any two of the above powder resistivities.

[0122] In some embodiments, the specific surface area of the positive electrode material is 10 m 2 / g to 13 m 2 / g, preferably 11 m 2 / g to 12.7 m 2 / g.

[0123] In this embodiment, within the range of the specific surface area of the above-mentioned positive electrode material, it is beneficial to control the contact area with the electrolyte and the reaction activity of the positive electrode material, thereby enhancing the electrochemical performance such as the charging rate and discharging rate of the positive electrode material. Optionally, the specific surface area of the positive electrode material is 10 m 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 positive electrode material may also be within the range between any two of the above specific surface areas.

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

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

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

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

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

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

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

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

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

[0134] In some embodiments, the 5C first discharge specific capacity (25 °C, 2V - 3.75V) of the positive electrode material is 98.98 mAh / g - 112.37 mAh / g. Preferably, the 5C first discharge specific capacity (25 °C, 2V - 3.75V) of the positive electrode material is 110.06 mAh / g - 112.37 mAh / g.

[0135] In some embodiments, the 5C first discharge efficiency (25 °C, 2V - 3.75V) of the positive electrode material is 87.98% - 97.89%. Preferably, the 5C first discharge efficiency (25 °C, 2V - 3.75V) of the positive electrode material is 94.99% - 97.89%.

[0136] In a third aspect, an embodiment of the present application provides a method for preparing a positive electrode material, including the following steps:

[0137] Mix the first doping source with the ferrous solution to form a mixed solution;

[0138] Mix the mixed solution with the first phosphorus source and the first oxidant, and after the first reaction treatment, obtain a first slurry;

[0139] Mix the first slurry with the second phosphorus source and the second oxidant, and after the second reaction treatment, obtain a second slurry;

[0140] Perform the first solid-liquid separation treatment on the second slurry to obtain a first solid-phase material;

[0141] Mix the first solid-phase material with phosphoric acid, and after the aging treatment, obtain a third slurry;

[0142] Perform the second solid-liquid separation treatment on the third slurry to obtain a second solid-phase material;

[0143] The second solid-phase material is subjected to crystallization treatment to obtain an iron phosphate material;

[0144] The iron phosphate material, a lithium source, a second doping source, a surfactant, a carbon source and a solvent are mixed to obtain a precursor slurry;

[0145] The precursor slurry is subjected to grinding treatment and drying treatment to obtain a precursor; and,

[0146] The precursor is subjected to sintering treatment to obtain a cathode material;

[0147] Wherein, the first doping source contains a first doping element, the first doping element is selected from one or more of Mg and Ce, and the molar ratio of the iron element 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, the second doping element is selected from one or more of Ti and Mn, and the molar ratio of the iron element in the iron phosphate material to the second doping element in the second doping source is (1-y-z):z, 0.008≤y≤0.016, 0.001≤z≤0.03.

[0148] In the technical solution of the embodiment of the present application, the preparation of the first solid-phase material is carried out in two steps. During the first reaction treatment, part of the crystal nuclei are formed. During the second reaction treatment, the crystal nuclei formed during the first reaction treatment are promoted to grow, thereby reducing the generation of small particles, making the particle size distribution of the obtained iron phosphate material uniform and the particle size appropriate; during the preparation of the iron phosphate material, the ferrous solution is mixed with the first doping source, and the cations of the first doping element and ferrous ions co-precipitate to form a compound with internal doping, facilitating the uniform doping and growth of the iron phosphate material, thereby obtaining an 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, partially replacing the iron element, the iron-phosphorus ratio of the iron phosphate material is reduced within an appropriate range, promoting the growth of the iron phosphate material particles, being beneficial to obtaining an iron phosphate material with a uniform particle size, and being beneficial to reducing the content of magnetic foreign matters and improving the capacity in the prepared cathode material, thereby improving the electrochemical performance of the cathode material; during the preparation of the precursor, the second doping element is doped, and the molar ratio of the iron element in the iron phosphate material to the second doping element in the second doping source is controlled to be (1 - y - z):z, 0.008 ≤ y ≤ 0.016, 0.001 ≤ z ≤ 0.03. Through the two-step doping method, under the condition of a lower secondary doping amount, the cathode material obtains better rate performance; in the preparation method of the present application, a surfactant is added during the grinding process to improve the dispersibility of the iron phosphate material, reduce the agglomeration of the iron phosphate material generated during the grinding process, and be beneficial to the growth of particles during the sintering process, thereby obtaining a cathode material with a more uniform particle size distribution and a more suitable particle size; the cathode material prepared by the preparation method of the cathode material in the embodiment of the present application has electrochemical performances such as a higher tap density, a higher charge specific capacity, a higher discharge specific capacity, and a better rate performance while having a higher tap density.

[0149] Optionally, x = 0.008, 0.009, 0.010, 0.011, 0.012, 0.013, 0.014, 0.015 or 0.016, or x can also be within the range between any two of the above values.

[0150] Optionally, y = 0.008, 0.009, 0.010, 0.011, 0.012, 0.013, 0.014, 0.015 or 0.016, or y can also be within the range between any two of the above values.

[0151] Optionally, z = 0.001, 0.005, 0.01, 0.015, 0.02, 0.025 or 0.003, or z can also be within the range between any two of the above values.

[0152] Preferably, 0.012 ≤ x ≤ 0.016.

[0153] Preferably, 0.012 ≤ y ≤ 0.016.

[0154] Preferably, 0.01 ≤ z ≤ 0.03, more preferably, 0.02 ≤ z ≤ 0.025.

[0155] In some embodiments, in the method for preparing the positive electrode material provided by the embodiments of the present application, the prepared iron phosphate material is the iron phosphate material as described above.

[0156] In some embodiments, in the method for preparing the positive electrode material provided by the embodiments of the present application, the prepared positive electrode material is the positive electrode material as described above.

[0157] In some embodiments, the first doping source includes at least one of magnesium sulfate heptahydrate and cerium nitrate.

[0158] In some embodiments, the first phosphorus source includes at least one of lithium dihydrogen phosphate and lithium hydrogen phosphate.

[0159] In some embodiments, the first oxidant includes hydrogen peroxide, and the mass fraction of hydrogen peroxide in the hydrogen peroxide is 25% - 35%.

[0160] Optionally, the mass fraction of hydrogen peroxide in the hydrogen peroxide of the first oxidant is 25%, 27.5%, 30%, 32.5% or 35%, or the mass fraction of hydrogen peroxide in the hydrogen peroxide of the first oxidant can also be within the range between any two of the above mass fractions. Preferably, the mass fraction of hydrogen peroxide in the hydrogen peroxide of the first oxidant is 27.5% or 30%.

[0161] In some embodiments, the second phosphorus source includes at least one of lithium dihydrogen phosphate and lithium hydrogen phosphate

[0162] In some embodiments, the second oxidant includes hydrogen peroxide, and the mass fraction of hydrogen peroxide in the hydrogen peroxide is 25% - 35%.

[0163] Optionally, the mass fraction of hydrogen peroxide in the hydrogen peroxide of the second oxidant is 5%, 27.5%, 30%, 32.5% or 35%, or the mass fraction of hydrogen peroxide in the hydrogen peroxide of the second oxidant can also be within the range between any two of the above mass fractions. Preferably, the mass fraction of hydrogen peroxide in the hydrogen peroxide of the second oxidant is 27.5% or 30%.

[0164] Using the above first doping source, first phosphorus source, first oxidant, second phosphorus source and second oxidant reduces the introduction of impurities, which is beneficial to preparing an iron phosphate material with higher purity, and further preparing a positive electrode material with higher purity.

[0165] In some embodiments, the mass fraction of hydrogen peroxide in the hydrogen peroxide solution of the first oxidant may be the same as that of the 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.

[0166] In some embodiments, the lithium source includes at least one of lithium carbonate, lithium hydroxide, lithium oxalate, and lithium acetate.

[0167] In some embodiments, the second doping source includes at least one of titanium dioxide and manganese carbonate.

[0168] In some embodiments, the carbon source includes at least one of glucose and sucrose.

[0169] Using the above lithium source, second doping source, and carbon source reduces the introduction of impurities and is beneficial to preparing a cathode material with higher purity.

[0170] In some embodiments, the drying treatment method is spray drying.

[0171] In some embodiments, the inlet air temperature of the spray drying is 150°C to 350°C, and the outlet air temperature of the spray drying is 60°C to 110°C.

[0172] Optionally, the inlet air temperature of the spray drying is 150°C, 180°C, 200°C, 220°C, 250°C, 280°C, 300°C, 320°C, or 350°C, or the inlet air temperature of the spray drying can also be within the range between any two of the above temperatures. Optionally, the outlet air temperature of the spray drying is 60°C, 70°C, 80°C, 90°C, 100°C, or 110°C, or the outlet air temperature of the spray drying can also be within the range between any two of the above temperatures.

[0173] In some embodiments, the sintering treatment is carried out in a protective gas atmosphere.

[0174] In some embodiments, the protective gas includes at least one of nitrogen and argon.

[0175] In some embodiments, the steps of mixing the mixed solution with the first phosphorus source and the first oxidant and obtaining the first slurry through the first reaction treatment include:

[0176] The mixed solution, the first phosphorus source, and the first oxidant are mixed at the first mixing temperature for the first mixing time and then reacted at the first reaction temperature for the first reaction time to obtain the first slurry;

[0177] Among them, the first mixing temperature is 25°C to 50°C, the first mixing time is 20 min to 40 min, the first reaction time is 20 min to 40 min, and the first reaction temperature is 50°C to 70°C.

[0178] In this embodiment, within the ranges of the above-mentioned first mixing temperature, first mixing time, first reaction time, and first reaction temperature, it is beneficial for the crystal nuclei to grow more completely, and thus it is conducive to obtaining a iron phosphate material with a more uniform particle size distribution and a more suitable particle size.

[0179] Optionally, the first mixing temperature is 25°C, 30°C, 35°C, 40°C, 45°C, or 50°C, or the first mixing temperature can also be within the range between any two of the above temperatures.

[0180] Optionally, the first mixing time is 20 min, 25 min, 30 min, 35 min, or 40 min, or the first mixing time can also be within the range between any two of the above times.

[0181] Optionally, the first reaction time is 20 min, 25 min, 30 min, 35 min, or 40 min, or the first reaction time can also be within the range between any two of the above times.

[0182] Optionally, the first reaction temperature is 50°C, 55°C, 60°C, 65°C, or 70°C, or the first reaction temperature can also be within the range between any two of the above temperatures.

[0183] In some embodiments, the step of mixing the first slurry with the second phosphorus source and the second oxidant and obtaining the second slurry through the second reaction treatment includes:

[0184] The mixed liquid and the second phosphorus source are mixed at the second mixing temperature for the second mixing time to obtain the fourth slurry;

[0185] The fourth slurry and the second oxidant are mixed at the third mixing temperature for the third mixing time, and then at the second reaction temperature for the second reaction time to obtain the second slurry;

[0186] wherein, the second mixing temperature is 45°C to 60°C, the second mixing time is 3 min to 8 min, the third mixing temperature is 50°C to 60°C, the third mixing time is 10 min to 16 min, the second reaction time is 50 min to 70 min, and the second reaction temperature is 50°C to 70°C;

[0187] 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).

[0188] In this embodiment, within the ranges of the above reaction parameters, it is beneficial to promote the growth of crystal nuclei during the second reaction treatment, and thus obtain a iron phosphate material with a more uniform particle size distribution and a more suitable particle size.

[0189] Optionally, the second mixing temperature is 45 °C, 50 °C, 55 °C or 60 °C, or the second mixing temperature can also be within the range between any two of the above temperatures.

[0190] Optionally, the second mixing time is 3 min, 4 min, 5 min, 6 min, 7 min or 8 min, or the second mixing time can also be within the range between any two of the above times.

[0191] 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 also be within the range between any two of the above temperatures.

[0192] 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 can also be within the range between any two of the above times.

[0193] Optionally, the second reaction time is 50 min, 55 min, 60 min, 65 min or 70 min, or the second reaction time can also be within the range between any two of the above times.

[0194] 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 can also be within the range between any two of the above temperatures.

[0195] 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 can also be within the range between any two of the above mass ratios.

[0196] 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 can also be within the range between any two of the above mass ratios.

[0197] In some embodiments, the step of subjecting the second slurry to the first solid-liquid separation treatment to obtain the first solid-phase material includes:

[0198] The second slurry is subjected to the first solid-liquid separation to obtain the first solid material;

[0199] The first solid material is washed until the conductivity of the first washing liquid after washing is less than or equal to 500 μS / cm to obtain the first solid-phase material.

[0200] In some embodiments, the first washing liquid is selected from at least one of deionized water, secondary water, distilled water, pure water, or ultrapure water.

[0201] In some embodiments, the first solid-liquid separation can be carried out by at least one of normal pressure filtration, pressure filtration, suction filtration, centrifugation, etc.

[0202] In some embodiments, the step of mixing the first solid-phase material with phosphoric acid and subjecting it to aging treatment to obtain the third slurry includes:

[0203] Mix the first solid-phase material with phosphoric acid until the pH value is 1.2 - 1.7, and after the aging time at the aging temperature, obtain the third slurry;

[0204] The aging temperature is 75°C - 95°C, the aging time is 1.5 h - 2.5 h, and the pH value of the third slurry is 1.7 - 2.

[0205] In some embodiments, the concentration of phosphoric acid is 2.5 mol / L - 4.0 mol / L.

[0206] In this embodiment, within the range of the parameters of the above aging treatment, it is beneficial to the further uniform growth of particles, and thus a iron phosphate material with a more uniform particle size distribution and a more suitable particle size can be obtained.

[0207] 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 alternatively, the concentration of phosphoric acid can also be within the range between any two of the above concentrations.

[0208] Optionally, the first solid-phase material is mixed with phosphoric acid until the pH value is 1.5, 1.55, 1.6, 1.65, or 1.7, or alternatively, the first solid-phase material is mixed with phosphoric acid until the pH value can also be within the range between any two of the above pH values.

[0209] In some embodiments, the step of mixing the first solid-phase material with phosphoric acid until the pH value is 1.2 - 1.7, and after the aging time at the aging temperature, obtaining the third slurry includes;

[0210] The first solid-phase material is mixed with water and slurried to form a premixed slurry;

[0211] The premixed slurry is mixed with phosphoric acid until the pH value is 1.2 - 1.7, and after the aging time at the aging temperature, obtain the third slurry.

[0212] In some embodiments, the water is selected from at least one of deionized water, secondary water, distilled water, pure water, or ultrapure water.

[0213] Optionally, the aging temperature is 75°C, 80°C, 85°C, 90°C or 95°C, or the aging temperature can also be within the range between any two of the above temperatures.

[0214] Optionally, the aging time is 1.5 h, 1.8 h, 2 h, 2.2 h or 2.5 h, or the aging time can also be within the range between any two of the above times.

[0215] 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 can also be within the range between any two of the above pH values.

[0216] In some embodiments, after the precursor slurry is subjected to sand milling treatment, the D50 particle size of the solid particles in the precursor slurry is 0.2 μm to 0.5 μm.

[0217] In this embodiment, within the range of the D50 particle size of the solid particles in the above 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 subjected to sand milling treatment, the D50 particle size of the solid particles in the precursor slurry is 0.2 μm, 0.25 μm, 0.3 μm, 0.35 μm, 0.4 μm, 0.45 μm or 0.5 μm, or after the precursor slurry is subjected to sand milling treatment, 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.

[0218] In some embodiments, the D50 particle size of the precursor is 3 μm to 6 μm.

[0219] In this embodiment, within the range of the D50 particle size of the above precursor, it is beneficial 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 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm or 6 μm, or the D50 particle size of the precursor can also be within the range between any two of the above particle sizes.

[0220] In some embodiments, the solid content of the precursor slurry is 40% to 55%, that is, the mass fraction of the solid particles in the precursor slurry is 40% to 55%, preferably 45%, 46%, 47%, 48%, 49%, 50%, 52%, etc.

[0221] In some embodiments, the step of obtaining the second solid-phase material by subjecting the third slurry to a second solid-liquid separation treatment includes:

[0222] The third slurry is subjected to a second solid-liquid separation to obtain a second solid material.

[0223] In some embodiments, the second solid-liquid separation can be carried out by at least one of atmospheric pressure filtration, pressure filtration, suction filtration, centrifugation and the like.

[0224] In some embodiments, the steps of obtaining the iron phosphate material by subjecting the second solid-phase material to crystallization treatment include:

[0225] Subject the second solid-phase material to flash evaporation treatment to obtain the iron phosphate material.

[0226] 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.

[0227] In this embodiment, within the range of the proportion of the mass of the above surfactant in 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 the sintering process, so as to enhance the consistency of particle growth, thereby preparing a cathode material with a relatively 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 iron phosphate material can also be within the range between any two of the above percentages.

[0228] In some embodiments, the steps of obtaining the cathode material by subjecting the precursor to sintering treatment include:

[0229] After the precursor is sintered at the first sintering temperature for the first sintering time, a pre-sintered material is obtained; and,

[0230] The pre-sintered material is sintered at the second sintering temperature for the second sintering time to obtain the cathode material;

[0231] Wherein, the first sintering temperature is 400°C to 500°C, the first sintering time is 1h to 6h, the second sintering temperature is 700°C to 900°C, and the second sintering time is 4h to 12h.

[0232] In this embodiment, within the ranges of the above sintering treatment parameters, it is beneficial to ensure sufficient dehydration time and ensure uniform heating of the particles, so that the growth of the cathode material particles has better consistency, thereby preparing a cathode material with a relatively uniform particle size distribution and a more suitable particle size.

[0233] Optionally, the first sintering temperature is 400°C, 420°C, 440°C, 460°C, 480°C or 500°C, or the first sintering temperature can also be within the range between any two of the above temperatures.

[0234] Optionally, the first sintering time is 1 h, 2 h, 3 h, 4 h, 5 h or 6 h, or the first sintering time may also be within the range between any two of the above times.

[0235] Optionally, the second sintering temperature is 700 °C, 750 °C, 800 °C, 850 °C or 900 °C, or the second sintering temperature may also be within the range between any two of the above temperatures.

[0236] Optionally, the second sintering time is 4 h, 6 h, 8 h, 10 h or 12 h, or the second sintering time may also be within the range between any two of the above times.

[0237] Fourthly, an electrode sheet is provided in an embodiment of the present application. 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 of any one of the above, or the electrode active layer includes the positive electrode material prepared by the preparation method of any one of the above.

[0238] In this embodiment, the active layer of the positive electrode sheet includes the above positive electrode material, and thus has good electrochemical performance.

[0239] Fifthly, a secondary battery is provided in an embodiment of the present application. The secondary battery includes a positive electrode sheet and a negative electrode sheet, and the positive electrode sheet includes the above electrode sheet.

[0240] In this embodiment, the secondary battery includes the above positive electrode sheet, and thus has comprehensively improved electrochemical performance, and can thus be well applied to multiple usage scenarios.

[0241] Sixthly, an electrical device is provided in an embodiment of the present application.

[0242] The electrical device provided in the embodiment of the present application may be, but is not limited to, a mobile phone, a tablet computer, a laptop computer, an electric toy, an electric tool, a battery car, an electric vehicle, a ship, a spacecraft, etc. Among them, the electric toy may include a fixed or mobile electric toy, for example, a game console, an electric vehicle toy, an electric ship toy and an electric aircraft toy, etc., and the spacecraft may include an airplane, a rocket, a space shuttle and a spaceship, etc.

[0243] The following further describes the present application in detail with specific embodiments, and these embodiments should not be construed as limiting the scope claimed by the present application.

[0244] Unless otherwise defined, all professional terms used hereinafter have the same meaning as commonly understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments, and are not intended to limit the protection scope of the present invention.

[0245] Some specific embodiments are listed below. It should be noted that the embodiments described below are exemplary and are only used to explain the present application, and should not be construed as a limitation to the present application. For those without specific technologies or conditions noted in the embodiments, the technologies or conditions described in the literature in the art or according to the product specifications are followed. For reagents or instruments without the manufacturer noted, they are all conventional products that can be obtained through commercial purchase.

[0246] I. Preparation method

[0247] Example 1

[0248] Preparation method of the positive electrode material:

[0249] (1) Heat and dissolve the by-product of titanium dioxide containing ferrous sulfate, add liquid caustic soda with a concentration of 5% (by mass fraction) for sedimentation, filter and remove impurities by pressure filtration to obtain a ferrous ion solution with a concentration of 1.5 mol / L and a pH value of 2.8;

[0250] (2) Dissolve industrial ammonium dihydrogen phosphate in phosphoric acid and water, filter, and then adjust the pH value to neutral with ammonia water to obtain a phosphorus source solution with a PO4 3- concentration of 2 mol / L;

[0251] (3) Based on 1 mol of iron element, first add the ferrous ion solution to the reaction kettle as the bottom material, then add 0.012 mol of magnesium sulfate heptahydrate and stir to dissolve. Then, add 50% of the phosphorus source (50% when the total molar amount of phosphorus element is 1 mol) and 70% of the hydrogen peroxide solution with a mass fraction of 30% (i.e., the molar amount of hydrogen peroxide is 0.35 mol) dropwise within 30 min for the synthesis reaction. The dropping temperature is 35 °C. After the dropping is completed, stir and react at 60 °C for 30 min. Then, add the remaining phosphorus source (the remaining 50% when the total molar amount of phosphorus element is 1 mol) at 52 °C at one time, stir for 5 min, and then slowly add the remaining 30% of the hydrogen peroxide solution with a mass fraction of 30% (i.e., the molar amount of hydrogen peroxide is 0.15 mol) within 13 min at 55 °C, keep the reaction temperature at 60 °C, stir and react for 1 h, then perform pressure filtration, rinse until the conductivity of the first washing liquid after rinsing ≤ 500 us / cm, then make a slurry, add phosphoric acid to adjust the pH value to 1.4, then raise the temperature to 80 °C and stir and react at a constant speed for 2 h until the pH value is 1.8, perform secondary pressure filtration and then flash evaporation to obtain the iron phosphate material. The chemical formula of the iron phosphate material is Fe 0.988 Mg 0.012 PO4·2H2O, and the iron-to-phosphorus ratio is 0.966.

[0252] (4) Mix iron phosphate material, lithium carbonate with a molar amount of lithium element being 1.04 times that of the iron element in the iron phosphate material, titanium dioxide accounting for 0.47% of the mass of the iron phosphate material, glucose monohydrate accounting for 6.9% of the mass of the iron phosphate material, isooctyl polyoxyethylene polyoxypropylene ether-9 accounting for 0.06% of the mass of the iron phosphate material, and pure water to form a precursor slurry with a solid content of 48.0%. After regulating the D50 particle size of the solid particles in the precursor slurry to 0.36 μm by sand grinding, spray drying is carried out under the conditions of an inlet air temperature of 250 °C and an outlet air temperature of 85 °C to obtain a precursor, and the D50 particle size of the precursor is controlled to be 4.5 μm. Then, under a nitrogen protection atmosphere, it is heated to 450 °C at a heating rate of 2 °C / min and held for 2 h. Then, it is heated to 783 °C at a heating rate of 5 °C / min and held for 8 h. Then, it is cooled to below 100 °C by water cooling and air cooling and taken out of the furnace, and pulverized to obtain the cathode material.

[0253] In this example, the chemical formula of the cathode material is LiFe 0.966 Ti 0.022 Mg 0.012 PO4@C.

[0254] Example 2

[0255] Preparation method of the cathode material:

[0256] The preparation method of the cathode material in Example 2 is the same as or similar to that in Example 1. The difference is that in step (3) of this example, based on 1 mol of iron element, the ferrous solution is first added to the reaction kettle as the bottom material, and then 0.016 mol of magnesium sulfate heptahydrate is added and stirred to dissolve. Then, 60% of the phosphorus source (60% when the total molar amount of phosphorus element is 1 mol) and 75% of the hydrogen peroxide solution with a mass fraction of 30% (i.e., the molar amount of hydrogen peroxide is 0.375 mol) are added dropwise within 20 min for the synthesis reaction. The dropping temperature is 25 °C. After the dropping is completed, the reaction is stirred at 50 °C for 20 min. Then, the remaining phosphorus source (the remaining 40% when the total molar amount of phosphorus element is 1 mol) is added all at once at 45 °C and stirred for 3 min. Then, the remaining hydrogen peroxide solution (i.e., the molar amount of hydrogen peroxide is 0.125 mol) is slowly added dropwise within 10 min at 50 °C, keeping the reaction temperature not exceeding 50 °C. After stirring and reacting for 50 min, pressure filtration is carried out, and it is rinsed until the conductivity of the first washing liquid after rinsing is ≤500 us / cm, then pulped, phosphoric acid is added to adjust the pH value to 1.2, and then the temperature is raised to 75 °C and stirred evenly for 1.5 h until the pH value is 1.7. After secondary pressure filtration, flash evaporation is carried out to obtain the iron phosphate material. The chemical formula of the iron phosphate material is Fe 0.984 Mg 0.016 PO4·2H2O, and the iron-to-phosphorus ratio is 0.964.

[0257] In this embodiment, the chemical formula of the cathode material is LiFe 0.962 Ti 0.022 Mg 0.016 PO4@C.

[0258] Example 3

[0259] Preparation method of the cathode material:

[0260] The preparation method of the cathode material in Example 3 is the same as or similar to that in Example 1. The difference is that in step (3) of this embodiment, based on 1 mol of iron element, the ferrous solution is first added to the reaction kettle as the bottom 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 element 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 within 40 min for the synthesis reaction. The dropping temperature is 50 °C. After the dropping is completed, the reaction is stirred at 70 °C for 40 min. Then, the remaining phosphorus source (55% when the total molar amount of phosphorus element is 1 mol) is added all at once at 60 °C and stirred for 8 min. Then, the remaining hydrogen peroxide solution (i.e., the molar amount of hydrogen peroxide is 0.075 mol) is slowly added dropwise within 16 min at 60 °C while maintaining the reaction temperature at 70 °C. After stirring and reacting for 70 min, pressure filtration is carried out, and it is rinsed until the conductivity of the first washing solution after rinsing ≤ 500 us / cm, then slurried, and phosphoric acid is added to adjust the pH value to 1.7. Subsequently, the temperature is raised to 95 °C and stirred evenly for 2.5 h until the pH value is 2. After secondary pressure filtration, flash evaporation is carried out to obtain the iron phosphate material. The chemical formula of the iron phosphate material is Fe 0.986 Mg 0.014 PO4·2H2O, and the iron-to-phosphorus ratio is 0.968.

[0261] In this embodiment, the chemical formula of the cathode material is LiFe 0.964 Ti 0.022 Mg 0.014 PO4@C.

[0262] Example 4

[0263] Preparation method of the cathode material:

[0264] The preparation method of the cathode material in Example 4 is the same as or similar to that in Example 1, and the difference lies in that: in step (3) of this example, based on 1 mol of iron element, the ferrous solution is first added to the reaction kettle as the bottom 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 element 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 within 30 min for the synthesis reaction. The dropping temperature is 35 °C. After the dropping is completed, the reaction is stirred at 60 °C for 30 min; then, the remaining phosphorus source (45% remaining when the total molar amount of phosphorus element is 1 mol) is added all at once at 52 °C and stirred for 5 min. Then, the remaining hydrogen peroxide solution (i.e., the molar amount of hydrogen peroxide is 0.125 mol) is slowly added dropwise within 13 min at 55 °C while maintaining the reaction temperature at 60 °C. After stirring the reaction for 1 h, filtration is carried out, and it is rinsed until the conductivity of the first washing solution after rinsing is ≤ 500 us / cm, and then it is slurried. Phosphoric acid is added to adjust the pH value to 1.6, and then the temperature is raised to 85 °C and stirred uniformly for 2 h until the pH value reaches 1.8. After secondary filtration, flash evaporation is carried out to obtain the iron phosphate material. The chemical formula of the iron phosphate material is Fe 0.986 Ce 0.014 PO4·2H2O, and the iron-to-phosphorus ratio is 0.967.

[0265] The chemical formula of the cathode material in this example is LiFe 0.964 Ti 0.022 Ce 0.014 PO4@C.

[0266] Example 5

[0267] Preparation method of the cathode material:

[0268] The preparation method of the cathode material in Example 5 is the same as or similar to that in Example 4, and the difference lies in that: in step (4) of this example, the iron phosphate material, lithium carbonate with a molar amount of 1.04 times that of the iron element in the iron phosphate material, titanium dioxide with a mass of 0.53% of the iron phosphate material, glucose monohydrate with a mass of 6.9% of the iron phosphate material, polyoxyethylene polyoxypropylene ether-9 with a mass of 0.08% of the iron phosphate material, and pure water are stirred and mixed to form a precursor slurry with a solid content of 48.0%. After regulating the D50 particle size of the solid particles in the precursor slurry to 0.2 μm by sand grinding, spray drying is carried out under the conditions of an inlet air temperature of 150 °C and an outlet air temperature of 60 °C to obtain the precursor, and the D50 particle size of the precursor is controlled to be 3 μm; then, it is heated at a rate of 2 °C / min to 400 °C under a nitrogen protection atmosphere and held for 6 h. Then, it is heated at a rate of 5 °C / min to 700 °C and held for 12 h. Then, it is cooled to below 100 °C by water cooling and air cooling and taken out of the furnace, and pulverized to obtain the cathode material.

[0269] In this embodiment, the chemical formula of the cathode material is LiFe 0.961 Ti 0.025 Ce 0.014 PO4@C.

[0270] Example 6

[0271] Preparation method of the cathode material:

[0272] The preparation method of the cathode material in Example 6 is the same as or similar to that in Example 4. The difference is that in step (4) of this embodiment, ferric phosphate material, lithium carbonate with a molar amount of 1.04 times that of the iron element in the ferric phosphate material, manganese carbonate with a mass of 0.53% of the ferric phosphate material, glucose monohydrate with a mass of 7.1% of the ferric phosphate material, polyoxyethylene polyoxypropylene ether-9 with a mass of 0.02% of the ferric phosphate material, and pure water are stirred and mixed to form a precursor slurry with a solid content of 48.0%. After controlling the D50 particle size of the solid particles in the precursor slurry to be 0.5 μm by sand grinding, spray drying is carried out under the conditions of an inlet air temperature of 350 °C and an outlet air temperature of 110 °C to obtain a precursor, and the D50 particle size of the precursor is controlled to be 6 μm; then it is heated from room temperature to 500 °C at a rate of 2 °C / min under a nitrogen protection atmosphere and held for 1 h, then heated to 900 °C at a rate of 5 °C / min and held for 4 h, and then cooled to below 100 °C by water cooling and air cooling and taken out of the furnace, and pulverized to obtain the cathode material.

[0273] In this embodiment, the chemical formula of the cathode material is LiFe 0.968 Mn 0.018 Ce 0.014 PO4@C.

[0274] Example 7

[0275] Preparation method of the cathode material:

[0276] The preparation method of the cathode material in Example 7 is the same as or similar to that in Example 4. The difference is that in step (4) of this embodiment, titanium dioxide and manganese carbonate with a mass ratio of 3:1 are used to replace titanium dioxide, and their total mass is 0.54% of the mass of the ferric phosphate material, and the mass of monohydrate glucose is 7.1% of the mass of the ferric phosphate material; it is heated from room temperature to 400 °C at a rate of 2 °C / min under a nitrogen protection atmosphere and held for 2 h, then heated to 785 °C at a rate of 5 °C / min and held for 8 h.

[0277] Cathode material

[0278] In this embodiment, the chemical formula of the cathode material is LiFe 0.969 Ti 0.017 Mn 0.0005 Ce 0.014 PO4@C.

[0279] Example 8

[0280] Preparation method of the positive electrode material:

[0281] The preparation method of the positive electrode material in Example 8 is the same as or similar to that in Example 4, and the difference is that: in this example, the mass of titanium dioxide is 0.24% of the mass of the iron phosphate material.

[0282] The chemical formula of the positive electrode material in this example is LiFe 0.976 Ti 0.01 Ce 0.014 PO4@C.

[0283] Example 9

[0284] Preparation method of the positive electrode material:

[0285] The preparation method of the positive electrode material in Example 9 is the same as or similar to that in Example 4, and the difference is that: in this example, the mass of titanium dioxide is 0.63% of the mass of the iron phosphate material.

[0286] The chemical formula of the positive electrode material in this example is LiFe 0.956 Ti 0.03 Ce 0.014 PO4@C.

[0287] Example 10

[0288] Preparation method of the positive electrode material:

[0289] The preparation method of the positive electrode material in Example 10 is the same as or similar to that in Example 1, and the difference is 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, and the iron to phosphorus ratio is 0.978.

[0290] The chemical formula of the positive electrode material in this example is LiFe 0.968 Ti 0.022 Mg 0.01 PO4@C.

[0291] Example 11

[0292] Preparation method of the positive electrode material:

[0293] The preparation method of the positive electrode material in Example 11 is the same as or similar to that in Example 1, and the difference is 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.

[0294] In this example, the chemical formula of the cathode material is LiFe 0.970 Ti 0.022 Mg 0.008 PO4@C.

[0295] Example 12

[0296] Preparation method of the cathode material:

[0297] The preparation method of the cathode material in Example 12 is the same as or similar to that in Example 4. The difference is that in step (4) of this example, ferric phosphate material, lithium carbonate with a molar amount of 1.04 times that of the iron element in the ferric phosphate material, titanium dioxide at 0.47% of the mass of the ferric phosphate material, monohydrate glucose at 6.9% of the mass of the ferric phosphate material, and polyethylene glycol at 0.1% of the mass of the ferric phosphate material are stirred and mixed with pure water to form a precursor slurry with a solid content of 55.0%. After controlling the D50 particle size of the solid particles in the precursor slurry to be 0.24 μm by sand grinding, spray drying is carried out under the conditions of an inlet air temperature of 250 °C and an outlet air temperature of 85 °C to obtain a precursor, and the D50 particle size of the precursor is controlled to be 4.5 μm; then it is heated from room temperature to 400 °C at a rate of 2 °C / min under a nitrogen protection atmosphere, held for 4 h, then heated to 850 °C at a rate of 5 °C / min and held for 5 h, and then cooled to below 100 °C by water cooling and air cooling and taken out of the furnace, and pulverized to obtain the cathode material.

[0298] In this example, the chemical formula of the cathode material is LiFe 0.964 Ti 0.022 Ce 0.014 PO4@C.

[0299] Comparative Example 1

[0300] The preparation method of the cathode material in Comparative Example 1 is the same as or similar to that in Example 1. The difference is that in step (4) of Comparative Example 1, titanium dioxide and dispersant are not added, and the chemical formula of the ferric phosphate material is Fe 0.988 Mg 0.012 PO4·2H2O, with an iron to phosphorus ratio of 0.966.

[0301] In Comparative Example 1, the chemical formula of the cathode material is LiFe 0.988 Mg 0.012 PO4@C.

[0302] Comparative Example 2

[0303] Preparation method of the cathode material:

[0304] The preparation method of the positive electrode material in Comparative Example 2 is the same as or similar to that in Example 1, and the difference is that: in step (3) of Comparative Example 2, magnesium sulfate heptahydrate is not added, and the chemical formula of the iron phosphate material is FePO4·2H2O, and the iron to phosphorus ratio is 0.974.

[0305] The chemical formula of the positive electrode material in Comparative Example 2 is LiFe 0.978 Ti 0.022 PO4@C.

[0306] Comparative Example 3

[0307] Preparation method of the positive electrode material:

[0308] The preparation method of the positive electrode material in Comparative Example 3 is the same as or similar to that in Example 1, and the difference is that: in step (3) of Comparative Example 3, the flash-evaporated iron phosphate material is changed to anhydrous iron phosphate obtained by rotary kiln drying. The chemical formula of the anhydrous iron phosphate is Fe 0.988 Mg 0.012 PO4.

[0309] The chemical formula of the positive electrode material in Comparative Example 3 is LiFe 0.966 Ti 0.022 Mg 0.012 PO4@C.

[0310] II. Test method

[0311] The element contents of the positive electrode materials prepared in Examples 1 to 12 and Comparative Examples 1 to 3 were tested. The element composition was detected by ICP-OES; the content of free lithium element was determined by potentiometric titration; the C content was tested by a carbon-sulfur analyzer; the test results are shown in Table 1 below:

[0312] Table 1

[0313]

[0314] The properties of the iron phosphate materials and cathode materials prepared in Examples 1 to 12 and Comparative Examples 1 to 3 were tested. Among them, the powder resistivity was measured by the four-probe method with a measurement pressure of 8 MPa; the tap density was measured under a pressure of 3 tons; the specific surface area was determined by the gas adsorption BET method; the particle size was statistically analyzed using Nano Measurer 1.2.5 after SEM photography; for the content of magnetic foreign matters: weigh 100 g of the material, pour it into a plastic bottle with a lid, add 1000 g of pure water, then add a magnetic stirrer of 8000 GS, make a polytetrafluoroethylene protection outside the magnetic stirrer, then tighten the lid, place the plastic bottle horizontally and rotate the plastic bottle at a speed of 10 - 20 r / min for 30 - 45 min, stop rotating, take out the magnetic stirrer, add 1000 g of pure water, put it into the plastic bottle, tighten the lid, place the plastic bottle horizontally and rotate the plastic bottle at a speed of 10 - 20 r / min for 5 - 10 min, stop rotating, take out the magnetic stirrer, dissolve it with aqua regia, measure the dissolved solution with ICP, make up the volume, measure the contents of nickel, chromium, copper, zinc and iron in it, calculate the total mass of nickel, chromium, copper, zinc and iron, and then divide it by the weight of the material to obtain the content of magnetic foreign matters in the material.

[0315] The test results of the iron phosphate materials are shown in Table 2 below:

[0316] Table 2

[0317]

[0318]

[0319] The test results of the cathode materials are shown in Tables 3 and 4 below:

[0320] Table 3

[0321]

[0322]

[0323] Table 4

[0324]

[0325] The cathode materials prepared in Examples 1 to 12 and Comparative Examples 1 to 3 were mixed with conductive carbon black and PVDF binder in a mass ratio of 90:5:5, coated on an aluminum foil with a thickness of 12 μm, and then the electrode sheet was placed in an oven at 110 °C and dried for 10 h. The dried electrode sheet was punched into a positive electrode disc with a diameter of 15 mm, and it was pressed at a density of 2.5 g / cm 3Rolling, using a lithium sheet with a diameter of 16 mm as the counter electrode, and the electrolyte is 1 M LiPF6 dissolved in EC:EMC:DEC with a volume ratio of 1:1:1. The battery was assembled in an LG2400 / 1000TS glove box produced by Wig Gas Purification Technology (Suzhou) Co., Ltd. to obtain a button-type half cell, and its rate performance was tested.

[0326] Using the battery performance test system (model: CT3002A) of Wuhan Blue Electronic Technology Co., Ltd., the test temperature was 25 °C, the voltage range was 2 V to 3.75 V, and the tests were carried out at 1C rate and 5C rate respectively. The test results are shown in Table 5 below:

[0327] Table 5

[0328]

[0329]

[0330] III. Analysis of Test Results of Each Example and Comparative Example

[0331] From the data in Tables 1 to 5, it can be seen that the tap density of the cathode materials provided by each example of the present application is 2.57 g / ml to 2.68 g / ml. The first discharge efficiency (2 V to 3.75 V) at 1C of each example is 93.21% to 94.83%, and the first discharge efficiency (2 V to 3.75 V) at 5C is 87.98% to 97.89%. In each example, iron phosphate dihydrate doped with M element is used as the precursor, and the particle size distribution of the iron phosphate material and the cathode material can be controlled through two-step doping, thereby obtaining a cathode material with high tap density and rate performance.

[0332] Compared with the cathode material obtained in the example, the growth consistency of the cathode material in Comparative Example 1 is poor, and the uniformity of the particle size distribution is poor, resulting in a lower tap density and poorer rate performance of the cathode material obtained in Comparative Example 1.

[0333] In Comparative Example 2, the first doping source is not added, the iron-phosphorus ratio of the iron phosphate material is 0.974, and the effect of controlling the uniform growth of the iron phosphate material particles is poor. As a result, the uniformity of the particle size distribution of the cathode material obtained in Comparative Example 2 is also poor compared with the cathode material obtained in the example, the tap density is lower, and the rate performance is poorer.

[0334] Compared with the cathode material obtained in the example, the uniformity of the particle size distribution of the anhydrous iron phosphate prepared by rotary kiln drying in Comparative Example 3 is poor. As a result, the uniformity of the particle size distribution of the cathode material obtained in Comparative Example 3 is also poor, and the content of magnetic foreign matters is relatively high. The tap density of the cathode material obtained in Comparative Example 3 is lower, and the rate performance is poorer.

[0335] ComparisonFigures 2 to 3 It can be seen that during the preparation of the iron phosphate dihydrate precursor, the morphology of the precursor was significantly improved by doping. In Example 1 of this application, an iron phosphate material combined with spherical and columnar shapes was prepared by doping with element M, while in Comparative Example 2, the iron phosphate dihydrate was not doped, and only an iron phosphate material with a single sheet-like morphology was prepared. Comparison Figures 4 to 7 It can be seen that compared with the cathode material obtained in Comparative Example 2, the primary particle size distribution of the particles of the cathode material prepared in Example 1 of this application is more concentrated, and there are fewer particles with a primary particle size greater than 1000 nm, so the electrochemical performance is more excellent.

[0336] Compared with other examples, in Example 8, the doping amount of element Ti is small, and the tap density of the prepared cathode material is higher, but the rate performance is poor. In Example 9, the doping amount of element Ti is large, and the rate performance of the prepared cathode material is good, but the tap density is low. By comparing Example 8, Example 9 and other examples, it can be seen that controlling 0.02 ≤ z ≤ 0.025 in the cathode material is beneficial to obtaining a cathode material with more balanced tap density and rate performance.

[0337] Compared with other examples, in Example 12, the sintering temperature during the preparation of the cathode material is relatively high at 850 °C. The relatively high temperature will lead to an increase in side reactions, which in turn promotes the formation of magnetic foreign substances such as iron phosphide, resulting in a relatively high content of magnetic foreign substances in the cathode material obtained in Example 12.

[0338] It should be noted that this application is not limited to the above embodiments. The above embodiments are only examples, and embodiments with the same composition and the same function and effect as the technical idea within the technical solution scope of this application are all included in the technical scope of this application. In addition, within the scope of not departing from the gist of this application, various modifications that can be thought of by those skilled in the art to the embodiments and other ways constructed by combining some constituent elements of the embodiments are also included in the scope of this application.

Claims

1. An iron 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 200nm to 300nm; and / or, Among the primary particles of the iron phosphate material, the number of particles with a primary particle size less than 100 nm accounts for 15.3% to 23.7%, the number of particles with a primary particle size between 100 nm and 400 nm accounts for 63.3% to 73.6%, the number of particles with a primary particle size greater than 400 nm and less than or equal to 1000 nm accounts for 9.6% to 17.5%, and the number of particles with a primary particle size greater than 1000 nm accounts for 0.8% to 2.8%.

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

981.

4. A positive electrode material, characterized in that The general formula of the positive electrode 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 positive electrode material is 340nm to 415nm; and / or, Among the primary particles of the positive electrode material, the number of particles with a primary particle size less than 200 nm accounts for 36.29% to 53.01%, the number of particles with a primary particle size between 200 nm and 400 nm accounts for 34.02% to 44.30%, the number of particles with a primary particle size greater than 400 nm and less than or equal to 1000 nm accounts for 8.05% to 17.48%, and the number of particles with a primary particle size greater than 1000 nm accounts for 0.60% to 1.93%.

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

7. A method for preparing a positive electrode material, characterized in that: The steps include: mixing a first doping source with a ferrous solution to form a mixed solution; The mixed solution is mixed with a first phosphorus source and a first oxidant, and subjected to a first reaction treatment to obtain a first slurry; The first slurry is mixed with a second phosphorus source and a second oxidant, and subjected to a second reaction treatment to obtain a second slurry; The second slurry is subjected to a first solid-liquid separation process to obtain a first solid phase material; The first solid phase material is mixed with phosphoric acid and subjected to aging treatment to obtain a third slurry; The third slurry is subjected to a second solid-liquid separation process to obtain a second solid phase material; The second solid phase material is subjected to crystallization treatment to obtain an iron phosphate material; The iron phosphate material, the lithium source, the second doping source, the surfactant, the carbon source and the solvent are mixed to obtain a precursor slurry; The precursor slurry is subjected to grinding and drying to obtain a precursor; as well as, The precursor is sintered to obtain the positive electrode material; Among them, the first doping source contains a first doping element, the first doping element is selected from one or more of Mg and Ce, and the amount ratio of the iron element 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, the second doping element is selected from one or more of Ti and Mn, and the amount ratio of the iron element 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 positive electrode material according to claim 7, characterized in that: The mixed solution is mixed with a first phosphorus source and a first oxidant, and subjected to a first reaction treatment to obtain a first slurry, comprising: The mixed solution is mixed with the first phosphorus source and the first oxidant at a first mixing temperature for a first mixing time, and then at a first reaction temperature for a first reaction time to obtain the first slurry; Wherein, the first mixing temperature is 25°C to 50°C, the first mixing time is 20min to 40min, the first reaction time is 20min to 40min, and the first reaction temperature is 50°C to 70°C.

9. The method for preparing the positive electrode material according to claim 7, characterized in that: The first slurry is mixed with a second phosphorus source and a second oxidant, and subjected to a second reaction treatment to obtain a second slurry, comprising: After mixing the mixed solution and the second phosphorus source at the second mixing temperature for the second mixing time, a fourth slurry is obtained; The fourth slurry is mixed with the second oxidant 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°C to 60°C, the second mixing time is 3min to 8min, the third mixing temperature is 50°C to 60°C, the third mixing time is 10min to 16min, the second reaction time is 50min to 70min, and the second reaction temperature is 50°C to 70°C; 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 positive electrode material according to claim 7, characterized in that: The step of mixing the first solid phase material with phosphoric acid and subjecting the mixture to an aging treatment to obtain a third slurry comprises: The first solid phase material is mixed with phosphoric acid to a pH value of 1.2 to 1.7, and the third slurry is obtained after aging at an aging temperature and for an aging time; The aging temperature is 75° C. to 95° C., the aging time is 1.5 h to 2.5 h, and the pH value of the third slurry is 1.7 to 2.

11. The method for preparing the positive electrode material according to claim 7, characterized in that: After the precursor slurry is sand-milled, the D50 particle size of the solid particles in the precursor slurry is 0.2 μm to 0.5 μm; and / or, The D50 particle size of the precursor is 3 μm to 6 μm; and / or, The surfactant is selected from at least one of isooctyl 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 positive electrode material according to claim 7, characterized in that: The precursor is sintered to obtain the positive electrode material, comprising: After the precursor is sintered at a first sintering temperature for a first time, a pre-sintered material is obtained; and, After the pre-sintered material is sintered at a second sintering temperature for a second time, the positive electrode material is obtained; Wherein, the first sintering temperature is 400°C to 500°C, the first sintering time is 1h to 6h, the second sintering temperature is 700°C to 900°C, and the second sintering time is 4h to 12h.

13. An electrode plate, characterized in that: The electrode plate 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 comprises a positive electrode sheet and a negative electrode sheet, and the positive electrode sheet comprises the electrode sheet as claimed in claim 13.

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