Iron phosphate material, preparation method therefor, and use thereof

Abstract

An iron phosphate material, a preparation method therefor, and a use thereof. The iron phosphate material is secondary particles formed by the agglomeration of primary particles, wherein the equivalent particle size of the primary particles is 20 nm-600 nm, and the D50 of the secondary particles is 5 μm-20 μm. The value of the hardness index of the iron phosphate material is less than or equal to 5; and in hardness index = (I), (II) is the average major-to-minor axis ratio of the primary particles. The average major-to-minor axis ratio refers to the ratio of the average length of the longest axis to the average length of the shortest axis of the primary particles. Vp is the specific pore volume of the iron phosphate material, with a unit of cm3 / g. The iron phosphate material satisfying these characteristics has a loose structure and relatively low overall hardness, can improve the efficiency of grinding with a lithium source when used for preparing a positive electrode material, and has less wear on machinery. The prepared positive electrode material has good electrochemical performance.

Description

Iron phosphate material, preparation method and application thereof

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] The present application claims priority to the Chinese patent application No. 202410994099.5, filed on July 24, 2024, and entitled "Iron phosphate material, preparation method and application thereof", the content of which is incorporated herein by reference in its entirety. TECHNICAL FIELD

[0003] The present disclosure relates to the technical field of battery materials, in particular, to an iron phosphate material, a preparation method and application thereof. BACKGROUND

[0004] Lithium iron phosphate is one of the most competitive positive active materials for lithium-ion batteries on the market. Compared with lithium cobaltate and ternary positive materials, lithium iron phosphate has the advantages of long service life and good safety performance. In addition, lithium iron phosphate also has considerable energy density.

[0005] At present, lithium iron phosphate is mostly prepared by solid phase method, specifically by sintering anhydrous iron phosphate and lithium salt. Anhydrous iron phosphate needs to be ground before sintering, but since anhydrous iron phosphate is in a crystalline state and has strong lattice strength, it results in a relatively large macro hardness of the material, which causes a relatively large wear of the machine during grinding of the anhydrous iron phosphate, and a relatively low grinding efficiency.

[0006] In view of this, the present disclosure is proposed.

[0007] SUMMARY

[0008] The purpose of the present disclosure includes providing an iron phosphate material, a preparation method and application thereof to solve or improve the above technical problems.

[0009] The present disclosure can be achieved as follows:

[0010] In a first aspect, the present disclosure provides an iron phosphate material, which is secondary particles formed by agglomeration of primary particles, the equivalent particle diameter of the primary particles is 20 nm to 600 nm, and the equivalent particle diameter is the diameter of a standard sphere having the same volume as the primary particles; the D 50 of the secondary particles is 5 μm to 20 μm;

[0011] The hardness index of the iron phosphate material is ≤5; wherein, is the average length-to-short-axis ratio of the primary particles, which refers to the ratio of the average length of the longest axis to the average length of the shortest axis of the primary particles; V p is the specific pore volume of the iron phosphate material, and the unit is cm 3 / g.

[0012] In optional embodiments, The V is obtained by scanning electron microscopy (SEM) test and calculation.

[0013] In optional embodiments, the V of the iron phosphate material is 0.3 cm3 / g-1.3 cm3 / g. p The V is obtained by nitrogen adsorption-desorption isotherm curve calculation.

[0014] In optional embodiments, the iron phosphate material is an anhydrous iron phosphate material.

[0015] In optional embodiments, the V of the iron phosphate material is 0.3 cm3 / g-1.3 cm3 / g. p 0.3 cm3 / g-1.3 cm3 / g. 3 0.3 cm3 / g-1.3 cm3 / g. 3 0.3 cm3 / g-1.3 cm3 / g.

[0016] In some optional embodiments, the V of the iron phosphate material is 0.72 cm3 / g-1.28 cm3 / g. p 0.72 cm3 / g-1.28 cm3 / g. 3 0.72 cm3 / g-1.28 cm3 / g. 3 0.72 cm3 / g-1.28 cm3 / g.

[0017] In optional embodiments, the average long-short axis ratio of the primary particles is not more than 3.5.

[0018] In some optional embodiments, the average long-short axis ratio of the primary particles is 1.11-3.14.

[0019] In optional embodiments, the hardness index of the iron phosphate material has a value of 0.98-3.57.

[0020] In optional embodiments, the equivalent particle diameter of the primary particles is 254 nm-411 nm.

[0021] In optional embodiments, the D of the secondary particles is 8.74 μm-10.28 μm. 50 8.74 μm-10.28 μm.

[0022] In a second aspect, the disclosure provides a preparation method of the iron phosphate material according to the foregoing embodiments, comprising the following steps: mixing an iron source solution and a phosphorus source solution to form a mixed solution, and then mixing the mixed solution with an oxidizing agent and a pH adjuster after the mixed solution is subjected to air action by a micro-bubble generator, and performing a synthesis reaction, and collecting an amorphous iron phosphate precipitate obtained by the reaction; aging and crystallizing the amorphous iron phosphate precipitate to obtain iron phosphate dihydrate crystals; and calcining the iron phosphate dihydrate crystals to obtain an anhydrous iron phosphate material;

[0023] The oxidizing agent comprises at least one of hydrogen peroxide, ozone, sodium persulfate, ammonium persulfate, sodium hypochlorite, sodium ferrate, and oxygen.

[0024] The aging and crystallization comprises dispersing the amorphous iron phosphate precipitate in an aging solution to perform a crystallization reaction.

[0025] The aging solution is a phosphoric acid solution containing a surfactant.

[0026] The surfactant includes at least one of lignin sulfonate and naphthalene sulfonate formaldehyde condensate; the lignin sulfonate includes at least one of sodium lignin sulfonate and ammonium lignin sulfonate; the naphthalene sulfonate formaldehyde condensate includes at least one of β-naphthalene sulfonate sodium formaldehyde condensate, benzyl naphthalene sulfonate sodium formaldehyde condensate, α-methyl naphthalene sulfonate sodium formaldehyde condensate, and alkyl benzene sulfonate sodium formaldehyde condensate.

[0027] The stirring rate of the crystal transformation reaction is 100 rpm to 300 rpm.

[0028] In optional embodiments, the synthesis reaction includes at least one of the following features:

[0029] Feature 1: the iron source solution is a soluble ferrous salt solution.

[0030] Feature 2: the phosphorus source includes at least one of phosphoric acid, sodium dihydrogen phosphate, sodium monohydrogen phosphate, ammonium dihydrogen phosphate, and ammonium monohydrogen phosphate.

[0031] Feature 3: the pH regulator includes at least one of ammonia, sodium hydroxide, sulfuric acid, hydrochloric acid, and nitric acid.

[0032] In optional embodiments, the iron source includes at least one of ferrous sulfate, ferrous chloride, ferrous nitrate, ferrous oxalate, and ferrous acetate.

[0033] In optional embodiments, the oxidizing agent includes hydrogen peroxide and air.

[0034] In optional embodiments, the synthesis reaction further includes at least one of the following features:

[0035] Feature 4: the concentration of the iron source solution is 0.8 mol / L to 1.5 mol / L.

[0036] Feature 5: the concentration of the phosphorus source solution is 0.85 mol / L to 3 mol / L.

[0037] In optional embodiments, the iron source and the phosphorus source are fed in a ratio of the amount of substance of P to the amount of substance of Fe of 1.05:1 to 1.5:1.

[0038] In optional embodiments, the amount of the oxidizing agent is not less than the amount of Fe 2+ that is theoretically oxidized to Fe 3+ in the iron source.

[0039] In optional embodiments, the synthesis reaction further includes at least one of the following features:

[0040] Feature 6: the pH value of the synthesis reaction is 1-2.5;

[0041] Feature 7: the temperature of the synthesis reaction is 50-70℃;

[0042] Feature 8: the time of the synthesis reaction is 1-4h;

[0043] Feature 9: the stirring speed of the synthesis reaction is 400-800rpm.

[0044] In an optional embodiment, the micro-nano bubble generator generates bubbles with a particle size of 200nm-4.0μm.

[0045] In an optional embodiment, the micro-nano bubble generator generates bubbles with a content of 10%-30% by volume.

[0046] In an optional embodiment, the crystal transformation reaction comprises at least one of the following features:

[0047] Feature 10: the pH value of the aging solution is 1-2.5;

[0048] Feature 11: the concentration of the surfactant contained in the aging solution is 1wt%-5wt%;

[0049] Feature 12: the ratio of the amorphous iron phosphate precipitate to the aging solution is 1g:100mL to 1g:300mL.

[0050] In an optional embodiment, the crystal transformation reaction further comprises at least one of the following features:

[0051] Feature 13: the temperature of the crystal transformation reaction is 80-90℃;

[0052] Feature 14: the time of the crystal transformation reaction is 1-3h.

[0053] In an optional embodiment, the calcination comprises at least one of the following features:

[0054] Feature 15: the temperature of the calcination is 600-750℃;

[0055] Feature 16: the time of the calcination is 2-3h;

[0056] Feature 17: the heating rate during the calcination is 3-5℃ / min.

[0057] In a third aspect, the disclosure provides a positive electrode material, which is prepared by mixing and sintering the above-mentioned iron phosphate material with a lithium source and a carbon source.

[0058] In an optional embodiment, the positive electrode material has at least one of the following features:

[0059] Feature 18: D of the positive electrode material is 0.87 μm to 1.17 μm. 50

[0060] Feature 19: The specific surface area of the positive electrode material is 12.13 cm 2 / g to 12.85 cm 2 / g.

[0061] Feature 20: The 0.1C charge specific capacity of the positive electrode material is not less than 161.5 mAh / g.

[0062] Feature 21: The 0.1C discharge specific capacity of the positive electrode material is not less than 158.5 mAh / g.

[0063] Feature 22: The 1C discharge specific capacity of the positive electrode material is not less than 143.0 mAh / g.

[0064] In an optional embodiment, the 0.1C charge specific capacity of the positive electrode material is 161.7 mAh / g to 163.5 mAh / g.

[0065] In an optional embodiment, the 0.1C discharge specific capacity of the positive electrode material is 158.8 mAh / g to 161.6 mAh / g.

[0066] In an optional embodiment, the 1C discharge specific capacity of the positive electrode material is 143.3 mAh / g to 149.0 mAh / g.

[0067] In a fourth aspect, the present disclosure provides a positive electrode sheet, wherein the active material in the positive electrode sheet comprises the positive electrode material of the foregoing embodiments.

[0068] In a fifth aspect, the present disclosure provides a battery comprising the positive electrode sheet of the foregoing embodiments.

[0069] The beneficial effects of the present disclosure include:

[0070] The present disclosure limits the primary particle equivalent particle diameter, D 50 of the secondary particles of the iron phosphate material, and the hardness index of the iron phosphate material in a specific range, so that the iron phosphate material satisfying the above features has a loose structure and a lower overall hardness, and when used to prepare a positive electrode material, the efficiency of grinding with a lithium source can be improved, the machine wear is small, the prepared positive electrode material has good electrochemical performance, and it is beneficial to further prepare a battery and a power utilization device with excellent electrochemical performance. BRIEF DESCRIPTION OF DRAWINGS

[0071] ​In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some of the embodiments of the present disclosure, and therefore should not be considered as a limitation to the scope. For those skilled in the art, other related drawings can also be obtained without creative labor.

[0072] FIG. 1 is an SEM image of the anhydrous iron phosphate prepared in Example 1;

[0073] FIG. 2 is an SEM image of the anhydrous iron phosphate prepared in Comparative Example 1;

[0074] FIG. 3 is an SEM image of the anhydrous iron phosphate prepared in Comparative Example 2;

[0075] FIG. 4 is an SEM image of the anhydrous iron phosphate prepared in Comparative Example 3;

[0076] FIG. 5 is an SEM image of the anhydrous iron phosphate prepared in Comparative Example 4;

[0077] FIG. 6 is an XRD image of the anhydrous iron phosphate prepared in Example 1 and Comparative Examples 1-4. DETAILED DESCRIPTION

[0078] In order to make the purpose, technical solutions and advantages of the embodiments of the present disclosure more clear, the technical solutions in the embodiments of the present disclosure will be clearly and completely described below. The specific conditions are not specified in the embodiments, and the conventional conditions or the conditions recommended by the manufacturer are used. The reagents or instruments used are not specified by the manufacturer, and are all conventional products that can be purchased in the market.

[0079] The iron phosphate material provided by the present disclosure and the preparation method and application thereof will be described in detail below.

[0080] The present disclosure provides an iron phosphate material, and the general formula of the iron phosphate material is FePO4.

[0081] The iron phosphate material is secondary particles formed by agglomeration of primary particles, the equivalent particle diameter of the primary particles is 20 nm-600 nm, and the equivalent particle diameter is the diameter of a standard sphere having the same volume as the primary particles; the D 50 is 5 μm-20 μm;

[0082] The hardness index of the iron phosphate material is ≤5; wherein, is the average length-to-short-axis ratio of the primary particles, and the average length-to-short-axis ratio refers to the ratio of the average length of the longest axis to the average length of the shortest axis of the primary particles; V p is the specific pore volume of the iron phosphate material, and the unit is cm 3 / g.

[0083] wherein the equivalent diameter of the primary particles can be obtained by scanning electron microscope (SEM) test and calculation, specifically, by testing the morphology parameters of the primary particles in the SEM test image of the iron phosphate material, calculating the volume V, and then according to the volume formula of the standard sphere V = 4 / 3π(d / 2) 3 , the equivalent particle size d is calculated.

[0084] wherein D 50 refers to the particle size of the secondary particles corresponding to the cumulative distribution ratio of 50%.

[0085] wherein, is the ratio of the average length of the longest axis to the average length of the shortest axis of the primary particles, the average length of the longest axis refers to the sum of the lengths of the longest axes of the primary particles divided by the number of the primary particles; the average length of the shortest axis refers to the sum of the lengths of the shortest axes of the primary particles divided by the number of the primary particles; can be obtained by scanning electron microscope (SEM) test and calculation.

[0086] wherein the hardness index does not consider dimension, and the numerical value is ≤5.

[0087] wherein V p can be understood as the pore volume per unit mass, and the unit is cm 3 / g. It can be calculated by nitrogen adsorption-desorption isotherm curve.

[0088] The iron phosphate material of the present disclosure is anhydrous iron phosphate after calcination and drying. Since the chemical composition is fixed and the surface properties of the crystalline anhydrous iron phosphate after calcination and drying are almost the same, the grinding difficulty of the iron phosphate material is related to the properties of the primary particles and the secondary particles formed by agglomeration of the primary particles.

[0089] In terms of the influence of the particle size of the primary particles on the grinding difficulty: on the one hand, the smaller the particle size of the primary particles, the larger the specific surface area of the material, the higher the specific surface energy of the material, and the more prone to agglomeration, which is not conducive to breaking; on the other hand, the primary particles are too large, which is not conducive to the preparation of positive electrode materials with large specific surface area, and it is also difficult to grind large iron phosphate particles into small particles. Therefore, the particle size of the primary particles needs to be controlled in an appropriate range.

[0090] In terms of the influence of the morphology of the primary particles on the grinding difficulty: the more spherical the primary particles, the smaller the specific surface area, the lower the surface energy, and the lower the tendency to agglomerate; in addition, the more spherical the primary particles, the smaller the contact area between the particles, and the easier to break.

[0091] In terms of the influence of the pore structure of the secondary particles on the grinding difficulty: the larger the pore volume of the secondary particles, the more loose the material, and the easier to break.

[0092] Although both the particle size of primary particles and the morphology of primary particles have an impact on the specific pore volume of the material, the specific pore volume of the material is also affected by the width of the particle size distribution of the primary particles and the preparation method. Specifically, the wider the particle size distribution, the more easily the material can be combined more tightly according to the packing principle (small particle size fills the pores formed by large particle size); the preparation method affects the strength and probability of collision between particles, such as increasing the temperature and increasing the stirring speed to intensify the collision between particles, thereby increasing the agglomeration and close contact of the primary particles.

[0093] That is, the specific pore volume, specific surface area or porosity of the material cannot comprehensively evaluate the grinding difficulty of the material. For example, the porosity is the ratio of the pore volume to the volume of the material, and the specific pore volume is the ratio of the pore volume to the mass of the material, both of which have similarities. On the one hand, the mass of the material is more accurately measured relative to the volume of the material, and the porosity is generally calculated by the ratio of the pore area to the solid area in the SEM of the material section; on the other hand, taking an extreme case, using spherical primary particles (which can be regarded as single crystals) and disc-shaped primary particles (which can be regarded as single crystals) with the same mass (or volume) as the shell material to assemble into a hollow material with the same hollow area, that is, the surface area of the spherical cavity is fixed, since the total surface area of the disc-shaped particles is larger than that of the spherical particles, the area of the disc-shaped particles overlapping with each other is larger, and therefore the disc-shaped particles are more difficult to break. In addition, the specific surface area of the secondary particles, that is, the total surface area per unit mass of the material, such as iron phosphate materials with equal mass (or volume), the specific surface area of disc-shaped particles is larger than that of spherical particles, but disc-shaped particles are more difficult to break.

[0094] The present disclosure creatively proposes to combine the equivalent particle size of the primary particles, the D 50 of the secondary particles and the hardness index of the iron phosphate material to represent the grinding difficulty of the material, and the representation result is consistent with the actual grinding difficulty of the material.

[0095] Specifically, by controlling the equivalent particle size of the primary particles of the iron phosphate material to be 20 nm to 600 nm, the D 50 of the secondary particles to be 5 μm to 20 μm and the hardness index of the iron phosphate material to be ≤5, the iron phosphate material satisfying the above characteristics has a loose structure and a low overall hardness, and when used for preparing a positive electrode material, the grinding efficiency with a lithium source can be improved, the machine wear is small, the prepared positive electrode material has good electrochemical performance, and it is beneficial to further prepare a battery and an electrical device with excellent electrochemical performance.

[0096] In some optional embodiments, the V p of the iron phosphate material is 0.3 cm 3 / g to 1.3 cm 3 / g, for example, can be 0.72cm 3 / g~1.28cm 3 / g, such as 0.72cm 3 / g, 0.84cm 3 / g, 0.88cm 3 / g, 0.91cm 3 / g, 1.05cm 3 / g, 1.19cm 3 / g or 1.28cm 3 / g, etc., can also be 0.72cm. 3 / g~1.28cm 3 Other values ​​within the / g range.

[0097] In some alternative embodiments, the average aspect ratio of the primary particles of the iron phosphate material does not exceed 3.5, and can be, for example, 1.11 to 3.14, such as 1.11, 1.25, 1.28, 1.31, 1.33, 2.34, or 3.14, or other values ​​within the range of 1.11 to 3.14. The average aspect ratio of the primary particles can reflect their morphology; the closer the average aspect ratio is to 1, the more the primary particles approximate standard spheres; the larger the average aspect ratio, the more the primary particles approximate plate-like shapes.

[0098] In some alternative embodiments, the hardness index of the iron phosphate material can be 0.98 to 3.57, such as 0.98, 1.08, 1.22, 1.27, 1.82, 2.79 or 3.57, or other values ​​within the range of 0.98 to 3.57.

[0099] In some optional embodiments, the equivalent particle size of the primary particles of the iron phosphate material can be 254 nm to 411 nm, such as 254 nm, 327 nm, 372 nm, 395 nm, 396 nm, 405 nm or 411 nm, or other values ​​in the range of 254 nm to 411 nm.

[0100] In some alternative implementations, the D of the secondary particles 50 It can be 8.74μm to 10.28μm, such as 8.74μm, 9.84μm, 10.06μm, 10.11μm, 10.12μm, 10.28μm or 11.2μm, or other values ​​within the range of 8.74μm to 10.28μm.

[0101] As mentioned above, the iron phosphate material provided in this disclosure is a secondary particle formed by the agglomeration of primary particles. The primary particles are approximately spherical and have a uniform particle size distribution. The secondary particles obtained by agglomeration have a relatively loose structure, high crystallinity, and low overall hardness, making them suitable for mixing and grinding with raw materials such as lithium sources to prepare cathode materials such as lithium iron phosphate.

[0102] Accordingly, the present disclosure also provides a preparation method of the above iron phosphate material, comprising the following steps: mixing an iron source solution with a phosphorus source solution, an oxidizing agent, and a pH adjusting agent and performing a synthesis reaction, and collecting an amorphous iron phosphate precipitate obtained by the reaction; performing aging and crystallization on the amorphous iron phosphate precipitate to obtain iron phosphate dihydrate crystals; and performing calcination on the iron phosphate dihydrate crystals to obtain an anhydrous iron phosphate material.

[0103] In some optional embodiments, the iron source solution is a soluble ferrous salt solution, wherein the iron source exemplarily but non-limitingly includes at least one of ferrous sulfate, ferrous chloride, ferrous nitrate, ferrous oxalate, and ferrous acetate.

[0104] In some optional embodiments, the concentration of the iron source solution can be 0.8 mol / L to 1.5 mol / L, such as 0.8 mol / L, 0.9 mol / L, 1.0 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, or 1.5 mol / L, etc., and can also be other values within the range of 0.8 mol / L to 1.5 mol / L.

[0105] The oxidizing agent exemplarily but non-limitingly includes at least one of hydrogen peroxide, ozone, sodium persulfate, ammonium persulfate, sodium hypochlorite, sodium ferrate, oxygen, and air.

[0106] The amount of the oxidizing agent is not less than the amount of Fe 2+ in the iron source solution theoretically oxidized to Fe 3+ .

[0107] In some embodiments, the oxidizing agent simultaneously includes gaseous oxidizing substances and liquid oxidizing substances, for example, the oxidizing agent simultaneously contains hydrogen peroxide and air. In this way, the mixed solution composed of the iron source solution and the phosphorus source solution is subjected to the action of the micro-bubble generator and air, and then mixed with hydrogen peroxide and the pH adjusting agent, which is beneficial to greatly increasing the contact area and time of air and liquid phase, and improving the oxidation efficiency. Moreover, in this way, the gas-liquid interface of the bubbles has a higher surface energy, which is more beneficial to adsorption on the surface of the agglomerates, so that the agglomerates are more loose.

[0108] Exemplarily, the particle size of the bubbles generated by the micro-nano bubble generator can be 200 nm to 4.0 μm. In terms of volume percentage, the content rate of the bubbles generated by the micro-nano bubble generator can be 10% to 30%, such as 10%, 15%, 20%, 25%, or 30%, etc.

[0109] The phosphorus source exemplarily but non-limitingly includes at least one of phosphoric acid, sodium dihydrogen phosphate, sodium monohydrogen phosphate, ammonium dihydrogen phosphate, and ammonium monohydrogen phosphate.

[0110] The concentration of the phosphorus source solution can be 0.85 mol / L to 3 mol / L, such as 0.85 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, or 3 mol / L, or other values within the range of 0.85 mol / L to 3 mol / L.

[0111] The iron source and the phosphorus source can be added in a ratio of the amount of substance of P to the amount of substance of Fe of 1.05:1 to 1.5:1, such as 1.05:1, 1.1:1, 1.15:1, 1.2:1, 1.25:1, 1.3:1, 1.35:1, 1.4:1, 1.45:1, or 1.5:1.

[0112] The pH regulator can exemplarily but non-limitingly include at least one of ammonia, sodium hydroxide, sulfuric acid, hydrochloric acid, and nitric acid.

[0113] In the present disclosure, the mixing order and the mixing method of each raw material are not particularly limited, and the mixing method includes but is not limited to titration mixing, one-pot mixing, or parallel flow mixing, etc.

[0114] In some embodiments, the iron source solution is first mixed with the phosphorus source solution to obtain a mixed solution; and then the mixed solution, the oxidizing agent, and the pH regulator are added into the reaction container in parallel flow by using a constant flow pump. The pH regulator is used to control the pH value of the synthesis reaction.

[0115] In some embodiments, the pH value of the synthesis reaction is 1 to 2.5, such as 1, 1.5, 2, or 2.5, or other values within the range of 1 to 2.5.

[0116] The temperature of the synthesis reaction can be 50°C to 70°C, such as 50°C, 55°C, 60°C, 65°C, or 70°C, or other values within the range of 50°C to 70°C.

[0117] The above synthesis reaction temperature is relatively low, which is conducive to the formation of loose agglomerates.

[0118] The time of the synthesis reaction can be 1 h to 4 h, such as 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h, or 4 h, or other values within the range of 1 h to 4 h.

[0119] The stirring speed of the synthesis reaction can be 400 rpm to 800 rpm, such as 400 rpm, 500 rpm, 600 rpm, 700 rpm, or 800 rpm, or other values within the range of 400 rpm to 800 rpm.

[0120] The above stirring speed is fast, which is beneficial to further loosen the structure of the agglomerates, reduce the particle size, and further improve the transformation efficiency in the transformation stage, so as to obtain crystal grains with uniform particle size and high crystallinity, and reduce the agglomeration of primary particles.

[0121] In some embodiments, the aging transformation includes: dispersing the amorphous iron phosphate precipitate in an aging solution to perform a transformation reaction.

[0122] The aging solution is a phosphoric acid solution containing a surfactant.

[0123] The feeding ratio of the amorphous iron phosphate precipitate to the aging solution can be 1 g:100 mL to 1 g:300 mL, such as 1 g:100 mL, 1 g:150 mL, 1 g:200 mL, 1 g:250 mL or 1 g:300 mL, etc., or other values within the range of 1 g:100 mL to 1 g:300 mL. The amorphous iron phosphate precipitate is calculated as wet material, and the solid content is 80wt%-90wt%.

[0124] The pH value of the above-mentioned aging solution can be 1-2.5, such as 1, 1.5, 2 or 2.5, etc., or other values within the range of 1-2.5.

[0125] The concentration of the surfactant contained in the aging solution can be 1wt%-5wt%, such as 1wt%, 2wt%, 3wt%, 4wt% or 5wt% etc., or other values within the range of 1wt%-5wt%.

[0126] As an enumeration, the surfactant can include at least one of lignin sulfonate and naphthalene sulfonate formaldehyde condensate. The lignin sulfonate exemplarily but non-limitingly can include at least one of sodium lignin sulfonate and ammonium lignin sulfonate. The naphthalene sulfonate formaldehyde condensate exemplarily but non-limitingly can include at least one of β-naphthalene sulfonate sodium formaldehyde condensate, benzyl naphthalene sulfonate sodium formaldehyde condensate, α-methyl naphthalene sulfonate sodium formaldehyde condensate and alkyl benzene sulfonate sodium formaldehyde condensate.

[0127] By adding an anionic polymer surfactant in the transformation stage, the anion is adsorbed on the surface of the positively charged iron phosphate particles, and the electrostatic effect and steric hindrance effect inhibit the agglomeration between the particles and induce the primary particles to be spherical crystals, which is beneficial to make the structure of the secondary particles more loose; in addition, since the surfactant contains a large number of benzene ring rigid structures, it can increase the looseness of the iron phosphate material as a pore-forming agent during calcination.

[0128] In some embodiments, the temperature of the transformation reaction can be 80℃-90℃, such as 80℃, 85℃ or 90℃, etc., or other values within the range of 80℃-90℃.

[0129] The time of the crystal transformation reaction can be 1 h to 3 h, such as 1 h, 1.5 h, 2 h, 2.5 h, or 3 h, and can also be other values in the range of 1 h to 3 h.

[0130] The stirring rate of the crystal transformation reaction can be 100 rpm to 300 rpm, such as 100 rpm, 150 rpm, 200 rpm, 250 rpm, or 300 rpm, and can also be other values in the range of 100 rpm to 300 rpm.

[0131] The stirring rate of the aging crystal transformation reaction is controlled at a low level to avoid the intensification of particle aggregation caused by violent collision between particles.

[0132] After the crystal transformation reaction is completed, filtration and washing are performed, and the filter residue is dried.

[0133] The above drying can be performed by normal pressure oven drying, vacuum oven drying, or spray drying. In some embodiments, the powder is dried by spray drying, which is beneficial to reducing the degree of powder aggregation.

[0134] In some embodiments, the calcination temperature can be 600℃ to 750℃, such as 600℃, 650℃, 700℃, or 750℃, and can also be other values in the range of 600℃ to 750℃.

[0135] The calcination time can be 2 h to 3 h, such as 2 h, 2.5 h, or 3 h, and can also be other values in the range of 2 h to 3 h.

[0136] The heating rate during calcination can be 3℃ / min to 5℃ / min, such as 3℃ / min, 3.5℃ / min, 4℃ / min, 4.5℃ / min, or 5℃ / min, and can also be other values in the range of 3℃ / min to 5℃ / min.

[0137] As described above, the present disclosure uses ferrous salt as the iron source to prepare the iron phosphate material by the oxidation precipitation crystallization method. In the preparation process, various means are used to control the morphology, particle size and distribution of the primary particles and the aggregation structure of the secondary particles of the iron phosphate material, so that the primary particles are approximately spherical, the particle size range is 20 nm to 600 nm and the distribution is relatively uniform, the secondary particle structure is loose, the D 50 The hardness index of the iron phosphate material is ≤5.

[0138] In addition, the present disclosure also provides a positive electrode material, which is prepared by mixing and sintering the above-mentioned iron phosphate material with a lithium source and a carbon source.

[0139] The lithium source can exemplarily but non-limitingly include lithium carbonate, and the carbon source can exemplarily but non-limitingly include glucose.

[0140] In some of the listed embodiments, the cathode material can be prepared by the following method: Iron phosphate material is mixed with lithium carbonate and glucose at a molar ratio of n(iron element in iron phosphate material):n(Li):n(glucose) = 1:1.04:0.05 to obtain a mixed raw material; the mixed raw material is mixed with ethanol and ground in a grinder for 6 hours to obtain a slurry; the slurry is dried in a vacuum oven at 80°C for 4 hours to obtain a dry material; the dry material is calcined at 750°C for 9 hours under a nitrogen atmosphere, and after sieving, the lithium iron phosphate cathode material is obtained.

[0141] In some implementations, the D of the positive electrode material 50 The value can be 0.87μm to 1.17μm, such as 0.87μm, 0.95μm, 1.05μm, 1.11μm, 1.12μm, 1.14μm or 1.17μm, or other values ​​within the range of 0.87μm to 1.17μm.

[0142] In some embodiments, the specific surface area of ​​the cathode material is 12.13 cm². 2 / g~12.85cm 2 / g, such as 12.13cm 2 / g, 12.21cm 2 / g, 12.28cm 2 / g, 12.47cm 2 / g, 12.67cm 2 / g, 12.85cm 2 / g or 13.24cm 2 / g, etc., can also be 12.13cm. 2 / g~12.85cm 2 Other values ​​within the / g range.

[0143] In some embodiments, the 0.1C charging specific capacity of the cathode material is not less than 161.5 mAh / g, for example, it can be 161.7 mAh / g to 163.5 mAh / g, such as 161.7 mAh / g, 162.2 mAh / g, 162.7 mAh / g, 162.8 mAh / g, 163.2 mAh / g or 163.5 mAh / g, or other values ​​within the range of 161.7 mAh / g to 163.5 mAh / g.

[0144] In some embodiments, the 0.1C discharge specific capacity of the positive electrode material is not less than 158.5 mAh / g, for example, can be 158.8 mAh / g-161.6 mAh / g, such as 158.8 mAh / g, 159.0 mAh / g, 159.4 mAh / g, 161.3 mAh / g, 161.5 mAh / g or 161.6 mAh / g, etc., and can also be other values in the range of 158.8 mAh / g-161.6 mAh / g.

[0145] In some embodiments, the 1C discharge specific capacity of the positive electrode material is not less than 143.0 mAh / g, for example, can be 143.3 mAh / g-149.0 mAh / g, such as 143.3 mAh / g, 144.1 mAh / g, 144.8 mAh / g, 147.3 mAh / g, 148.1 mAh / g, 148.8 mAh / g or 149.0 mAh / g, etc., and can also be other values in the range of 143.3 mAh / g-149.0 mAh / g.

[0146] In addition, the present disclosure also provides a positive electrode sheet, wherein the active material in the positive electrode sheet comprises the positive electrode material described above.

[0147] The present disclosure also provides a battery cell comprising the positive electrode sheet described above.

[0148] As an example, the battery cell described above can be used in, but is not limited to, an electric device such as a vehicle, a ship or an aircraft.

[0149] The present disclosure also provides a battery comprising the battery cell described above.

[0150] The present disclosure also provides an electric device comprising the battery cell and / or the battery described above. As an example, the electric device can be, but is not limited to, a mobile phone, a tablet, a notebook computer, an electric toy, an electric tool, an electric vehicle, an electric car, a ship, a spacecraft, etc. Among them, the electric toy can include a fixed or mobile electric toy, for example, a game console, an electric car toy, an electric ship toy and an electric aircraft toy, etc., and the spacecraft can include an airplane, a rocket, a space shuttle and a spacecraft, etc.

[0151] The features and performances of the present disclosure are further described in detail below in combination with examples.

[0152] Example 1

[0153] The present example provides an anhydrous iron phosphate, and a preparation method thereof comprises:

[0154] Step (1): A mixed solution was prepared according to the ratio of the iron source and the phosphorus source, n(P):n(Fe) = 1.3:1, wherein the iron source was ferrous sulfate heptahydrate aqueous solution with a ferrous ion concentration of 1.5 mol / L, and the phosphorus source was phosphoric acid solution with a phosphate ion concentration of 1.92 mol / L.

[0155] Step (2): The mixed solution, hydrogen peroxide with a concentration of 0.6 mol / L, and ammonia water with a concentration of 2 mol / L were added into the reactor by constant flow pumps, the flow rate of the mixed solution and the hydrogen peroxide was 120 mL / h, and the flow rate of the ammonia water was controlled to maintain the pH of the reaction solution at 1.2±0.1, and the temperature was controlled to maintain at 60℃ during the reaction, the reaction time was 2 h, and the stirring speed was 600 rpm. After the reaction, the amorphous ferric phosphate precipitate (wet material, solid content of 87.6 wt%) was obtained by filtration and washing with deionized water.

[0156] The mixed solution was introduced into the reactor after being acted on by the micro-bubble generator and air, the micro-nano bubble generator generated bubbles with a particle size of 200 nm-4.0 μm, and the bubble content was 20 vol%.

[0157] Step (3): The amorphous ferric phosphate precipitate was uniformly dispersed in the aging solution for aging and crystallization reaction, and then filtered and washed with deionized water. The filter residue was taken for spray drying to obtain ferric phosphate dihydrate crystals.

[0158] The aging solution was ammonium lignosulfonate-containing phosphoric acid solution, the pH value of the aging solution was 2, the concentration of the ammonium lignosulfonate in the aging solution was 2.5 wt%, the feeding ratio of the amorphous ferric phosphate precipitate to the aging solution was 1 g:200 mL, the temperature of the aging and crystallization reaction was 90℃, the time was 2 h, and the stirring speed was 200 rpm.

[0159] Step (4): The ferric phosphate dihydrate crystals were calcined to obtain anhydrous ferric phosphate.

[0160] The calcination temperature was 700℃, the heating rate was 4℃ / min, and the calcination time was 2 h.

[0161] Example 2

[0162] The difference between this example and Example 1 was that the concentration of the ammonium lignosulfonate in the aging solution was 1 wt%.

[0163] Example 3

[0164] The difference between this example and Example 1 was that the concentration of the ammonium lignosulfonate in the aging solution was 5 wt%.

[0165] Example 4

[0166] The difference between this embodiment and embodiment 1 is that the micro-nano bubble generator generates bubbles with a particle size of 200 nm to 4.0 μm, and the bubble content is 10 vt%.

[0167] Embodiment 5

[0168] The difference between this embodiment and embodiment 1 is that the micro-nano bubble generator generates bubbles with a particle size of 200 nm to 4.0 μm, and the bubble content is 30 vt%.

[0169] Embodiment 6

[0170] The embodiment provides anhydrous ferric phosphate, and a preparation method thereof comprises the following steps:

[0171] Step (1): a mixed solution is prepared according to the feeding ratio of an iron source and a phosphorus source, that is, n(P):n(Fe) is 1.05:1, wherein the iron source is a ferrous chloride aqueous solution with a ferrous ion concentration of 0.8 mol / L, and the phosphorus source is a sodium dihydrogen phosphate solution with a phosphate ion concentration of 0.85 mol / L.

[0172] Step (2): the mixed solution, sodium hypochlorite with a concentration of 1 mol / L and sodium hydroxide solution with a concentration of 1 mol / L are added into a reaction kettle by a constant flow pump, the flow rate of the mixed solution and the sodium hypochlorite is 200 mL / h, the flow rate of the sodium hydroxide solution is controlled according to the control of the pH of the reaction solution to be 1.1±0.1, the temperature in the reaction process is controlled to be 70 DEG C, the reaction time is 1 h, and the stirring speed is 400 rpm. After the reaction is completed, filtration is carried out, and then the amorphous ferric phosphate precipitate (wet material, solid content is 88.1 wt%) is obtained after washing with deionized water.

[0173] The mixed solution is subjected to air action through a micro-bubble generator and then enters the reaction kettle, the micro-nano bubble generator generates bubbles with a particle size of 200 nm to 4.0 μm, and the bubble content is 30 vt%.

[0174] Step (3): the amorphous ferric phosphate precipitate is uniformly dispersed in the aging solution for an aging and crystallization reaction, after the reaction is completed, filtration is carried out and then washing is carried out with deionized water, and then the filter residue is vacuum dried at 100 DEG C for 12 h, so that the ferric phosphate dihydrate crystal is obtained.

[0175] The aging solution is a phosphoric acid solution containing a sodium beta-naphthalenesulfonate formaldehyde condensate, the pH value of the aging solution is 1, the concentration of the sodium beta-naphthalenesulfonate formaldehyde condensate in the aging solution is 2.5 wt%, the feeding ratio of the amorphous ferric phosphate precipitate and the aging solution is 1 g:300 mL, the temperature of the aging and crystallization reaction is 80 DEG C, the time is 1 h, and the stirring speed is 100 rpm.

[0176] Step (4): the ferric phosphate dihydrate crystal is calcined, so that the anhydrous ferric phosphate is obtained.

[0177] The calcination temperature was 700℃, the heating rate was 4℃ / min, and the calcination time was 2h.

[0178] Example 7

[0179] Step (1): A mixed solution was prepared according to the feeding ratio of iron source and phosphorus source, n(P):n(Fe) = 1.5:1, wherein the iron source was a ferrous ion concentration of 2 mol / L ferrous nitrate aqueous solution, and the phosphorus source was an ammonium monohydrogen phosphate solution with a phosphate ion concentration of 3 mol / L.

[0180] Step (2): The above mixed solution, ammonium persulfate with a concentration of 0.8 mol / L, and ammonia water with a concentration of 4 mol / L were added into the reaction kettle by constant flow pump, the flow rate of the mixed solution and ammonium persulfate was 150 mL / h, and the flow rate of ammonia water was controlled according to the control of the pH of the reaction solution to maintain at 1.5±0.1, and the temperature was controlled to maintain at 50℃ during the reaction process, the reaction time was 4h, and the stirring speed was 800rpm. After the reaction was completed, filtration was carried out, and then the amorphous iron phosphate precipitate (wet material, solid content was 85.9wt%) was obtained after washing with deionized water.

[0181] The mixed solution was introduced into the reaction kettle after being acted on by air through a micro-bubble generator, the micro-nano bubble generator generated bubbles with a particle size of 200nm-4.0μm, and the bubble content was 20vt%.

[0182] Step (3): The amorphous iron phosphate precipitate was uniformly dispersed in the aging solution for aging and crystallization reaction, and then filtration was carried out after the reaction was completed, and the filter residue was washed with deionized water, and then the filter residue was vacuum dried at 100℃ for 12h to obtain iron phosphate dihydrate crystals.

[0183] The aging solution was a phosphoric acid solution containing sodium α-methylnaphthalene sulfonate formaldehyde condensate, the pH value of the aging solution was 1, the concentration of the sodium α-methylnaphthalene sulfonate formaldehyde condensate in the aging solution was 1wt%, the feeding ratio of the amorphous iron phosphate precipitate to the aging solution was 1g:100mL, the temperature of the aging and crystallization reaction was 80℃, the time was 3h, and the stirring speed was 300rpm.

[0184] Step (4): The iron phosphate dihydrate crystals were calcined to obtain anhydrous iron phosphate.

[0185] The calcination temperature was 700℃, the heating rate was 4℃ / min, and the calcination time was 2h.

[0186] Comparative Example 1

[0187] The difference between this comparative example and Example 1 was that air was introduced into the liquid phase of the reaction kettle in the form of ordinary air inlet, and the flow rate was 1mL / min.

[0188] Comparative Example 2

[0189] The difference between this comparative example and Example 1 is that sodium hexadecyl benzene sulfonate is used instead of ammonium lignosulfonate.

[0190] Comparative Example 3

[0191] The difference between this comparative example and Example 1 is that hydroxymethyl cellulose is used instead of ammonium lignosulfonate.

[0192] Comparative Example 4

[0193] The difference between this comparative example and Example 1 is that the aging solution does not contain a surfactant.

[0194] Comparative Example 5

[0195] The difference between this comparative example and Example 1 is that the oxidizing agent is only hydrogen peroxide and does not contain air.

[0196] Comparative Example 6

[0197] The difference between this comparative example and Example 1 is that the stirring rate of the crystallization conversion reaction in step (3) is 400 rpm.

[0198] Test Example 1

[0199] The iron phosphate materials prepared in Examples 1-7 and Comparative Examples 1-6 were subjected to the following performance tests.

[0200] (1) The microstructure of the material was observed using a JEOL JSM-6490LV scanning electron microscope, and the particle size and average aspect ratio of primary particles of the scanning electron microscope image were measured using ImageJ. The average diameter of the primary particles is the number average of the equivalent particle diameter of the primary particles, and the equivalent particle diameter refers to the diameter of a spherical shape having an equal volume to the primary particle. The average aspect ratio of the primary particles refers to the ratio of the average length of the longest axis to the average length of the shortest axis of the primary particles. The average length of the longest axis is the sum of the lengths of the longest axes of the primary particles divided by the number of primary particles, and the longest axis refers to the length of the longest diagonal in the image. The average length of the shortest axis is the sum of the lengths of the shortest axes of the primary particles divided by the number of primary particles, and the longest axis refers to the length of the shortest diagonal in the image. The number of measurement samples of primary particles for each sample is 50, which is randomly selected.

[0201] (2) Particle size D 50 : Tested using an MS3000 laser particle size analyzer.

[0202] (3) Specific surface area and specific pore volume determination: According to GB / T 21650.2-2008 "Porous Solid Materials - Determination of Pore Volume and Surface Area - Gas Adsorption Method - Analysis of Mesopores and Macropores". The nitrogen adsorption-desorption curve was obtained by testing the powder sample with an Autosorb IQ2 full-automatic specific surface area pore size analyzer, the temperature condition was constant temperature-196℃, and the pressure condition was 0.005 MPa-0.100 MPa; the specific surface area was calculated by the BET formula and the specific pore volume was calculated by the BJH model based on the data in the middle-low pressure stage.

[0203] (4) Grinding efficiency determination: The same mass of anhydrous iron phosphate was subjected to dry ball milling, and the particle size was measured at several time points and the particle size distribution width span = (D 90 -D 10 ) / D 50 was calculated. The ball milling conditions were as follows: the frequency was 30 Hz, the zirconia beads with a size of 1 mm were used, the volume ratio of the zirconia beads to the anhydrous iron phosphate was 1:1, and the rotation speed was 600 rpm.

[0204] (5) XRD: The X-ray powder diffractometer (XRD, Rigaku D / max-2600PC, Japan) was used to study the crystal phase and crystal structure of the material, and Cu K α radiation was used during the test, the wavelength λ was 0.154056 nm, the voltage was 40 kV, the current was 40 mA, and the scanning range 2θ was 10° to 80°. The XRD test results were analyzed using Jade 6 software.

[0205] (6) The Fe and P contents in FePO3·2H2O were tested by titration analysis, as follows: the sample was completely dissolved with hydrochloric acid, Fe 3+ was reduced to Fe 2+ by SnCl2solution, a saturated solution of mercuric chloride was added, the indicator was sodium diphenylamine sulfonate, and K2Cr2O7standard solution was used for titration to calculate the iron content of the sample. The sample was dissolved with hydrochloric acid, quinoline molybdate reagent and nitric acid were added, at this time, yellow precipitate was produced, after filtration, the precipitate was dissolved with NaOH, and the excess NaOH was titrated with HCl to calculate the phosphorus content of the sample.

[0206] The test results are shown in FIGS. 1 to 6, Table 1 and Table 2.

[0207] As can be seen from FIGS. 1 to 5, the primary particles of the anhydrous iron phosphate prepared in Example 1 are spherical, have uniform particle sizes, and have an average particle size of about 400 nm, and the agglomeration of the primary particles is relatively loose. In Comparative Example 1, air is introduced in a common way, and the obtained particles have poor uniformity, and thus the agglomeration is more compact than that in Example 1; in Comparative Example 2, sodium dodecyl benzene sulfonate is used as a surfactant, and the obtained crystal particles have a large particle size, with an average particle size of about 800 nm, and the electrochemical performance is poor due to the excessively large particle size, because although the sodium dodecyl benzene sulfonate can be electrostatically adsorbed on the surface of the crystal particles to control the crystal morphology, the provided steric hindrance effect is low, and the growth and agglomeration of the particles cannot be inhibited; in Comparative Example 3, sodium hydroxymethyl cellulose is used as a surfactant, and the obtained primary particles are spherical, but have poor size uniformity, and the agglomeration is serious, because the overall polarity of the sodium hydroxymethyl cellulose is relatively uniform, and thus the dispersibility of the crystal particles is poor; in Comparative Example 4, no surfactant is added, and the obtained primary particles are disc-shaped and have serious agglomeration.

[0208] As can be seen from FIG. 6, the standard pattern of each sample is consistent with that of FePO4·2H2O (PDF #33-0666) in a monoclinic system, indicating that the addition of the surfactant has no effect on the structure of the iron phosphate dihydrate; however, the peak value of the main peak of the diffraction peak of Example 1, Comparative Examples 2 and 3 is higher, and the half-peak width is reduced, and the crystallinity of the product is improved, indicating that the addition of the surfactant can improve the crystallinity of the material; the crystallinity of Comparative Example 1 is low, because the gaseous oxidant is introduced in a common way, and cannot play a role in loosening the amorphous agglomerates, and the obtained amorphous agglomerates have a large particle size, and in the subsequent crystal transformation stage, part of the amorphous substance remains in the crystal, resulting in a decrease in the crystallinity.

[0209] Table 1: Test results

[0210] Table 2: Test results

[0211] As can be seen from Tables 1 and 2:

[0212] The surfactants provided in the embodiments of the present disclosure have similar effects on the morphology control of the iron phosphate dihydrate, and can obtain nearly spherical primary particles, and play a steric hindrance effect to inhibit the agglomeration of the primary particles. In Examples 1 to 3, different amounts of surfactants are added, and when the amount of the surfactant is small, the average length-to-short-axis ratio of the primary particles is large; when the amount of the surfactant is large, the average length-to-short-axis ratio of the primary particles decreases, but the particle size of the primary particles decreases, resulting in an increase in the specific surface area, which is conducive to agglomeration, and thus the specific pore volume decreases. Although the hardness index of Example 3 is smaller than that of Examples 1 to 2, the particle size of Example 3 is the smallest, resulting in a poorer grinding effect (the smaller the Span, the poorer the grinding effect) than that of Examples 1 and 2.

[0213] The difference between Examples 1, 4 and 5 is the bubble content of the mixed solution after passing through the micro-nano bubble generator. Comparative Example 1 uses a common aeration method to add air. When the bubble content is low or the air is added in a common way, the bubble has a poorer loosening effect on the agglomerates, and the obtained agglomerates have a larger volume, and the crystal transformation efficiency is lower in the crystal transformation stage. On the one hand, part of the amorphous is left in the crystal, resulting in a lower crystallinity (poor electrochemical performance); on the other hand, the initial formed crystal nucleus is less, the crystal grain size is large, and the combination is tight, which is not conducive to grinding, so the span is low. When the bubble content is too high, the primary particles become small, which is also not conducive to grinding, so the span of Example 1 is the highest.

[0214] Examples 1 and Comparative Examples 2, 3 and 4 are single-factor tests of surfactants. Comparative Example 2 uses a small-molecule surfactant, which has a poor steric hindrance effect, so the primary particle size obtained is large, and the specific surface area decreases. However, because the primary particle size is large and the distribution is uniform, the specific pore volume is smaller than that of Example 1. In addition, because the primary particle size is too large, the lithium iron phosphate particles obtained under the same grinding conditions are also large, and the electrochemical performance decreases. Although Comparative Example 3 is a high-molecular surfactant, the polarity of the molecular chain is low, the dispersibility of the particles is poor, and the steric hindance effect is not as good as that of Example 1. Therefore, the iron phosphate dihydrate particles obtained have a wide particle size distribution, a high bulk density, a low specific pore volume, a low grinding efficiency, and a low span. In addition, the secondary particles formed are large, so the particles obtained after grinding are still large, resulting in a large D 50 of the lithium iron phosphate, and low chemical performance. Comparative Example 4 does not add a surfactant, and the primary particles obtained are disc-shaped, so the BET is large. Because the diameter is too large, the hardness index is high, the grinding efficiency is low, the D 50 of the sintered iron phosphate is large, so the chemical performance is low.

[0215] Test Example 2

[0216] The lithium iron phosphate materials obtained in Examples 1 to 7 and Comparative Examples 1 to 6 are mixed with lithium carbonate and glucose according to a molar ratio of n (iron element in the lithium iron phosphate material): n (Li): n (glucose) = 1: 1.04: 0.05 to obtain a mixed raw material. The mixed raw material is mixed with ethanol and ground in a grinding machine for 6 h to obtain a slurry. The slurry is dried in a vacuum oven at 80°C for 4 h to obtain a dry material. The dry material is calcined at 750°C for 9 h under a nitrogen atmosphere, and after screening, a lithium iron phosphate positive electrode material is obtained.

[0217] The positive electrode materials above were mixed into a uniform slurry according to a mass ratio of positive electrode material: acetylene black: PVDF = 75: 15: 10, and uniformly coated on an aluminum foil substrate as a positive electrode of a simulated battery. Lithium pieces were used as the negative electrode of the simulated battery, a polypropylene porous membrane was used as the separator, and the electrolyte was 1 mol LiPF6 dissolved in 1 L of a mixed solvent of EC and DMC (volume ratio 1:1). The positive electrode, negative electrode, electrolyte, and separator were assembled into a battery in an argon glove box.

[0218] The LAND battery test system was used for the constant current charge and discharge and cycle performance test of the battery, and the charge and discharge voltage range was 2.5 V to 4.2 V at 25°C.

[0219] The electrochemical performance test results of the positive electrode materials are shown in Table 3.

[0220] Table 3 test results

[0221] As can be seen from Table 3, the positive electrode materials prepared from the various phosphorus iron materials provided by the embodiments of the present disclosure can have a higher charge and discharge specific capacity.

[0222] In summary, by limiting the primary particle equivalent particle diameter, the secondary particle D 50 and the hardness index of the phosphorus iron material to a specific range, the phosphorus iron material that meets the above characteristics has a loose structure and a lower overall hardness, which can improve the efficiency of grinding with a lithium source when used to prepare a positive electrode material, has less wear on the machine, and the prepared positive electrode material has good electrochemical performance, which is conducive to further preparing batteries and electrical devices with excellent electrochemical performance, and the like. Industrial applicability

[0223] The phosphorus iron material provided by the embodiments of the present disclosure has a loose structure and a lower overall hardness, which can improve the efficiency of grinding with a lithium source when used to prepare a positive electrode material, has less wear on the machine, and the prepared positive electrode material has good electrochemical performance, which is conducive to further preparing batteries and electrical devices with excellent electrochemical performance, and the like.

Claims

1. An iron phosphate material, characterized in that, The iron phosphate material is secondary particles formed by agglomeration of primary particles, the equivalent particle diameter of the primary particles is 20 nm to 600 nm, the equivalent particle diameter is the diameter of a standard sphere having the same volume as the primary particles; the D 50 of the secondary particles is 5 μm to 20 μm; The hardness index of the iron phosphate material has a value < 5; the wherein V represents the average length-to-minor axis ratio of the primary particles, where the average length-to-minor axis ratio is the ratio of the average length of the longest axis to the average length of the shortest axis of the primary particles. p The specific pore volume of the iron phosphate material is expressed in cm³. 3 / g.

2. The iron phosphate material of claim 1, wherein, The iron phosphate material is an anhydrous iron phosphate material.

3. The iron phosphate material according to claim 1 or 2, characterized in that, V of the iron phosphate material is 0.3 cm / g p 0.3 cm / g 3 0.3 cm / g 3 0.3 cm / g.

4. The iron phosphate material according to any one of claims 1 to 3, characterized in that The average ratio of long axis to short axis of the primary particles is not more than 3.

5.

5. The iron phosphate material according to any one of claims 1 to 4, characterized in that, The hardness index of the iron phosphate material is 0.98-3.

57.

6. The iron phosphate material according to any one of claims 1 to 5, characterized in that, The equivalent particle diameter of the primary particles is 254 nm-411 nm.

7. The iron phosphate material according to any one of claims 1 to 6, characterized in that, The secondary particles' D 50 The range is 8.74 μm to 10.28 μm.

8. A method for producing the iron phosphate material according to any one of claims 1 to 7, characterized by, The method comprises the following steps: mixing an iron source solution and a phosphorus source solution to form a mixed solution, and then mixing the mixed solution with an oxidizing agent and a pH regulator after the mixed solution is subjected to air action by a micro-bubble generator, and performing a synthesis reaction; collecting an amorphous iron phosphate precipitate obtained by the reaction; performing aging and crystallization on the amorphous iron phosphate precipitate to obtain iron phosphate dihydrate crystals; and performing calcination on the iron phosphate dihydrate crystals to obtain an anhydrous iron phosphate material. The oxidizing agent comprises at least one of hydrogen peroxide, ozone, sodium persulfate, ammonium persulfate, sodium hypochlorite, sodium ferrate and oxygen. The aging and crystallization comprises: dispersing the amorphous iron phosphate precipitate in an aging solution to perform a crystallization reaction. The aging solution is a phosphoric acid solution containing a surfactant. The surfactant comprises at least one of lignin sulfonate and naphthalene sulfonate formaldehyde condensate; the lignin sulfonate comprises at least one of sodium lignin sulfonate and ammonium lignin sulfonate; and the naphthalene sulfonate formaldehyde condensate comprises at least one of beta-naphthalene sulfonate sodium formaldehyde condensate, benzyl naphthalene sulfonate sodium formaldehyde condensate, alpha-methyl naphthalene sulfonate sodium formaldehyde condensate and alkyl benzene sulfonate sodium formaldehyde condensate. The stirring rate of the crystallization reaction is 100 rpm-300 rpm.

9. The production method according to claim 8, characterized by, The synthesis reaction comprises at least one of the following characteristics: Characteristic 1: the iron source solution is a soluble ferrous salt solution; Characteristic 2: the phosphorus source comprises at least one of phosphoric acid, sodium dihydrogen phosphate, sodium monohydrogen phosphate, ammonium dihydrogen phosphate and ammonium monohydrogen phosphate; Characteristic 3: the pH regulator comprises at least one of ammonia, sodium hydroxide, sulfuric acid, hydrochloric acid and nitric acid.

10. The production method according to claim 8 or 9, characterized by, The synthesis reaction further comprises at least one of the following characteristics: Characteristic 4: the concentration of the iron source solution is 0.8 mol / L-1.5 mol / L; Characteristic 5: the concentration of the phosphorus source solution is 0.85 mol / L-3 mol / L.

11. The method of any one of claims 8 to 10, wherein the method further comprises, The iron source and the phosphorus source are fed in a ratio of the amount of substance of P to the amount of substance of Fe of 1.05:1 to 1.5:

1.

12. The method of any one of claims 8 to 11, wherein, The total amount of the air and the oxidizing agent is not less than the theoretical amount to oxidize Fe in the iron source to Fe 2+ to the amount of Fe 3+ in the iron source.

13. The method of any one of claims 8 to 12, wherein the method further comprises, The synthesis reaction further comprises at least one of the following characteristics: Characteristic 6: the pH value of the synthesis reaction is 1-2.5; Characteristic 7: the temperature of the synthesis reaction is 50°C-70°C; Characteristic 8: the time of the synthesis reaction is 1 h-4 h; Characteristic 9: the stirring speed of the synthesis reaction is 400 rpm-800 rpm.

14. The method of any one of claims 8 to 13, wherein, The crystallization reaction comprises at least one of the following characteristics: Characteristic 10: the pH value of the aging solution is 1-2.5; Characteristic 11: the concentration of the surfactant contained in the aging solution is 1 wt%-5 wt%; Characteristic 12: the feeding ratio of the amorphous iron phosphate precipitate to the aging solution is 1 g:100 mL to 1 g:300 mL.

15. The method of any one of claims 8 to 14, wherein the method further comprises, The crystallization reaction further comprises at least one of the following characteristics: Characteristic 13: the temperature of the crystallization reaction is 80°C-90°C; Feature 14: the time of the crystallization reaction is 1h-3h.

16. The method of any one of claims 8 to 15, wherein, The calcination comprises at least one of the following features: Feature 15: the temperature of the calcination is 600℃-750℃; Feature 16: the time of the calcination is 2h-3h; Feature 17: the heating rate during the calcination is 3℃ / min-5℃ / min.

17. A positive electrode material, characterized in that, The positive electrode material is prepared by mixing and sintering the iron phosphate material according to any one of claims 1-7 with a lithium source and a carbon source.

18. The cathode material of claim 17, wherein, The positive electrode material has at least one of the following features: Feature 18: D50 of the positive electrode material is 0.87 pm to 1.17 pm 50 0.87 pm to 1.17 pm; Feature 19: The specific surface area of the positive electrode material is 12.13 cm 2 / g ~ 12.85 cm 2 / g; Feature 20: the specific charge capacity of the positive electrode material at 0.1C is not less than 161.5mAh / g; Feature 21: the specific discharge capacity of the positive electrode material at 0.1C is not less than 158.5mAh / g; Feature 22: the specific discharge capacity of the positive electrode material at 1C is not less than 143.0mAh / g.

19. A positive electrode sheet characterized by comprising: The active material in the positive electrode sheet comprises the positive electrode material according to claim 17 or 18.

20. A battery, characterized by The battery contains the positive electrode sheet according to claim 19.

Images