Iron phosphate and preparation method therefor, lithium iron phosphate and use thereof

Abstract

The present application discloses an iron phosphate and a preparation method therefor, a lithium iron phosphate and use thereof. The iron phosphate of the present application has a crystallinity of 90% to 100% and a specific surface area of 15 m2 / g to 20 m2 / g. The lithium iron phosphate which is made from the iron phosphate of the present application has excellent low-temperature performance, and the capacity retention rate of button cell is greater than 70% at -20℃.

Description

[0001]IRON PHOSPHATE AND PREPARATION METHOD THEREFOR, LITHIUM IRON PHOSPHATE AND USE THEREOF FIELD OF THE INVENTION The present application relates to the technical field of cathode material precursors, in particular to an iron phosphate and a preparation method therefor, a lithium iron phosphate and use thereof. BACKGROUND OF THE INVENTION Iron phosphate is an important precursor for preparing lithium iron phosphate (LiFePO4). “Preparation of lithium iron phosphate from the iron phosphate route” has gradually developed into a mainstream process due to the simple process, high utilization of raw materials, good reproducibility, high activity of cathode materials, and increasingly mature production technology. The properties of iron phosphate largely determine the comprehensive performance of the prepared lithium iron phosphate. The lithium iron phosphate prepared by using the existing iron phosphate has poor low-temperature performance. SUMMARY OF THE INVENTION The present application provides an iron phosphate and a preparation method therefor, a lithium iron phosphate and use thereof, so as to solve the problem of poor low-temperature performance of lithium iron phosphate produced from iron phosphate. In a first aspect, the present application provides an iron phosphate, wherein the iron phosphate has a crystallinity of 90% to 100% and a specific surface area of 15 m2 / g to 20 m2 / g. In an optional embodiment, the iron phosphate has a crystallinity of greater than or equal to 92%; and / or, the iron phosphate has a specific surface area of greater than or equal to 16 m2 / g. In a second aspect, the present application provides a method for preparing an iron phosphate, comprising the following steps: S1, mixing an iron source, a phosphorus source and an alkaline substance in a reactor, performing a precipitation reaction under near-infrared light radiation, and performing solid-liquid separation to obtain a precipitate; S2, aging the precipitate, performing solid-liquid separation to obtain a solid, and drying the solid to obtain an aged product; and S3, calcining the aged product to obtain the iron phosphate; wherein, a rotating speed of a rotor in the reactor is 2,500 rpm to 3,000 rpm, optionally 2,600 rpm to 2,900 rpm, and a porous filler is fixed on the rotor; a molar amount of the alkaline substance is 60% to 100% of the molar amount of the iron source; and the iron source is a water-soluble ferrous salt. In an optional embodiment, the phosphorus source comprises at least one of ammonium dihydrogen phosphate, sodium dihydrogen phosphate and phosphoric acid; and / or the alkaline substance comprises at least one of ammonia, sodium hydroxide and sodium carbonate; and / or the iron source comprises at least one of ferrous sulfate heptahydrate and ferrous chloride; and / or the porous filler is made from plastic, ceramic or stainless steel. In an optional embodiment, S1 satisfies at least one of the following conditions: (1) a molar ratio of iron element in the iron source to phosphorus element in the phosphorus source is 1: (0.8 - 1.2); (2) the precipitation reaction is performed at a temperature of 20°C to 70 °C; and (3) the near-infrared light has a wavelength of 800 nm to 2,500 nm. In an optional embodiment, mixing an iron source, a phosphorus source and an alkaline substance in a reactor comprises: preparing an iron source and deionized water into a precursor solution; preparing a phosphorus source, an alkaline substance and deionized water into a mixed solution; and pumping the precursor solution and the mixed solution synchronously into the reactor; wherein a molar ratio of iron element in the iron source to phosphorus element in the phosphorus source pumped into the reactor per unit time is 1: (0.8 - 1.2). In an optional embodiment, the precursor solution has a concentration of 1 mol / L to 1.4 mol / L; and / or the precursor solution is pumped into the reactor at a flow rate of 80 mL / min to 160 mL / min; and / or the mixed solution is pumped into the reactor at a flow rate of 80 mL / min to 160 mL / min. In an optional embodiment, S2 comprises: mixing the precipitate with deionized water and an aging agent to obtain a slurry to be aged; stirring for reacting the slurry to be aged at 70°C to 95 °C for a time period of 2h to 4h to obtain an aged slurry; and performing solid-liquid separation to the aged slurry to obtain a solid, and drying the solid to obtain an aged product. In an optional embodiment, S2 satisfies at least one of the following conditions: (1) the aging agent is phosphoric acid; (2) the molar amount of the aging agent is 10% to 30% of the molar amount of the iron source; (3) a solid content of the slurry to be aged is 8wt% to 20wt%; wherein, the solid content of the slurry to be aged = theoretical weight of iron phosphate dehydrate / weight of slurry to be aged × 100%; (4) a stirring rate of the stirring for reacting is 300 rpm to 600 rpm; and (5) the drying is performed at 80 °C to 100 °C for a time period of 6 h to 10h. In an optional embodiment, in S3, the calcining is performed at 550°C to 650 °C for a time period of 2 h to 4h; optionally, a heating rate during calcining is 5 °C / min to 10 °C / min. In a third aspect, the present application also provides a lithium iron phosphate, which is made from the above iron phosphate or an iron phosphate prepared by the above method for preparing an iron phosphate. In a fourth aspect, the present application also provides a positive electrode plate, comprising: a positive electrode current collector, and a cathode active material layer provided on at least one side of the positive electrode current collector; wherein the cathode active material layer comprises said lithium iron phosphate. In a fifth aspect, the present application also provides a secondary battery, comprising said positive electrode plate. In a sixth aspect, the present application also provides a powered device, comprising said secondary battery. The technical solution of the present application has the following advantages. The iron phosphate provided in the present application has a crystallinity of 90% to 100% and a specific surface area of 15 m2 / g to 20 m2 / g. The lithium iron phosphate produced using the iron phosphate of the present application has excellent low-temperature performance. The capacity retention rate of the button cell is greater than 70% at -20℃. Capacity retention rate = discharge capacity at 1C (-20℃) / discharge capacity at 0.1C (25℃). BRIEF DESCRIPTION OF THE DRAWINGS In order to more clearly illustrate the technical solutions in the specific embodiments of the present application or prior art, the following will briefly introduce the accompanying drawings that need to be used in the description of specific embodiments or prior art, and it is obvious that the accompanying drawings in the following description are some of the embodiments of the present application, and that for those skilled in the art, other accompanying drawings can be obtained based on these drawings without creative work. FIG.1 is a flow chart of the process of the present application; FIG.2 shows a scanning electron micrograph of iron phosphate obtained in Example 1 and its specific surface area (BET); FIG.3 shows a scanning electron micrograph of iron phosphate obtained in Example 2 and its specific surface area (BET); FIG.4 shows a scanning electron micrograph of iron phosphate obtained in Example 5 and its specific surface area (BET); FIG.5 shows a scanning electron micrograph of iron phosphate obtained in Example 7 and its specific surface area (BET); FIG. 6 shows a scanning electron micrograph of iron phosphate obtained in Comparative Example 1 and its specific surface area (BET); FIG.7 shows a scanning electron micrograph of hydroxyl ammonium ferric phosphate obtained in Comparative Example 2 and its specific surface area (BET); FIG.8 shows a XRD spectrum of iron phosphate obtained in Example 1; FIG. 9 shows a XRD spectrum of hydroxyl ammonium ferric phosphate obtained in Comparative Example 2; FIG. 10 shows a schematic diagram of the near-infrared light coupling high-speed rotating porous filler reactor and nanobubble generation; and FIG. 11 shows a schematic diagram of the precipitation reaction process of iron phosphate by nanobubble-assisted oxidation. DETAILED DESCRIPTION OF THE INVENTION Reference will be made clearly and completely technical solutions in the embodiments of the present application with accompanying drawings. The embodiments described here are only part of the embodiments of the present application and are not all embodiments of the present application. Based on the embodiments of the present application, other embodiments obtained by those skilled in the art without creative work are within the scope of the present application. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present application belongs. The terms used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present application. The terms “comprise” and “include” and any variation thereof in the description and claims of the present application are intended to indicate a non-exclusive inclusion. In the description of the embodiments of the present application, the technical terms “first”, “second” and the like are only used for distinction between different objects and are not to be understood as indicating or implying relative importance or implicitly indicating a number, a particular order or a primary or secondary relationship of the technical features. In the description of the embodiments of the present application, “a plurality of” means two or more, unless specified otherwise. Reference to an “embodiment” herein means that a feature, structure or characteristic described in connection with the embodiment may be comprised in at least one embodiment of the present application. The “embodiment” in various places in the specification does not necessarily mean the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. One skilled in the art explicitly and implicitly understands that an embodiment described herein may be combined with other embodiments. Term “range” disclosed in the present application is defined in the form of a lower limit and an upper limit, a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The range defined in this way can be inclusive or exclusive, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is understood that ranges of 60-110 and 80-120 are also obtained. In addition, if the listed minimum values are 1 and 2, and if the listed maximum values are 3, 4 and 5, the ranges of 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5 may be obtained. In the present application, unless otherwise specified, the numerical range “a-b” means the abbreviated representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range “0-5” means that all the real numbers between “0-5” have been listed, and “0-5” is only the abbreviated representation of these numerical combinations. In addition, when a parameter is an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. In the description of the present application, the term “and / or”, which describes an associated relationship of associated objects, means that there may be three relationships, for example, A and / or B, which may mean that A exists alone, A and B exist at the same time, and B exists alone. A character “ / ” generally indicates that contextual objects are in an “or” relationship. The lithium iron phosphate prepared using the existing iron phosphate has relatively poor low-temperature performance. In order to solve the problems in the above related technology, the first aspect of the present application provides an iron phosphate having a crystallinity of 90% to 100% and a specific surface area of 15 m2 / g to 20m2 / g. The lithium iron phosphate produced using the iron phosphate of the present application has excellent low-temperature performance. For example, the present application provides an iron phosphate having a crystallinity of 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or 100%; for example, the present application provides an iron phosphate having a specific surface area of 15 m2 / g, 16 m2 / g, 17 m2 / g, 18 m2 / g, 19 m2 / g or 20 m2 / g. In an optional embodiment, the present application provides an iron phosphate having a crystallinity of greater than or equal to 92%; and / or, the present application provides an iron phosphate having a specific surface area of greater than or equal to 16 m2 / g. In a second aspect, the present application also provides a method for preparing an iron phosphate, comprising the following steps: S1, mixing an iron source, a phosphorus source and an alkaline substance in a reactor, performing a precipitation reaction under near-infrared light radiation, and performing solid-liquid separation to obtain a precipitate; S2, aging the precipitate, performing solid-liquid separation to obtain a solid, and drying the solid to obtain an aged product; and S3, calcining the aged product to obtain the iron phosphate; wherein a rotating speed of a rotor in the reactor is 2,500 rpm to 3,000 rpm, and a porous filler is fixed on the rotor; a molar amount of the alkaline substance is 60% to 100% of a molar amount of the iron source; and the iron source is a water-soluble ferrous salt. For example, the rotating speed of the rotor is 2,500 rpm, 2,600 rpm, 2,700 rpm, 2,800 rpm, 2,900 rpm, or 3,000 rpm; for example, the molar amount of the alkaline substance is 60%, 70%, 80%, 90%, or 100% of the molar amount of the iron source. Near-infrared light refers to electromagnetic waves with wavelengths ranging from 780 nm to 2,526 nm. Optionally, a device for generating near-infrared light in the experiment is a modulatable optical fiber laser coupled beam expander mirror device with a center wavelength of 980 nm. Based on the analysis of chemical process intensification theory at nano-micro scale, the present application proposes a method for preparing iron phosphate with high specific surface area and high crystallinity by using near-infrared light radiation-assisted intensification reaction at nano-micro scale. As shown in FIGS.10 and 11, according to the present application, high-density cavitation bubbles are generated through near-infrared light radiation and high-speed rotating porous filler to form a large number of nanobubbles with ultra-small particle diameters within the reaction solution, and by using hydroxyl radicals on the surface of the nanobubbles as an oxidizing agent, ferrous ions are instantly oxidized into ferric ions which reacted with the phosphorus source to precipitate, thereby obtaining iron phosphate precipitates adsorbed with nanobubbles on the surface. In the process section of aging and calcining, the migration, aggregation, and bursting process of the nanobubbles in the reaction solution prompts the formation of a large number of nano-microporous structures within the iron phosphate precipitates, thereby obtaining iron phosphate powder materials with high specific surface area and high crystallinity. The method of the present application can realize the continuous production of iron phosphate, which is easy to control the stability of product quality, and the produced iron phosphate material has a larger specific surface area and higher crystallinity. The crystallinity of iron phosphate of the present application is in a range from 90% to 100%. In the present application, the molar amount of the alkaline substance is 60% to 100% of the molar amount of the iron source. If the content of the alkaline substance is too high, it will lead to the result that the aged product obtained in S2 is not the required iron phosphate dihydrate, and the BET of the iron phosphate obtained after calcining will be decreased substantially, which is not in line with the practical requirements. In an optional embodiment, the phosphorus source comprises at least one of ammonium dihydrogen phosphate, sodium dihydrogen phosphate and phosphoric acid; and / or the alkaline substance comprises at least one of ammonia, sodium hydroxide and sodium carbonate; and / or the iron source comprises at least one of ferrous sulfate heptahydrate and ferrous chloride; and / or the porous filler is made from plastic, ceramic or stainless steel. Optionally, the porous filler has a pore diameter of 0.02 mm to 1 mm. In an optional embodiment, S1 satisfies at least one of the following conditions: (1) a molar ratio of iron element in the iron source to phosphorus element in the phosphorus source is 1: (0.8 - 1.2); for example, the molar ratio may be 1:0.8, 1:0.9, 1:1, 1:1.1 or 1:1.2; (2) the precipitation reaction is performed at a temperature of 20°C to 70 °C; for example, 20°C, 30°C, 40°C, 50°C, 60°C, or 70°C; and (3) the near-infrared light has a wavelength ranging from 800 nm to 2,500 nm. In an optional embodiment, mixing an iron source, a phosphorus source and an alkaline substance in a reactor comprises: preparing an iron source and deionized water into a precursor solution; preparing a phosphorus source, an alkaline substance and deionized water into a mixed solution; and pumping the precursor solution and the mixed solution synchronously into the reactor; wherein a molar ratio of iron element in the iron source to phosphorus element in the phosphorus source pumped into the reactor per unit time is 1: (0.8 - 1.2). In an optional embodiment, the precursor solution has a concentration of 1 mol / L to 1.4 mol / L; for example, 1 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, or 1.4 mol / L. In an optional embodiment, S2 comprises: mixing the precipitate with deionized water and an aging agent to obtain a slurry to be aged; stirring for reacting the slurry to be aged at 70°C to 95 °C for a time period of 2h to 4h to obtain an aged slurry; and performing solid-liquid separation to the aged slurry to obtain a solid, and drying the solid to obtain an aged product. For example, the stirring for reacting is performed at a temperature of 70°C, 80°C, 90°C or 95°C for 2h, 3h or 4h. In an optional embodiment, S2 satisfies at least one of the following conditions: (1) the aging agent is phosphoric acid; (2) the molar amount of the aging agent is 10% to 30% of the molar amount of the iron source; for example, 10%, 20%, 25%, or 30%; (3) a solid content of the slurry to be aged is 8wt% to 20wt%; for example, 10wt%, 15wt% or 20wt%; (4) a stirring rate of the stirring for reacting is in a range from 300 rpm to 600 rpm; for example, 300 rpm, 400 rpm, 500 rpm, or 600 rpm; and (5) the drying is performed at 80 °C to 100 °C for a time period of 6 h to 10h; for example, the drying is performed at a temperature of 80°C, 90°C or 100°C for a time period of 6h, 7h, 8h, 9h or 10h. In an optional embodiment, in S3, the calcining is performed at 550°C to 650 °C for 2 h to 4h; for example, the calcining is performed at a temperature of 550°C, 580°C, 600°C, 620°C or 650°C for a time period of 2h, 3h or 4h. optionally, a heating rate during calcining is in a range from 5 °C / min to 10 °C / min; for example, 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min, or 10°C / min. In a third aspect, the present application also provides a lithium iron phosphate, which is made from said iron phosphate or iron phosphate prepared by said method for preparing an iron phosphate. The lithium iron phosphate produced using the iron phosphate of the present application has excellent low-temperature performance. The capacity retention rate of the button cell is greater than 70% at -20℃. Capacity retention rate = discharge capacity at 1C (-20℃) / discharge capacity at 0.1C (25℃). In a fourth aspect, the present application provides a positive electrode plate, comprising: a positive electrode current collector, and a cathode active material layer provided on at least one side of the positive electrode current collector, wherein the cathode active material layer comprises said lithium iron phosphate. As an example, the positive electrode current collector has two surfaces facing in opposite directions along the thickness direction itself, and the cathode active material layer is provided on either or both of the two surfaces of the positive electrode current collector facing in opposite directions. In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, an aluminum foil may be used. The composite current collector may comprise a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metallic material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a substrate of a high molecular material such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc. In some embodiments, the positive electrode film layer optionally comprises a binder. As an example, the binder may comprise at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin. In some embodiments, the positive electrode film layer optionally comprises a conductive agent. As an example, the conductive agent may comprise at least one selected from superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the positive electrode plate may be prepared by: dispersing the above-mentioned components for preparing the positive electrode plate, such as the cathode active material, the conductive agent, the binder and any other components in a solvent (such as N-methyl pyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on the positive electrode current collector, and obtaining the positive electrode plate after drying, cold pressing and other processes. In a fifth aspect, the present application provides a secondary battery, comprising said positive electrode plate. The following illustrates the secondary battery of the present application. [Negative electrode plate] The negative electrode plate comprises a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector. The negative electrode film layer comprises an anode active material. As an example, the negative electrode current collector has two surfaces along a thickness direction thereof and facing in opposite directions, and the negative electrode film layer is provided on either or both of the two surfaces. In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, a copper foil may be used. The composite current collector may comprise a polymeric material substrate and a metal layer formed on at least one surface of the polymeric material substrate. The composite current collector may be formed by forming a metallic material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a substrate of a high molecular material such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc. In some embodiments, the anode active material may be an anode active material known in the art. As an example, the anode active material may comprise at least one selected from artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials and lithium titanate. The silicon-based material may be at least one selected from elemental silicon, silicon-oxygen compounds, silicon-carbon complexes, silicon-nitrogen complexes, and silicon alloys. The tin-based material may be at least one selected from elemental tin, tin oxide compounds, and tin alloys. The present application is not limited to these materials, and other materials that may be used as an anode active material for a battery may be used. These anode active materials may be used separately or in combination (for example two or more kinds of materials are used). In some embodiments, the negative electrode film layer optionally comprises a binder. The binder may be at least one selected from styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA) and carboxymethyl chitosan (CMCS). In some embodiments, the negative electrode film layer optionally comprises a conductive agent. The conductive agent may be at least one selected from superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the negative electrode film layer optionally comprises other adjuvants, such as thickeners (e.g. sodium carboxymethylcellulose (CMC-Na)). In some embodiments, the negative electrode plate may be prepared by: dispersing the above-mentioned components for preparing the negative electrode plate, such as the anode active material, the conductive agent, the binder and any other components in a solvent (such as deionized water) to form a negative electrode slurry; coating the negative electrode slurry on the negative electrode current collector, and obtaining the negative electrode plate after drying, cold pressing and other processes. [Electrolyte] The electrolyte serves to conduct ions between the positive electrode plate and the negative electrode plate. The kind of the electrolyte is not particularly limited in the present application, and may be selected according to requirements. For example, the electrolyte may be liquid, gel, or solid. In some embodiments, the electrolyte is an electrolyte solution. The electrolyte comprises an electrolyte salt and a solvent. In some embodiments, the electrolyte salt may comprise at least one selected from lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonimide, lithium bis-trifluoromethane sulfonimide, lithium triflate, lithium difluorophosphate, lithium difluorooxalato borate, lithium dioxalato borate, lithium difluorooxalato phosphate, and lithium tetrafluorooxalato phosphate. In some embodiments, the solvent may comprise at least one selected from ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone. In some embodiments, the electrolyte optionally comprises an additive. For example, the additive may comprise a negative electrode film-forming additive, a positive electrode film-forming additive, and may further comprise an additive capable of improving properties of the battery, such as an additive for improving overcharge properties of the battery, and an additive for improving high-temperature or low-temperature properties of the battery. In some embodiments, the electrolyte is a solid electrolyte, which may be a variety of lithium ion solid electrolytes commonly used in the art. In some of these embodiments, the solid electrolyte substrate is a lithium ion solid electrolyte. Examples of the lithium ion solid electrolyte comprise, but are not limited to: LISICON type materials, for example, γ-Li3PO4, etc.; NASICON type materials, for example, Li(1+x1)QxM(2-x1)(PO4)3, where 0 ≤ x1 <1, and Q comprises at least one selected from Al, Cr, Ba, Fe, Sc, In, Lu, Y and La; Garnet type materials, for example, Li(7-x2)La3Zr(2-x2)Mx2O12, where 0 ≤ x2 <1, and M comprises at least one selected from Sb, Nb, Ta, Te and W; LIPON type materials, for example, Lix3POy1Nz1; where 0<x3≤1, 0<y1≤1, and 0<z1≤1; Perovskite type materials, for example, Lix4Q(2 / 3-x4)MO3, where 0.04 <x4 <0.17, Q comprises at least one selected from La, Sr, Ba and Nd, M comprises at least one selected from Al, Ti and Ge; Anti-Perovskite type materials, for example, Li3OCl; Thio-LiSICON type materials, for example, Li(3+x5)My2A(1-y2)Q(4-z2)Tz2, where -1 <x5 <2, 0 ≤ y2 ≤ 1, and 0 ≤ z2 ≤ 2, M comprises at least one selected from B, Al, In, Si, Ge, Sn, Ti, W and Mo, A comprises at least one selected from P, As, Sb and Bi, Q comprises at least one selected from S or Se, and T comprises at least one selected from F, Cl, Br and I; sulfide solid electrolytes, comprising: Thiophosphate type materials, for example, Li3PS4, Argyrodite type materials, for example, Li6PS5Cl, Halide type materials, for example, Li3InCl6, Hydride type materials, for example at least one selected from 0.7Li(CB9H10) - 0.3Li(CB11H12); for example, a material of Li(10+x6)M(1+y3)A(2-y3)Q(12-z3)Hz3, where -2 < x6 <2, 0 ≤ y3 ≤ 2, and 0 ≤ z3 ≤ 2, M comprises at least one selected from B, Al, In, Si, Ge, Sn, Ti, W and Mo, A comprises at least one selected from P, As, Sb and Bi, Q comprises at least one selected from S and Se, H comprises at least one selected from F, Cl, Br and I, for another example, a material of (100-x7)Li2S•x7M•y4Q, where 20 ≤ x7 ≤ 30 and 0 ≤ y4 ≤ 50, M comprises at least one selected from B2S3, Al2S3, In2S3, SiS2, GeS2, SnS2, P2S5, As2S3, Sb2S5, Bi2S3, WS2 and MoS2, Q comprises at least one selected from B2O3, Al2O3, In2O3, SiO2, GeO2, SnO2, P2O5, Sb2O5, Bi2O3, WO2, WO3, MoO2, MoO3, Fe2O3, ZnO, MgO, CuO, CaO, LiN, Li2O, LiF, LiCl, LiBr and LiI; Argyrodite type materials, for example, Li(6+x8)My5A(1-y5)Q(5-z5)T(1+z5), where -1 ≤ x8 ≤ 1, 0 ≤ y5 ≤ 1 and -1 <z5 ≤ 1, M comprises at least one selected from B, Al, In, Si, Ge, Sn, Ti, W and Mo, A comprises at least one selected from P, As, Sb and Bi, Q comprises at least one selected from S and Se, T comprises at least one selected from F, Cl, Br and I; Halide type materials, for example, Li3MJ or Li2Sc2 / 3J, where M comprises at least one selected from Y, Er, In, Sc and Ga, and J comprises at least one selected from F, Cl, Br and I. The sulfide solid electrolyte comprises, but is not limited to, sulfur silver germanium mineral electrolytes; binary sulfide solid materials such as Li2S-P2S5, Li2S-SiS2, Li2S-GeS and Li2S-B2S3, and ternary materials such as Li2S-Me-P2S5, where Me is selected from Si, Ge, Sn and Al. Specifically, the sulfide electrolyte is selected from at least one of Li2S-P2S5, Li2S-SiS2, Li2S-GeS, Li2S-B2S3 and Li2S-Me-P2S5. [separator] In some embodiments, the separator is further comprised in the secondary battery. The type of the separator is not particularly limited in the present application, and any known separator having a porous structure and good chemical and mechanical stability may be used. In some embodiments, the material of the separator may be at least one selected from glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film, which is not limited in the present application. In a case where the separator is a multilayer composite film, the materials of individual layers may be the same or different. In some embodiments, the positive electrode plate, the negative electrode plate, and the separator may be prepared into an electrode assembly by a winding process or a lamination process. In some embodiments, a secondary battery may comprise an outer package. The outer package may be used to encapsulate the electrode assembly and the electrolyte. In some embodiments, the outer package of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell and the like. Alternatively, the outer package of the secondary battery may be a soft package, such as a soft bag. The soft bag may be made from a polymer material such as plastics, polypropylene, polybutylene terephthalate and polybutylene succinate. The shape of the secondary battery may be cylindrical, square or any other shape, which is not limited in the present application. In some embodiments, the secondary battery may be assembled into a battery module, and the number of secondary batteries contained in the battery module may be one or more, the specific number of which can be selected by a person skilled in the art according to the application and capacity of the battery module. In some embodiments, the above battery module can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by a person skilled in the art according to the application and capacity of the battery pack. In a sixth aspect, the present application provides a powered device, comprising said secondary battery. In some embodiments, the above powered device may also comprise a battery module or a battery pack obtained by assembling the secondary battery. The secondary battery, battery module, or battery pack may be used as a power source for the powered device or as an energy storage unit for the powered device. The powered device may comprise, but is not limited to, mobile devices (e.g., cell phones, laptop computers, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, and the like. As the powered device, a secondary battery, a battery module or a battery pack can be selected according to the needs of its use. As an example, for a powered device that is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc., a battery pack or a battery module may be used to meet the demand for high power and high energy density of the secondary battery of the powered device. As another example, the device may be a cell phone, a tablet computer, a laptop computer, and the like. This device usually requires thinness and lightness, and a secondary battery may be used as the power source. The present application is described in further detail below in connection with specific examples, which are not to be construed as limiting the scope of the protection claimed in the present application. Example 1 The present example provided a method for preparing an iron phosphate, as shown in FIG.1, comprising the following steps: S1, dissolving 0.24 mol of ferrous sulfate heptahydrate (analytically pure) in deionized water to prepare into a precursor solution of 200 mL; weighing 0.24 mol of ammonium dihydrogen phosphate and dissolving in 80 mL of water, adding 25.09 mL of ammonia water (NH3·H2O) with a concentration of 28 wt%, adding deionized water to prepare into a mixed solution of 200 mL; pumping the precursor solution and the mixed solution simultaneously into the reactor at 80 mL / min, subjecting to a precipitation reaction in an air atmosphere, under near-infrared light radiation with near-infrared light wavelength of 1,400 nm to 1,500 nm, at a rotor rotating speed of 2,800 rpm and a temperature of 60 °C to generate a yellow precipitate to obtain a reaction slurry, wherein a porous filler was fixed on the rotor, and the porous filler was a stainless steel wire mesh; and performing a suction filtration to the reaction slurry to obtain a filer cake, and washing the filter cake with 2L of deionized water to obtain a pure filter cake; S2: mashing the pure filter cake by adding deionized water to prepare into a slurry of 408g, weighing 0.03 mol of phosphoric acid and adding into the slurry, obtaining a slurry to be aged having a solid content of 11 wt%, heating the slurry to be aged to 90 °C for aging reaction in a stirred reactor (a 1L glass container with a stirring paddle) at a rotating speed of 500 rpm, and reacting for 2h to obtain an aged slurry, performing a suction filtration to the aged slurry to obtain a filter cake, and washing the filter cake with 1.8L of deionized water to obtain a pure aged filter cake; placing the pure aged filter cake in a blast drying oven and drying at 90 °C for 8h, and grinding to obtain iron phosphate dihydrate; and S3, placing iron phosphate dihydrate in a muffle furnace, heating to 600 °C at a heating rate of 10 °C / min, and calcining for 3h for dehydration to obtain iron phosphate. Example 2 The present example provided a method for preparing an iron phosphate, which was essentially the same as Example 1, with the difference that in the present example, ammonia water was added in an amount of 20.07 ml. Example 3 The present example provided a method for preparing an iron phosphate, which was essentially the same as Example 1, with the difference that in the present example, ammonia water was added in an amount of 30.11 ml. Example 4 The present example provided a method for preparing an iron phosphate, which was essentially the same as Example 1, with the difference that in the present example, ammonia water was added in an amount of 33.45 ml. Example 5 The present example provided a method for preparing an iron phosphate, which was essentially the same as Example 1, with the difference that in the present example, the precursor solution and the mixed solution were pumped simultaneously into the reactor at 160 mL / min. Example 6 The present example provided a method for preparing an iron phosphate, which was essentially the same as Example 5, with the difference that in the present example, a rotating speed of the rotor is 2,500 rpm. Example 7 The present example provided a method for preparing an iron phosphate, which was essentially the same as Example 6, with the difference that in the present example, the precursor solution and the mixed solution were pumped simultaneously into the reactor at 80 mL / min. Example 8 The present example provided a method for preparing an iron phosphate, which was essentially the same as Example 1, with the difference that in the present example, a rotating speed of the rotor is 2,750 rpm. Example 9 The present example provided a method for preparing an iron phosphate, comprising the following steps: S1, dissolving 0.2 mol of ferrous chloride (analytically pure) in deionized water to prepare into a precursor solution of 200 mL; weighing 0.2 mol of sodium dihydrogen phosphate and dissolving in 80 mL of water, adding 0.15 mol of sodium hydroxide, adding deionized water to prepare into a mixed solution of 200 mL; pumping the precursor solution and the mixed solution simultaneously into the reactor at 100 mL / min, subjecting to a precipitation reaction in an air atmosphere, under near-infrared light radiation with near-infrared light wavelength of 800 nm to 1,000 nm, at a rotor rotating speed of 3,000 rpm and a temperature of 25 °C to generate a yellow precipitate to obtain a reaction slurry, wherein a porous filler was fixed on the rotor, and the porous filler was made from ceramic; and performing a suction filtration to the reaction slurry to obtain a filer cake, and washing the filter cake with 2L of deionized water to obtain a pure filter cake; S2: mashing the pure filter cake by adding deionized water to prepare into a slurry of 408g, weighing 0.06 mol of phosphoric acid and adding into the slurry, obtaining a slurry to be aged, heating the slurry to be aged to 70 °C for aging reaction in a stirred reactor (a 1L glass container with a stirring paddle) at a rotating speed of 500 rpm, and reacting for 4h to obtain an aged slurry, performing a suction filtration to the aged slurry to obtain a filter cake, and washing the filter cake with 1.8L of deionized water to obtain a pure aged filter cake; placing the pure aged filter cake in a blast drying oven and drying at 90 °C for 8h, and grinding to obtain iron phosphate dihydrate; and S3, placing iron phosphate dihydrate in a muffle furnace, heating to 600 °C at a heating rate of 10 °C / min, and calcining for 3h for dehydration to obtain iron phosphate. Example 10 The present example provided a method for preparing an iron phosphate, comprising the following steps: S1, dissolving 0.24 mol of ferrous sulfate heptahydrate (analytically pure) in deionized water to prepare into a precursor solution of 200 mL; weighing 0.24 mol of phosphoric acid and dissolving in 80 mL of water, adding 0.24mol of sodium carbonate, adding deionized water to prepare into a mixed solution of 200 mL; pumping the precursor solution and the mixed solution simultaneously into the reactor at 120 mL / min, subjecting to a precipitation reaction in an air atmosphere, under near-infrared light radiation with near-infrared light wavelength of 2,300 nm to 2,500 nm, at a rotor rotating speed of 2,600 rpm and a temperature of 50 °C to generate a yellow precipitate to obtain a reaction slurry, wherein a porous filler was fixed on the rotor, and the porous filler was made from plastic; and performing a suction filtration to the reaction slurry to obtain a filer cake, and washing the filter cake with 2L of deionized water to obtain a pure filter cake; S2: mashing the pure filter cake by adding deionized water to prepare into a slurry of 408g, weighing 0.024 mol of phosphoric acid and adding into the slurry, obtaining a slurry to be aged, heating the slurry to be aged to 95 °C for aging reaction in a stirred reactor (a 1L glass container with a stirring paddle) at a rotating speed of 500 rpm, and reacting for 2h to obtain an aged slurry, performing a suction filtration to the aged slurry to obtain a filter cake, and washing the filter cake with 1.8L of deionized water to obtain a pure aged filter cake; and placing the pure aged filter cake in a blast drying oven and drying at 90 °C for 8h, and grinding to obtain iron phosphate dihydrate; and S3, placing iron phosphate dihydrate in a muffle furnace, heating to 600 °C at a heating rate of 10 °C / min, and calcining for 3h for dehydration to obtain iron phosphate. Comparative Example 1 This comparative example provided a method for preparing an iron phosphate, comprising the following steps: S1, dissolving 0.24 mol of ferrous sulfate heptahydrate (analytically pure) in deionized water to prepare into a precursor solution of 200 mL; weighing 0.24 mol of ammonium dihydrogen phosphate and dissolving in 80 mL of water, adding 25.09 mL of ammonia water with a concentration of 28 wt%, adding 20.2 mL of hydrogen peroxide solution with a concentration of 27.5 wt%, adding deionized water to prepare into a mixed solution of 200 mL; using a stirred tank reactor as the precipitation reaction device, setting the stirring blade speed to 500rpm, setting the temperature to 60 ℃, and setting the flow rate of two peristaltic pumps to 80 mL / min; pumping the precursor solution and the mixed solution into the stirred tank reactor, subjecting to a precipitation reaction to generate a yellow precipitate to obtain a reaction slurry; and performing a suction filtration to the reaction slurry to obtain a filer cake, and washing the filter cake with 2L of deionized water to obtain a pure filter cake; S2: mashing the pure filter cake by adding deionized water to prepare into a slurry of 408g, weighing 0.03 mol of phosphoric acid and adding into the slurry, obtaining a slurry to be aged, heating the slurry to be aged to 90 °C for aging reaction in a stirred reactor (a 1L glass container with a stirring paddle) at a rotating speed of 500 rpm, and reacting for 2h to obtain an aged slurry, performing a suction filtration to the aged slurry to obtain a filter cake, and washing the filter cake with 1.8L of deionized water to obtain a pure aged filter cake; and placing the pure aged filter cake in a blast drying oven and drying at 90 °C for 8h, and grinding to obtain iron phosphate dihydrate; and S3, placing iron phosphate dihydrate in a muffle furnace, heating to 600 °C at a heating rate of 10 °C / min, and calcining for 3h for dehydration to obtain iron phosphate. Comparative Example 2 This comparative example provided a method for preparing an iron phosphate, which was essentially the same as Example 1, with the difference that in this comparative example, ammonia water was added in an amount of 66.90 ml. Comparative Example 3 This comparative example provided a method for preparing an iron phosphate, which was essentially the same as Example 1, with the difference that in this comparative example, there was no near-infrared light radiation. Table 1. Process parameters in various examples and comparative examples NH3 / Fe Feeding flow rotating speed of rate (mL / min) porous filler (rpm) Example 1 75% Example 2 60% 80 2,800 Example 3 90% Example 4 100% Example 5 160 2,800 Example 6 75% 160 2,500 Example 7 80 2,500 Example 8 80 2,750 Example 9 75% 100 3,000 Example 10 100% 120 2,600 Comparative Example 1 75% 80 - Comparative Example 2 200% 160 2,800 Comparative Example 3 75% 160 2,800 The porous filler was fixed on the rotor, and the rotating speed of the porous filler was the same as that of the rotor. Test Example (1) The specific surface area (BET) of iron phosphate was tested using a physical adsorption meter. The ratio of iron to phosphorus in iron phosphate was measured by artificial chemical titration, and the reference standard was “Iron phosphate for battery materials (HG / T4701-2021)”. The crystallinity of iron phosphate was characterized by XRD refinement as well as the internal standard method, with a PDF card number of 29-0715. The test results are shown in Table 2. Table 2. Performance parameters of iron phosphate BET (m2 / g) Crystallinity (%) Example 1 19.79 99.9 Example 2 17.84 95.4 Example 3 19.50 96.2 Example 4 17.69 95.0 Example 5 17.06 94.7 Example 6 16.66 94.3 Example 7 19.16 98.2 Example 8 19.60 99.8 Example 9 19.55 98.9 Example 10 15.65 92.1 Comparative Example 1 6.25 85% Comparative Example 2 2.38 60% Comparative Example 3 12.45 86% It can be seen from the comparison between Examples 1-10 and Comparative Examples 1-3 that the specific surface area and crystallinity of the iron phosphate prepared by the method of the present application are substantially improved. It can be seen from Examples 1-4 that the ratio of the alkaline substance to the iron source directly affects the specific surface area and the crystallinity of the finished product. When the molar amount of the alkaline substance is 75% to 90% of the molar amount of the iron source, the prepared iron phosphate can have higher specific surface area and higher crystallinity. It can be seen from the comparison between Example 1 and Example 5 that higher feeding speed results in a slight decrease in specific surface area and crystallinity. It can be seen from comparison between Example 5 and Example 6 that when the rotating speed is reduced, the specific surface area and the crystallinity are slightly reduced. (2) Zeiss Sigma 500 field type emission scanning electron microscope (SEM) was used to characterize the iron phosphate material, and the results of the characterization are shown in FIG.2 - FIG.7. It can be seen from the comparison between FIGS.2-5 (results of Examples 1, 2, 5 and 7) and FIGS. 6-7 (results of Comparative Examples 1-2) that the iron phosphate primary particles prepared in the present application have smaller particle diameter and better uniformity. (3) Japan Rigaku type X-ray powder diffractometer (XRD) was used to characterize the iron phosphate material obtained in Example 1 and Comparative Example 2, and the results of the characterization are shown in FIGS.8-9. The XRD characterization results of Comparative Example 2 are shown in FIG. 9. In Comparative Example 2, the molar amount of NH3 reached 200% of Fe, and the XRD spectrum showed that the intermediate product obtained after drying under this condition was hydroxyl ammonium ferric phosphate, which was not the desired intermediate product ferric phosphate dihydrate, and the iron phosphate obtained after calcining had a BET of only 2.38 m2 / g. (4) The iron phosphate prepared from the examples and the comparative examples were prepared into lithium iron phosphate, and the specific preparation process comprised the following steps: mixing iron phosphate, lithium carbonate, polyethylene glycol, titanium dioxide and water according to a weight ratio of 1000: 252: 200: 7: 2200 and performing wet grinding to form a slurry, spray drying the slurry to obtain a spray dried intermediate, sintering the spray dried intermediate under a nitrogen atmosphere at 650 °C for 10 h with a heating speed of 3 °C / min to obtain a sintered product, and finally carrying out airflow pulverizing on the sintered product to obtain the lithium iron phosphate product. The low-temperature performance of lithium iron phosphate was tested with the following specific test process: 1) the lithium iron phosphate, acetylene black and polyvinylidene fluoride in a weight ratio of 80:10:10 were dissolved in N-methyl-pyrrolidone, stirred uniformly, and then coated on an aluminum foil, and then dried at 100°C in a blasting blowing drying oven; 2) the dried product was punched and sliced into small round pieces with a diameter of 12 mm as the positive electrode plate; and 3) lithium metal piece were used as negative electrode plate, polypropylene microporous membrane was used as a separator, and a mixture of 1 mol / L of LiPF6, EC and DMC (volume ratio of 1:1:1) was used as the electrolyte solution to assemble the CR2025-type button cell in a glove box filled with argon gas. NEWARE BTS-5 V / 5 mA battery test system was used to test the charging and discharging performance of the battery at a voltage ranging from 4.3 V to 2.5 V. The discharge capacity at 0.1C was tested at 25°C, and the discharge capacity at 1C was tested at -20°C, and the capacity retention rate at -20°C = discharge capacity at 1C (-20°C) / discharge capacity at 0.1C (25°C). The test results are shown in Table 3. Table 3. Low-temperature performances of lithium iron phosphate made from the iron phosphate of Examples 1-10 and Comparative Example 1 Capacity retention rate at -20°C (%) Example 1 78.2 Example 2 75.6 Example 3 75.9 Example 4 74.9 Example 5 74.9 Example 6 73.9 Example 7 75.1 Example 8 77.5 Example 9 76.9 Example 10 72.3 Comparative Example 1 35.9 As can be seen from Table 3, the low-temperature performance of lithium iron phosphate prepared using the iron phosphate obtained by the method of the present application has been greatly improved compared with that of lithium iron phosphate prepared using conventional methods. Obviously, the above examples are merely examples for the purpose of clear illustration, and are not a limitation of the embodiments. For those skilled ordinary in the art, other variations or changes in different forms can be made on the basis of the above description. It is neither necessary nor possible to exhaust all of the embodiments herein. The obvious variations or changes derived therefrom are still within the scope of protection of the present application.

Claims

CLAIMS 1. An iron phosphate, wherein the iron phosphate has a crystallinity of 90% to 100% and a specific surface area of 15 m2 / g to 20 m2 / g.

2. The iron phosphate of claim 1, wherein the iron phosphate has a crystallinity of greater than or equal to 92%; and / or, the iron phosphate has a specific surface area of greater than or equal to 16 m2 / g.

3. A method for preparing an iron phosphate, comprising the following steps: S1, mixing an iron source, a phosphorus source and an alkaline substance in a reactor, performing a precipitation reaction under near-infrared light radiation, and performing solid-liquid separation to obtain a precipitate; S2, aging the precipitate, performing solid-liquid separation to obtain a solid, and drying the solid to obtain an aged product; and S3, calcining the aged product to obtain the iron phosphate; wherein a rotating speed of a rotor in the reactor is 2,500 rpm to 3,000 rpm, optionally 2,600 rpm to 2,900 rpm, and a porous filler is fixed on the rotor; a molar amount of the alkaline substance is 60% to 100% of a molar amount of the iron source; and the iron source is a water-soluble ferrous salt.

4. The method for preparing an iron phosphate of claim 3, wherein, the phosphorus source comprises at least one of ammonium dihydrogen phosphate, sodium dihydrogen phosphate and phosphoric acid; and / or the alkaline substance comprises at least one of ammonia, sodium hydroxide and sodium carbonate; and / or the iron source comprises at least one of ferrous sulfate heptahydrate and ferrous chloride; and / or the porous filler is made from plastic, ceramic or stainless steel.

5. The method for preparing an iron phosphate of claim 3, wherein, S1 satisfies at least one of the following conditions: 1(1) a molar ratio of iron element in the iron source to phosphorus element in the phosphorus source is 1: (0.8 - 1.2); (2) the precipitation reaction is performed at a temperature of 20°C to 70 °C; and (3) the near-infrared light has a wavelength of 800 nm to 2,500 nm.

6. The method for preparing an iron phosphate of claim 3, wherein mixing an iron source, a phosphorus source and an alkaline substance in a reactor comprises: preparing an iron source and deionized water into a precursor solution; preparing a phosphorus source, an alkaline substance and deionized water into a mixed solution; and pumping the precursor solution and the mixed solution synchronously into the reactor; wherein a molar ratio of iron element in the iron source to phosphorus element in the phosphorus source pumped into the reactor per unit time is 1: (0.8 - 1.2).

7. The method for preparing an iron phosphate of claim 6, wherein the precursor solution has a concentration of 1 mol / L to 1.4 mol / L; and / or the precursor solution is pumped into the reactor at a flow rate of 80 mL / min to 160 mL / min; and / or the mixed solution is pumped into the reactor at a flow rate of 80 mL / min to 160 mL / min.

8. The method for preparing an iron phosphate of claim 3, wherein S2 comprises: mixing the precipitate with deionized water and an aging agent to obtain a slurry to be aged; stirring for reacting the slurry to be aged at 70°C to 95 °C for a time period of 2h to 4h to obtain an aged slurry; and performing solid-liquid separation to the aged slurry to obtain a solid, and drying the solid to obtain an aged product.

9. The method for preparing an iron phosphate of claim 8, wherein S2 satisfies at least one of the following conditions: (1) the aging agent is phosphoric acid; 2(2) a molar amount of the aging agent is 10% to 30% of the molar amount of the iron source; (3) a solid content of the slurry to be aged is 8wt% to 20wt%; (4) a stirring rate of the stirring for reacting is 300 rpm to 600 rpm; and (5) the drying is performed at a condition of 80 °C to 100 °C for a time period of 6 h to 10h.

10. The method for preparing an iron phosphate of claim 3, wherein in S3, the calcining is performed at 550°C to 650 °C for a time period of 2 h to 4h; optionally, a heating rate during calcining is 5 °C / min to 10 °C / min.

11. A lithium iron phosphate, wherein the lithium iron phosphate is made from the iron phosphate of claim 1 or 2 or an iron phosphate prepared by the method for preparing an iron phosphate of any one of claims 3 to 10.

12. A positive electrode plate, comprising: a positive electrode current collector, and a cathode active material layer provided on at least one side of the positive electrode current collector; wherein the cathode active material layer comprises the lithium iron phosphate of claim 11.

13. A secondary battery, comprising the positive electrode plate of claim 12.

14. A powered device, comprising the secondary battery of claim 13. 3

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