Iron phosphate, preparation method of iron phosphate, lithium iron phosphate and application of lithium iron phosphate

Abstract

The invention discloses iron phosphate, a preparation method of the iron phosphate, lithium iron phosphate and application of the lithium iron phosphate. The crystallinity of the iron phosphate is 90-100%, and the specific surface area of the iron phosphate is 15-20 m < 2 > / g. The lithium iron phosphate prepared from the iron phosphate has excellent low-temperature performance, and the capacity retention ratio of a button cell is greater than 70% at-20 DEG C.

Description

Technical Field

[0001] This application relates to the field of cathode material precursor technology, specifically to iron phosphate and its preparation method, lithium iron phosphate and its uses. Background Technology

[0002] Iron phosphate is an important precursor for the preparation of lithium iron phosphate (LiFePO4). The "iron phosphate linear preparation of lithium iron phosphate" has gradually become the mainstream process due to its simple process, high raw material utilization, good repeatability, and high cathode material activity.

[0003] The properties of iron phosphate largely determine the overall performance of the resulting lithium iron phosphate. Lithium iron phosphate produced using existing iron phosphate formulations exhibits poor low-temperature performance. Summary of the Invention

[0004] This application provides an iron phosphate and its preparation method, lithium iron phosphate and its uses, to solve the problem of poor low-temperature performance of lithium iron phosphate prepared from iron phosphate.

[0005] Firstly, this application provides an iron phosphate with a crystallinity of 90%–100% and a specific surface area of ​​15–20 m². 2 / g.

[0006] In one alternative embodiment, the crystallinity is ≥92%; and / or, the specific surface area is ≥16 m². 2 / g.

[0007] Secondly, this application provides a method for preparing ferric phosphate, comprising the following steps:

[0008] S1: Iron source, phosphorus source and alkaline substance are mixed in a reactor and a precipitation reaction is carried out under near-infrared light radiation. The solid and liquid are separated to obtain the precipitate.

[0009] S2: The precipitate is aged, solid-liquid separation is performed to obtain a solid, and the solid is dried to obtain the aged product;

[0010] S3: The aging product is calcined to obtain the iron phosphate;

[0011] The rotor in the reactor rotates at a speed of 2500-3000 rpm, optionally 2600-2900 rpm, and porous packing is fixed on the rotor.

[0012] The molar amount of the alkaline substance is 60% to 100% of the molar amount of the iron source;

[0013] The iron source is a water-soluble ferrous salt.

[0014] In one optional embodiment, the phosphorus source includes at least one selected from ammonium dihydrogen phosphate, sodium dihydrogen phosphate, and phosphoric acid; and / or

[0015] The alkaline substance includes at least one of ammonia, sodium hydroxide, and sodium carbonate; and / or

[0016] The iron source includes at least one of ferrous sulfate heptahydrate and ferrous chloride; and / or

[0017] The porous packing material is made of plastic, ceramic or stainless steel.

[0018] In one alternative implementation, S1 satisfies at least one of the following conditions:

[0019] (1) The molar ratio of iron in the iron source to phosphorus in the phosphorus source is 1:(0.8~1.2);

[0020] (2) The precipitation reaction temperature is 20–70℃;

[0021] (3) The wavelength of near-infrared light is 800-2500nm.

[0022] In one optional embodiment, mixing the iron source, phosphorus source, and alkaline substance in the reactor includes:

[0023] Iron source and deionized water were used to prepare a precursor solution;

[0024] Prepare a mixed solution by combining a phosphorus source, an alkaline substance, and deionized water;

[0025] The precursor solution and the mixed solution are pumped into the reactor simultaneously;

[0026] The molar ratio of iron in the iron source and phosphorus in the phosphorus source pumped into the reactor per unit time is 1:(0.8~1.2).

[0027] In one optional embodiment, the concentration of the precursor solution is 1–1.4 mol / L; and / or

[0028] The precursor solution is pumped into the reactor at a flow rate of 80–160 mL / min; and / or

[0029] The flow rate of the mixed solution pumped into the reactor is 80–160 mL / min.

[0030] In one alternative implementation, S2 includes:

[0031] The precipitate was mixed with deionized water and an aging agent to prepare a slurry to be aged.

[0032] The slurry to be aged is stirred and reacted at 70-95℃ for 2-4 hours to obtain the aged slurry;

[0033] The aged slurry is separated into solid and liquid components to obtain a solid. The solid is then dried to obtain the aged product.

[0034] In one alternative implementation, S2 satisfies at least one of the following conditions:

[0035] (1) The aging agent is phosphoric acid;

[0036] (2) The amount of the aging agent is 10-30% of the molar amount of the iron source;

[0037] (3) The weight solids content of the slurry to be aged is 8-20%;

[0038] The weight solids content of the slurry to be aged = theoretical weight of ferric phosphate dihydrate / weight of slurry to be aged × 100%.

[0039] (4) The stirring rate of the stirring reaction is 300-600 rpm;

[0040] (5) The drying is carried out at 80-100℃ for 6-10 hours.

[0041] In one optional embodiment, in step S3, calcination is carried out at 550–650°C for 2–4 hours;

[0042] Optionally, the heating rate during calcination is 5–10 °C / min.

[0043] Thirdly, this application also provides a lithium iron phosphate, which is made using the aforementioned iron phosphate or iron phosphate prepared by the aforementioned method.

[0044] Fourthly, this application also provides a positive electrode sheet, comprising:

[0045] Positive current collector, and

[0046] A positive electrode active material layer disposed on at least one side of the positive electrode current collector, the positive electrode active material layer comprising the lithium iron phosphate.

[0047] Fifthly, this application also provides a secondary battery, including the aforementioned positive electrode plate.

[0048] Sixthly, this application also provides an electrical device, including the aforementioned secondary battery.

[0049] The technical solution of this application has the following advantages:

[0050] The ferric phosphate provided in this application has a crystallinity of 90%–100% and a specific surface area of ​​15–20 m². 2 / g, the lithium iron phosphate prepared using the iron phosphate method of this application exhibits excellent low-temperature performance. At -20℃, the capacity retention rate of the coin cell is >70%. Capacity retention rate = 1C discharge capacity (-20℃) / 0.1C discharge capacity (25℃). Attached Figure Description

[0051] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0052] Figure 1 This is the process flow diagram of this application;

[0053] Figure 2 The image shows a scanning electron microscope (SEM) image of ferric phosphate obtained in Example 1 and its specific surface area (BET).

[0054] Figure 3 The image shows a scanning electron microscope (SEM) image of ferric phosphate obtained in Example 2 and its specific surface area (BET).

[0055] Figure 4 The image shows a scanning electron microscope (SEM) image of ferric phosphate obtained in Example 5 and its specific surface area (BET).

[0056] Figure 5 The image shows a scanning electron microscope (SEM) image of ferric phosphate obtained in Example 7 and its specific surface area (BET).

[0057] Figure 6 The image shows a scanning electron microscope (SEM) image of iron phosphate obtained in Comparative Example 1 and its specific surface area (BET).

[0058] Figure 7 The image shows a scanning electron microscope (SEM) image of ferric ammonium hydroxyphosphate obtained in Comparative Example 2 and its specific surface area (BET).

[0059] Figure 8 The XRD pattern of ferric phosphate prepared in Example 1;

[0060] Figure 9 The XRD pattern of ferric ammonium hydroxyphosphate prepared in Comparative Example 2 is shown.

[0061] Figure 10 A schematic diagram of a near-infrared light-coupled high-speed rotating porous packed reactor and the generation of nanobubbles;

[0062] Figure 11 A schematic diagram of the iron phosphate precipitation reaction process assisted by nanobubbles. Detailed Implementation

[0063] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0064] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification and claims of this application are intended to cover non-exclusive inclusion.

[0065] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0066] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0067] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints 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 expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​1 and 2 are listed, and if maximum range values ​​3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0068] In the description of the embodiments of this application, the term "and / or" is merely a description of the relationship between related objects, indicating that there can be three relationships. For example, A and / or B can represent three situations: A exists alone, A and B exist simultaneously, and B exists alone.

[0069] Lithium iron phosphate produced using existing iron phosphate technology has poor low-temperature performance.

[0070] To address the problems existing in the aforementioned related technologies, the first aspect of this application provides an iron phosphate with a crystallinity of 90-100% and a specific surface area of ​​15-20 m². 2 / g. The lithium iron phosphate prepared using the iron phosphate of this application exhibits excellent low-temperature performance. Exemplarily, the crystallinity of the iron phosphate provided in this application is 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100%; exemplarily, the specific surface area of ​​the iron phosphate provided in this application is 15m². 2 / g, 16m 2 / g、17m 2 / g、18m 2 / g、19m 2 / g or 20m 2 / g.

[0071] In one optional embodiment, the ferric phosphate provided in this application has a crystallinity ≥92%; and / or a specific surface area ≥16 m². 2 / g.

[0072] Secondly, this application also provides a method for preparing ferric phosphate, comprising the following steps: S1: mixing an iron source, a phosphorus source, and an alkaline substance in a reactor, and carrying out a precipitation reaction under near-infrared light radiation, and obtaining a precipitate by solid-liquid separation; S2: aging the precipitate, obtaining a solid by solid-liquid separation, and drying the solid to obtain an aged product; S3: calcining the aged product to obtain ferric phosphate; wherein the rotor speed in the reactor is 2500-3000 rpm, and porous packing is fixed on the rotor; the molar amount of the alkaline substance is 60%-100% of the molar amount of the iron source; and the iron source is a water-soluble ferrous salt. Exemplarily, the rotor speed is 2500, 2600, 2700, 2800, 2900, or 3000 rpm; and exemplaryly, the molar amount of the alkaline substance is 60%, 70%, 80%, 90%, or 100% of the molar amount of the iron source.

[0073] Near-infrared light refers to electromagnetic waves with wavelengths in the range of 780–2526 nm.

[0074] Optionally, the near-infrared light generating device in the experiment is a modulated fiber laser coupled beam expander device with a center wavelength of 980nm.

[0075] Based on the theoretical analysis of chemical nano- and micro-process intensification, this application proposes a method for preparing high specific surface area and high crystallinity iron phosphate using a near-infrared radiation-assisted nano- and micro-mixed intensified reaction. For example... Figure 10 , Figure 11 As shown, this application generates high-density cavitation bubbles through near-infrared radiation and high-speed rotating porous packing, forming a large number of ultra-small nanobubbles in the reaction solution. Utilizing the hydroxyl radicals on the surface of the nanobubbles as oxidants, ferrous ions are instantaneously oxidized to ferric ions, which then react with a phosphorus source to precipitate, resulting in an iron phosphate precipitate with nanobubbles adsorbed on its surface. In the aging and calcination process, the migration, aggregation, and bursting of nanobubbles in the reaction solution promote the formation of numerous microporous structures within the iron phosphate precipitate, yielding iron phosphate powder with high specific surface area and high crystallinity. The method of this application enables continuous production of iron phosphate, facilitates the control of product quality stability, and produces iron phosphate materials with a larger specific surface area and higher crystallinity. The crystallinity of the iron phosphate in this application is 90-100%.

[0076] The molar amount of alkaline substance in this application is 60% to 100% of the molar amount of iron source. If the content of alkaline substance is too high, the aging product obtained from S2 will not be the desired ferric phosphate dihydrate, and the BET of the ferric phosphate obtained after calcination will decrease significantly, which does not meet the actual requirements.

[0077] In one optional embodiment, the phosphorus source includes at least one selected from ammonium dihydrogen phosphate, sodium dihydrogen phosphate, and phosphoric acid; and / or

[0078] The alkaline substance includes at least one of ammonia, sodium hydroxide, and sodium carbonate; and / or

[0079] The iron source includes at least one of ferrous sulfate heptahydrate and ferrous chloride; and / or

[0080] The porous packing material is made of plastic, ceramic or stainless steel.

[0081] Optionally, the pore size of the porous packing is 0.02 to 1 mm.

[0082] In one alternative implementation, S1 satisfies at least one of the following conditions:

[0083] (1) The molar ratio of iron in the iron source to phosphorus in the phosphorus source is 1:(0.8~1.2); for example, it can be 1:0.8, 1:0.9, 1:1, 1:1.1 or 1:1.2.

[0084] (2) The temperature of the precipitation reaction is 20 to 70°C; for example, it can be 20°C, 30°C, 40°C, 50°C, 60°C, or 70°C.

[0085] (3) The wavelength of near-infrared light is 800-2500nm.

[0086] In one optional embodiment, mixing the iron source, phosphorus source, and alkaline substance in the reactor includes:

[0087] Iron source and deionized water were used to prepare a precursor solution;

[0088] Prepare a mixed solution by combining a phosphorus source, an alkaline substance, and deionized water;

[0089] The precursor solution and the mixed solution are pumped into the reactor simultaneously;

[0090] The molar ratio of iron in the iron source and phosphorus in the phosphorus source pumped into the reactor per unit time is 1:(0.8~1.2).

[0091] In one optional embodiment, the concentration of the precursor solution is 1–1.4 mol / L. Examples include 1 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, and 1.4 mol / L.

[0092] In one alternative implementation, S2 includes:

[0093] The precipitate was mixed with deionized water and an aging agent to prepare a slurry to be aged.

[0094] The slurry to be aged is stirred and reacted at 70-95℃ for 2-4 hours to obtain the aged slurry;

[0095] The aged slurry is separated into solid and liquid components to obtain a solid. The solid is then dried to obtain the aged product.

[0096] For example, the temperature of the stirring reaction is 70°C, 80°C, 90°C or 95°C, and the stirring reaction time is 2h, 3h or 4h.

[0097] In one alternative implementation, S2 satisfies at least one of the following conditions:

[0098] (1) The aging agent is phosphoric acid;

[0099] (2) The amount of the aging agent is 10 to 30% of the molar amount of the iron source; for example, it can be 10%, 20%, 25% or 30%.

[0100] (3) The weight solids content of the slurry to be aged is 8-20%. For example, it can be 10%, 15% or 20%.

[0101] (4) The stirring rate of the stirring reaction is 300 to 600 rpm; for example, it can be 300 rpm, 400 rpm, 500 rpm or 600 rpm.

[0102] (5) The drying conditions are drying at 80-100℃ for 6-10 hours. For example, the drying temperature is 80℃, 90℃ or 100℃, and the drying time is 6, 7, 8, 9 or 10 hours.

[0103] In one optional embodiment, in step S3, calcination is performed at 550–650°C for 2–4 hours; for example, the calcination temperature is 550°C, 580°C, 600°C, 620°C, or 650°C; and the calcination time is 2 hours, 3 hours, or 4 hours.

[0104] Optionally, the heating rate during calcination is 5 to 10 °C / min; for example, it can be 5 °C / min, 6 °C / min, 7 °C / min, 8 °C / min, 9 °C / min, or 10 °C / min.

[0105] Thirdly, this application provides a lithium iron phosphate, which is made using the aforementioned iron phosphate or iron phosphate prepared by the aforementioned method.

[0106] The lithium iron phosphate obtained from iron phosphate in this application exhibits excellent low-temperature performance. For coin cells at -20℃, the capacity retention rate is >70%. Capacity retention rate = 1C discharge capacity (-20℃) / 0.1C discharge capacity (25℃).

[0107] Fourthly, this application provides a positive electrode sheet, comprising:

[0108] Positive current collector, and

[0109] A positive electrode active material layer disposed on at least one side of the positive electrode current collector, the positive electrode active material layer comprising the lithium iron phosphate.

[0110] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive active material layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0111] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0112] In some embodiments, the positive electrode active material layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0113] In some embodiments, the positive electrode active material layer may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0114] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0115] Fifthly, this application provides a secondary battery, including the aforementioned positive electrode.

[0116] The secondary battery of this application is described below.

[0117] [Negative electrode plate]

[0118] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0119] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0120] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0121] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0122] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may be selected from at least one of 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).

[0123] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0124] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0125] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0126] [Electrolytes]

[0127] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0128] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0129] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0130] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl 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.

[0131] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0132] In some embodiments, the electrolyte is a solid electrolyte. The lithium-ion solid electrolyte can be any of the lithium-ion solid electrolytes commonly used in the art.

[0133] In some embodiments, the solid electrolyte substrate is a lithium-ion solid electrolyte.

[0134] Examples of lithium-ion solid electrolytes are provided here, including but not limited to:

[0135] LISICON type: such as γ-Li3PO4, etc.;

[0136] NASICON type; for example, Li (1+x1) Q x1 M (2-x1) (PO4)3, 0 ≤ x1 < 1, Q includes at least one of Al, Cr, Ba, Fe, Sc, In, Lu, Y, La;

[0137] Garnet type; for example, Li (7-x2) La3Zr (2-x2) M x2 O12, etc., 0 ≤ x2 < 1, M includes at least one of Sb, Nb, Ta, Te, W;

[0138] LIPON type: for example, Li x3 PO y1 N z1 ; 0 < x3 ≤ 1, 0 < y1 ≤ 1, 0 < z1 ≤ 1;

[0139] Perovskite type: for example, Li x4 Q (2 / 3-x4) MO3, etc., 0.04 < x4 < 0.17, Q includes at least one of La, Sr, Ba, Nd, M includes at least one of Al, Ti, Ge;

[0140] Anti-Perovskite type: for example, Li3OCl, etc.;

[0141] Thio-LiSICON type: for example, Li (3+x5) My2A (1-y2) Q (4-z2) T z2 , where -1 < x5 < 2, 0 ≤ y2 ≤ 1, 0 ≤ z2 ≤ 2, M includes at least one of B, Al, In, Si, Ge, Sn, Ti, W, Mo, A includes at least one of P, As, Sb, Bi, Q includes at least one of S, Se, T includes at least one of F, Cl, Br, I;

[0142] Sulfide solid electrolyte, including: Thiophosphate type: Li3PS4, etc., Argyrodite type: Li6PS5Cl, Halide type: Li3InCl6, Hydride type: 0.7Li(CB9H 10 ) - 0.3Li(CB 11 H 12 ) at least one of; for example, Li (10+x6) M (1+y3) A (2-y3) Q (12-z3) H z3Type: where -2 < x6 < 2, 0 ≤ y3 ≤ 2, 0 ≤ z3 ≤ 2, M includes at least one of B, Al, In, Si, Ge, Sn, Ti, W, Mo; A includes at least one of P, As, Sb, Bi, Q includes at least one of S, Se, H includes at least one of F, Cl, Br, I: (100 - x7)Li2S·x7M·y4Q type: where 20 ≤ x7 ≤ 30, 0 ≤ y4 ≤ 50, M includes at least one of B2S3, Al2S3, In2S3, SiS2, GeS2, SnS2, P2S5, As2S3, Sb2S5, Bi2S3, WS2, MoS2, Q includes at least one of B2O3, Al2O3, In2O3, SiO2, GeO2, SnO2, P2O5, Sb2O5, Bi2O3, WO2, WO3, MoO2, MoO3, Fe2O3, ZnO, MgO, CuO, CaO, LiN, Li2O, LiF, LiCl, LiBr, LiI; Argyrodite type: Li (6+x8) M y5 A (1-y5) Q (5-z5) T (1+z5) , where -1 ≤ x8 ≤ 1, 0 ≤ y5 ≤ 1, -1 < z5 ≤ 1, M includes at least one of B, Al, In, Si, Ge, Sn, Ti, W, Mo, A includes at least one of P, As, Sb, Bi, Q includes at least one of S, Se, T includes at least one of F, Cl, Br, I; Halide type: Li3MJ or Li2Sc 2 / 3 J; M includes at least one of Y, Er, In, Sc, Ga, J includes at least one of F, Cl, Br, I.

[0143] When the above sulfide solid electrolyte is a sulfide-based solid electrolyte, it includes, but is not limited to: argyrodite electrolyte; binary sulfide-based solid systems such as Li2S-P2S5, Li2S-SiS2, Li2S-GeS, and Li2S-B2S3, and Li2S-Me-P2S5 ternary systems, where Me is selected from Si, Ge, Sn, or Al, etc.

[0144] Specifically, the above sulfide electrolyte is selected from at least one of Li2S-P2S5, Li2S-SiS2, Li2S-GeS, LiS-B2S3, and Li2S-Me-P2S5.

[0145] [Separator membrane]

[0146] In some embodiments, the secondary battery further includes a separator membrane. The present application does not particularly limit the type of the separator membrane, and any well-known porous structure separator membrane with good chemical stability and mechanical stability can be selected.

[0147] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0148] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0149] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0150] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0151] This application does not impose any particular restrictions on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape.

[0152] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0153] In some embodiments, the battery modules described above 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 those skilled in the art according to the application and capacity of the battery pack.

[0154] Sixthly, this application provides an electrical device including the aforementioned secondary battery.

[0155] In some embodiments, the aforementioned electrical device may also include a battery module or battery pack assembled from the aforementioned secondary batteries. The secondary batteries, battery modules, or battery packs can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, 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, etc.

[0156] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements. An example electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the secondary battery for this electrical device, a battery pack or battery module can be used.

[0157] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0158] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0159] Example 1

[0160] This embodiment provides a method for preparing ferric phosphate, such as... Figure 1 As shown, it includes the following steps:

[0161] S1: Dissolve 0.24 mol of ferrous sulfate heptahydrate (analytical grade) in deionized water to prepare a 200 mL precursor solution.

[0162] Weigh 0.24 mol of ammonium dihydrogen phosphate, dissolve it in 80 mL of water, add 25.09 mL of ammonia water (NH3·H2O concentration 28 wt%), and then add deionized water to prepare a 200 mL mixed solution.

[0163] The precursor solution and the mixed solution were simultaneously pumped into the reactor at a rate of 80 mL / min. A precipitation reaction was carried out under air atmosphere, near-infrared radiation (wavelength 1400–1500 nm), a rotor speed of 2800 rpm, and a temperature of 60°C to generate a yellow precipitate, yielding a reaction slurry. A porous packing material, made of stainless steel wire mesh, was fixed on the rotor.

[0164] The reaction slurry was filtered to obtain a filter cake, which was then washed with 2L of deionized water to obtain a pure filter cake.

[0165] S2: Add deionized water, slurry the purified filter cake to prepare a 408g slurry, and weigh out 0.03mol of phosphoric acid to add to the slurry, resulting in a slurry with a solid content of 11wt% to be aged. Place the slurry to be aged in a stirred reactor (a 1L glass container with a stirrer) at 500rpm and heat to 90℃ for 2 hours to obtain an aged slurry. Filter the aged slurry to obtain a filter cake, and wash the filter cake with 1.8L of deionized water to obtain a purified aged filter cake.

[0166] The pure aged filter cake was placed in a forced-air drying oven and dried at 90°C for 8 hours, and then ground to obtain ferric phosphate dihydrate.

[0167] S3: Ferric phosphate dihydrate is placed in a muffle furnace and heated to 600℃ at a heating rate of 10℃ / min for 3 hours to remove water, thereby obtaining ferric phosphate.

[0168] Example 2

[0169] This embodiment provides a method for preparing ferric phosphate, which is basically the same as that in Example 1, except that the amount of ammonia added in this embodiment is 20.07 ml.

[0170] Example 3

[0171] This embodiment provides a method for preparing ferric phosphate, which is basically the same as that in Example 1, except that the amount of ammonia added in this embodiment is 30.11 ml.

[0172] Example 4

[0173] This embodiment provides a method for preparing ferric phosphate, which is basically the same as that in Example 1, except that the amount of ammonia added in this embodiment is 33.45 ml.

[0174] Example 5

[0175] This embodiment provides a method for preparing iron phosphate, which is basically the same as that in Example 1, except that in this embodiment, the precursor solution and the mixed solution are simultaneously pumped into the reactor at a rate of 160 mL / min.

[0176] Example 6

[0177] This embodiment provides a method for preparing iron phosphate, which is basically the same as that in embodiment 5, except that the rotor speed is 2500 rpm in this embodiment.

[0178] Example 7

[0179] This embodiment provides a method for preparing iron phosphate, which is basically the same as that in Example 6, except that in this embodiment, the precursor solution and the mixed solution are simultaneously pumped into the reactor at a rate of 80 mL / min.

[0180] Example 8

[0181] This embodiment provides a method for preparing iron phosphate, which is basically the same as that in Embodiment 1, except that the rotor speed is 2750 rpm in this embodiment.

[0182] Example 9

[0183] This embodiment provides a method for preparing ferric phosphate, including the following steps:

[0184] S1: Dissolve 0.2 mol of ferrous chloride (analytical grade) in deionized water to prepare a 200 mL precursor solution.

[0185] Weigh 0.2 mol of sodium dihydrogen phosphate, dissolve it in 80 mL of water, add 0.15 mol of sodium hydroxide, and then add deionized water to prepare a 200 mL mixed solution.

[0186] The precursor solution and the mixed solution were pumped into the reactor at a rate of 100 mL / min. A precipitation reaction was carried out under air atmosphere, near-infrared radiation (wavelength 800–1000 nm), a rotor speed of 3000 rpm, and a temperature of 25°C to generate a yellow precipitate, yielding a reaction slurry. A porous ceramic packing material was fixed on the rotor.

[0187] The reaction slurry was filtered to obtain a filter cake, which was then washed with 2L of deionized water to obtain a pure filter cake.

[0188] S2: Add deionized water, slurry the purified filter cake to prepare a 408g slurry, and weigh out 0.06mol of phosphoric acid to add to the slurry to obtain the slurry to be aged. Place the slurry to be aged in a stirred reactor (a 1L glass container with a stirrer, rotating at 500rpm) and heat to 70℃ for aging reaction for 4 hours to obtain an aged slurry. Filter the aged slurry to obtain a filter cake, and wash the filter cake with 1.8L of deionized water to obtain a purified aged filter cake.

[0189] The pure aged filter cake was placed in a forced-air drying oven and dried at 90°C for 8 hours, and then ground to obtain ferric phosphate dihydrate.

[0190] S3: Ferric phosphate dihydrate is placed in a muffle furnace and heated to 600℃ at a heating rate of 10℃ / min for 3 hours to remove water, thereby obtaining ferric phosphate.

[0191] Example 10

[0192] This embodiment provides a method for preparing ferric phosphate, including the following steps:

[0193] S1: Dissolve 0.24 mol of ferrous sulfate heptahydrate (analytical grade) in deionized water to prepare a 200 mL precursor solution.

[0194] Weigh 0.24 mol of phosphoric acid, dissolve it in 80 mL of water, then add 0.24 mol of sodium carbonate, and then add deionized water to prepare a 200 mL mixed solution.

[0195] The precursor solution and the mixed solution were simultaneously pumped into the reactor at a rate of 120 mL / min. A precipitation reaction was carried out under air atmosphere, near-infrared radiation (wavelength 2300–2500 nm), a rotor speed of 2600 rpm, and a temperature of 50°C to generate a yellow precipitate, yielding a reaction slurry. A porous packing material of plastic was fixed on the rotor.

[0196] The reaction slurry was filtered to obtain a filter cake, which was then washed with 2L of deionized water to obtain a pure filter cake.

[0197] S2: Add deionized water to the filter cake and slurry to prepare 408g of slurry. Weigh 0.024mol of phosphoric acid and add it to the slurry to obtain the slurry to be aged. Place the slurry to be aged in a stirred reactor (a 1L glass container with a stirrer, rotating at 500rpm) and heat to 95℃ for aging reaction for 2 hours to obtain aged slurry. Filter the aged slurry to obtain a filter cake, and wash the filter cake with 1.8L of deionized water to obtain a pure aged filter cake.

[0198] The pure aged filter cake was placed in a forced-air drying oven and dried at 90°C for 8 hours, and then ground to obtain ferric phosphate dihydrate.

[0199] S3: Ferric phosphate dihydrate is placed in a muffle furnace and calcined at 600℃ for 3 hours at a rate of 10℃ / min to remove water, thus obtaining ferric phosphate.

[0200] Comparative Example 1

[0201] This comparative example provides a method for preparing iron phosphate, including the following steps:

[0202] S1: Dissolve 0.24 mol of ferrous sulfate heptahydrate (analytical grade) in deionized water to prepare a 200 mL precursor solution.

[0203] Weigh 0.24 mol of ammonium dihydrogen phosphate, dissolve it in 80 mL of water, then add 25.09 mL of ammonia (28 wt%), then add 20.2 mL of hydrogen peroxide (27.5 wt%), and then add deionized water to prepare a 200 mL mixed solution.

[0204] A stirred tank reactor was used as the precipitation reaction device. The stirring speed was set to 500 rpm, the temperature was set to 60℃, and the flow rate of the two peristaltic pumps was set to 80 mL / min. The precursor solution and the mixed solution were pumped into the stirred tank reactor. The precipitation reaction produced a yellow precipitate and a reaction slurry was obtained.

[0205] The reaction slurry was filtered to obtain a filter cake, which was then washed with 2L of deionized water to obtain a pure filter cake.

[0206] S2: Add deionized water to the filter cake and slurry to prepare 408g of slurry. Weigh 0.03mol of phosphoric acid and add it to the slurry to obtain the slurry to be aged. Place the slurry to be aged in a stirred reactor (a 1L glass container with a stirrer, rotating at 500rpm) and heat to 90℃ for 2 hours to obtain an aged slurry. Filter the aged slurry to obtain a filter cake, and wash the filter cake with 1.8L of deionized water to obtain a pure aged filter cake.

[0207] The pure aged filter cake was placed in a forced-air drying oven and dried at 90°C for 8 hours, and then ground to obtain ferric phosphate dihydrate.

[0208] S3: Ferric phosphate dihydrate is placed in a muffle furnace and calcined at 600℃ for 3 hours at a rate of 10℃ / min to remove water, thus obtaining ferric phosphate.

[0209] Comparative Example 2

[0210] This comparative example provides a method for preparing ferric phosphate, which is basically the same as that in Example 1, except that the amount of ammonia added in this comparative example is 66.90 ml.

[0211] Comparative Example 3

[0212] This comparative example provides a method for preparing iron phosphate, which is basically the same as that in Example 1, except that there is no near-infrared light radiation in this comparative example.

[0213] Table 1. Process parameters in each embodiment and comparative example

[0214]

[0215]

[0216] The porous packing is fixed on the rotor, and the rotational speed of the porous packing is the same as that of the rotor.

[0217] Test case

[0218] (1) The specific surface area (BET) of ferric phosphate was tested using a physical adsorption apparatus.

[0219] The iron-to-phosphorus ratio in ferric phosphate is measured by artificial chemical titration, with the reference standard being "Ferric phosphate for batteries (HG / T4701-2021)".

[0220] The crystallinity of ferric phosphate was characterized by XRD refinement and internal standard method. PDF card number: 29-0715.

[0221] The test results are shown in Table 2.

[0222] Table 2. Performance parameters of iron phosphate

[0223] <![CDATA[BET(m 2 / 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％

[0224] As can be seen from the comparison between Examples 1-10 and Comparative Examples 1-3, the specific surface area and crystallinity of the iron phosphate prepared by the method of this application are significantly improved.

[0225] As shown in Examples 1-4, the ratio of alkaline substance to iron source directly affects the specific surface area and crystallinity of the finished product. When the molar amount of alkaline substance is 75% to 90% of the molar amount of iron source, ferric phosphate with higher specific surface area and crystallinity can be obtained.

[0226] A comparison of Examples 1 and 5 shows that a higher feed rate leads to a slight decrease in specific surface area and crystallinity.

[0227] A comparison of Examples 5 and 6 shows that a decrease in rotational speed results in a slight decrease in specific surface area and crystallinity.

[0228] (2) The iron phosphate material was characterized using a Zeiss Sigma 500 field emission scanning electron microscope (SEM). The characterization results are shown in the figure. Figures 2-7 .

[0229] Depend on Figure 2-5 (Results of Examples 1, 2, 5, and 7) and Figure 6-7 (Comparison of the results of Examples 1-2) shows that the primary iron phosphate particles prepared in this application have smaller particle size and better uniformity.

[0230] (3) The iron phosphate materials prepared in Example 1 and Comparative Example 2 were characterized using a Rigaku X-ray powder diffractometer (XRD). The characterization results are shown in the figure. Figure 8 and Figure 9 .

[0231] The XRD characterization results of iron phosphate in Comparative Example 2 are shown in the figure. Figure 9 In Comparative Example 2, the molar amount of NH3 reached 200% of that of Fe. XRD patterns showed that the intermediate product obtained after drying under these conditions was ammonium hydroxyphosphate, not the desired intermediate product, ferric phosphate dihydrate. The ferric phosphate obtained after calcination had a BET of only 2.38 m. 2 / g.

[0232] (4) The iron phosphate obtained in the examples and comparative examples was used to prepare lithium iron phosphate. The specific preparation process was as follows: iron phosphate, lithium carbonate, polyethylene glycol, titanium dioxide, and water were mixed in a weight ratio of 1000:252:200:7:2200 and formed into a slurry by wet grinding. The slurry was then sprayed.

[0233] The intermediate product was obtained by drying. The intermediate product was then sintered at 650°C for 10 hours under a nitrogen atmosphere with a heating rate of 3°C / min to obtain the sintered product. Finally, the sintered product was subjected to air jet milling to obtain the lithium iron phosphate product.

[0234] The low-temperature performance of lithium iron phosphate was tested using the following process: 1) Lithium iron phosphate, acetylene black, and polyvinylidene fluoride were dissolved in N-methyl-pyrrolidone at a weight ratio of 80:10:10. After stirring evenly, the solution was coated onto aluminum foil and dried in a forced-air drying oven at 100°C. 2) The dried product was cut into small round pieces with a diameter of 12 mm to serve as the positive electrode. 3) Using lithium metal sheets as the negative electrode, a polypropylene microporous membrane as the separator, and 1 mol / L LiPF6 / EC+DMC (volume ratio 1:1:1) as the electrolyte, CR2025 coin cells were assembled in an argon-filled glove box. The charge-discharge performance of the cells was tested using a Xinwei BTS-5V / 5mA battery testing system, with a voltage range of 4.3-2.5V. The 0.1C discharge capacity was tested at 25℃, and the 1C discharge capacity was tested at -20℃. The capacity retention rate at -20℃ = 1C discharge capacity (-20℃) / 0.1C discharge capacity (25℃).

[0235] The test results are shown in Table 3.

[0236] Table 3. Low-temperature performance of lithium iron phosphate prepared from iron phosphate in Examples 1-10 and Comparative Example 1

[0237] -20℃ capacity retention % 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

[0238] As shown in Table 3, the lithium iron phosphate prepared by the method of this application has a significantly improved low-temperature performance compared with lithium iron phosphate prepared by conventional methods.

[0239] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this application.

Claims

1. A type of iron phosphate, characterized in that, Crystallinity is 90%–100%, and specific surface area is 15–20 m². 2 / g.

2. The iron phosphate according to claim 1, characterized in that, Crystallinity ≥ 92%; And / or, specific surface area ≥16m² 2 / g.

3. A method for preparing ferric phosphate, characterized in that, Includes the following steps: S1: Iron source, phosphorus source and alkaline substance are mixed in a reactor and a precipitation reaction is carried out under near-infrared light radiation. The precipitate is obtained by solid-liquid separation. S2: The precipitate is aged, solid-liquid separation is performed to obtain a solid, and the solid is dried to obtain the aged product; S3: The aging product is calcined to obtain the iron phosphate; The rotor in the reactor rotates at a speed of 2500-3000 rpm, optionally 2600-2900 rpm, and porous packing is fixed on the rotor. The molar amount of the alkaline substance is 60% to 100% of the molar amount of the iron source; The iron source is a water-soluble ferrous salt.

4. The method for preparing ferric phosphate according to claim 3, characterized in that, The phosphorus source includes at least one of ammonium dihydrogen phosphate, sodium dihydrogen phosphate, and phosphoric acid; and / or The alkaline substance includes at least one of ammonia, sodium hydroxide, and sodium carbonate; and / or The iron source includes at least one of ferrous sulfate heptahydrate and ferrous chloride; and / or The porous packing material is made of plastic, ceramic or stainless steel.

5. The method for preparing ferric phosphate according to claim 3, characterized in that, S1 satisfies at least one of the following conditions: (1) The molar ratio of iron in the iron source to phosphorus in the phosphorus source is 1:(0.8~1.2); (2) The precipitation reaction temperature is 20–70℃; (3) The wavelength of near-infrared light is 800-2500nm.

6. The method for preparing ferric phosphate according to claim 3, characterized in that, The mixing of iron source, phosphorus source and alkaline substance in the reactor includes: Iron source and deionized water were used to prepare a precursor solution; Prepare a mixed solution by combining a phosphorus source, an alkaline substance, and deionized water; The precursor solution and the mixed solution are pumped into the reactor simultaneously; The molar ratio of iron in the iron source and phosphorus in the phosphorus source pumped into the reactor per unit time is 1:(0.8~1.2).

7. The method for preparing ferric phosphate according to claim 6, characterized in that, The concentration of the precursor solution is 1–1.4 mol / L; and / or The precursor solution is pumped into the reactor at a flow rate of 80–160 mL / min; and / or The flow rate of the mixed solution pumped into the reactor is 80–160 mL / min.

8. The method for preparing ferric phosphate according to claim 3, characterized in that, S2 includes: The precipitate was mixed with deionized water and an aging agent to prepare a slurry to be aged. The slurry to be aged is stirred and reacted at 70-95℃ for 2-4 hours to obtain the aged slurry; The aged slurry is separated into solid and liquid components to obtain a solid. The solid is then dried to obtain the aged product.

9. The method for preparing ferric phosphate according to claim 8, characterized in that, 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) The weight solids content of the slurry to be aged is 8-20%; (4) The stirring rate of the stirring reaction is 300-600 rpm; (5) The drying conditions are 80-100℃ for 6-10 hours.

10. The method for preparing ferric phosphate according to claim 3, characterized in that, In S3, calcination is carried out at 550-650°C for 2-4 hours. Optionally, the heating rate during calcination is 5–10 °C / min.

11. A lithium iron phosphate, characterized in that, It is made using ferric phosphate as described in claim 1 or 2, or ferric phosphate prepared by any one of claims 3-10.

12. A positive electrode plate, characterized in that, include: Positive current collector, and A positive electrode active material layer disposed on at least one side of the positive electrode current collector, the positive electrode active material layer comprising lithium iron phosphate as described in claim 11.

13. A secondary battery, characterized in that, Includes the positive electrode sheet as described in claim 12.

14. An electrical appliance, characterized in that, Includes the secondary battery as described in claim 13.

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