Low-antiposition lithium iron phosphate precursor prepared by reactive emulsification as well as preparation method and application of low-antiposition lithium iron phosphate precursor

Abstract

The lithium iron phosphate precursor material simultaneously meets the following two conditions: (1) # imgabs0 # is 2.44-2.86 g / cm < 3 >, (2) # imgabs1 # = # imgabs2 # is more than or equal to 0.4 and less than or equal to 2.5, C in the formula is average circularity, and circularity is equal to (4 * pi * A) / G2; wherein rho is the density of the lithium iron phosphate precursor material measured by a gas replacement method, K90 = (Dv90-Dv10) / Dv50, A is the projected area of the particle sample of the lithium iron phosphate precursor material, and G is the projected perimeter of the particle sample of the lithium iron phosphate precursor material. The lithium iron phosphate precursor material has relatively high tap density and good processability, and lithium iron phosphate prepared from the lithium iron phosphate precursor material through a carbon reduction method has relatively high tap density, so that the lithium iron phosphate precursor material has relatively high volumetric specific capacity, and the prepared battery has relatively high energy density.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion battery positive electrode materials, and in particular to a low-inversion lithium iron phosphate precursor prepared by reactive emulsification, a preparation method thereof, and applications thereof. Background Art

[0002] Lithium iron phosphate is one of the most competitive cathode active materials for lithium-ion batteries on the market. Compared with lithium cobalt oxide and ternary cathode materials, lithium iron phosphate has a longer life and better safety performance. In addition, lithium iron phosphate has a 170mAh.g -1 The theoretical specific capacity and platform discharge voltage of 3.4V give it a considerable energy density.

[0003] Tap density refers to the bulk density of the powder material after tapping, which reflects the mass of the positive electrode material contained in unit volume. Tap density is an important indicator for evaluating positive electrode materials, which will directly affect the compaction density of the prepared electrode, thereby affecting the energy density of the battery.

[0004] At present, the synthesis methods of lithium iron phosphate mainly include high-temperature solid-phase method, hydrothermal method and sol-gel method. Among them, the high-temperature solid-phase method has a simple and controllable process flow, which is suitable for industrial production. The high-temperature solid-phase method refers to using iron phosphate and a lithium source as raw materials, mixing them evenly and then calcining them to produce lithium iron phosphate. Iron phosphate as a precursor material has a similar structure to lithium iron phosphate, and the morphology of the precursor material has a significant influence on the morphology of lithium iron phosphate. Therefore, the quality of iron phosphate will have a direct impact on the battery performance of lithium iron phosphate, such as energy density, cycle life, and safety. However, the existing battery-grade iron phosphate has the problem of low tap density or the inability to balance tap density and grinding efficiency, which restricts the tap density and iron-lithium antisite defect concentration of the lithium iron phosphate prepared therefrom.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] The object of the present invention is to provide a low-antiposition lithium iron phosphate precursor prepared by reactive emulsification, a preparation method thereof, and an application thereof, wherein the lithium iron phosphate precursor material can achieve both solid density and grinding efficiency.

[0007] The present invention is achieved in that: In a first aspect, the present invention provides a lithium iron phosphate precursor material, wherein the lithium iron phosphate precursor material satisfies the following two conditions simultaneously: ① 2.6 g / cm 3 ~3.2g / cm 3 ,②0.8≤ = ≤5, where C is the average circularity of two or more lithium iron phosphate precursor material particles, circularity = (4×π×A) / G2 ; Wherein, ρ is the density of lithium iron phosphate precursor material measured by gas replacement method, K 90 = (Dv90-Dv10) / Dv50, Dv90, Dv50, and Dv10 are the particle size values ​​when the volume cumulative distribution reaches 90%, 50%, and 10% respectively in the particle size distribution, A is the projected area of ​​the lithium iron phosphate precursor material particle sample, and G is the projected circumference of the lithium iron phosphate precursor material particle sample.

[0008] In an optional embodiment, the total pore volume corresponding to the pores with a pore diameter of less than 200 nm of the lithium iron phosphate precursor material obtained by analyzing the nitrogen adsorption and desorption isotherm by the BJH method is less than 0.2 cm 3 / g; and / or, 2.2 ≤ = ≤4.1; and / or, the lithium iron phosphate precursor material is doped with at least one of Al, Ni, Co, Mn, Ti, La, Ce, Cr, Mo, Ca, Ga, V, Nb, Zr, In, Zn, and Y elements.

[0009] In an optional embodiment, the lithium iron phosphate precursor material satisfies at least one of the following characteristics ae: aK 90 0.45~2; preferably 0.77~1.63; bC is 0.35~0.6; preferably 0.38~0.45; c. Dv50 is 2μm ~ 7.5μm; preferably 4μm ~ 6μm; d. The total pore volume corresponding to the pores with a pore diameter of less than 200 nm of the lithium iron phosphate precursor material obtained by analyzing the nitrogen adsorption and desorption isotherms by the BJH method is less than 0.05 cm 3 / g; e. Tap density TD is 0.6 g / cm 3 ~2.0g / cm 3 .

[0010] In a second aspect, the present invention provides a method for preparing the lithium iron phosphate precursor material according to any one of the aforementioned embodiments, comprising: preparing a solution, namely, preparing a water-soluble metal salt aqueous solution and a phosphorus source aqueous solution; emulsion preparation, mixing the water-soluble metal salt aqueous solution with an emulsifier, an initiator, and an oil phase solvent and homogenizing to obtain a water-in-oil emulsion, wherein the emulsifier includes a reactive emulsifier; preparing amorphous ferric phosphate by adding the phosphorus source aqueous solution to the water-in-oil emulsion to react and generate amorphous ferric phosphate; Calcination: calcining the amorphous iron phosphate to obtain the lithium iron phosphate precursor material.

[0011] In an optional embodiment, the solution preparation step satisfies at least one of the following features af: a. The water-soluble metal salt aqueous solution further comprises ethylene glycol, wherein the mass fraction of ethylene glycol in the water-soluble metal salt aqueous solution is 4% to 8%.

[0012] b. The metal ions in the water-soluble metal salt solution include ferric ions; c. The concentration of metal ions in the water-soluble metal salt aqueous solution is 0.2M~1M; d. The phosphorus concentration in the aqueous solution of the phosphorus source is 0.5M~1.2M; e. The pH value of the phosphorus source aqueous solution is 0.5~2; f. The metal ions in the water-soluble metal salt aqueous solution include doping metal ions.

[0013] In an optional embodiment, the emulsion preparation step satisfies at least one of the following features ai: a. The emulsifier further includes a nonionic emulsifier, and the amount of the nonionic emulsifier is 1% to 3% by mass of the oil phase solvent.

[0014] b. The oil phase solvent is selected from C6~C12 alkanes; c. The volume ratio of the water-soluble metal salt aqueous solution to the oil phase solvent is 1:3~5; d. The reactive emulsifier is a phosphate reactive emulsifier; e. The mass ratio of the reactive emulsifier to the oil phase solvent is 1% to 6.5%; f. The initiator is selected from at least one of azobisisobutyronitrile, azobisisovaleronitrile, dibenzoyl peroxide, diisopropyl peroxydicarbonate and di-tert-butyl peroxide; g. The initiator is 1% to 2% by mass of the reactive emulsifier; h. The speed of the homogenization step is 1000 rpm ~5000 rpm, and the time is 20min~40min; i. The average particle size of the droplets in the water-in-oil emulsion is 3 μm to 10 μm.

[0015] In an optional embodiment, in the step of preparing amorphous ferric phosphate, the molar ratio of phosphorus to iron is 1.05 to 1.5; And / or, the reaction temperature is 50° C. to 80° C., the reaction time is 3 h to 6 h, and the reaction is carried out under stirring at a stirring speed of 300 rpm to 500 rpm.

[0016] In an optional embodiment, the calcination temperature is 600° C. to 750° C., the heating rate is 3° C. / min to 5° C. / min, and the calcination time is 2 h to 3 h.

[0017] In a third aspect, the present invention provides an application of the lithium iron phosphate precursor material described in any one of the aforementioned embodiments, wherein the lithium iron phosphate precursor is used to prepare a lithium iron phosphate material, and the lithium iron phosphate material is prepared from the lithium iron phosphate precursor material and a lithium salt.

[0018] In a fourth aspect, the present invention provides an application of the aforementioned lithium iron phosphate material, wherein the lithium iron phosphate material is used to prepare a secondary battery.

[0019] It should be noted that the name of the invention, i.e., a low-anti position lithium iron phosphate precursor prepared by reactive emulsification and its application, should include the following understandings: reactive emulsification refers to the use of a reactive emulsifier as a component of an emulsifier in the process of preparing iron phosphate by an emulsion method, so that while the iron phosphate precipitate is generated, the reactive emulsifier polymerizes at the interface of the emulsion droplets and covers the surface of the precipitate, which can serve as a porogen and excipient, and is vaporized during calcination to form pores on the surface of the particles and maintain the spherical morphology of the particles, thereby increasing the number and circularity of the pores in the lithium iron phosphate precursor material; reactive emulsification preparation is only one of the means to obtain the low-anti position lithium iron phosphate precursor defined by the present invention, and does not limit the product of the present invention. The product of the present invention obtained by other means The lithium iron phosphate precursor material to be defined also falls within the scope of protection of the claims of the present invention, because the present invention has fully explained that the lithium iron phosphate precursor material that meets specific conditions has good compaction density and processing performance, and the lithium iron phosphate positive electrode material prepared therefrom has low iron-lithium antisite defects, indicating that the solution to the technical problem is to obtain the lithium iron phosphate precursor material that meets specific conditions, rather than its preparation method; in addition, the low-antisite lithium iron phosphate precursor specifically refers to the lithium iron phosphate positive electrode material with low iron-lithium antisite defects that can be obtained by using the lithium iron phosphate precursor defined in the present invention. This effect is due to the fact that the lithium iron phosphate precursor material that meets the limited range has good compaction density and processing and grinding performance, so that when it is mixed with the lithium source, ground and sintered, Li + Spreads faster and more evenly.

[0020] The present invention has the following beneficial effects: The lithium iron phosphate precursor material provided by the present invention satisfies 2.6 g / cm 3 ~3.2g / cm 3 and 0.8≤ = ≤5, the lithium iron phosphate precursor material has a high tap density and good processing performance, the lithium iron phosphate prepared by the carbon reduction method has a high tap density, thereby having a high volumetric capacity, and the prepared battery has a high energy density. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0022] Figure 1 This is a SEM image of the lithium iron phosphate precursor material prepared in Example 1; Figure 2 This is a SEM image of the lithium iron phosphate precursor material prepared in Example 4; Figure 3 This is the XRD pattern of lithium iron phosphate prepared from the lithium iron phosphate precursor material of Example 1. DETAILED DESCRIPTION

[0023] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, all are conventional products that can be purchased commercially.

[0024] An embodiment of the present invention provides a lithium iron phosphate precursor material, which satisfies the following two conditions at the same time: ① 2.6 g / cm 3 ~3.2g / cm 3 ,②0.8≤ = ≤5, where C is the average circularity of two or more lithium iron phosphate precursor material particles, circularity = (4×π×A) / G 2 ; Wherein, ρ is the density of lithium iron phosphate precursor material measured by gas replacement method, K 90 = (Dv90-Dv10) / Dv50, Dv90, Dv50, and Dv10 are the particle size values ​​when the volume cumulative distribution reaches 90%, 50%, and 10% respectively in the particle size distribution, A is the projected area of ​​the lithium iron phosphate precursor material particle sample, and G is the projected circumference of the lithium iron phosphate precursor material particle sample.

[0025] Iron phosphate, as a precursor material for lithium iron phosphate, has a similar structure to lithium iron phosphate, and the morphology of the lithium iron phosphate precursor material has a significant influence on the morphology of lithium iron phosphate. Based on this, the present invention obtains a lithium iron phosphate positive electrode material with a higher tap density and a lower iron-lithium antisite defect concentration by regulating the morphology structure of the lithium iron phosphate precursor material.

[0026] Specifically, in this application, 2.6 g / cm 3 ~3.2g / cm 3 , for example, it can be 2.6 g / cm 3 , 2.7 g / cm 3 , 2.8 g / cm 3 , 2.9 g / cm 3 、3.0 g / cm 3 , 3.1 g / cm 3 , 3.2 g / cm 3 The reciprocal of ρ reflects the volume of the unit mass of the lithium iron phosphate precursor material, including the closed pores and the material skeleton. The closed pores in the lithium iron phosphate precursor material will hinder the Li + diffusion and reduce the tap density, so The larger the size, the greater the proportion of the skeleton volume in the lithium iron phosphate precursor material, the greater the tap density, and the greater the tap density of the lithium iron phosphate prepared by it; but if If the size is too large, the structure of the lithium iron phosphate precursor material will be too compact, making it difficult to break during processing and grinding, resulting in greater processing difficulty and increased damage to the grinding equipment. It should not be too high or too low. It is beneficial to balance the solid density and processing performance within the appropriate range.

[0027] K 90 It reflects the particle size distribution width of the lithium iron phosphate precursor material, and the circularity reflects the degree of spherical shape of the lithium iron phosphate precursor material particles. The closer the circularity is to 1, the higher the sphericity is. High circularity is conducive to the sintering of lithium iron phosphate with high sphericity, thereby improving the processing fluidity, dispersibility, tap density and cycle life of lithium iron phosphate. However, at the same time, too high sphericity will make it difficult to grind the lithium iron phosphate precursor material, so K 90 Properly increasing the particle size distribution and reducing the circularity can increase the collision probability during iron phosphate sand grinding and improve the sand grinding efficiency. On the other hand, when the particle circularity is high, K 90 Appropriate increase is conducive to improving the tap density, but if the roundness of the particles is poor, small particles are difficult to fill the gaps between large particles, which will reduce the tap density. It can be seen that regulating K alone 90Or the average circularity C cannot simultaneously optimize the tap density and processing performance of the precursor, and both need to be regulated to a certain range at the same time. The present invention provides a method that satisfies 0.8≤ = ≤5 lithium iron phosphate precursor material, where λ can be 0.8, 1.0, 1.2, 1.4, 1.6, 1.8, 2, 2.5, 3, 3.5, 4, 4.5, 5. Adjusting λ means simultaneously regulating K 90 and average circularity C taking into account good tap density and processing performance, wherein preferably 2.2≤ = ≤4.1.

[0028] It should be noted that in order to calculate the average circularity C in this application, a sample of lithium iron phosphate precursor material particles can be selected, photographed or subjected to SEM testing, etc., to obtain the projected area and projected perimeter of several lithium iron phosphate precursor material particle samples. The circularity of multiple lithium iron phosphate precursor material particle samples is obtained and the average value is calculated. Specifically, the number of samples can be 5, 10, 20, or even more. In theory, the more samples there are, the higher the accuracy.

[0029] In summary, and λ together affect the tap density and processing performance of the lithium iron phosphate precursor material. The present invention provides a lithium iron phosphate precursor material that satisfies 2.6 g / cm 3 ~3.2g / cm 3 and 0. 0.8≤ = ≤5, the lithium iron phosphate precursor material has a high tap density and good processing performance, the lithium iron phosphate prepared by the carbon reduction method has a high tap density, thereby having a high volumetric capacity, and the prepared battery has a high energy density.

[0030] In an optional embodiment, the total pore volume corresponding to the pores with a pore diameter of less than 200 nm of the lithium iron phosphate precursor material obtained by analyzing the nitrogen adsorption and desorption isotherm by the BJH method is less than 0.2 cm 3 / g, for example, 0.2 cm 3 / g, 0.18 cm 3 / g, 0.16 cm 3 / g, 0.14 cm 3 / g, 0.12 cm 3 / g, 0.10cm 3 / g, 0.08cm 3 / g, 0.06cm 3 / g, 0.04cm 3 / g, 0.02cm3 / g; preferably, the total pore volume of the lithium iron phosphate precursor material with pores less than 200 nm obtained by analyzing the nitrogen adsorption and desorption isotherm by the BJH method is less than 0.05 cm 3 / g.

[0031] Pores below 200 nm are not conducive to mixing with lithium sources and are not conducive to the Li + Diffusion and Fe 3+ The reduction of the pores reduces the number of these pores, which is beneficial to reducing the concentration of iron-lithium antisite defects in the lithium iron phosphate cathode material and improving its crystallization properties.

[0032] In an optional embodiment, the lithium iron phosphate precursor material is doped with at least one of the elements Al, Ni, Co, Mn, Ti, La, Ce, Cr, Mo, Ca, Ga, V, Nb, Zr, In, Zn, and Y. A small amount of doped metal elements is beneficial to improving the comprehensive performance of the lithium iron phosphate material prepared therefrom.

[0033] In an optional embodiment, the K of the lithium iron phosphate precursor material 90 is 0.45 to 2, for example, 0.45, 0.7, 1.0, 1.3, 1.6, 2.0, preferably 0.77 to 1.63; K 90 Within this range, the effect of large and small particle grading can be achieved, which is beneficial to increasing the tap density of the lithium iron phosphate precursor material and optimizing the processing performance.

[0034] In an optional embodiment, the C of the lithium iron phosphate precursor material is 0.35~0.6, for example, it can be 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, and preferably 0.38~0.45; the roundness within this range is beneficial to increase the collision probability between iron phosphate particles during sanding, and at the same time, small particles of iron phosphate can also fill the gaps between large particles of iron phosphate, which is beneficial to both solid density and processing performance.

[0035] In an optional embodiment, the Dv50 of the lithium iron phosphate precursor material is 2μm~7.5μm, for example, it can be 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 7.5μm, preferably 4μm~6μm; if the particle size is too large, the processing difficulty will increase; conversely, if the particle size is too small, the tap density will decrease, so the particle size needs to be reasonably selected.

[0036] In an optional embodiment, the tap density TD of the lithium iron phosphate precursor material is 0.6 g / cm 3 ~2.0g / cm 3 , for example, it can be 0.6 g / cm 3 , 0.8 g / cm 3, 1.0 g / cm 3 , 1.2 g / cm 3 , 1.4 g / cm 3 , 1.6 g / cm 3 , 1.8 g / cm 3 , 2.0g / cm 3 The improvement of the tap density of the lithium iron phosphate precursor material is beneficial to the improvement of the tap density of the lithium iron phosphate material prepared therefrom.

[0037] An embodiment of the present invention further provides a method for preparing the lithium iron phosphate precursor material according to any one of the aforementioned embodiments, comprising: preparing a solution, namely, preparing a water-soluble metal salt aqueous solution and a phosphorus source aqueous solution; Emulsion preparation: mixing an aqueous solution of a water-soluble metal salt with an emulsifier, an initiator, and an oil phase solvent and homogenizing to obtain a water-in-oil emulsion, wherein the emulsifier includes a reactive emulsifier; preparing amorphous ferric phosphate by adding an aqueous solution of a phosphorus source to the water-in-oil emulsion to react and generate amorphous ferric phosphate; Calcination: calcining the amorphous iron phosphate to obtain the lithium iron phosphate precursor material.

[0038] The present invention adopts an emulsion method to prepare amorphous ferric phosphate with controllable particle size and density. After calcination, the amorphous ferric phosphate can simultaneously meet the following two conditions: ① 2.6 g / cm 3 ~3.2g / cm 3 ,②0.8≤ = ≤5, where C=(4×π×A) / G 2 A lithium iron phosphate precursor material having good tap density and processing performance.

[0039] The present invention uses a water-soluble metal salt aqueous solution as the water phase and an oil phase solvent containing a reactive emulsifier and an initiator as the oil phase to prepare a water-in-oil emulsion. The emulsifier is distributed at the interface between the two phases. Its amphiphilicity stabilizes the droplets, thereby forming small independent reaction spaces, thereby effectively controlling the particle size and sphericity of the ferric phosphate precipitate formed therein and facilitating the avoidance of ferric phosphate agglomeration.

[0040] In an optional embodiment, during the solution preparation step, the water-soluble metal salt aqueous solution further includes ethylene glycol, and the mass fraction of ethylene glycol in the water-soluble metal salt aqueous solution is 4% to 8%, for example, 4%, 5%, 7%, 6%, or 8%. Ethylene glycol can serve as a dispersant, helping to prevent the generated ferric phosphate from agglomerating and improving the circularity of the ferric phosphate.

[0041] In an optional embodiment, in the liquid preparation step, the metal ions in the water-soluble metal salt aqueous solution include trivalent iron ions. In an optional embodiment, the metal ions in the water-soluble metal salt aqueous solution also include doped metal ions. The presence of doped metal ions is beneficial to improving the performance of the lithium iron phosphate positive electrode material; wherein the trivalent iron salt is selected from at least one of ferric sulfate, ferric chloride, ferric nitrate, and ferric acetate; the doped metal ions are also added to the metal salt aqueous solution in the form of sulfate, chloride, nitrate, and acetate.

[0042] In an optional embodiment, in the solution preparation step, the concentration of metal ions in the water-soluble metal salt aqueous solution is 0.2M~1M, for example, it can be 0.2M, 0.4M, 0.6M, 0.8M, or 1M.

[0043] In an optional embodiment, in the solution preparation step, the phosphorus concentration in the phosphorus source aqueous solution is 0.5M~1.2M, for example, it can be 0.5M, 0.6M, 0.8M, 1M, or 1.2M; the phosphorus source can be a mixture of phosphoric acid and phosphate, and the phosphate is at least one of ammonium dihydrogen phosphate, ammonium hydrogen phosphate, ammonium phosphate, sodium dihydrogen phosphate, sodium hydrogen phosphate, and sodium phosphate.

[0044] In an optional embodiment, in the solution preparation step, the pH value of the phosphorus source aqueous solution is 0.5-2, for example, it can be 0.5, 1.0, 1.5, or 2.

[0045] The concentration of metal ions and phosphorus source and pH will affect the precipitation rate and purity of ferric phosphate, so they need to be selected reasonably.

[0046] In an optional embodiment, during the emulsion preparation step, the emulsifier further comprises a nonionic emulsifier, which may be Span 80. The amount of the nonionic emulsifier used is 1% to 3% by weight of the oil phase solvent, for example, 1%, 1.5%, 2%, 2.5%, or 3%. The use of a nonionic emulsifier in combination with a reactive emulsifier is beneficial for improving the stability of the emulsion.

[0047] In an optional embodiment, in the emulsion preparation step, the oil phase solvent is selected from C6-C12 alkanes, and the number of carbon atoms can be 6, 7, 8, 9, 10, 11, or 12.

[0048] In an optional embodiment, in the emulsion preparation step, the volume ratio of the water-soluble metal salt aqueous solution to the oil phase solvent is 1:3-5, for example, 1:3, 1:3.5, 1:4, 1:4.5, or 1:5.

[0049] In an optional embodiment, in the emulsion preparation step, the reactive emulsifier is a phosphate reactive emulsifier, which can be selected from at least one of British Croda 6112, Idico REASOAP PP70, Solvay RHODAFAC RS610, and phosphate reactive emulsifier LRP-10; using the phosphate reactive emulsifier as the emulsifier, on the one hand, the phosphate reactive emulsifier can be used to react with Fe in the initial stage of the precipitation reaction. 3+ Complexation is carried out to avoid excessive precipitation and thus excessive internal closed pores; on the other hand, as the heating reaction proceeds, the phosphate reactive emulsifier polymerizes under thermal initiation, and Fe 3+ The precipitation reaction is slowly released, the droplets gradually break up, and the reactive emulsifier after polymerization covers the surface of the precipitate and can act as a porogen and excipient. It is gasified during calcination to form pores on the surface of the particles and maintain the spherical morphology of the particles, thereby increasing the number and circularity of the pores in the lithium iron phosphate precursor material and promoting Li + of the spread.

[0050] In an optional embodiment, in the emulsion preparation step, the mass ratio of the reactive emulsifier to the oil phase solvent is 1% to 6.5%, for example, 1%, 2%, 3%, 4%, 5%, or 6.5%.

[0051] In an optional embodiment, in the emulsion preparation step, the initiator is selected from at least one of azobisisobutyronitrile, azobisisovaleronitrile, dibenzoyl peroxide, diisopropyl peroxydicarbonate, and di-tert-butyl peroxide.

[0052] In an optional embodiment, in the emulsion preparation step, the initiator is 1% to 2% by mass of the reactive emulsifier, for example, 1%, 1.5%, or 2%.

[0053] In an optional embodiment, in the emulsion preparation step, the rotation speed of the homogenization step is 1000 rpm ~ 5000 rpm, for example, it can be 1000 rpm, 2000 rpm, 3000 rpm, 4000 rpm, 5000 rpm, and the time is 20 min ~ 40 min, for example, it can be 20 min, 30 min, 40 min.

[0054] In an optional embodiment, in the emulsion preparation step, the average particle size of droplets in the water-in-oil emulsion is 3 μm to 10 μm, for example, 3 μm, 5 μm, 7 μm, 9 μm, or 10 μm.

[0055] By rationally selecting the types and amounts of emulsifiers, initiators, and oil phase solvents and controlling the homogenization conditions, the stability of the emulsion can be improved. At the same time, the size of the droplets in the emulsion can be adjusted, which in turn helps to improve the purity, sphericity, particle size and pore volume of the subsequently prepared iron phosphate.

[0056] In an optional embodiment, in the step of preparing amorphous ferric phosphate, the molar ratio of phosphorus to iron is 1.05 to 1.5, for example, 1.05, 1.10, 1.15, 1.20, 1.25, 1.30, 1.35, 1.40, 1.45, or 1.5; In an optional embodiment, the reaction temperature is 50°C to 80°C, for example, 50°C, 60°C, 70°C, or 80°C; the reaction time is 3h to 6h, for example, 3h, 4h, 5h, or 6h; the reaction is carried out under stirring at a stirring speed of 300 rpm to 500 rpm, for example, 300 rpm, 350 rpm, 400 rpm, 450 rpm, or 500 rpm.

[0057] Controlling the reaction conditions is beneficial to adjusting the reaction rate and obtaining iron phosphate materials with satisfactory void structure and particle size.

[0058] In an optional embodiment, the calcination temperature is 600°C to 750°C, for example, 600°C, 650°C, 700°C, or 750°C; the heating rate is 3°C / min to 5°C / min, for example, 3°C / min, 4°C / min, or 5°C / min; and the calcination time is 2h to 3h, for example, 2h, 2.5h, or 3h.

[0059] The main purpose of the calcination step is to achieve the conversion of amorphous iron phosphate into iron phosphate that meets the above-mentioned ρ and λ requirements. At the same time, the organic matter included in the amorphous iron phosphate particles will be removed to form a relatively rich void structure.

[0060] An embodiment of the present invention further provides an application of the lithium iron phosphate precursor material described in any of the aforementioned embodiments, wherein the lithium iron phosphate precursor is used to prepare a lithium iron phosphate material, and the lithium iron phosphate material is prepared from the lithium iron phosphate precursor material and a lithium salt.

[0061] In an optional embodiment, the lithium iron phosphate material is used to prepare a secondary battery.

[0062] An embodiment of the present invention further provides a lithium iron phosphate material, which is prepared using the lithium iron phosphate precursor material and lithium salt described in any one of the aforementioned embodiments.

[0063] An embodiment of the present invention further provides a secondary battery, comprising the lithium iron phosphate material described in the aforementioned embodiment.

[0064] The features and performance of the present invention are further described in detail below with reference to the embodiments.

[0065] Example 1 This embodiment provides a method for preparing a lithium iron phosphate precursor material, comprising the following steps: Step S1: preparing an aqueous solution of ferric sulfate with an iron concentration of 0.8 M and ethylene glycol of 6% by mass, and an aqueous solution of a phosphorus source with a phosphorus concentration of 0.9 M and a pH of 1.5, wherein the phosphorus source is prepared by mixing phosphoric acid and ammonium dihydrogen phosphate; The ferric sulfate aqueous solution and the phosphorus source solution are fed in a ratio of n(P):n(Fe) of 1.05.

[0066] Step S2: adding an emulsifier, an initiator, and an oil phase solvent to the ferric sulfate aqueous solution, mixing and homogenizing to obtain a water-in-oil emulsion; Among them, the emulsifier is a mixture of British Croda 6112 and Span80 in a mass ratio of 1:1; the initiator is dibenzoyl peroxide; the oil phase solvent is n-octane; the volume ratio of ferric sulfate aqueous solution to the oil phase solvent is 1:4; the emulsifier is 4% of the mass of the oil phase solvent, and the initiator is 2% of the mass of British Croda 6112; the homogenization speed is 3000 rpm, and the time is 30 minutes; the average particle size of the droplets in the oil-in-water emulsion is 6.8 μm.

[0067] Step S3: adding the phosphorus source aqueous solution to the water-in-oil emulsion under stirring, then heating the solution for reaction, and after solid-liquid separation, washing with ethanol and drying the solution to obtain amorphous iron phosphate; The heating reaction temperature was 60° C., the stirring speed was 300 rpm, and the reaction time was 4 h; the drying temperature was 120° C. and the time was 8 h.

[0068] Step S4: calcining the amorphous iron phosphate to obtain a lithium iron phosphate precursor material. The SEM image of the lithium iron phosphate precursor material is as follows: Figure 1 As shown, the calcination temperature is 700°C, the heating rate is 3°C / min, and the calcination time is 3h.

[0069] Example 2 This embodiment provides a method for preparing a lithium iron phosphate precursor material, which differs from Example 1 in that, in step S2, the volume ratio of the aqueous solution of ferric sulfate to the oil phase solvent is 1:5; the emulsifier is 6% of the mass of the oil phase solvent; the homogenization speed is 1000 rpm, and the time is 40 minutes; and the average particle size of the droplets in the oil-in-water emulsion is 6.9 μm.

[0070] Example 3 This embodiment provides a method for preparing a lithium iron phosphate precursor material, which differs from Example 1 in that, in step S2, the volume ratio of the aqueous ferric sulfate solution to the oil phase solvent is 1:3; the emulsifier is 2% of the mass of the oil phase solvent; the homogenization speed is 5000 rpm, and the time is 20 minutes; and the average particle size of the droplets in the oil-in-water emulsion is 6.8 μm.

[0071] Example 4 This embodiment provides a method for preparing a lithium iron phosphate precursor material, wherein step S1 differs from step S1 of embodiment 1 in that: ethylene glycol is not added to the ferric sulfate aqueous solution; Step S2 differs from step S2 of Example 1 in that: the emulsifier is Croda 6122 from the UK; the oil phase solvent is cyclohexane; the volume ratio of the aqueous ferric sulfate solution to the oil phase solvent is 1:3; the initiator is 1% of the mass of the reactive emulsifier; and the average particle size of the droplets in the water-in-oil emulsion is 6.2 μm.

[0072] The difference between step S3 and step S3 of embodiment 1 is that the heating reaction temperature is 50° C., the stirring speed is 300 rpm, and the reaction time is 4 h.

[0073] Step S4 is the same as step S4 in Example 1. The SEM image of the lithium iron phosphate precursor material is as follows: Figure 2 shown.

[0074] Example 5 This embodiment provides a method for preparing a lithium iron phosphate precursor material, wherein step S1 is the same as step S1 in embodiment 1; Step S2 differs from step S2 of Example 1 in that: the emulsifier is a mixture of British Croda 6112: span80=1:1.2 (mass ratio); the oil phase solvent is n-dodecane; the emulsifier accounts for 6% of the mass of the oil phase solvent, and the initiator accounts for 2% of the mass of the reactive emulsifier; and the average particle size of the droplets in the water-in-oil emulsion is 7.1 μm.

[0075] The difference between step S3 and step S3 of Example 1 is that the heating reaction temperature is 80° C., the stirring speed is 300 rpm, and the reaction time is 4 h.

[0076] Step S4 is the same as step S4 in Example 1.

[0077] Example 6 This embodiment provides a method for preparing a lithium iron phosphate precursor material, comprising the following steps: Step S1: preparing a 1M aqueous solution of ferric sulfate and a 1.2M aqueous solution of a phosphorus source with a pH of 2, wherein the phosphorus source is prepared by mixing phosphoric acid and ammonium hydrogen phosphate; The ferric sulfate aqueous solution and the phosphorus source solution are fed in a ratio of n(P):n(Fe) of 1.2.

[0078] Step S2: adding an emulsifier, an initiator, and an oil phase solvent to the ferric sulfate aqueous solution, mixing and homogenizing to obtain a water-in-oil emulsion; Among them, the emulsifier is a sulfonate reactive emulsifier: Aidico SR10; the initiator is di-tert-butyl peroxide; the oil phase solvent is cyclohexane; the volume ratio of aqueous ferric sulfate solution to the oil phase solvent is 1:4; the emulsifier is 6% of the mass of the oil phase solvent, and the initiator is 2% of the mass of the reactive emulsifier; the homogenization speed is 3000 rpm, and the time is 30 minutes; the average particle size of the droplets in the oil-in-water emulsion is 6.5 μm.

[0079] Step S3: adding the phosphorus source aqueous solution to the water-in-oil emulsion under stirring, and then heating the emulsion for reaction. After the reaction is completed and solid-liquid separation is performed, washing with ethanol and drying are performed to obtain amorphous iron phosphate; The heating reaction temperature was 80° C., the stirring speed was 400 rpm, and the reaction time was 4 h; the drying temperature was 120° C. and the time was 8 h.

[0080] In step S4, the amorphous iron phosphate is calcined to obtain a lithium iron phosphate precursor material.

[0081] The calcination temperature is 750°C, the heating rate is 3°C / min, and the calcination time is 3h.

[0082] Example 7 This embodiment provides a method for preparing a lithium iron phosphate precursor material, wherein step S1 is different from step S1 of embodiment 1 in that: the pH of the phosphorus source aqueous solution is 2; Step S2 differs from step S2 of Example 1 in that: the emulsifier is RS610; the oil phase solvent is n-hexane; the emulsifier is 2% of the mass of the oil phase solvent; the homogenization speed is 1000 rpm and the time is 20 min; and the average particle size of the droplets in the oil-in-water emulsion is 4.4 μm.

[0083] Step S3 is the same as step S3 in Example 1.

[0084] Step S4 is the same as step S4 in Example 1.

[0085] Example 8 This embodiment provides a method for preparing a lithium iron phosphate precursor material, wherein step S1 differs from step S1 of embodiment 1 in that: ethylene glycol is not added to the ferric sulfate aqueous solution; Step S2 differs from step S2 of Example 1 in that: the oil phase solvent is n-dodecane; and the average particle size of droplets in the water-in-oil emulsion is 8.9 μm.

[0086] Step S3 is the same as step S3 in Example 1.

[0087] Step S4 is the same as step S4 in Example 1.

[0088] Comparative Example 1 This comparative example provides a method for preparing a lithium iron phosphate precursor material, wherein step S1 differs from step S1 of embodiment 1 in that: the pH of the phosphorus source aqueous solution is 1; Step S2 differs from step S2 of Example 1 in that: the emulsifier is a sulfonate reactive emulsifier: Aidico SR10; the emulsifier accounts for 6% of the mass of the oil phase solvent; the homogenization speed is 5000 rpm, and the time is 40 min; and the average particle size of the droplets in the oil-in-water emulsion is 7.1 μm.

[0089] Step S3 is the same as step S3 in Example 1.

[0090] Step S4 is the same as step S4 in Example 1.

[0091] Comparative Example 2 This comparative example provides a method for preparing a lithium iron phosphate precursor material, wherein step S1 differs from step S1 of embodiment 1 in that: the pH of the phosphorus source aqueous solution is 2.5; The difference between step S2 and step S2 of Example 1 is that the emulsifier is a sulfonate reactive emulsifier: Aidico SR10; the emulsifier is 6% of the mass of the oil phase solvent; the homogenization speed is 2000 rpm and the time is 40 min; and the average particle size of the droplets in the oil-in-water emulsion is 5.9 μm.

[0092] Step S3 is the same as step S3 in Example 1.

[0093] Step S4 is the same as step S4 in Example 1.

[0094] Comparative Example 3 This comparative example provides a method for preparing a lithium iron phosphate precursor material, wherein step S1 differs from step S1 of Example 1 in that: the mass percentage of ethylene glycol in the ferric sulfate aqueous solution is 8%; Step S2 differs from step S2 of Example 1 in that: the oil phase solvent is n-hexane; the emulsifier is 4% by mass of the oil phase solvent; the volume ratio of the aqueous ferric sulfate solution to the oil phase solvent is 1:2; the homogenization speed is 4000 rpm and the time is 30 min; and the average particle size of the droplets in the water-in-oil emulsion is 6.5 μm.

[0095] The difference between step S3 and step S3 of Example 1 is that the heating reaction temperature is 60° C., the stirring speed is 500 rpm, and the reaction time is 6 h.

[0096] Step S4 is the same as step S4 in Example 1.

[0097] Comparative Example 4 This comparative example provides a method for preparing a lithium iron phosphate precursor material, wherein step S1 is the same as step S1 of embodiment 1; Step S2 differs from step S2 of Example 1 in that: the oil phase solvent is n-dodecane; the emulsifier is 3% of the mass of the oil phase solvent; the volume ratio of the aqueous ferric sulfate solution to the oil phase solvent is 1:8; the homogenization speed is 5000 rpm and the time is 20 min; and the average particle size of the droplets in the water-in-oil emulsion is 5.9 μm.

[0098] Step S3 is the same as step S3 in Example 1.

[0099] Step S4 is the same as step S4 in Example 1.

[0100] Comparative Example 5 This comparative example provides a method for preparing a lithium iron phosphate precursor material, wherein step S1 is the same as step S1 of embodiment 1; The difference between step S2 and step S2 of embodiment 1 is that the emulsifier is all Span80; and the average particle size of the droplets in the water-in-oil emulsion is 6.2 μm.

[0101] Step S3 is the same as step S3 in Example 1.

[0102] Step S4 is the same as step S4 in Example 1.

[0103] Test method: (1) Tap density: measured in accordance with GB / T 5162-2021.

[0104] (2) SEM: Nova NanoSEM 450 was used. Circularity test method: The obtained SEM images were analyzed using ImageJ image analysis software. ImageJ was used to identify the individual particles that could be analyzed, and then ImageJ was used to calculate the circularity of each particle = (4×π×A) / G 2 , where A is the projected area, G is the projected perimeter, and the average circularity value of the statistical samples is C. The sample size is not less than 30.

[0105] (3) Particle size and its distribution: tested using a laser particle size analyzer in accordance with GB / T 19077-2024.

[0106] (4) Density: Refer to GB / T 24203-2024 helium method and use true density tester for testing.

[0107] (5) Nitrogen adsorption and desorption test: The total pore volume corresponding to the pores with a pore diameter of less than 200 nm in the lithium iron phosphate precursor material was determined in accordance with GB / T 21650, which is hereinafter referred to as V.

[0108] (6) Grinding test: Weigh the same mass of lithium iron phosphate precursor material and perform dry ball milling. After t=0.5h, take a sample and measure the Dv50. Calculate the change rate of Dv50. Ball milling conditions: frequency of 30 Hz, 1 mm zirconia beads, and a ball-to-material mass ratio of 1:1.

[0109] Table 1

[0110] As can be seen from Table 1, the lithium iron phosphate precursor material prepared in the embodiment of the present invention has both good tap density and grinding efficiency compared with the comparative example.

[0111] Comparative Examples 1 and 2 do not meet the 2.6 g / cm 3 ≤ρ≤3.1 g / cm 3 , the ρ of Comparative Example 1 is lower than 2.6 g / cm 3 , indicating that there are more closed pores in the material particles, resulting in a lower tap density; the ρ of comparative example 2 is higher than 3.1 g / cm 3 , resulting in a low grinding efficiency. Comparative Examples 3 and 4 do not meet 0.8≤λ≤5. Since λ is greater than 5, Comparative Example 3 has good processing performance, but its tap density is low. This is because when the circularity is 0.48, if the particle size distribution is too wide, the packing density decreases; since λ is less than 0.8 in Comparative Example 4, it indicates that its particle size distribution is too narrow and / or the circularity is large, which makes its grinding efficiency low and not conducive to processing. Although Comparative Example 5 K 90 , C satisfies 0.45≤K90≤2, 0.35≤C≤0.6, but K 90 / C does not meet the requirement of 0.8≤λ≤5, resulting in poor tap density, indicating that K 90 Together with C, it determines the tap density and processing performance of the material.

[0112] Examples 1 to 3 have similar Dv50, λ, and V, but different ρ. As ρ increases, the tap density increases, but the grinding efficiency decreases.

[0113] Examples 1, 4, and 5 have similar ρ, Dv50, and V, but different λ. As λ increases, the grinding efficiency increases, and the tap density first increases and then decreases. The smaller λ is, the higher the roundness of the particles and / or the narrower the distribution, which is not conducive to grinding, and thus the grinding efficiency is low. In addition, since the tap density first increases and then decreases with the increase of λ, it indicates that K 90 Maintaining / C within an appropriate range is beneficial to improving the tap density, while too low or too high is not conducive to the tap density.

[0114] The lithium iron phosphate precursor materials prepared in the above embodiments and comparative examples were used to prepare lithium iron phosphate positive electrode materials by solid phase carbon reduction method, and the performance of the obtained lithium iron phosphate positive electrode materials was tested.

[0115] The preparation process conditions are as follows: The lithium iron phosphate precursor material, lithium carbonate, glucose, and polyethylene glycol 1500 were mixed and ground in a mass ratio of 23:5.9:1:1.5 for 4 hours, and zirconium balls were used with a ball-to-material mass ratio of 2:1 and a rotation speed of 500 rpm to obtain a slurry; the slurry was then spray-dried at a temperature of 200°C to obtain a granulated precursor; the granulated precursor was calcined at 750°C for 12 hours, and the lithium iron phosphate positive electrode material was obtained after air flow crushing, sieving, and demagnetization. The XRD pattern of the lithium iron phosphate prepared from the lithium iron phosphate precursor material in Example 1 is as shown in FIG. Figure 3 shown.

[0116] Performance testing: (1) Tap density The measurement is carried out in accordance with GB / T5162-2021.

[0117] (2) Lithium iron antisite defect The crystalline phase and structure of the lithium iron phosphate cathode material were determined using an X-ray powder diffractometer (Rigku Ultima IV). A Cu-Ka diffraction source, a wavelength of δ = 0.15406 nm, and a scan rate of 2° / min were used to obtain XRD patterns. The resulting XRD patterns were refined using GSAS-II to obtain analytical patterns. The refined results had an Rwp (weighted pattern variance factor) of ≤5%. The concentration of lithium iron phosphate antisite defects was then calculated.

[0118] Table 2

[0119] It can be seen from Table 2 that since the precursor materials prepared in different specific embodiments adopt the same preparation process, the lithium iron phosphate positive electrode material obtained by calcining in Example 1, which takes into account good tap density and grinding efficiency, has a higher tap density and a lower iron-lithium antisite defect concentration. Specifically, under the same process conditions, the tap density of the lithium iron phosphate positive electrode material obtained by sintering is related to the tap density and grinding efficiency of its precursor. Comparing Example 3 and Example 7, the tap density of the precursor is 0.98 g / cm 3 However, due to the higher grinding efficiency of Example 3, the positive electrode material prepared therefrom has a higher tap density. Furthermore, although the tap density of Comparative Example 2 is higher than that of Example 1, due to the low grinding efficiency, the tap density of the lithium iron phosphate positive electrode material obtained under the same process is lower. Therefore, in order to obtain lithium iron phosphate with a high tap density, it is necessary to simultaneously optimize the tap density and processing performance of its precursor.

[0120] Iron-lithium antisite defect is an inherent lattice dislocation phenomenon, which means that iron ions occupy the position that should be occupied by lithium ions. The existence of this defect will reduce the storage points of lithium ions, seriously hinder or even cut off the diffusion of lithium ions in the lithium iron phosphate positive electrode material, increase the activation energy of the reaction of lithium ion extraction and embedding, and cause a significant reduction in electrochemical performance. The particle size, pore structure and uniformity of mixing of the lithium iron phosphate precursor with the lithium source have an impact on the concentration of iron-lithium antisite defects contained in the prepared lithium iron phosphate positive electrode material. Specifically, suitable particle size, improved mixing uniformity and reduced small-diameter pores have a beneficial effect on reducing the concentration of iron-lithium antisite defects, which is beneficial to Li + Diffusion results in a positive electrode material with fewer defects.

[0121] In the process of preparing cathode materials from precursors, under the same process conditions, Li + The diffusion capacity of the FeLi antisite defect concentration is affected by Figure 1 It can be seen that the morphology of the lithium iron phosphate precursor has a porous structure, which is conducive to mixing with the lithium source and is beneficial to the Li + However, there are actually pores with a pore size of less than 200 nm that cannot be observed in SEM. These pores are not conducive to mixing with the lithium source and are not conducive to the Li + The diffusion of the pores reduces the number of these pores, which is beneficial to reducing the concentration of iron-lithium antisite defects.

[0122] As can be seen from the data in the table, the specific pore volume V (pore volume of pores with a pore diameter less than 200 nm) and Dv50 of Comparative Example 4 are similar to those of Example 1, but its low grinding efficiency leads to a higher concentration of iron-lithium antisite defects. Examples 3 and 4 have similar Dv50 and grinding efficiency, but because the specific pore volume V of Example 3 is larger than that of Example 4, its antisite defect concentration is higher. The V values ​​of Examples 6 and 8 are higher, resulting in higher concentrations of iron-lithium antisite defects in the lithium iron phosphate positive electrode materials prepared by both.

[0123] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A lithium iron phosphate precursor material, characterized in that: The lithium iron phosphate precursor material satisfies the following two conditions at the same time: ① 2.6 g / cm 3 ~3.2g / cm 3 ,②0.8≤ = ≤5, where C is the average circularity of two or more lithium iron phosphate precursor material particles, circularity = (4×π×A) / G 2 ; Wherein, ρ is the density of lithium iron phosphate precursor material measured by gas replacement method, K 90 = (Dv90-Dv10) / Dv50, Dv90, Dv50, and Dv10 are the particle size values ​​when the volume cumulative distribution reaches 90%, 50%, and 10% respectively in the particle size distribution, A is the projected area of ​​the lithium iron phosphate precursor material particle sample, and G is the projected circumference of the lithium iron phosphate precursor material particle sample.

2. The lithium iron phosphate precursor material according to claim 1, characterized in that The total pore volume corresponding to the pores with a pore diameter of less than 200 nm of the lithium iron phosphate precursor material obtained by analyzing the nitrogen adsorption and desorption isotherms by the BJH method is less than 0.2 cm 3 / g; and / or, 2.2 ≤ = ≤4.1; And / or, the lithium iron phosphate precursor material is doped with at least one of Al, Ni, Co, Mn, Ti, La, Ce, Cr, Mo, Ca, Ga, V, Nb, Zr, In, Zn, and Y elements.

3. The lithium iron phosphate precursor material according to claim 1, characterized in that The lithium iron phosphate precursor material satisfies at least one of the following characteristics ae: aK 90 0.45~2; preferably 0.77~1.63; bC is 0.35~0.6; preferably 0.38~0.45; c. Dv50 is 2μm ~ 7.5μm; preferably 4μm ~ 6μm; d. The total pore volume corresponding to the pores with a pore diameter of less than 200 nm of the lithium iron phosphate precursor material obtained by analyzing the nitrogen adsorption and desorption isotherms by the BJH method is less than 0.05 cm 3 / g; e. Tap density TD is 0.6 g / cm 3 ~2.0g / cm 3 .

4. A method for preparing the lithium iron phosphate precursor material according to any one of claims 1 to 3, characterized in that: include: preparing a solution, namely, preparing a water-soluble metal salt aqueous solution and a phosphorus source aqueous solution; emulsion preparation, mixing the water-soluble metal salt aqueous solution with an emulsifier, an initiator, and an oil phase solvent and homogenizing to obtain a water-in-oil emulsion, wherein the emulsifier includes a reactive emulsifier; preparing amorphous ferric phosphate by adding the phosphorus source aqueous solution to the water-in-oil emulsion to react and generate amorphous ferric phosphate; Calcination: calcining the amorphous iron phosphate to obtain the lithium iron phosphate precursor material.

5. The method for preparing a lithium iron phosphate precursor material according to claim 4, wherein: The solution preparation step satisfies at least one of the following characteristics a-f: a. The water-soluble metal salt aqueous solution further comprises ethylene glycol, wherein the mass fraction of ethylene glycol in the water-soluble metal salt aqueous solution is 4% to 8%; b. The metal ions in the water-soluble metal salt solution include ferric ions; c. The concentration of metal ions in the water-soluble metal salt aqueous solution is 0.2M~1M; d. The phosphorus concentration in the aqueous solution of the phosphorus source is 0.5M~1.2M; e. The pH value of the phosphorus source aqueous solution is 0.5 to 2; f. The metal ions in the water-soluble metal salt aqueous solution include doping metal ions.

6. The method for preparing a lithium iron phosphate precursor material according to claim 4, wherein: The emulsion preparation step satisfies at least one of the following features ai: a. The emulsifier further includes a nonionic emulsifier, wherein the nonionic emulsifier is used in an amount of 1% to 3% by mass of the oil phase solvent; b. The oil phase solvent is selected from C6~C12 alkanes; c. The volume ratio of the water-soluble metal salt aqueous solution to the oil phase solvent is 1:3~5; d. The reactive emulsifier is a phosphate reactive emulsifier; e. The mass ratio of the reactive emulsifier to the oil phase solvent is 1% to 6.5%; f. The initiator is selected from at least one of azobisisobutyronitrile, azobisisovaleronitrile, dibenzoyl peroxide, diisopropyl peroxydicarbonate and di-tert-butyl peroxide; g. The initiator is 1% to 2% of the mass of the reactive emulsifier; h. The speed of the homogenization step is 1000rpm ~5000rpm, and the time is 20min~40min; i. The average particle size of the droplets in the water-in-oil emulsion is 3 μm to 10 μm.

7. The method for preparing a lithium iron phosphate precursor material according to claim 4, wherein: In the step of preparing amorphous ferric phosphate, the molar ratio of phosphorus to iron is 1.05 to 1.5; And / or, the reaction temperature is 50° C. to 80° C., the reaction time is 3 h to 6 h, and the reaction is carried out under stirring at a stirring speed of 300 rpm to 500 rpm.

8. The method for preparing a lithium iron phosphate precursor material according to claim 4, wherein: The calcination temperature is 600°C~750°C, the heating rate is 3°C / min~5°C / min, and the calcination time is 2h~3h.

9. An application of a lithium iron phosphate precursor material, characterized in that: The lithium iron phosphate precursor is used to prepare a lithium iron phosphate material, and the lithium iron phosphate material is prepared using the lithium iron phosphate precursor material according to any one of claims 1 to 3 and a lithium salt.

10. The use according to claim 9, characterized in that The lithium iron phosphate material is used for preparing secondary batteries.

Images