Low-reversibility lithium iron phosphate precursor prepared by reaction emulsification, and preparation method and application thereof

Abstract

The application discloses a low-reversibility lithium iron phosphate precursor prepared by a reaction type emulsion method and a preparation method and application thereof. The lithium iron phosphate precursor material meets the following two conditions: ①2.44-2.86 g / cm 3 , and ②0.4<=<=2.5, wherein C is an average circularity, the circularity=(4*π*A) / G 2 ; wherein ρ is the density of the lithium iron phosphate precursor material measured by a gas displacement method, K 90 =(Dv90-Dv10) / Dv50, A is the projected area of a 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 a high tap density and good processing performance, the lithium iron phosphate prepared by a carbon reduction method from the lithium iron phosphate precursor material has a high tap density, thereby having a high volume specific capacity, and the prepared battery has a high energy density.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery cathode material technology, and more specifically, to a low-trans-site lithium iron phosphate precursor prepared by reactive emulsification, its preparation method, and its application. Background Technology

[0002] Lithium iron phosphate (LFP) is one of the most competitive cathode active materials for lithium-ion batteries currently on the market. Compared with lithium cobalt oxide and ternary cathode materials, LFP has a longer lifespan and better safety performance. Furthermore, LFP has a capacity of 170 mAh / g. -1 With its theoretical specific capacity and a plateau discharge voltage of 3.4V, it possesses considerable energy density.

[0003] Tap density refers to the packing density of powdered materials after tapping. It reflects the mass of cathode material per unit volume. Tap density is an important indicator for evaluating cathode materials and directly affects the compaction density of the prepared electrode sheet, thereby affecting the energy density of the battery.

[0004] Currently, the main methods for synthesizing lithium iron phosphate (LFP) include the high-temperature solid-state method, the hydrothermal method, and the sol-gel method. Among these, the high-temperature solid-state method has a simple and controllable process flow, making it suitable for industrial production. The high-temperature solid-state method involves using iron phosphate and a lithium source as raw materials, mixing them uniformly, and then calcining to produce LFP. Iron phosphate, as a precursor material, has a similar structure to LFP, and the morphology of the precursor material has a significant impact on the morphology of LFP. Therefore, the quality of iron phosphate directly affects the battery performance of LFP, including energy density, cycle life, and safety. However, existing battery-grade iron phosphate suffers from low tap density or an inability to simultaneously achieve both tap density and grinding efficiency, thus limiting the tap density and lithium iron phosphate antisite defect concentration of the LFP prepared from it.

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

[0006] The purpose of this invention is to provide a low-trans-site lithium iron phosphate precursor prepared by reactive emulsification, its preparation method and application, wherein the lithium iron phosphate precursor material can combine high density and grinding efficiency.

[0007] This invention is implemented as follows:

[0008] In a first aspect, the present invention provides a lithium iron phosphate precursor material, wherein the lithium iron phosphate precursor material simultaneously satisfies the following two conditions: ① 2.6 g / cm 3 ~3.2g / cm 3 ②0.8≤ = ≤5, where C is the average sphericity of two or more lithium iron phosphate precursor material particles, sphericity = (4 × π × A) / G 2 ;

[0009] Where ρ is the density of the lithium iron phosphate precursor material measured by the gas displacement method, and K 90 = (Dv90-Dv10) / Dv50, where Dv90, Dv50, and Dv10 are the particle size values ​​when the cumulative volume 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 perimeter of the lithium iron phosphate precursor material particle sample.

[0010] In an optional embodiment, the total pore volume corresponding to pores with a diameter less than 200 nm in the lithium iron phosphate precursor material, obtained by analyzing the nitrogen adsorption-desorption isotherm using the BJH method, is less than 0.2 cm³. 3 / g;

[0011] And / or, 2.2≤ = ≤4.1; and / or, the lithium iron phosphate precursor material is doped with at least one of the elements selected from Al, Ni, Co, Mn, Ti, La, Ce, Cr, Mo, Ca, Ga, V, Nb, Zr, In, Zn, and Y.

[0012] In an optional embodiment, the lithium iron phosphate precursor material satisfies at least one of the following characteristics:

[0013] aK 90 The value is 0.45~2; preferably 0.77~1.63.

[0014] bC is 0.35~0.6; preferably 0.38~0.45;

[0015] c. Dv50 is 2μm ~ 7.5μm; preferably 4μm ~ 6μm;

[0016] d. The total pore volume corresponding to pores with a diameter less than 200 nm in the lithium iron phosphate precursor material obtained by analyzing the nitrogen adsorption-desorption isotherm using the BJH method is less than 0.05 cm³. 3 / g;

[0017] e. Tap density TD is 0.6 g / cm³ 3 ~2.0g / cm 3 .

[0018] Secondly, the present invention provides a method for preparing the lithium iron phosphate precursor material according to any one of the foregoing embodiments, comprising:

[0019] Prepare the solutions: prepare aqueous solutions of water-soluble metal salts and phosphorus source solutions;

[0020] Emulsion preparation involves mixing and homogenizing the aqueous solution of the water-soluble metal salt with an emulsifier, an initiator, and an oil phase solvent to obtain a water-in-oil emulsion, wherein the emulsifier includes a reactive emulsifier;

[0021] Amorphous iron phosphate is prepared by adding the aqueous phosphorus source solution to the water-in-oil emulsion to generate amorphous iron phosphate.

[0022] The amorphous iron phosphate is calcined to obtain the lithium iron phosphate precursor material.

[0023] In an optional implementation, the liquid preparation step satisfies at least one of the following features:

[0024] a. The aqueous solution of the water-soluble metal salt also includes ethylene glycol, and the mass fraction of ethylene glycol in the aqueous solution of the water-soluble metal salt is 4% to 8%.

[0025] b. The metal ions in the aqueous solution of the water-soluble metal salt include ferric ions;

[0026] c. The concentration of metal ions in the aqueous solution of the water-soluble metal salt is 0.2M~1M;

[0027] d. The phosphorus concentration in the phosphorus source aqueous solution is 0.5M~1.2M;

[0028] e. The pH value of the phosphorus source aqueous solution is 0.5~2;

[0029] f. The metal ions in the aqueous solution of the water-soluble metal salt include doped metal ions.

[0030] In an optional implementation, the emulsion preparation step satisfies at least one of the following characteristics ai:

[0031] a. The emulsifier also includes a nonionic emulsifier, wherein the amount of the nonionic emulsifier is 1% to 3% of the mass of the oil phase solvent.

[0032] b. The oil phase solvent is selected from C6-C12 alkanes;

[0033] c. The volume ratio of the aqueous solution of the water-soluble metal salt to the oil phase solvent is 1:3~5;

[0034] d. The reactive emulsifier is a phosphate ester reactive emulsifier;

[0035] e. The mass ratio of the reactive emulsifier to the oil phase solvent is 1% to 6.5%;

[0036] f. The initiator is selected from at least one of azobisisobutyronitrile, azobisisovalerate, benzoyl peroxide, diisopropyl peroxide, and di-tert-butyl peroxide;

[0037] g. The initiator is 1% to 2% of the mass of the reactive emulsifier;

[0038] h. The homogenization step is performed at a speed of 1000 rpm to 5000 rpm for 20 min to 40 min;

[0039] i. The average droplet size in the water-in-oil emulsion is 3 μm to 10 μm.

[0040] In an optional embodiment, the phosphorus-to-iron molar ratio is 1.05 to 1.5 in the step of preparing amorphous iron phosphate.

[0041] And / or, the reaction temperature is 50℃~80℃, the reaction time is 3h~6h, and the reaction is carried out under stirring conditions at a stirring speed of 300 rpm~500 rpm.

[0042] In an optional embodiment, the calcination temperature is 600℃~750℃, the heating rate is 3℃ / min~5℃ / min, and the calcination time is 2h~3h.

[0043] Thirdly, the present invention provides the application of the lithium iron phosphate precursor material according to any one of the foregoing embodiments, wherein the lithium iron phosphate precursor is used to prepare lithium iron phosphate material, and the lithium iron phosphate material is prepared by the lithium iron phosphate precursor material and lithium salt.

[0044] Fourthly, the present invention provides the application of the aforementioned lithium iron phosphate material, wherein the lithium iron phosphate material is used in the preparation of secondary batteries.

[0045] It should be noted that the title of this invention, namely, "A Low-Trans-Potassium Iron Phosphate Precursor Prepared by Reactive Emulsification and Its Application," should be understood in the following ways: Reactive emulsification refers to the use of a reactive emulsifier as a component of the emulsifier during the preparation of lithium iron phosphate using the emulsion method. This allows the reactive emulsifier to polymerize at the droplet interface and coat the precipitate surface simultaneously with the formation of lithium iron phosphate precipitate, acting as a pore-forming agent and excipient. During calcination, it vaporizes, forming openings on the particle surface and maintaining the spherical morphology of the particles, thereby increasing the number and roundness of openings in the lithium iron phosphate precursor material. Reactive emulsification is only one means of obtaining the low-trans-potassium lithium iron phosphate precursor as defined in this invention and does not limit the product of this invention. Other methods of obtaining the precursor of this invention are not applicable. The lithium iron phosphate precursor materials specified herein also fall within the scope of protection of the claims of this invention, because this invention has fully described the good compaction density and processing performance of lithium iron phosphate precursor materials that meet specific conditions, and the low lithium iron phosphate antisite defects of the lithium iron phosphate cathode materials prepared therefrom. This indicates that the solution to the technical problem is to obtain lithium iron phosphate precursor materials that meet specific conditions, rather than their preparation methods. Furthermore, the low antisite lithium iron phosphate precursor specifically refers to the lithium iron phosphate cathode material with low lithium iron phosphate antisite defects that can be prepared using the lithium iron phosphate precursors specified in this invention. This effect is due to the good compaction density and processing and grinding performance of the lithium iron phosphate precursor materials that meet the specified range, which allows for better mixing, grinding, and sintering of the lithium source materials. + It spreads faster and more evenly.

[0046] The present invention has the following beneficial effects:

[0047] The lithium iron phosphate precursor material provided by this invention simultaneously satisfies 2.6 g / cm 3 ~3.2g / cm 3 and 0.8≤ = With a strength of ≤5, this lithium iron phosphate precursor material has a high tap density and good processing performance. The lithium iron phosphate prepared from it by carbon reduction has a high tap density, resulting in a high volumetric specific capacity and a high energy density in the prepared battery. Attached Figure Description

[0048] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0049] Figure 1The image shows a SEM image of the lithium iron phosphate precursor material prepared in Example 1.

[0050] Figure 2 The image shows a SEM image of the lithium iron phosphate precursor material prepared in Example 4.

[0051] Figure 3 The image shows the XRD pattern of lithium iron phosphate prepared from the lithium iron phosphate precursor material of Example 1. Detailed Implementation

[0052] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0053] This invention provides a lithium iron phosphate precursor material, which simultaneously satisfies the following two conditions: ① 2.6 g / cm 3 ~3.2g / cm 3 ②0.8≤ = ≤5, where C is the average sphericity of two or more lithium iron phosphate precursor material particles, sphericity = (4 × π × A) / G 2 ;

[0054] Where ρ is the density of the lithium iron phosphate precursor material measured by the gas displacement method, and K 90 = (Dv90-Dv10) / Dv50, where Dv90, Dv50, and Dv10 are the particle size values ​​when the cumulative volume 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 perimeter of the lithium iron phosphate precursor material particle sample.

[0055] 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 impact on the morphology of lithium iron phosphate. Based on this, the present invention obtains a lithium iron phosphate cathode material with high tap density and low iron lithium antisite defect concentration by controlling the morphology and structure of the lithium iron phosphate precursor material.

[0056] Specifically, in this application, 2.6 g / cm 3 ~3.2g / cm 3 For example, it can be 2.6 g / cm³. 3 2.7 g / cm 32.8 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 per unit mass of lithium iron phosphate precursor material, including closed pores and the material framework. Closed pores in the lithium iron phosphate precursor material hinder the flow of Li. + Diffusion, and reduction of tap density, therefore The larger the volume, 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 from it; however, if... If the material is too large, it will result in an overly dense structure of the lithium iron phosphate precursor material, making it difficult to break during processing and grinding, thus increasing processing difficulty and damage to grinding equipment; therefore The value should not be too high or too low; within a suitable range, it is beneficial to balance the density and processing performance of the product.

[0057] K 90 The particle size distribution width of lithium iron phosphate precursor materials is reflected, while sphericity reflects the degree to which the precursor particles resemble spheres. A sphericity closer to 1 indicates higher sphericity. High sphericity is beneficial for obtaining lithium iron phosphate with high sphericity during sintering, thereby improving the processing flowability, dispersibility, tap density, and cycle life of lithium iron phosphate. However, excessively high sphericity can lead to difficulties in grinding the lithium iron phosphate precursor materials. Therefore, K... 90 Appropriately increasing the particle size distribution and decreasing the roundness can increase the collision probability during iron phosphate grinding, thereby improving grinding efficiency. On the other hand, when the particle roundness is high, K... 90 Appropriately increasing K can improve the tapped density, but if the particle roundness is poor, small particles will have difficulty filling the gaps between large particles, thus reducing the tapped density. Therefore, adjusting K alone is not sufficient. 90 Neither the average roundness C nor the average roundness C can simultaneously optimize the tap density and processing performance of the precursor; both need to be adjusted to a certain range. This invention provides a method that satisfies 0.8 ≤ = Lithium iron phosphate precursor materials with a value ≤5, wherein λ can be 0.8, 1.0, 1.2, 1.4, 1.6, 1.8, 2, 2.5, 3, 3.5, 4, 4.5, or 5. Adjusting λ simultaneously controls K. 90 The average roundness C balances good tap density and machinability, with the preferred value being 2.2 ≤ = ≤4.1.

[0058] It should be noted that, in order to calculate the average sphericity C in this application, lithium iron phosphate precursor material particle samples can be selected, photographed, or subjected to SEM testing to obtain the projected area and projected perimeter of several lithium iron phosphate precursor material particle samples. After obtaining the sphericity of multiple lithium iron phosphate precursor material particle samples, the average value is calculated. Specifically, the number of samples can be 5, 10, 20, or even more; theoretically, the more samples, the higher the accuracy.

[0059] In summary, λ, along with other parameters, influences the tap density and processing properties of lithium iron phosphate precursor materials. This invention provides a lithium iron phosphate precursor material that simultaneously satisfies these properties. 2.6 g / cm 3 ~3.2g / cm 3 and 0. 0.8≤ = With a strength of ≤5, this lithium iron phosphate precursor material has a high tap density and good processing performance. The lithium iron phosphate prepared from it by carbon reduction has a high tap density, resulting in a high volumetric specific capacity and a high energy density in the prepared battery.

[0060] In an optional embodiment, the total pore volume corresponding to pores with a diameter less than 200 nm in the lithium iron phosphate precursor material, obtained by analyzing the nitrogen adsorption-desorption isotherm using the BJH method, is less than 0.2 cm³. 3 / g, for example, can be 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, 0.02cm 3 / g; Preferably, the total pore volume of the lithium iron phosphate precursor material with pores smaller than 200 nm, obtained by analyzing the nitrogen adsorption-desorption isotherm using the BJH method, is less than 0.05 cm³. 3 / g.

[0061] Pores smaller than 200 nm are detrimental to mixing with the lithium source and to the calcination process of Li. + diffusion and Fe 3+ The reduction of these pores helps to decrease the concentration of lithium iron phosphate antisite defects and improve the crystallinity of lithium iron phosphate cathode materials.

[0062] 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. Doping with a small amount of metal elements is beneficial to improving the overall performance of the lithium iron phosphate material prepared therefrom.

[0063] In an optional embodiment, the K of the lithium iron phosphate precursor material 90 The value is 0.45~2, for example, it can be 0.45, 0.7, 1.0, 1.3, 1.6, 2.0, preferably 0.77~1.63; K 90 Within this range, it can achieve the effect of particle size distribution, which is beneficial to increasing the tap density of lithium iron phosphate precursor materials and optimizing processing performance.

[0064] 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, or 0.6, preferably 0.38~0.45; the roundness within this range is beneficial to increasing the probability of collision between iron phosphate particles during sand milling, and at the same time, the small iron phosphate particles can also fill the gaps between the large iron phosphate particles, which is beneficial to both density and processing performance.

[0065] In an optional embodiment, the Dv50 of the lithium iron phosphate precursor material is 2μm to 7.5μm, for example, it can be 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, or 7.5μm, preferably 4μm to 6μm. If the particle size is too large, it will increase the processing difficulty; conversely, if the particle size is too small, it will lead to a decrease in tap density. Therefore, the particle size needs to be selected reasonably.

[0066] In an optional embodiment, the tap density (TD) of the lithium iron phosphate precursor material is 0.6 g / cm³. 3 ~2.0g / cm 3 For example, it can be 0.6 g / cm³ 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 Improving the tap density of lithium iron phosphate precursor materials is beneficial to improving the tap density of lithium iron phosphate materials prepared from them.

[0067] The present invention also provides a method for preparing the lithium iron phosphate precursor material according to any one of the foregoing embodiments, comprising:

[0068] Prepare the solutions: prepare aqueous solutions of water-soluble metal salts and phosphorus source solutions;

[0069] Emulsion preparation involves mixing and homogenizing an aqueous solution of a water-soluble metal salt with an emulsifier, an initiator, and an oil phase solvent to obtain a water-in-oil emulsion, wherein the emulsifier includes a reactive emulsifier;

[0070] Amorphous iron phosphate is prepared by adding an aqueous phosphorus source to the water-in-oil emulsion to generate amorphous iron phosphate.

[0071] Calcination: Amorphous iron phosphate is calcined to obtain the lithium iron phosphate precursor material.

[0072] This invention employs 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 that combines good tap density and processing performance.

[0073] This invention uses an aqueous solution of a water-soluble metal salt as the aqueous 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, and its amphiphilicity stabilizes the droplets, thereby forming small, independent reaction spaces. This effectively controls the particle size and sphericity of the iron phosphate precipitate formed therein, and helps to avoid the agglomeration of iron phosphate.

[0074] In an optional embodiment, the aqueous solution of the water-soluble metal salt further includes ethylene glycol in the solution preparation step. The mass fraction of ethylene glycol in the aqueous solution of the water-soluble metal salt is 4% to 8%, for example, 4%, 5%, 7%, 6%, or 8%. Ethylene glycol can act as a dispersant, which helps prevent the agglomeration of the generated ferric phosphate and improves the sphericity of the ferric phosphate.

[0075] In an optional embodiment, during the preparation step, the metal ions in the water-soluble metal salt aqueous solution include ferric 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 cathode material. The ferric 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, or acetate.

[0076] In an optional embodiment, during the solution preparation step, the concentration of metal ions in the aqueous solution of the water-soluble metal salt is 0.2M to 1M, for example, 0.2M, 0.4M, 0.6M, 0.8M, or 1M.

[0077] In an optional embodiment, during the solution preparation step, the phosphorus concentration in the phosphorus source aqueous solution is 0.5M to 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 can be at least one of ammonium dihydrogen phosphate, ammonium hydrogen phosphate, ammonium phosphate, sodium dihydrogen phosphate, sodium hydrogen phosphate, and sodium phosphate.

[0078] In an optional embodiment, during the solution preparation step, the pH value of the phosphorus source aqueous solution is 0.5 to 2, for example, it can be 0.5, 1.0, 1.5, or 2.

[0079] The concentration of metal ions, phosphorus source, and pH can affect the precipitation rate and purity of ferric phosphate, so they need to be selected appropriately.

[0080] In an optional embodiment, the emulsifier in the emulsion preparation step further includes a nonionic emulsifier, which may be Span 80. The amount of the nonionic emulsifier is 1% to 3% of the mass of the oil phase solvent, for example, 1%, 1.5%, 2%, 2.5%, or 3%. The combined use of a nonionic emulsifier and a reactive emulsifier is beneficial for improving the stability of the emulsion.

[0081] 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.

[0082] 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 to 5, for example, it can be 1:3, 1:3.5, 1:4, 1:4.5, or 1:5.

[0083] In an optional embodiment, in the emulsion preparation step, the reactive emulsifier is a phosphate ester reactive emulsifier, which can be selected from at least one of Croda 6112, Aldecone REASOAP PP70, Solvay RHODAFAC RS610, and phosphate ester reactive emulsifier LRP-10; using a phosphate ester reactive emulsifier as the emulsifier has the advantage that, in the initial stage of the precipitation reaction, it can react with Fe 3+ Complexation is performed to prevent excessively rapid precipitation and thus excessive internal closed pores; on the other hand, as the heating reaction proceeds, phosphate ester reactive emulsifiers polymerize under thermal initiation, Fe... 3+Slow release facilitates the precipitation reaction, causing the droplets to gradually break up. The polymerized reactive emulsifier, covering the precipitate surface, acts as a pore-forming agent and excipient. During calcination, it vaporizes, forming openings on the particle surface and maintaining the spherical morphology of the particles. This increases the number and roundness of openings in the lithium iron phosphate precursor material, promoting the formation of Li... + The spread of.

[0084] 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, it can be 1%, 2%, 3%, 4%, 5%, or 6.5%.

[0085] In an optional embodiment, in the emulsion preparation step, the initiator is selected from at least one of azobisisobutyronitrile, azobisisovalerate, benzoyl peroxide, diisopropyl peroxide, and di-tert-butyl peroxide.

[0086] In an optional embodiment, in the emulsion preparation step, the initiator is 1% to 2% of the mass of the reactive emulsifier, for example, 1%, 1.5%, or 2%.

[0087] In an optional embodiment, in the emulsion preparation step, the rotation speed of the homogenization step is 1000 rpm to 5000 rpm, for example, 1000 rpm, 2000 rpm, 3000 rpm, 4000 rpm, or 5000 rpm, and the time is 20 min to 40 min, for example, 20 min, 30 min, or 40 min.

[0088] In an optional embodiment, during the emulsion preparation step, the average droplet size in the water-in-oil emulsion is 3μm to 10μm, for example, it can be 3μm, 5μm, 7μm, 9μm, or 10μm.

[0089] By rationally selecting the types and amounts of emulsifiers, initiators, and oil phase solvents, and controlling homogenization conditions, it is beneficial to improve the stability of the emulsion. At the same time, adjusting the size of droplets in the emulsion is beneficial to improving the purity, sphericity, particle size, and pore volume of the subsequently prepared iron phosphate.

[0090] In an optional embodiment, in the step of preparing amorphous iron phosphate, the molar ratio of phosphorus to iron is 1.05 to 1.5, for example, it can be 1.05, 1.10, 1.15, 1.20, 1.25, 1.30, 1.35, 1.40, 1.45, or 1.5.

[0091] In an optional embodiment, the reaction temperature is 50℃~80℃, for example, 50℃, 60℃, 70℃, or 80℃, the reaction time is 3h~6h, for example, 3h, 4h, 5h, or 6h, the reaction is carried out under stirring conditions, and the stirring speed is 300 rpm~500 rpm, for example, 300 rpm, 350 rpm, 400 rpm, 450 rpm, or 500 rpm.

[0092] Controlling the reaction conditions helps to adjust the reaction rate and obtain iron phosphate materials with satisfactory porosity structure and particle size.

[0093] In an optional embodiment, the calcination temperature is 600℃~750℃, for example, 600℃, 650℃, 700℃, or 750℃; the heating rate is 3℃ / min~5℃ / min, for example, 3℃ / min, 4℃ / min, or 5℃ / min; and the calcination time is 2h~3h, for example, 2h, 2.5h, or 3h.

[0094] The main purpose of the calcination step is to convert amorphous iron phosphate into iron phosphate that meets the above requirements of ρ and λ. At the same time, the organic matter mixed in the amorphous iron phosphate particles will be removed, forming a relatively rich porosity structure.

[0095] The present invention also provides the application of the lithium iron phosphate precursor material described in any of the foregoing embodiments, wherein the lithium iron phosphate precursor is used to prepare lithium iron phosphate material, and the lithium iron phosphate material is prepared by the lithium iron phosphate precursor material and lithium salt.

[0096] In an optional embodiment, the lithium iron phosphate material is used to prepare a secondary battery.

[0097] The present invention also provides a lithium iron phosphate material, which is prepared by using the lithium iron phosphate precursor material and lithium salt described in any one of the foregoing embodiments.

[0098] The present invention also provides a secondary battery comprising the lithium iron phosphate material described in the foregoing embodiments.

[0099] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0100] Example 1

[0101] This embodiment provides a method for preparing lithium iron phosphate precursor materials, including the following steps:

[0102] Step S1 involves preparing an aqueous solution of ferric sulfate with an iron concentration of 0.8 M and an ethylene glycol mass percentage of 6%, and an aqueous solution of phosphorus source with an iron concentration of 0.9 M and a pH of 1.5. The phosphorus source is prepared by mixing phosphoric acid and ammonium dihydrogen phosphate.

[0103] The ferric sulfate aqueous solution and the phosphorus source solution were added in a ratio of n(P):n(Fe) of 1.05.

[0104] Step S2: Add emulsifier, initiator, and oil phase solvent to the ferric sulfate aqueous solution, mix and homogenize to obtain a water-in-oil emulsion;

[0105] The emulsifier was a mixture of Croda 6112 and Span 80 in a mass ratio of 1:1; the initiator was benzoyl peroxide; the oil phase solvent was n-octane; the volume ratio of ferric sulfate aqueous solution to oil phase solvent was 1:4; the emulsifier accounted for 4% of the mass of the oil phase solvent, and the initiator accounted for 2% of the mass of Croda 6112; the homogenization speed was 3000 rpm and the time was 30 min; the average droplet size in the water-in-oil emulsion was 6.8 μm.

[0106] In step S3, the aqueous phosphorus source solution is added to the water-in-oil emulsion under stirring, and then the reaction is carried out by heating. After solid-liquid separation, the mixture is washed with ethanol and dried to obtain amorphous iron phosphate.

[0107] The heating reaction was carried out at a temperature of 60℃, a stirring speed of 300 rpm, and a reaction time of 4 hours; the drying temperature was 120℃ and the drying time was 8 hours.

[0108] Step S4 involves calcining amorphous iron phosphate to obtain lithium iron phosphate precursor material. The SEM image of this lithium iron phosphate precursor material is shown below. Figure 1 As shown, the calcination temperature is 700℃, the heating rate is 3℃ / min, and the calcination time is 3h.

[0109] Example 2

[0110] This embodiment provides a method for preparing lithium iron phosphate precursor material. The difference from Embodiment 1 is 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 min; and the average particle size of the droplets in the water-in-oil emulsion is 6.9 μm.

[0111] Example 3

[0112] This embodiment provides a method for preparing lithium iron phosphate precursor material. The difference from Embodiment 1 is that in step S2, the volume ratio of ferric sulfate aqueous solution to oil phase solvent is 1:3; the emulsifier is 2% of the mass of oil phase solvent; the homogenization speed is 5000 rpm and the time is 20 min; the average particle size of droplets in the water-in-oil emulsion is 6.8 μm.

[0113] Example 4

[0114] This embodiment provides a method for preparing lithium iron phosphate precursor material. The difference between step S1 and step S1 in Example 1 is that ethylene glycol is not added to the ferric sulfate aqueous solution.

[0115] The difference between step S2 and step S2 in Example 1 is that: the emulsifier is Croda 6122 from the UK; the oil phase solvent is cyclohexane; the volume ratio of ferric sulfate aqueous solution to oil phase solvent is 1:3; the initiator is 1% of the mass of the reactive emulsifier; and the average droplet size in the water-in-oil emulsion is 6.2 μm.

[0116] Step S3 differs from Step S3 in Example 1 in that the heating temperature is 50°C, the stirring speed is 300 rpm, and the reaction time is 4 hours.

[0117] Step S4 is the same as step S4 in Example 1. The SEM image of the lithium iron phosphate precursor material is shown below. Figure 2 As shown.

[0118] Example 5

[0119] This embodiment provides a method for preparing lithium iron phosphate precursor material, and step S1 is the same as step S1 in Example 1;

[0120] The difference between step S2 and step S2 in Example 1 is 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 is 6% of the mass of the oil phase solvent, and the initiator is 2% of the mass of the reactive emulsifier; the average droplet size in the water-in-oil emulsion is 7.1 μm.

[0121] Step S3 differs from Step S3 in Example 1 in that the heating temperature is 80°C, the stirring speed is 300 rpm, and the reaction time is 4 hours.

[0122] Step S4 is the same as step S4 in Example 1.

[0123] Example 6

[0124] This embodiment provides a method for preparing lithium iron phosphate precursor materials, including the following steps:

[0125] Step S1: Prepare a 1M ferric sulfate aqueous solution and a phosphorus source aqueous solution with a phosphorus concentration of 1.2M and a pH of 2. The phosphorus source is prepared by mixing phosphoric acid and ammonium hydrogen phosphate.

[0126] The ferric sulfate aqueous solution and the phosphorus source solution were added in a ratio of n(P):n(Fe) of 1.2.

[0127] Step S2: Add emulsifier, initiator, and oil phase solvent to the ferric sulfate aqueous solution, mix and homogenize to obtain a water-in-oil emulsion;

[0128] The emulsifier was a sulfonate reactive emulsifier, Aidi Ke SR10; the initiator was di-tert-butyl peroxide; the oil phase solvent was cyclohexane; the volume ratio of ferric sulfate aqueous solution to oil phase solvent was 1:4; the emulsifier accounted for 6% of the mass of the oil phase solvent, and the initiator accounted for 2% of the mass of the reactive emulsifier; the homogenization speed was 3000 rpm, and the time was 30 min; the average droplet size in the water-in-oil emulsion was 6.5 μm.

[0129] In step S3, the aqueous phosphorus source solution is added to the water-in-oil emulsion under stirring, and then the reaction is heated. After the reaction is completed and solid-liquid separation is performed, the mixture is washed with ethanol and dried to obtain amorphous iron phosphate.

[0130] The heating reaction was carried out at a temperature of 80℃, a stirring speed of 400 rpm, and a reaction time of 4 hours; the drying temperature was 120℃ and the drying time was 8 hours.

[0131] Step S4 involves calcining amorphous iron phosphate to obtain lithium iron phosphate precursor material.

[0132] The calcination temperature was 750℃, the heating rate was 3℃ / min, and the calcination time was 3h.

[0133] Example 7

[0134] This embodiment provides a method for preparing lithium iron phosphate precursor material. The difference between step S1 and step S1 in Example 1 is that the pH of the phosphorus source aqueous solution is 2.

[0135] The difference between step S2 and step S2 in Example 1 is 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; the average droplet size in the water-in-oil emulsion is 4.4 μm.

[0136] Step S3 is the same as step S3 in Example 1.

[0137] Step S4 is the same as step S4 in Example 1.

[0138] Example 8

[0139] This embodiment provides a method for preparing lithium iron phosphate precursor material. The difference between step S1 and step S1 in Example 1 is that ethylene glycol is not added to the ferric sulfate aqueous solution.

[0140] The difference between step S2 and step S2 in Example 1 is that the oil phase solvent is n-dodecane; and the average droplet size in the water-in-oil emulsion is 8.9 μm.

[0141] Step S3 is the same as step S3 in Example 1.

[0142] Step S4 is the same as step S4 in Example 1.

[0143] Comparative Example 1

[0144] This comparative example provides a method for preparing lithium iron phosphate precursor material. The difference between step S1 and step S1 in Example 1 is that the pH of the phosphorus source aqueous solution is 1.

[0145] The difference between step S2 and step S2 in Example 1 is that: the emulsifier is a sulfonate reactive emulsifier: Adico SR10; the emulsifier is 6% of the mass of the oil phase solvent; the homogenization speed is 5000 rpm and the time is 40 min; the average droplet size in the water-in-oil emulsion is 7.1 μm.

[0146] Step S3 is the same as step S3 in Example 1.

[0147] Step S4 is the same as step S4 in Example 1.

[0148] Comparative Example 2

[0149] This comparative example provides a method for preparing lithium iron phosphate precursor material. The difference between step S1 and step S1 in Example 1 is that the pH of the phosphorus source aqueous solution is 2.5.

[0150] The difference between step S2 and step S2 in Example 1 is that: the emulsifier is a sulfonate reactive emulsifier: Adico 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; the average droplet size in the water-in-oil emulsion is 5.9 μm.

[0151] Step S3 is the same as step S3 in Example 1.

[0152] Step S4 is the same as step S4 in Example 1.

[0153] Comparative Example 3

[0154] This comparative example provides a method for preparing a lithium iron phosphate precursor material. The difference between step S1 and step S1 in Example 1 is that the mass percentage of ethylene glycol in the ferric sulfate aqueous solution is 8%.

[0155] The difference between step S2 and step S2 in Example 1 is that: the oil phase solvent is n-hexane; the emulsifier is 4% of the mass of the oil phase solvent; the volume ratio of ferric sulfate aqueous solution to oil phase solvent is 1:2; the homogenization speed is 4000 rpm and the time is 30 min; the average droplet size in the water-in-oil emulsion is 6.5 μm.

[0156] Step S3 differs from Step S3 in Example 1 in that the heating temperature is 60°C, the stirring speed is 500 rpm, and the reaction time is 6 hours.

[0157] Step S4 is the same as step S4 in Example 1.

[0158] Comparative Example 4

[0159] This comparative example provides a method for preparing lithium iron phosphate precursor material, and step S1 is the same as step S1 in Example 1.

[0160] The difference between step S2 and step S2 in Example 1 is that: the oil phase solvent is n-dodecane; the emulsifier is 3% of the mass of the oil phase solvent; the volume ratio of ferric sulfate aqueous solution to oil phase solvent is 1:8; the homogenization speed is 5000 rpm and the time is 20 min; the average droplet size in the water-in-oil emulsion is 5.9 μm.

[0161] Step S3 is the same as step S3 in Example 1.

[0162] Step S4 is the same as step S4 in Example 1.

[0163] Comparative Example 5

[0164] This comparative example provides a method for preparing lithium iron phosphate precursor material, and step S1 is the same as step S1 in Example 1.

[0165] The difference between step S2 and step S2 in Example 1 is that the emulsifier is entirely Span80; and the average droplet size in the water-in-oil emulsion is 6.2 μm.

[0166] Step S3 is the same as step S3 in Example 1.

[0167] Step S4 is the same as step S4 in Example 1.

[0168] Test method:

[0169] (1) Tap density: determined in accordance with GB / T 5162-2021.

[0170] (2) SEM: Nova NanoSEM 450 was used. Circularity test method: Based on the obtained SEM images, ImageJ image analysis software was used for analysis. ImageJ was used to identify analyzable individual particles, and then ImageJ was used to calculate the circularity of each particle = (4 × π × A) / G. 2 Where A is the area of ​​the projection, G is the perimeter of the projection, and C is obtained by statistically analyzing the average circularity of the samples. The sample size is no less than 30.

[0171] (3) Particle size and its distribution: The particle size was tested using a laser particle size analyzer in accordance with GB / T 19077-2024.

[0172] (4) Density: The density was tested using the helium method according to GB / T 24203-2024 and a true density tester.

[0173] (5) Nitrogen adsorption-desorption test: The total pore volume corresponding to the pores with a pore size of less than 200 nm in the lithium iron phosphate precursor material was determined according to GB / T 21650 and hereinafter referred to as V.

[0174] (6) Grinding test: Weigh the same mass of lithium iron phosphate precursor material and perform dry ball milling. Take samples at t=0.5h to measure Dv50 and calculate the rate of change of Dv50. ×100%. Ball milling conditions: frequency 30Hz, 1mm zirconia beads used for ball milling, ball-to-material mass ratio 1:1.

[0175] Table 1

[0176]

[0177] As shown in Table 1, the lithium iron phosphate precursor material prepared in the embodiments of the present invention has both good tap density and grinding efficiency compared with the comparative example.

[0178] Comparative Examples 1 and 2 do not meet the requirement of 2.6 g / cm³. 3 ≤ρ≤3.1 g / cm 3 The ρ of Comparative Example 1 is less than 2.6 g / cm³. 3 This indicates that the material particles have a large number of closed pores, resulting in a low tap density; the ρ of Comparative Example 2 is higher than 3.1 g / cm³. 3 This results in lower grinding efficiency. Comparative Examples 3 and 4 do not satisfy 0.8≤λ≤5. Comparative Example 3, due to λ being greater than 5, exhibits good processing performance, but its tap density is low. This is because, at a roundness of 0.48, if the particle size distribution is too wide, the packing density decreases. Comparative Example 4, with λ less than 0.8, indicates that its particle size distribution is too narrow and / or its roundness is too large, resulting in lower grinding efficiency and making it unfavorable for processing. Although Comparative Example 5 has K... 90C satisfies 0.45≤K90≤2 and 0.35≤C≤0.6, but K 90 / C does not satisfy 0.8≤λ≤5, resulting in a poor tap density, indicating that K 90 Together with C, it determines the tap density and processing properties of the material.

[0179] Examples 1-3 have similar Dv50, λ, and V, but different ρ. As ρ increases, the tap density increases, but the grinding efficiency decreases.

[0180] Examples 1, 4, and 5 have similar ρ, Dv50, and V, but different λ. As λ increases, the grinding efficiency increases, while the tap density first increases and then decreases. A smaller λ indicates higher particle roundness and / or narrower particle distribution, both of which are unfavorable for grinding, resulting in low grinding efficiency. Furthermore, since the tap density first increases and then decreases with increasing λ, it indicates that K... 90 Maintaining the tap density within a suitable range is beneficial for increasing the tap density; however, both excessively low and excessively high values ​​are detrimental to the tap density.

[0181] The lithium iron phosphate precursor materials prepared according to the above embodiments and comparative examples were used to prepare lithium iron phosphate cathode materials by solid-phase carbon reduction method, and the performance of the obtained lithium iron phosphate cathode materials was tested.

[0182] The preparation process conditions are as follows:

[0183] Lithium iron phosphate precursor material, lithium carbonate, glucose, and polyethylene glycol 1500 were mixed and ground for 4 hours at a mass ratio of 23:5.9:1:1.5 using zirconium balls with a ball-to-material mass ratio of 2:1 at a rotation speed of 500 rpm to obtain a slurry. The slurry was then spray-dried at 200°C to obtain a granulation precursor. The granulation precursor was calcined at 750°C for 12 hours, followed by airflow crushing, sieving, and demagnetization to obtain the lithium iron phosphate cathode material. The XRD pattern of the lithium iron phosphate prepared from the lithium iron phosphate precursor material in Example 1 is shown below. Figure 3 As shown.

[0184] Performance testing:

[0185] (1) Tap density

[0186] The determination was carried out in accordance with GB / T5162-2021.

[0187] (2) Lithium iron antisite defects

[0188] The crystal phase and structure of the lithium iron phosphate cathode material were analyzed using an X-ray powder diffractometer (Rigku Ultima IV). The diffraction source was Cu-Ka, the wavelength was δ = 0.15406 nm, and the scanning speed was 2° / min. The obtained XRD patterns were then refined using GSAS-II to obtain analytical patterns. The Rwp (weighted variance factor) of the refined pattern was ≤5%, and the concentration of antisite defects in lithium iron phosphate was calculated.

[0189] Table 2

[0190]

[0191] As shown in Table 2, since the precursor materials prepared using different specific implementation methods all employed the same preparation process, the lithium iron phosphate cathode material obtained by calcination in Example 1, which balances good tap density and grinding efficiency, exhibits higher tap density and lower lithium iron phosphate antisite defect concentration. Specifically, under the same process conditions, the tap density of the sintered lithium iron phosphate cathode material is related to the tap density and grinding efficiency of its precursor. Comparing Examples 3 and 7, the tap density of the precursor is 0.98 g / cm³. 3 However, since Example 3 has a higher grinding efficiency, the cathode material prepared from it has a higher tap density. Furthermore, although Comparative Example 2 has a higher tap density than Example 1, its lower grinding efficiency results in a lower tap density of the lithium iron phosphate cathode material under the same process conditions. Therefore, in order to obtain lithium iron phosphate with high tap density, it is necessary to simultaneously optimize the tap density and processing performance of its precursor.

[0192] Lithium iron phosphate (LiFePO4) antisite defects are an inherent lattice dislocation phenomenon where iron ions occupy positions that should be occupied by lithium ions. The presence of these defects reduces the number of lithium-ion storage sites, severely hindering or even blocking lithium-ion diffusion in LiFePO4 cathode materials, increasing the activation energy for lithium-ion extraction and insertion, and causing a significant decrease in electrochemical performance. The particle size, pore structure, and mixing uniformity of the LiFePO4 precursor with the lithium source affect the concentration of LiFePO4 antisite defects in the prepared LiFePO4 cathode material. Specifically, suitable particle size, improved mixing uniformity, and reduced small-pore size are beneficial in reducing the concentration of LiFePO4 antisite defects, which is conducive to the formation of LiFePO4 cathode materials. + Diffusion yields cathode materials with fewer defects.

[0193] During the preparation of cathode materials from precursors, under the same process conditions, Li + The diffusion capacity affects the concentration of antisite defects in lithium iron phosphate, by Figure 1 It can be seen that the lithium iron phosphate precursor has a porous structure, which is beneficial for mixing with the lithium source and for the Li-P calcination process. +Diffusion; however, there are also pores with a diameter of less than 200 nm that cannot be observed in SEM. These pores are not conducive to mixing with the lithium source and to the calcination process of Li. + The diffusion of these pores reduces the number of such pores, which helps to lower the concentration of inverse defects in lithium iron phosphate.

[0194] The data in the table show that Comparative Example 4 has a similar pore volume V (pore volume of pores with a diameter less than 200 nm) and Dv50 to Example 1, but its low grinding efficiency results in a higher concentration of lithium iron phosphate antisite defects. Examples 3 and 4 have similar Dv50 and grinding efficiency, but Example 3 has a larger pore volume V than Example 4, resulting in a higher concentration of lithium iron phosphate antisite defects. Examples 6 and 8 have higher V values, leading to a higher concentration of lithium iron phosphate antisite defects in the prepared lithium iron phosphate cathode materials.

[0195] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included 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 simultaneously meets the following conditions: 2.6 g / cm 3 ~3.2g / cm 3 ρ is the density of the lithium iron phosphate precursor material measured by the gas displacement method; 0.8≤ = ≤5, where C is the average sphericity of two or more lithium iron phosphate precursor material particles, sphericity = (4 × π × A) / G 2 , where K 90 = (Dv90 - Dv10) / Dv50, where Dv90, Dv50, and Dv10 are the particle size values ​​when the cumulative volume distribution reaches 90%, 50%, and 10%, respectively; A is the projected area of ​​the lithium iron phosphate precursor material particle sample; G is the projected perimeter of the lithium iron phosphate precursor material particle sample; C is 0.35~0.6; K 90 The value is 0.45~2, and the Dv50 value is 2μm~7.5μm; The total pore volume corresponding to pores with a diameter less than 200 nm in the lithium iron phosphate precursor material, obtained by analyzing the nitrogen adsorption-desorption isotherm using the BJH method, is less than 0.2 cm³. 3 / g; The tap density (TD) is 0.6 g / cm³. 3 ~2.0g / cm 3 .

2. The lithium iron phosphate precursor material according to claim 1, characterized in that, 2.2≤ = ≤4.1； And / or, the lithium iron phosphate precursor material is doped with at least one of the elements selected from Al, Ni, Co, Mn, Ti, La, Ce, Cr, Mo, Ca, Ga, V, Nb, Zr, In, Zn, and Y.

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: a. K 90 The value ranges from 0.77 to 1.

63. b. C is 0.38~0.45; c. Dv50 is 4μm~6μm; d. The total pore volume corresponding to pores with a diameter less than 200 nm in the lithium iron phosphate precursor material obtained by analyzing the nitrogen adsorption-desorption isotherm using the BJH method is less than 0.05 cm³. 3 / g.

4. A method for preparing the lithium iron phosphate precursor material according to any one of claims 1-3, characterized in that, include: Prepare the solutions: prepare aqueous solutions of water-soluble metal salts and phosphorus source solutions; Emulsion preparation involves mixing and homogenizing the aqueous solution of the water-soluble metal salt with an emulsifier, an initiator, and an oil phase solvent to obtain a water-in-oil emulsion, wherein the emulsifier includes a reactive emulsifier; Amorphous iron phosphate is prepared by adding the aqueous phosphorus source solution to the water-in-oil emulsion to generate amorphous iron phosphate. The amorphous iron phosphate is calcined to obtain the lithium iron phosphate precursor material.

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

6. The method for preparing the lithium iron phosphate precursor material according to claim 4, characterized in that, The emulsion preparation steps satisfy at least one of the following characteristics ai: a. The emulsifier further includes a nonionic emulsifier, wherein the amount of the nonionic emulsifier is 1% to 3% of the mass of the oil phase solvent; b. The oil phase solvent is selected from C6-C12 alkanes; c. The volume ratio of the aqueous solution of the water-soluble metal salt to the oil phase solvent is 1:3~5; d. The reactive emulsifier is a phosphate ester 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, azobisisovalerate, benzoyl peroxide, diisopropyl peroxide, and di-tert-butyl peroxide; g. The initiator is 1% to 2% of the mass of the reactive emulsifier; h. The homogenization step is performed at a speed of 1000 rpm to 5000 rpm for 20 min to 40 min; i. The average droplet size in the water-in-oil emulsion is 3 μm to 10 μm.

7. The method for preparing the lithium iron phosphate precursor material according to claim 4, characterized in that, In the preparation of amorphous iron phosphate, the molar ratio of phosphorus to iron is 1.05~1.5; And / or, the reaction temperature is 50℃~80℃, the reaction time is 3h~6h, and the reaction is carried out under stirring conditions at a stirring speed of 300 rpm~500 rpm.

8. The method for preparing the lithium iron phosphate precursor material according to claim 4, characterized in that, The calcination temperature is 600℃~750℃, the heating rate is 3℃ / min~5℃ / 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 lithium iron phosphate materials, which are prepared using the lithium iron phosphate precursor material and lithium salt as described in any one of claims 1-3.

10. The application according to claim 9, characterized in that, The lithium iron phosphate material is used in the preparation of secondary batteries.

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