Iron phosphate material and preparation method thereof, lithium iron phosphate material and preparation method and application thereof

Abstract

The application belongs to the technical field of batteries, and provides a kind of iron phosphate material and its preparation method, a kind of lithium iron phosphate material and its preparation method and application.The iron phosphate material includes large particle hollow iron phosphate and small particle solid iron phosphate, and the large particle hollow iron phosphate includes an iron phosphate shell layer and a carbon layer on the inner surface of the shell layer.The preparation method of the iron phosphate material includes: after preparing an emulsion, the emulsion is gelled to form a hollow template agent, and an iron phosphate shell layer is formed on the outer surface of the hollow template agent;solid iron phosphate is formed using spherical nano iron phosphate as a seed crystal.Lithium iron phosphate is prepared using the iron phosphate material, and the morphology of the above-mentioned iron phosphate material is inherited, and a carbon layer is further coated on the outer surface of the hollow lithium iron phosphate and the solid lithium iron phosphate, which shortens the lithium ion transmission path, alleviates the reduction of the tap density of the hollow material, and improves the rate performance and tap density.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of lithium battery materials, and in particular relates to a kind of iron phosphate material and preparation method thereof, a kind of lithium iron phosphate material and preparation method and application thereof. BACKGROUND

[0002] The main advantages of lithium iron phosphate (LiFePO4) material include wide raw material sources, environmental friendliness, high theoretical capacity (170 mAh / g), and stable discharge platform. However, due to the olivine structure characteristics, FeO6 does not form a continuous shared octahedral network, so it cannot form a good electronic conduction network, resulting in low electronic conductivity of LiFePO4. At the same time, PO4 tetrahedron is located between FeO6 layers, limiting the change of crystal volume and hindering the diffusion movement of Li+, resulting in extremely low lithium ion diffusion rate. +

[0003] In view of the shortcomings of lithium iron phosphate battery, common improvement methods include preparation of hollow structure, carbon coating, and nanocrystallization of the material.

[0004] CN113540455A discloses a kind of hollow carbon-coated lithium iron phosphate particles and preparation method and application thereof. Hollow lithium phosphate is prepared, then iron salt and phosphorus source are added to convert into hollow lithium iron phosphate precursor particles. By mixing with carbon source, hollow carbon-coated lithium iron phosphate is obtained by spray drying and sintering under protective atmosphere.

[0005] Hollow lithium iron phosphate affects the tap density of the material. In order to improve the tap density, the prior art uses large and small particle grading to improve the rate performance. However, large particle hollow lithium iron phosphate makes it difficult for lithium ions to be inserted / extracted, and during calcination, the size grading of particles can cause "overburning".

[0006] Therefore, the present application is proposed. SUMMARY

[0007] The present application aims to provide a kind of iron phosphate material and preparation method thereof, a kind of lithium iron phosphate material and preparation method and application thereof, which aims to improve the lithium ion diffusion rate of the positive electrode material and improve the rate performance. At the same time, the size grading of particles can alleviate the reduction of tap density caused by hollow lithium iron phosphate material.

[0008] In a first aspect, the present application provides an iron phosphate material containing large particle hollow iron phosphate and small particle solid iron phosphate. The large particle hollow iron phosphate includes an iron phosphate shell layer and a carbon layer on the inner surface of the iron phosphate shell layer.

[0009] In some embodiments of the present application, the iron phosphate material has at least one of the following characteristics one to three:

[0010] ​Feature one: the average particle size of the large-particle hollow iron phosphate is in the range of 2.0-4.0 μm, and the average particle size of the small-particle solid iron phosphate is in the range of 0.9-2 μm;

[0011] Feature two: the shell thickness of the iron phosphate is in the range of 300-700 nm;

[0012] Feature three: the thickness of the carbon layer on the inner surface of the shell of the iron phosphate is in the range of 100-200 nm.

[0013] In a second aspect, the present application further provides a preparation method of the iron phosphate material, comprising the following steps:

[0014] adding the solid template agent into the dispersion of the hollow template agent to obtain a suspension, adding a second iron salt and a phosphorus source into the suspension to obtain a reaction solution, stirring the reaction solution, and calcining the obtained solid to obtain the iron phosphate material;

[0015] In some embodiments of the present application, the dispersion of the hollow template agent is prepared by mixing soybean protein isolate, a surfactant and water to form a dispersion system, mixing and stirring the dispersion system with an oil phase solvent to obtain an emulsion, and further adding a first iron salt into the emulsion to perform a gelation reaction, thereby obtaining the dispersion of the hollow template agent.

[0016] In some embodiments of the present application, the suspension further comprises ethanol, and the mixing order of the components is as follows: first, the dispersion of the hollow template agent is prepared, then the solid template agent is added into the dispersion and mixed uniformly, and finally the ethanol is added and stirred uniformly.

[0017] In some embodiments of the present application, the preparation method of the iron phosphate material satisfies at least one of the following preparation conditions ①-⑨:

[0018] Condition ①: the added amount of the ethanol is 15%-20% of the volume of the dispersion;

[0019] Condition ②: the concentration of the phosphorus source in the reaction solution is 0.9-2 mol / L;

[0020] Condition ③: the molar ratio of iron element to phosphorus element in the reaction solution is 1:(1-1.03);

[0021] Condition ④: the solid template agent is spherical nano-iron phosphate with an average diameter of 200-500 nm;

[0022] Condition ⑤: the added amount of the solid template agent is 5wt%-10wt% of the mass of the dispersion;

[0023] Condition ⑥: the second iron salt comprises at least one of ferric chloride and ferric nitrate;

[0024] Condition ⑦: the phosphorus source comprises at least one of ammonium hydrogen phosphate, ammonium phosphate, ammonium dihydrogen phosphate, sodium hydrogen phosphate, sodium dihydrogen phosphate and sodium phosphate;

[0025] Condition ⑧: the stirring speed of the stirring reaction is 400-500 rpm, the reaction temperature is 60-90℃, and the reaction time is 8-12h.

[0026] Condition ⑨: in the calcination process, the calcination temperature is controlled to be 400-700℃, and the calcination time is 2-4h.

[0027] In some embodiments of the present application, the preparation method of the dispersion of the hollow template agent satisfies at least one of the following conditions I-VII:

[0028] Condition I: the stirring speed of the mixing and stirring is 12000-16000 rpm, and the stirring time is 3-6 min.

[0029] Condition II: the surfactant comprises at least one of polyoxyethylene fatty alcohol ether, alkyl glycoside compound, polyoxyethylene sorbitan monooleate, alkyl phenol polyoxyethylene ether, fatty alcohol polyoxyethylene ether, polyoxyethylene fatty amine, polyoxyethylene castor oil and polyoxyethylene oleyl ether; the mass fraction of the surfactant in the dispersion system is 1wt%-3wt%.

[0030] Condition III: the concentration of the soybean protein isolate in the dispersion system is 10-30mg / ml.

[0031] Condition IV: the oil phase solvent comprises at least one of kerosene, heptane, n-hexane, cyclohexane, vegetable oil and liquid paraffin.

[0032] Condition V: the volume ratio of the dispersion system to the oil phase solvent is (3-8):2.

[0033] Condition VI: the gelation reaction refers to a stirring reaction at room temperature, and the time is 10-20 min.

[0034] Condition VII: the first iron salt comprises at least one of ferric chloride and ferric nitrate; the feeding ratio of the first iron salt to the dispersion system is (0.1-0.3) mol:1L.

[0035] In a third aspect, the present application also provides a preparation method of a lithium iron phosphate material, which comprises the following steps: mixing a lithium source, a carbon source and ethanol to obtain a slurry, grinding and drying the slurry, and calcining the slurry in an inert atmosphere to obtain the lithium iron phosphate material; wherein the lithium iron phosphate material is the lithium iron phosphate material in any of the above embodiments or the lithium iron phosphate material prepared by the preparation method in any of the above embodiments.

[0036] In some embodiments, the present application provides a method for preparing a lithium iron phosphate material, wherein at least one of the following conditions a-f is satisfied:

[0037] Condition a: the lithium source is selected from at least one of lithium oxalate, lithium carbonate and lithium hydroxide;

[0038] Condition b: the carbon source is selected from at least one of glucose, sucrose, dopamine, cyclodextrin, citric acid, aniline, cellulose acetate and polyvinylpyrrolidone;

[0039] Condition c: the carbon source is 5-10% of the total mass of the lithium source and the lithium iron phosphate material;

[0040] Condition d: the slurry grinding time is 2-6h;

[0041] Condition e: the calcination temperature is 700-850℃, and the calcination time is 6-15h;

[0042] Condition f: the inert atmosphere is selected from at least one of nitrogen, helium and argon.

[0043] In a fourth aspect, the present application also provides a lithium iron phosphate material, which comprises large-particle hollow lithium iron phosphate and small-particle solid lithium iron phosphate; the large-particle hollow lithium iron phosphate comprises a lithium iron phosphate shell layer, a first carbon coating layer on the outer surface of the lithium iron phosphate shell layer, and a carbon layer on the inner surface of the lithium iron phosphate shell layer; and the small-particle solid lithium iron phosphate comprises lithium iron phosphate and a second carbon coating layer on the outer surface of the lithium iron phosphate.

[0044] In a fifth aspect, the present application also provides a positive electrode sheet, which is prepared from the lithium iron phosphate material of the third aspect and / or the fourth aspect.

[0045] The present application has the following advantages:

[0046] The lithium iron phosphate material provided by the present application comprises large-particle hollow lithium iron phosphate and small-particle solid lithium iron phosphate, the inner surface of the shell layer of the large-particle hollow lithium iron phosphate has a carbon layer, the prepared lithium iron phosphate material inherits the morphology of the above-mentioned lithium iron phosphate material, and the outer surface of the lithium iron phosphate, including the solid and hollow, is further coated with a carbon layer, the uniform and diverse carbon layer can improve the rate performance; meanwhile, the combination of the large-particle hollow lithium iron phosphate and the small-particle solid lithium iron phosphate can effectively alleviate the reduction of tap density caused by the hollow material on the basis of shortening the lithium ion transmission path. BRIEF DESCRIPTION OF DRAWINGS

[0047] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some of the embodiments of the present application, and therefore should not be considered as limiting the scope. For those skilled in the art, other related drawings can also be obtained without creative labor.

[0048] Figure 1 Process flow chart of the preparation method of lithium iron phosphate provided by the embodiments of the present application;

[0049] Figure 2 TEM image of the lithium iron phosphate material obtained in Embodiment 1. DETAILED DESCRIPTION

[0050] The embodiments of the present application will be described in detail below with reference to the embodiments, but those skilled in the art will understand that the following embodiments are only used to illustrate the present application and should not be considered as limiting the scope of the present application. The specific conditions not mentioned in the embodiments are carried out according to the conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments used are not marked with the manufacturer, which are all conventional products that can be purchased on the market.

[0051] The endpoints of the ranges and any values disclosed in the present application are not limited to the precise values stated. The ranges or values should be construed to include values adjacent and approximating such ranges or values. For values whose range is expressed in lower and upper limits, any intervening value and any value within those intervening values derived by using the same dimension between them are meant to be encompassed in the range. For values whose range is expressed in lower and upper limits, any intervening value and any value within those intervening values derived by using the same dimension between them are meant to be encompassed in the range.

[0052] The embodiments of the present application provide a lithium iron phosphate material, which includes large-particle hollow lithium iron phosphate and small-particle solid lithium iron phosphate. The large-particle hollow lithium iron phosphate includes a lithium iron phosphate shell layer and a carbon layer on the inner surface of the shell layer. The large-particle hollow lithium iron phosphate is formed by using a hollow template agent, and the small-particle solid lithium iron phosphate is formed by using a solid template agent as a seed to continue growing. The combination of large and small particles can improve the tap density of the material.

[0053] In some embodiments, the solid template agent is a nanometer lithium iron phosphate with a spherical shape and an average diameter of 200-500 nm (such as 200 nm, 300 nm, 400 nm, 500 nm, etc.).

[0054] In some embodiments, the large-particle hollow lithium iron phosphate has an average particle size in the range of 2.0 μm-4 μm (such as 2.0 μm, 2.5 μm, 3.0 μm, 3.5 μm, 4.0 μm, etc.).

[0055] In some embodiments, the iron phosphate shell layer of the large-particle hollow iron phosphate has a thickness ranging from 300 nm to 700 nm (e.g., 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, etc.).

[0056] In some embodiments, the carbon layer on the inner surface of the shell layer of the large-particle hollow iron phosphate material has a thickness ranging from 100 nm to 200 nm (e.g., 100 nm, 150 nm, 200 nm, etc.).

[0057] In some embodiments, the small-particle solid iron phosphate has an average particle size ranging from 0.9 μm to 2.0 μm (e.g., 0.9 μm, 1.2 μm, 1.6 μm, 2.0 μm, etc.).

[0058] The present application also provides a lithium iron phosphate material, which includes large-particle hollow lithium iron phosphate and small-particle solid lithium iron phosphate. The large-particle hollow lithium iron phosphate includes a lithium iron phosphate shell layer, a carbon layer on the inner surface of the lithium iron phosphate shell layer, and a first carbon-coated carbon layer on the outer surface of the lithium iron phosphate shell layer. The small-particle solid lithium iron phosphate includes a lithium iron phosphate and a second carbon-coated layer on the outer surface of the lithium iron phosphate.

[0059] Further, the present application also provides a positive electrode tab, which includes the above lithium iron phosphate and a positive electrode current collector. The lithium iron phosphate is distributed on the positive electrode current collector as a positive electrode active material.

[0060] The present application provides a preparation method of lithium iron phosphate. The process flow chart is shown in Figure 1 , which specifically includes the following steps:

[0061] S1, preparing a dispersion of hollow template agent

[0062] Soybean protein isolate, a surfactant, and water are mixed to form a dispersion system. The dispersion system is mixed with an oil phase solvent to obtain an emulsion. A first iron salt is further added to the emulsion to perform a gelation reaction, thereby obtaining a dispersion of hollow template agent. The mixed stabilizer is obtained by compounding the surfactant and the soybean protein isolate. By adding iron ions, on the one hand, the soybean protein isolate in the emulsion is gelled, so that the soybean protein isolate is combined more closely, thereby improving the stabilizing effect of the soybean protein isolate on the emulsion. On the other hand, the hollow template surface is loaded with Fe 3+ as a reaction center of iron phosphate.

[0063] In some embodiments, the surfactant is selected from at least one of polyoxyethylene fatty alcohol ether, alkyl glycoside compound, polyoxyethylene sorbitan monooleate, alkyl phenol polyoxyethylene ether, fatty alcohol polyoxyethylene ether, polyoxyethylene fatty amine, polyoxyethylene castor oil, and polyoxyethylene oleyl ether, and the surfactant can be any one or several of the above. The above surfactants can be well mixed with the soybean protein isolate, and after subsequent calcination, the surfactants can form a carbon layer together with the soybean protein isolate.

[0064] In some embodiments, the concentration of the soybean protein isolate in the dispersion system is 10-30 mg / ml, and the mass fraction of the surfactant in the dispersion system is 1wt%-3wt%. By further controlling the concentration and content of the soybean protein isolate and the surfactant, the emulsion microspheres are more stable, and the thickness of the carbon layer after calcination is controlled, which is beneficial to improve the rate performance and low-temperature stability of the lithium iron phosphate.

[0065] Specifically, the concentration of the soybean protein isolate in the dispersion system can be 10 mg / ml, 15 mg / ml, 20 mg / ml, 25 mg / ml, 30 mg / ml, etc., and the mass fraction of the surfactant can be 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, etc.

[0066] In some embodiments, an oil phase solvent is added to the dispersion system of the soybean protein isolate and the surfactant to form a mixed system, and the volume ratio of the dispersion system to the oil phase solvent is (3-8):2. By further controlling the volume ratio of the dispersion system to the oil phase solvent, the sphericity of the emulsion microspheres is higher, and the stability is better, thereby improving the tap density of the final product.

[0067] Specifically, in the solution system of the dispersion system and the oil phase solvent, the volume ratio of the dispersion system to the oil phase solvent can be 3:2, 2:1, 7:3, 3:1, 4:1, etc.

[0068] In some embodiments, a first iron salt is further added to the emulsion for gelation reaction. The gelation reaction refers to a stirring reaction at room temperature, and the time is 10-20 min. The feeding ratio of the first iron salt to the dispersion system is (0.1-0.3) mol:1 L. By controlling the concentration of the first iron salt, the soybean protein isolate in the emulsion is gelled, the soybean protein isolate is combined more closely, the stability of the emulsion is improved, and on the other hand, the surface of the soybean protein isolate is loaded with Fe 3+ as a reaction center of iron phosphate.

[0069] Specifically, the stirring time of the gelation reaction can be 10 min, 15 min, 20 min, etc., and the feeding ratio of the first iron salt to the dispersion system can be 0.1 mol:1 L, 0.2 mol:1 L, 0.3 mol:1 L, etc.

[0070] In some embodiments, the first iron salt is selected from at least one of ferric chloride and ferric nitrate, and the first iron salt can be any one or several of the above.

[0071] In some embodiments, during preparation of the dispersion of the hollow template agent, the soybean protein isolate and the surfactant can be first mixed with water to obtain a uniform dispersion system, a certain amount of oil phase solvent can be added to the dispersion system, and then high-speed stirring can be performed at 12000-16000 rpm for 3-6 min to obtain an emulsion. The first iron salt can be added to the above emulsion and stirred until completely dissolved and uniform to obtain gelled emulsion microspheres.

[0072] Specifically, after the oil phase solvent is added to the dispersion system, the mixing and stirring speed can be 12000 rpm, 13000 rpm, 14000 rpm, 15000 rpm, 16000 rpm, etc., and the stirring time can be controlled to be 3 min, 4 min, 5 min, 6 min, etc.

[0073] S2, forming large-particle hollow iron phosphate and small-particle solid iron phosphate

[0074] The solid template agent is added to the dispersion system of the hollow template agent, and ethanol is further added and mixed uniformly to obtain a suspension of the hollow template agent and the solid template agent. Since ethanol is added to the solution, the dispersibility of the nano iron phosphate in the solution is improved. The hollow template agent surface is loaded with Fe 3+ as a reaction center of iron phosphate, and the reaction forms large-particle hollow iron phosphate. At the same time, the solid template agent in the aqueous solution acts as a crystal seed, so that the iron phosphate grows further to form small-particle solid iron phosphate.

[0075] Specifically, the solid template agent is spherical nano iron phosphate with an average diameter of 200-500 nm (which can be 200 nm, 300 nm, 400 nm, 500 nm, etc.).

[0076] In some embodiments, the amount of the solid template agent added is 5wt%-10wt% of the mass of the dispersion system, and the amount of ethanol added is 15%-20% of the volume of the dispersion system, and the mixture is fully stirred and uniformly mixed. By controlling the amount of ethanol added, the dispersibility of the nano iron phosphate in the solution system is improved, and the agglomeration of the nano iron phosphate is reduced.

[0077] Specifically, the amount of the solid template agent added can be 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, etc. of the mass of the dispersion system, and the amount of ethanol added can be 15%, 16%, 17%, 18%, 19%, 20%, etc. of the volume of the dispersion system.

[0078] In some embodiments, the second iron salt and the phosphorus source are added into the suspension of the hollow template agent and the solid template agent to obtain a reaction solution, the concentration of the second iron salt and the phosphorus source in the reaction solution is 0.9-2.0 mol / L, and then the stirring reaction is performed. By controlling the concentration of the second iron salt and the phosphorus source, the shell thickness of the large particle hollow iron phosphate and the thickness of the small particle solid iron phosphate are controlled.

[0079] Specifically, the second iron salt in the reaction solution is selected from at least one of ferric chloride and ferric nitrate, and the second iron salt can be any one or several of the above; the phosphorus source in the reaction solution is selected from at least one of ammonium hydrogen phosphate, ammonium phosphate, ammonium dihydrogen phosphate, sodium hydrogen phosphate, sodium dihydrogen phosphate and sodium phosphate, and the phosphorus source can be any one or several of the above.

[0080] Further, the concentration of the second iron salt and the phosphorus source in the reaction solution can be 0.9 mol / L, 1.2 mol / L, 1.4 mol / L, 1.6 mol / L, 1.8 mol / L, 2.0 mol / L, etc.; the molar ratio of the iron element of the second iron salt to the phosphorus element of the phosphorus source in the reaction solution is 1:(1-1.03), which can be 1:1, 1:1.01, 1:1.02, 1:1.03, etc.

[0081] In some embodiments, first, the pH of the suspension of the hollow template agent and the solid template agent is controlled to be 1.5-2.2 by using an acid and / or a base, then the second iron salt and the phosphorus source are added into the suspension of the hollow template agent and the solid template agent to obtain a reaction solution, and then the stirring reaction is performed, the stirring speed is 400-500 rpm, the reaction temperature is 60-90°C, and the reaction time is 8-12 h. By controlling the reaction pH value, the reaction stirring speed, the reaction temperature and the reaction time, the iron phosphate can be uniformly deposited on the surface of the hollow template agent and the solid template agent. The acid is at least one of hydrochloric acid, nitric acid and sulfuric acid; the base is at least one of ammonia and sodium hydroxide.

[0082] Specifically, the pH of the suspension of the hollow template agent and the solid template agent can be 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.2, etc., the reaction stirring speed can be 400 rpm, 500 rpm, 600 rpm, etc., and the reaction time can be 8 h, 9 h, 10 h, 11 h, 12 h, etc.

[0083] In some embodiments, after the stirring reaction is completed, solid-liquid separation is performed, and through filtration, washing and drying, hydrated iron phosphate is obtained, the crystal water in the iron phosphate is removed by calcination, the hollow template agent is carbonized at the same time, the calcined iron phosphate material is ground to obtain anhydrous iron phosphate material.

[0084] In some embodiments, the calcination process controls the calcination temperature to be 400-700℃ and the calcination time to be 2-4h. By controlling the calcination temperature and time, the ideal particle size and iron phosphate structure are obtained.

[0085] Specifically, the calcination temperature of the calcination process can be 400℃, 450℃, 500℃, 550℃, 600℃, 650℃, 700℃, etc., and the calcination time can be 2h, 2.5h, 3h, 3.5h, 4h, etc.

[0086] S3, calcination with lithium source and carbon source

[0087] The iron phosphate material obtained in step S2, the lithium source and the carbon source are calcined. By optimizing the process of the iron phosphate material, the prepared lithium iron phosphate positive electrode material has excellent rate performance.

[0088] In some embodiments, the iron phosphate material, the lithium source, the carbon source and ethanol are mixed to obtain a slurry, the slurry is ground and then dried to obtain lithium iron phosphate precursor powder, and the precursor powder is calcined. By grinding, the precursor powder is more uniform, and by calcining, the carbon source is coated on the surface of lithium iron phosphate.

[0089] In some embodiments, the lithium source is selected from at least one of lithium oxalate, lithium carbonate and lithium hydroxide, and can be any one or several of the above. By controlling the molar ratio of lithium element in the lithium source and iron element in the iron phosphate in the mixing process, the molar ratio of lithium to iron is (1-1.04):1. By increasing the content of lithium element, it helps to refine the grain size and relieve the sintering fusion between the grains, which helps to improve the rate discharge performance of lithium iron phosphate.

[0090] Specifically, the molar ratio of lithium element in the lithium source and iron element in the iron phosphate in the mixing process can be 1.00:1, 1.01:1, 1.02:1, 1.03:1, 1.04:1, etc.

[0091] In some embodiments, the carbon source can be selected from at least one of glucose, sucrose, dopamine, cyclodextrin, citric acid, aniline, cellulose acetate, polyvinylpyrrolidone (PVP), and can be any one or several of the above. After calcination, the carbon source is coated on the surface of lithium iron phosphate to form a coating layer, forming a carbon layer.

[0092] Specifically, the carbon source is 5%-10% of the total mass of the iron phosphate material and the lithium source, such as 5%, 6%, 7%, 8%, 9%, 10%, etc.

[0093] In some embodiments, ethanol is used as a dispersant to form a slurry, the slurry is ground for 2-6h, and then dried at 60-80℃. The dried lithium iron phosphate precursor powder is calcined at 700-850℃ for 6-15h in a nitrogen atmosphere to obtain lithium iron phosphate.

[0094] Specifically, the grinding time of the slurry can be 2h, 3h, 4h, 5h, 6h, etc., the drying temperature can be 60℃, 70℃, 80℃, etc., the calcination temperature can be 700℃, 750℃, 800℃, 850℃, etc., and the calcination time can be 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, etc.

[0095] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0096] Example 1

[0097] A method for preparing an iron phosphate material includes the following steps:

[0098] (1) Soy protein isolate and polyoxyethylene sorbitan monooleate were added to deionized water and stirred until homogeneous to form a dispersion. The concentration of soy protein isolate was 20 mg / ml, and the mass percentage of polyoxyethylene sorbitan monooleate in the dispersion was 2 wt%. The dispersion was mixed with heptane at a volume ratio of 7:3 and stirred at 15000 rpm for 4 min. Ferric chloride was added at a feed ratio of 0.2 mol: 1 L and stirred at room temperature for 15 min to obtain a dispersion of hollow template agent.

[0099] (2) Spherical nano-iron phosphate with an average diameter of 350 nm, i.e., solid template agent, was added to the above dispersion at 8 wt% of the dispersion mass, and 18% of the dispersion volume of ethanol was added at the same time. The mixture was stirred evenly, and the pH of the solution was adjusted to 1.6 using hydrochloric acid or ammonia. Then, ammonium hydrogen phosphate and ferric chloride were added to obtain the reaction solution. The iron concentration in the reaction solution after the addition of ferric chloride was 1 mol / L, and the concentration of ammonium hydrogen phosphate in the reaction solution was 1.01 mol / L. The mixture was stirred at 400 rpm and reacted at 70°C for 9 h. After filtration, washing and drying, hydrated iron phosphate material was obtained. After calcination at 500°C in a nitrogen atmosphere for 3 h, iron phosphate material was obtained.

[0100] The TEM image of the iron phosphate material obtained in this embodiment is as follows: Figure 2 As shown, by Figure 2 It can be seen that this iron phosphate material contains both large-particle hollow iron phosphate material and small-particle solid iron phosphate material. The large-particle hollow iron phosphate material has a carbon layer on the inner surface of its shell. The average particle size of the large-particle hollow iron phosphate material is 3.4 μm, the average shell thickness is 480 nm, and the average carbon layer thickness on the inner surface of its shell is 150 nm. The average particle size of the small-particle solid iron phosphate material is 1.5 μm.

[0101] A preparation method of a lithium iron phosphate material, comprising the following steps:

[0102] The lithium iron phosphate material is mixed with lithium hydroxide in a molar ratio of 1:1.02, 8wt% of glucose is added to the total mass of the lithium iron phosphate material and lithium hydroxide, and then a mixed material is obtained by using ethanol as a dispersant, the amount of ethanol added is 2.5wt% of the total mass of the mixed material, the mixed material is placed in a grinding machine for grinding and stirring for 5h, and then is placed in a drying box at 70°C for drying; the dried mixed material is placed in a tube furnace, calcined at 850°C for 9h under a nitrogen atmosphere, and a lithium iron phosphate material is obtained.

[0103] The preparation steps of the lithium iron phosphate are described in the description Figure 1 .

[0104] Example 2

[0105] A preparation method of a lithium iron phosphate material, comprising the following steps:

[0106] (1) Soybean protein isolate and polyoxyethylene fatty alcohol ether are added to deionized water to form a dispersion system, the concentration of the soybean protein isolate is 10mg / ml, and the mass percentage of the polyoxyethylene fatty alcohol ether in the dispersion system is 1wt%. The above dispersion system is mixed with vegetable oil in a volume ratio of 3:2, stirred and mixed at a speed of 12000rpm for 4min; iron chloride salt is added, the feeding ratio of iron chloride to the dispersion system is 0.1mol:1L, and stirring is performed at room temperature for 10min to obtain a dispersion liquid of a hollow template agent.

[0107] (2) The average diameter of the spherical nanometer iron phosphate, i.e. a solid template agent, is 350nm, which is added to the above dispersion liquid in an amount of 5wt% of the mass of the dispersion liquid, and 15% of the volume of the dispersion liquid is added with ethanol, and then the pH of the solution is adjusted to 1.5 by using hydrochloric acid or ammonia water, and then ammonium hydrogen phosphate and iron chloride salt are added to obtain a reaction liquid, the concentration of iron in the reaction liquid after the addition of the iron chloride is 0.9mol / L, and the concentration of ammonium hydrogen phosphate in the reaction liquid is 0.92mol / L, and then stirring is performed at a speed of 400rpm, and after stirring at a temperature of 70°C for 9h, a hydrated iron phosphate material is obtained by filtration, washing and drying, and after calcination at 500°C in a nitrogen atmosphere for 3h, an iron phosphate material is obtained.

[0108] The obtained iron phosphate material is subjected to TEM testing, wherein the inner surface of the shell layer of the large-particle hollow iron phosphate material has a carbon layer, the average particle size corresponding to the large-particle hollow iron phosphate material is 3.8μm, the average thickness of the shell of the large-particle hollow iron phosphate material is 350nm, the average thickness of the carbon layer on the inner surface of the shell layer of the large-particle hollow iron phosphate material is 108nm, and the average particle size corresponding to the small-particle solid iron phosphate material is 2.0μm.

[0109] A preparation method of a lithium iron phosphate material, comprising the following steps:

[0110] The lithium iron phosphate material is obtained by mixing the above-mentioned iron phosphate material with lithium hydroxide at a molar ratio of 1:1, adding 5wt% of sucrose based on the total mass of the iron phosphate material and lithium hydroxide, and then adding ethanol as a dispersant to obtain a mixed material, wherein the amount of ethanol added is 2.5wt% of the total mass of the mixed material, and then placing the mixed material in a grinder for grinding and stirring for 6h, and then placing it in a drying box at 60°C for drying; and then placing the dried mixed material in a tube furnace, calcining at 700°C for 15h under a nitrogen atmosphere to obtain the lithium iron phosphate material.

[0111] Example 3

[0112] A preparation method of an iron phosphate material, comprising the following steps:

[0113] (1) Soybean protein isolate and fatty alcohol polyoxyethylene ether are added to deionized water to form a dispersion system, the concentration of the soybean protein isolate is 30mg / ml, and the mass percentage of the fatty alcohol polyoxyethylene ether in the dispersion system is 3wt%. The above-mentioned dispersion system is mixed with n-hexane at a volume ratio of 4:1, and then stirred at a speed of 16000rpm for 4min; then, iron chloride salt is added, and the feeding ratio of the iron chloride to the dispersion system is 0.3mol:1L, and then stirred at room temperature for 20min to obtain a dispersion liquid of a hollow template agent.

[0114] (2) The average diameter of the spherical nanometer iron phosphate, i.e. a solid template agent, is 350nm, which is added to the above-mentioned dispersion liquid at a mass percentage of 10wt% of the dispersion liquid, and at the same time, 20% of the volume of the dispersion liquid is added to ethanol, and then stirred uniformly, and then the pH of the solution is adjusted to 2.2 by using hydrochloric acid or ammonia water, and then ammonium hydrogen phosphate and iron chloride salt are added to obtain a reaction liquid, wherein the concentration of the iron element in the reaction liquid after the addition of the iron chloride is 1.98mol / L, and the concentration of the ammonium hydrogen phosphate in the reaction liquid is 2.00mol / L, and then stirred at a speed of 400rpm, and then stirred at a temperature of 70°C for 9h, and then filtered, washed and dried to obtain a hydrated iron phosphate material, and then calcined at 700°C for 2h under a nitrogen atmosphere to obtain an iron phosphate material.

[0115] The obtained iron phosphate material is subjected to TEM testing, and the obtained observation results are similar to those of Figure 2 , wherein the inner surface of the shell layer of the large-particle hollow iron phosphate material has a carbon layer, the average particle size of the large-particle hollow iron phosphate material is 2.6μm, the average thickness of the shell of the large-particle hollow iron phosphate material is 650nm, the average thickness of the carbon layer on the inner surface of the shell layer of the large-particle hollow iron phosphate material is 186nm, and the average particle size of the small-particle solid iron phosphate material is 1.2μm.

[0116] A preparation method of a lithium iron phosphate material, comprising the following steps:

[0117] The above lithium iron phosphate material is mixed with lithium hydroxide in a molar ratio of 1:1.04, 10wt% of cyclodextrin is added to the total mass of the lithium iron phosphate material and lithium hydroxide, and then a mixed material is obtained by using ethanol as a dispersant, the amount of ethanol added is 2.5wt% of the total mass of the mixed material, the mixed material is placed in a grinding machine for grinding and stirring for 6h, and then is placed in a drying box at 80℃ for drying; the dried mixed material is placed in a tube furnace, calcined at 850℃ for 9h under a nitrogen atmosphere, and a lithium iron phosphate material is obtained.

[0118] Example 4

[0119] The difference between this example and Example 1 is that in step (1), the feeding ratio of ferric chloride to the dispersion system is 0.1mol:1L, and other conditions and parameters are completely the same as those in Example 1.

[0120] The obtained lithium iron phosphate material is subjected to TEM testing, wherein the large-particle hollow lithium iron phosphate material has a carbon layer on the inner surface of the shell, the average particle size of the large-particle hollow lithium iron phosphate material is 3.6μm, the average thickness of the shell of the large-particle hollow lithium iron phosphate material is 450nm, the average thickness of the carbon layer on the inner surface of the shell of the large-particle hollow lithium iron phosphate material is 140nm, and the average particle size of the small-particle solid lithium iron phosphate material is 2.0μm.

[0121] Example 5

[0122] The difference between this example and Example 1 is that in step (1), the feeding ratio of ferric chloride to the dispersion system is 0.3mol:1L, and other conditions and parameters are completely the same as those in Example 1.

[0123] The obtained lithium iron phosphate material is subjected to TEM testing, wherein the large-particle hollow lithium iron phosphate material has a carbon layer on the inner surface of the shell, the average particle size of the large-particle hollow lithium iron phosphate material is 3.5μm, the average thickness of the shell of the large-particle hollow lithium iron phosphate material is 500nm, the average thickness of the carbon layer on the inner surface of the shell of the large-particle hollow lithium iron phosphate material is 130nm, and the average particle size of the small-particle solid lithium iron phosphate material is 1.6μm.

[0124] Example 6

[0125] The difference between this example and Example 1 is that in step (2), 5wt% of spherical nano lithium iron phosphate with an average diameter of 350nm is added to the above dispersion liquid, and other conditions and parameters are completely the same as those in Example 1.

[0126] The obtained iron phosphate material is subjected to TEM test, wherein the large particle hollow iron phosphate material shell inner surface has a carbon layer, the average particle size of the large particle hollow iron phosphate material is 3.5 μm, the average shell thickness of the large particle hollow iron phosphate material is 490 nm, the average carbon layer thickness of the large particle hollow iron phosphate material shell inner surface is 150 nm, and the average particle size of the small particle solid iron phosphate material is 1.2 μm.

[0127] Example 7

[0128] The difference between this example and Example 1 is that in step (2), 10 wt% of the spherical iron phosphate nanomaterial with an average diameter of 350 nm is added to the above solution, and other conditions and parameters are completely the same as those in Example 1.

[0129] The obtained iron phosphate material is subjected to TEM test, wherein the large particle hollow iron phosphate material shell inner surface has a carbon layer, the average particle size of the large particle hollow iron phosphate material is 3.4 μm, the average shell thickness of the large particle hollow iron phosphate material is 460 nm, the average carbon layer thickness of the large particle hollow iron phosphate material shell inner surface is 150 nm, and the average particle size of the small particle solid iron phosphate material is 1.6 μm.

[0130] Example 8

[0131] The difference between this example and Example 1 is that in step (2), 15% of the volume of the dispersion is added, and other conditions and parameters are completely the same as those in Example 1.

[0132] The obtained iron phosphate material is subjected to TEM test, wherein the large particle hollow iron phosphate material shell inner surface has a carbon layer, the average particle size of the large particle hollow iron phosphate material is 3.4 μm, the average shell thickness of the large particle hollow iron phosphate material is 470 nm, the average carbon layer thickness of the large particle hollow iron phosphate material shell inner surface is 150 nm, and the average particle size of the small particle solid iron phosphate material is 1.6 μm.

[0133] Example 9

[0134] The difference between this example and Example 1 is that in step (2), 20% of the volume of the dispersion is added, and other conditions and parameters are completely the same as those in Example 1.

[0135] The obtained iron phosphate material is subjected to TEM test, wherein the large particle hollow iron phosphate material shell inner surface has a carbon layer, the average particle size of the large particle hollow iron phosphate material is 3.4 μm, the average shell thickness of the large particle hollow iron phosphate material is 490 nm, the average carbon layer thickness of the large particle hollow iron phosphate material shell inner surface is 150 nm, and the average particle size of the small particle solid iron phosphate material is 1.4 μm.

[0136] Comparative Example 1

[0137] The difference between the present example and Example 1 is that the dispersing system of step (1) does not contain soybean protein isolate. The specific steps are as follows:

[0138] (1) Polyoxyethylene sorbitan monooleate was added to deionized water and stirred to form a dispersing system. The mass percentage of polyoxyethylene sorbitan monooleate in the dispersing system was 3wt%. The dispersing system was mixed with heptane at a volume ratio of 7:3, and stirred at a speed of 15000 rpm for 4 min. Then, ferric chloride salt was added, and the ratio of ferric chloride to the dispersing system was 0.2 mol: 1 L. The mixture was stirred at room temperature for 15 min to obtain an emulsion dispersion.

[0139] (2) Solid spherical nanometer iron phosphate with an average diameter of 350 nm, i.e. a solid template agent, was added to the above dispersing system at a mass percentage of 8wt% of the dispersing system. Ethanol was also added at a volume percentage of 18% of the dispersing system, and the mixture was stirred to form a uniform solution. The pH of the solution was adjusted to 1.6 using hydrochloric acid or ammonia. Then, sodium hydrogen phosphate and ferric chloride salt were added to obtain a reaction solution. The concentration of iron in the reaction solution after the addition of ferric chloride was 1 mol / L, and the concentration of sodium hydrogen phosphate was 1.01 mol / L. The mixture was stirred at a speed of 400 rpm and a temperature of 70°C for 9 h. After filtration, washing and drying, a hydrated iron phosphate material was obtained. The material was calcined at 500°C in a nitrogen atmosphere for 3 h to obtain an iron phosphate material.

[0140] The iron phosphate material obtained in the present example includes hollow iron phosphate and solid iron phosphate materials. The hollow iron phosphate has an irregular shape.

[0141] A method for preparing a lithium iron phosphate material includes the following steps:

[0142] The above iron phosphate material was mixed with lithium hydroxide at a molar ratio of iron to lithium of 1:1.02. Glucose was added at a mass percentage of 8wt% of the total mass of the iron phosphate material and lithium hydroxide. Then, ethanol was used as a dispersing agent to obtain a mixed material. The amount of ethanol added was 2.5wt% of the total mass of the mixed material. The mixed material was placed in a grinder and stirred for 5 h. Then, the mixed material was dried in a 70°C drying oven. The dried mixed material was placed in a tube furnace and calcined at 850°C for 9 h in a nitrogen atmosphere to obtain a lithium iron phosphate material.

[0143] Comparative Example 2

[0144] The difference between the present example and Example 1 is that the dispersing system of step (1) does not contain a surfactant. The specific steps are as follows:

[0145] (1) Soybean protein isolate was added to deionized water to form a dispersion system, and the concentration of the soybean protein isolate was 20 mg / ml. The dispersion system solution was mixed with heptane at a volume ratio of 7:3, and stirred at a speed of 15000 rpm for 4 min. Then, ferric chloride salt was added, and the ratio of ferric chloride to the dispersion system was 0.2 mol: 1 L. The mixture was stirred at room temperature for 15 min to obtain a dispersion of gelled soybean protein isolate emulsion.

[0146] (2) Solid nanometer iron phosphate with an average diameter of 350 nm, i.e. a solid template agent, was added to the dispersion system at a weight percentage of 8% of the dispersion system, and 18% of the volume of the dispersion system was added with ethanol. The mixture was stirred uniformly, and the pH of the solution was adjusted to 1.6 using hydrochloric acid or ammonia. Then, sodium hydrogen phosphate and ferric chloride salt were added to obtain a reaction solution, and the concentration of iron in the reaction solution after the addition of ferric chloride was 1 mol / L, and the concentration of sodium hydrogen phosphate in the reaction solution was 1.01 mol / L. The mixture was stirred at a speed of 400 rpm, and the reaction was carried out at a temperature of 70°C for 9 h. After filtration, washing and drying, a hydrated iron phosphate material was obtained. The material was calcined at 500°C in a nitrogen atmosphere for 3 h to obtain an iron phosphate material.

[0147] The iron phosphate material obtained in the comparative example includes hollow iron phosphate and solid iron phosphate material, and the shape of the hollow iron phosphate is irregular.

[0148] A method for preparing a lithium iron phosphate material includes the following steps:

[0149] The above-mentioned iron phosphate material was mixed with lithium hydroxide at a molar ratio of iron to lithium of 1:1.02, and 8wt% of the total mass of the iron phosphate material and lithium hydroxide was added with glucose. Then, ethanol was used as a dispersant to obtain a mixed material. The amount of ethanol added was 2.5wt% of the total mass of the mixed material. The mixed material was placed in a grinder for grinding and stirring for 5 h, and then dried in a 70°C drying box. The dried mixed material was placed in a tube furnace and heated at 850°C for 9 h in a nitrogen atmosphere to obtain a lithium iron phosphate material.

[0150] Comparative Example 3:

[0151] A method for preparing an iron phosphate material includes the following steps:

[0152] (1) Soybean protein isolate and polyoxyethylene sorbitan monooleate were added to deionized water to form a dispersion system, and the concentration of the soybean protein isolate was 20 mg / ml. The mass percentage of polyoxyethylene sorbitan monooleate in the dispersion system was 2wt%. Then, ferric chloride salt was added to make the concentration of the dispersion system 0.2 mol / L at room temperature.

[0153] (2) The above dispersion system is mixed with heptane at a ratio of 7:3 by volume, and mixed and stirred at a speed of 15000 rpm for 4 min to obtain a dispersion liquid; the dispersion liquid is a flocculated suspension of soybean protein and cannot form a stable emulsion.

[0154] Spherical nanometer iron phosphate with an average diameter of 350 nm, i.e., a solid template agent, is added to the above dispersion liquid at 8 wt% of the mass of the dispersion liquid, and 18% of the volume of the dispersion liquid of ethanol is added, and stirred uniformly, and the pH of the solution is adjusted to 1.6 by using hydrochloric acid or ammonia water, and then sodium hydrogen phosphate and ferric chloride salt are added to obtain a reaction liquid, the concentration of iron element in the reaction liquid after the addition of the ferric chloride is 1 mol / L, and the concentration of the sodium hydrogen phosphate solution is 1.01 mol / L, and then stirred at a speed of 400 rpm, and after stirring at a temperature of 70℃ for 9 h, a hydrated iron phosphate material is obtained after filtration, washing and drying, and after calcination at 500℃ in a nitrogen atmosphere for 3 h, an iron phosphate material is obtained.

[0155] The iron phosphate material obtained in the present comparative example is composed of irregular iron phosphate particles and solid iron phosphate.

[0156] A preparation method of a lithium iron phosphate material, comprising the following steps:

[0157] The above iron phosphate material is mixed with lithium hydroxide at a molar ratio of iron to lithium of 1:1.02, 8 wt% of the total mass of the iron phosphate material and lithium hydroxide is added to glucose, and then a mixed material is obtained by using ethanol as a dispersant, the amount of ethanol added is 2.5 wt% of the total mass of the mixed material, the mixed material is put into a grinding machine for grinding and stirring for 5 h, and then dried in a 60℃ drying box; the dried mixed material is put into a tube furnace, and heated at 850℃ for 9 h in a nitrogen atmosphere to obtain a lithium iron phosphate material.

[0158] Example 1

[0159] In order to verify the product and the use effect of the product described in the present application, a simulated battery is prepared by using the lithium iron phosphate material prepared in each example and comparative example, and the preparation method is as follows:

[0160] A uniform slurry is prepared by mixing each lithium iron phosphate, acetylene black and binder PVDF at a mass ratio of 75:15:10, and uniformly coated on an aluminum foil substrate as a positive electrode of the simulated battery. Lithium sheet is used as the negative electrode of the simulated battery, a polypropylene porous membrane is used as the separator, and the electrolyte is 1 mol LiPF6 dissolved in 1 L of a mixed solvent of ethylene carbonate and dimethyl carbonate (volume ratio 1:1). The positive electrode, negative electrode, electrolyte and separator are assembled into a battery in an argon glove box.

[0161] The obtained simulated battery is subjected to rate performance test at a voltage of 2.0V-4.2V, and the specific test steps are as follows:

[0162] First, the capacitor is charged to 4.2V using a constant current, then discharged to 2.0V using a higher rate current. The capacity discharged is the discharge capacity at that rate. After the discharge is complete, it is discharged to 2.0V again using a constant current current. Then, the test is performed at the next rate. The test results are shown in Table 1.

[0163] Example 2

[0164] To verify the performance of the lithium iron phosphate product of this invention, the lithium iron phosphate materials prepared in each embodiment and comparative example were subjected to tap density testing. The specific steps are as follows:

[0165] Weigh the mass m1 (g) of the dry graduated cylinder. Add a certain amount of solid sample (to about 5 ml) into the graduated cylinder, plug the cylinder opening, and shake the graduated cylinder vertically until the volume of the sample in the cylinder no longer decreases. Record the sample volume V (ml). Weigh the mass m2 (g) of the graduated cylinder and the sample. Use the formula ρ=(m2-m1) / V to obtain ρ (g / cm³). 3 The tap density of the sample to be tested is obtained. The results are shown in Table 1.

[0166] Example 3

[0167] To verify the performance of the lithium iron phosphate product of the present invention, the specific surface area of ​​the lithium iron phosphate materials prepared in each embodiment and comparative example was tested. Specifically, the specific surface area and pore size were analyzed using a BETA201A fully automatic static capacity method specific surface area and pore size analyzer. The results are shown in Table 1.

[0168] Table 1. Performance test results of the cathode materials in the examples and comparative examples.

[0169]

[0170] As shown in Table 1, based on Examples 1-3 and Comparative Examples 1-3, the lithium iron phosphate products prepared by this invention possess ideal physical and chemical properties, with each product achieving a specific surface area of ​​up to 20.12 m². 2 The tap density of each product can reach 1.20 g / cm³. 3 In the above tests, the discharge specific capacity at 0.2C can reach over 161mAh / g, the discharge specific capacity at 2C can reach over 146mAh / g, and the discharge specific capacity at 5C can reach over 141mAh / g. Even when the rate performance reaches 10C, the discharge specific capacity of the products in each embodiment can reach over 130mAh / g.

[0171] In the preparation process of the hollow template agent, no soybean protein isolate is added in Comparative Example 1. The prepared iron phosphate material includes hollow iron phosphate and solid iron phosphate material. Only using the surfactant can reduce the stability of the hollow template agent. In the reaction solution containing the solid template agent, the hollow template agent is easily deformed or even destroyed, which finally leads to the formation of irregular shape of the hollow iron phosphate; in the preparation process of the hollow template agent, no surfactant is added in Comparative Example 2. The prepared iron phosphate material includes hollow iron phosphate and solid iron phosphate material. Since only soybean protein isolate is used, the soybean protein isolate in the hollow template agent is aggregated to a certain extent during the gelation process, which causes the deformation or even rupture of the hollow template, and finally leads to the formation of irregular shape of the hollow iron phosphate; in the preparation process of the hollow template agent, the iron salt is first added and then the emulsion is prepared in Comparative Example 3. In the prepared iron phosphate material, the gelation reaction of the iron salt and the soybean protein isolate is first added, which makes it impossible to form a hollow template agent, and finally forms irregular solid iron phosphate particles and spherical solid iron phosphate. Therefore, the specific surface area, tap density and rate performance of the lithium iron phosphate material prepared by Comparative Examples 1-3 are affected. As shown in Table 1, the performance parameters of the products of Examples 1-3 are obviously better than those of the products of Comparative Examples 1-3.

[0172] From the comparison of Example 1 and Examples 4-5, it can be seen that in the preparation process of the iron phosphate material, the first iron salt is added to the gelation treatment of the emulsion. The feeding ratio of the first iron salt to the dispersion system in step (1) is controlled to be (0.1-0.3) mol:1L. If the proportion of the first iron salt in the dispersion system is too low, the gelation degree is too low, the stability of the hollow template agent is poor, the morphology of the iron phosphate material prepared from the hollow template agent is affected, and further the rate performance of the lithium iron phosphate positive material inheriting the morphology of the iron phosphate material is reduced, and the tap density and specific surface area are decreased. If the proportion of the first iron salt in the dispersion system is too high, the gelation degree of the soybean protein isolate in the hollow template agent is too high, which can also destroy the stability and sphericity of the hollow template agent. Similarly, it can reduce the rate performance of the lithium iron phosphate positive material, and at the same time reduce the tap density and specific surface area of the lithium iron phosphate positive material. Therefore, the feeding ratio of the first iron salt to the dispersion system is controlled to be (0.1-0.3) mol:1L. The performance of the lithium iron phosphate positive material prepared from the iron phosphate material obtained within this range is better.

[0173] From the comparison of Example 1 and Examples 6-7, it can be seen that in the preparation of the iron phosphate material according to the present application, the amount of the solid template agent added affects the proportion of the small-particle solid iron phosphate material in the product. If the amount of the solid template agent added in step (2) is controlled to be 5wt%-10wt% of the mass of the dispersion, if the content of the solid template agent added is too low, the proportion of the small-particle solid iron phosphate material is reduced, which further leads to a decrease in the tap density of the lithium iron phosphate positive electrode material inheriting the morphology of the iron phosphate material. If the content of the solid template agent added is too high, the stability of the hollow template agent is affected, the sphericity of the hollow template agent is reduced, and the proportion of the small-particle solid iron phosphate in the iron phosphate product is increased, which further leads to a decrease in the tap density, a decrease in the specific surface area, and a decrease in the rate capability of the lithium iron phosphate positive electrode material inheriting the morphology of the iron phosphate material. Therefore, the amount of the solid template agent added is controlled to be 5wt%-10wt% of the mass of the dispersion, and the performance of the lithium iron phosphate positive electrode material prepared from the iron phosphate material prepared in this range is better.

[0174] From the comparison of Example 1 and Examples 8-9, it can be seen that in the preparation of the iron phosphate material according to the present application, the addition of ethanol affects the dispersibility of the solid template agent. If the amount of the ethanol added in step (2) is controlled to be 15wt%-20wt% of the volume of the dispersion, if the content of the ethanol added is too low, the agglomeration of the solid template agent is increased, the average particle size of the small-particle solid iron phosphate in the iron phosphate product is increased, which further leads to a decrease in the tap density and a decrease in the specific surface area of the lithium iron phosphate positive electrode material inheriting the morphology of the iron phosphate material. If the content of the ethanol added is too high, on the basis of an increase in the economic cost, the lithium iron phosphate positive electrode material prepared from the iron phosphate material does not have substantial improvement in the physicochemical properties. Therefore, the amount of the ethanol added is controlled to be 15wt%-20wt% of the volume of the dispersion, and the performance of the lithium iron phosphate positive electrode material prepared from the iron phosphate material prepared in this range is better.

[0175] The preferred embodiments of the present application have been described above by way of example only, not for limitation of the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for producing a ferric phosphate material, characterized by, The iron phosphate material comprises large-particle hollow iron phosphate and small-particle solid iron phosphate, the large-particle hollow iron phosphate comprises an iron phosphate shell layer, and a carbon layer on the inner surface of the iron phosphate shell layer; The preparation method comprises the following steps: adding a solid template agent into a dispersion solution of a hollow template agent to obtain a suspension, adding a second iron salt and a phosphorus source into the suspension to obtain a reaction solution, stirring the reaction, and calcining the obtained solid to obtain the iron phosphate material; The preparation of the dispersion solution of the hollow template agent comprises the following steps: mixing soybean protein isolate, a surfactant and water to form a dispersion system, mixing and stirring the dispersion system and an oil phase solvent to obtain an emulsion, adding a first iron salt into the emulsion to perform a gelation reaction, and obtaining the dispersion solution of the hollow template agent; The suspension further comprises ethanol, and the amount of the ethanol is 15%-20% of the volume of the dispersion solution; The amount of the solid template agent is 5wt%-10wt% of the mass of the dispersion solution; The surfactant comprises at least one of fatty alcohol polyoxyethylene ether and polyoxyethylene sorbitan monooleate, and the mass fraction of the surfactant in the dispersion system is 1wt%-3wt%; The first iron salt comprises at least one of ferric chloride and ferric nitrate, and the feeding ratio of the first iron salt to the dispersion system is (0.1-0.3) mol:1L.

2. The method of producing a ferric phosphate material according to claim 1, characterized by, The iron phosphate material has at least one of the following characteristics I-III: Characteristic I: the average particle size of the large-particle hollow iron phosphate ranges from 2.0 μm to 4.0 μm, and the average particle size of the small-particle solid iron phosphate ranges from 0.9 μm to 2 μm; Characteristic II: the thickness of the iron phosphate shell layer is 300 nm-700 nm; Characteristic III: the thickness of the carbon layer on the inner surface of the iron phosphate shell layer is 100 nm-200 nm.

3. The method of claim 1, wherein the iron phosphate material is prepared by the steps of: The mixing order of the components in the suspension is as follows: first, the dispersion solution of the hollow template agent is prepared, then the solid template agent is added into the dispersion solution and uniformly mixed, and finally, the ethanol is added and uniformly stirred; and the preparation method of the iron phosphate material satisfies at least one of the following preparation conditions ①-⑦: Condition ①: the stirring speed of the stirring reaction is 400-500 rpm, the reaction temperature is 60-90 ℃, and the reaction time is 8-12 h; Condition ②: the concentration of the phosphorus source in the reaction solution is 0.9-2 mol / L; Condition ③: the molar ratio of iron element to phosphorus element in the reaction solution is 1:(1-1.03); Condition ④: the solid template agent is spherical nano iron phosphate with an average diameter of 200-500 nm; Condition ⑤: in the calcination process, the calcination temperature is controlled to be 400-700 ℃, and the calcination time is 2-4 h; Condition ⑥: the second iron salt comprises at least one of ferric chloride or ferric nitrate; Condition ⑦: the phosphorus source comprises at least one of ammonium hydrogen phosphate, ammonium phosphate, ammonium dihydrogen phosphate, sodium hydrogen phosphate, sodium dihydrogen phosphate and sodium phosphate.

4. The method of producing a ferric phosphate material according to claim 1, characterized by, The preparation of the dispersion solution of the hollow template agent satisfies at least one of the following conditions I-V: Condition I: the stirring speed of the mixing and stirring is 12000-16000 rpm, and the stirring time is 3-6 min; Condition II: the gelation reaction refers to a reaction of stirring at room temperature, and the time is 10-20 min; Condition III: the concentration of the soybean protein isolate in the dispersion system is 10-30 mg / ml; Condition IV: the oil phase solvent includes at least one of kerosene, heptane, n-hexane, cyclohexane, vegetable oil and liquid paraffin; Condition V: the volume ratio of the dispersion system and the oil phase solvent is (3-8):

2.

5. A method of producing a lithium iron phosphate material, characterized by, The iron phosphate material, the lithium source, the carbon source and ethanol are mixed to obtain a slurry, the slurry is ground and dried, and then calcined in an inert atmosphere to obtain the lithium iron phosphate material; the iron phosphate material is prepared by the preparation method of the iron phosphate material in any one of claims 1-4.

6. The method of claim 5, wherein the lithium iron phosphate material is prepared by the steps of: mixing a lithium source, an iron source, and a phosphate source; and heating the mixture to a temperature of 600-800°C for 1-10 hours. The preparation method meets at least one of the following conditions a-f: Condition a: the lithium source is selected from at least one of lithium oxalate, lithium carbonate and lithium hydroxide; Condition b: the carbon source is selected from at least one of glucose, sucrose, dopamine, cyclodextrin, citric acid, aniline, cellulose acetate and polyvinylpyrrolidone; Condition c: the carbon source accounts for 5%-10% of the total mass of the lithium source and the iron phosphate material; Condition d: the grinding time of the slurry is 2-6 h; Condition e: the calcination temperature is 700-850℃, and the calcination time is 6-15 h; Condition f: the inert atmosphere is selected from at least one of nitrogen, helium and argon.

7. The lithium iron phosphate material prepared according to the method of any one of claims 5-6, wherein the lithium iron phosphate material has a tap density of at least 1.8 g / cm3. The lithium iron phosphate material includes large-particle hollow lithium iron phosphate and small-particle solid lithium iron phosphate; The large-particle hollow lithium iron phosphate includes a lithium iron phosphate shell layer, a first carbon coating layer on the outer surface of the lithium iron phosphate shell layer and a carbon layer on the inner surface of the lithium iron phosphate shell layer; The small-particle solid lithium iron phosphate includes lithium iron phosphate and a second carbon coating layer on the outer surface of the lithium iron phosphate.

8. A positive electrode sheet characterized by comprising: The positive electrode piece contains the lithium iron phosphate material of claim 7.

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