Preparation method of ferrophosphorus with high specific surface area, high performance and low impurity

Abstract

The invention discloses a preparation method of high-specific-surface-area high-performance low-impurity iron phosphate, which comprises the following steps: introducing a bionic hierarchical pore structure composite reagent containing a good conductive carbon material, combining with the synergistic effect of an amino template remover, synchronously removing a template and optimizing a pore structure through alkaline dissolution, ion exchange and adsorption, and preparing the high-specific-surface-area high-performance low-impurity iron phosphate. The iron phosphate precursor material has a stable three-dimensional porous structure with uniform carbon distribution, so that the purpose of preparing the iron phosphate precursor material with high specific surface area, high performance and low impurity is achieved. Compared with a traditional technology, the method is innovated, compared with an existing technology in the market, the method can achieve multiple purposes of quality improvement and impurity removal, has excellent electrical performance, has the advantages of being simple in step, low in improvement cost and the like in the production process, and has wide industrial application prospects.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of iron phosphate material preparation, and particularly relates to a method for preparing a high-specific-surface high-performance low-impurity iron phosphate precursor by using a biomimetic multi-level pore composite reagent and an amino template remover. BACKGROUND

[0002] Iron phosphate (FePO4) is a key precursor of lithium iron phosphate (LiFePO4) positive electrode material, and its micro-morphology and physical and chemical properties (such as specific surface area, tap density, sulfur content, etc.) directly affect the electrochemical performance (such as charge-discharge efficiency, cycle life and energy density) of the final battery. At present, the preparation process of the iron phosphate precursor still faces the following technical bottlenecks and disadvantages: the primary particles of the current iron phosphate precursor are mostly in a spherical structure, and due to the geometric shape limitation, the specific surface area is relatively low (usually less than 10 m 2 / g), which leads to insufficient contact area of the material with the electrolyte, and the lithium ion migration rate is limited. CN202410348992.0 discloses a preparation method of a high-specific-surface battery-grade iron phosphate. By controlling the process flow and process parameters and the aging process, the BET of the product is increased from 7 m 2 / g to 12 m 2 / g, but the improvement is limited.

[0003] Sulfur impurity residue and environmental protection problem. In actual industrial application, in order to reduce the cost, enterprises usually use the by-product titanium dioxide ferrous sulfate after impurity removal as the iron source, but in the synthesis of iron phosphate by coprecipitation method, sulfur elements are easily wrapped in the iron phosphate crystal lattice, which leads to the sulfur content of the final material exceeding the standard (>200 ppm), significantly increasing the charge transfer impedance of the battery and reducing the cycle life. At present, the industry adopts multiple dispersion and washing to reduce the sulfur content, but the water consumption is huge, and the water treatment cost is high.

[0004] Influence of sintering process on structure and specific surface area. In the calcination and dehydration process, high temperature will cause the collapse between the material particles and the pores, leading to the decrease of the specific surface area and the deterioration of the material stability; but if the sintering temperature is too low, the crystal transformation is not complete, and the ion conductivity is reduced. Under the traditional sintering conditions, it is difficult to balance the high crystallinity and the specific surface area.

[0005] In view of the problems of low specific surface area, high sulfur residue and irreversible loss of active sites in the calcination process which are common in the preparation technology of the iron phosphate precursor, the application provides a preparation method of high-specific-surface high-activity low-impurity iron phosphate, which effectively solves the problems of low activity of the iron phosphate material, sintering pore collapse, poor conductivity and high sulfur content by using diatomite as a natural multi-level template and assembling it with a biomimetic multi-level pore structure composite reagent. The preparation method is simple and feasible, and is suitable for large-scale production. SUMMARY

[0006] The present application aims to solve the problems of low specific surface area, high sulfur residue and irreversible loss of active sites in the calcination process in the preparation of iron phosphate precursor of the current iron phosphate product.

[0007] In order to achieve the above-mentioned purpose, the present application provides a preparation method of high specific surface high performance low impurity phosphorus iron, comprising the following steps: (1) Preparation of purified ferrous sulfate: Dissolve the by-product ferrous sulfate of titanium white powder with water at high temperature to obtain a ferrous sulfate solution, then add a decontamination agent, and filter to obtain a purified ferrous sulfate solution.

[0008] (2) Preparation of biomimetic multi-level pore structure composite reagent: The pretreated biomimetic template agent is mixed with a carbon source and a crosslinking agent to prepare a biomimetic multi-level pore structure composite reagent.

[0009] (3) Preparation of primary filter cake: The purified ferrous sulfate solution prepared in step (1) is uniformly added with a phosphorus source, an oxidizing agent, a biomimetic multi-level pore structure composite reagent and a pH adjusting agent in sequence, and a primary slurry is obtained by reaction. The primary slurry is washed with pure water once and filtered to obtain a primary filter cake.

[0010] (4) Preparation of secondary filter cake: The primary filter cake prepared in step (2) is slurried by adding water, and then an amino template removal agent is uniformly added. After complete reaction, the secondary filter cake is obtained by washing with pure water twice and filtering.

[0011] (5) Preparation of phosphorus iron: The secondary filter cake prepared in step (4) is dried and sintered to obtain anhydrous iron phosphate.

[0012] In step (1), the decontamination agent is one or more of ammonia water with a mass concentration of 10-25%, potassium hydroxide, sodium hydroxide and iron powder.

[0013] Preferably, the pH after reaction in step (1) is 3.5-4.

[0014] Preferably, the concentration of the purified FeSO4 solution in step (1) is 0.5-1.0 mol / L.

[0015] Preferably, in step (1), the mass ratio of FeSO4 to decontamination agent is 1:1%-3% (mass percent).

[0016] In step (2), the preparation method of the biomimetic multi-level pore structure composite reagent is: the pretreated biomimetic template agent, carbon source and crosslinking agent are mixed at a mass ratio of 1-2:1-2:0.1-0.2, heated at 60-70°C for 60-100 min to obtain the biomimetic multi-level pore structure composite reagent.

[0017] Preferably, the pretreatment method of the biomimetic agent in step (2) is: pre-washing with 4-5 times the mass of the biomimetic agent and hydrochloric acid with a concentration of 0.5-1 mol / L, and then washing with 2-3 times the mass of pure water to wash away the metal impurities contained therein.

[0018] Preferably, the biomimetic agent in step (2) is any one of diatomite and silicon dioxide; the carbon source is any one of lignin sulfonate; and the cross-linking agent is any one of epoxy resin, silane coupling agent, and epoxide chloropropane.

[0019] The preparation method of the biomimetic multi-level pore structure composite reagent in step (3) is: mixing the pretreated biomimetic agent, the carbon source, and the cross-linking agent in a mass ratio of 1-2:1-2:0.01-0.02, heating at 60°C for 60 min to obtain the biomimetic multi-level pore structure composite reagent.

[0020] The phosphorus source in step (3) is selected from one or more of phosphoric acid, sodium dihydrogen phosphate, or ammonium dihydrogen phosphate; the oxidizing agent is any one of hydrogen peroxide, nitric acid, and sodium persulfate; and the pH adjuster is one or more of NaOH solution, ammonia water, and KOH solution.

[0021] Preferably, the mass ratio of the purified ferrous sulfate: the phosphorus source: the oxidizing agent: the biomimetic multi-level pore structure composite reagent in step (3) is 1:0.4-0.6:0.5-0.8:0.01-0.1.

[0022] Preferably, the pH adjuster is added dropwise in step (3) until the reaction pH is 2-3.

[0023] Preferably, the dropwise addition time of the phosphorus source, the oxidizing agent, the biomimetic multi-level pore structure composite reagent, and the pH adjuster in step (3) is 10-20 min, 60-120 min, 30-60 min, and 90-120 min, respectively.

[0024] Preferably, the reaction temperature in step (3) is 40-60°C, the reaction time (after the dropwise addition of the pH adjuster is completed) is 1-2 h, and the stirring rate is 300-500 rpm.

[0025] Preferably, after the reaction in step (3) is completed, the slurry is filtered and washed with pure water until the conductivity is <5 mS / cm to obtain a primary filter cake.

[0026] The mass ratio of the primary filter cake to the slurry water and the amino template removal agent in step (4) is 1:4-5:0.05-0.1.

[0027] Preferably, the reaction time in step (4) is 0.5-1 h, the reaction temperature is 40-60°C, and the stirring rate is 150-200 rpm.

[0028] Preferably, the amino template removing agent in step (4) is ammonia, ammonium carbonate, or dihydrogen ammonium. The amino template removing agent can selectively remove the biomass template, leaving a stable three-dimensional conductive structure, and inhibiting the collapse of the pore channel. The amino group can form a stable complex with Fe 3+ 3+ , and adsorb SO4 2- , effectively reducing the sulfur content of the product and achieving one dose for multiple uses.

[0029] Preferably, after the amino template agent is completely reacted in step (4), the slurry is washed with pure water again until the conductivity is less than 0.8 mS / cm.

[0030] The drying temperature of the secondary filter cake in step (5) is 70-90℃, and the drying time is 10-12 h.

[0031] Preferably, the sintering time in step (5) is 2-3 h, and the reaction temperature is 560-600℃.

[0032] The present application also provides a high specific surface area high performance low impurity iron phosphate, which is prepared according to the method described above. The specific surface area of the iron phosphate is more than 46 m 2 / g; the sulfur content is less than 20 ppm; and the Fe / P is more than 1.45.

[0033] The technical scheme of the present application also provides a lithium iron phosphate, which comprises the high specific surface area high performance low impurity iron phosphate, i.e., the high specific surface area high performance low impurity iron phosphate is used as a raw material for preparation.

[0034] Compared with the prior art, the present application has the following advantages: 1. Biomimetic template composite reagent By combining the biomimetic template agent with a multi-level pore structure and the carbon source under the action of a crosslinking agent, a biomimetic multi-level pore structure composite reagent with a multi-level pore structure and high conductivity is prepared. In the synthesis process of the iron phosphate precursor material, the natural pore channel of the reagent limits the growth direction of the iron phosphate, forming a hierarchical pore complementary to the template. The uniformly distributed carbon source provides a good conductive medium. The three-dimensional template effect in the precursor sintering process can effectively inhibit the pore collapse problem, increase the specific surface area of the material, increase the electrolyte contact area, shorten the ion transmission path, and improve the electrochemical activity of the material.

[0035] 2. Effect of the amino template removing agent. Effect (1): The amino template removing agent selectively removes the biomass template introduced in the synthesis process, forming a stable three-dimensional porous structure with uniform carbon distribution and improving the electrochemical activity; effect (2): The ammonium group in the amino template removing agent can form a stable complex with Fe 3+ ​forms a stable complex ([Fe(NH3)6 3+ ) and adsorbs SO4 2- , greatly reduces the sulfur content of the product, and realizes one dose for multiple uses.

[0036] 3. The regulation method is simple and feasible, has low modification difficulty for the production line, high adaptability, and is suitable for large-scale batch production. DETAILED DESCRIPTION

[0037] The endpoints of the ranges and any values disclosed in the present disclosure are not limited to the precise values recited as the exact dimensions are not critical to the present disclosure. The endpoints of the ranges and the individual values are not to be understood as limited to the precise values recited as the exact dimensions are not critical to the present disclosure. The ranges and individual points within the ranges can be combined to form new ranges, and the disclosure should be understood to include any and all possible combinations of the individual values.

[0038] In order to better understand the present disclosure, the content of the present disclosure will be further described below in combination with examples, but the content of the present disclosure is not limited to the following examples only.

[0039] Example 1 (1) Preparation of purified ferrous sulfate: add 70°C pure water to the by-product ferrous sulfate of titanium white powder, stir and dissolve to make the Fe% in the system 5%, add 25% ammonia water, stir at a speed of 200 rpm, and react until the pH is 4.0. Filter to obtain a purified ferrous sulfate solution; wherein the mass ratio is ferrous sulfate: 25% ammonia water = 1:2.5%.

[0040] (2) Preparation of biomimetic multi-level pore structure composite reagent: ① The biological template diatomite is pre-washed by 4 times the mass of 0.6 mol / L hydrochloric acid by filtration, and then washed by 2 times the mass of pure water by filtration; ② The pretreated diatomite, lignosulfonate and silane coupling agent are mixed at a ratio of 1:1:0.01, heated at 60°C, and stirred at 100 rpm for 60 min to obtain a biomimetic multi-level pore structure composite reagent.

[0041] (3) Preparation of primary filter cake: add phosphoric acid to the purified ferrous sulfate obtained in step (1) at a uniform speed of 10 min, add 20% hydrogen peroxide at a uniform speed of 80 min, add the biomimetic multi-level pore structure composite reagent at a uniform speed of 40 min, add the ammonia water solution with a mass concentration of 7% at a uniform speed of 120 min, adjust the pH to 2.9, and then incubate for 1.5 h at a stirring speed of 250 rpm; wherein the molar ratio is purified ferrous sulfate: phosphorus source: oxidizing agent: biomimetic multi-level pore structure composite reagent = 1:0.65:0.5:0.03; after incubation, the obtained slurry is washed by filtration with pure water until the conductivity is <5 mS / cm to obtain a primary filter cake.

[0042] (4) Preparation of secondary filter cake: add pure water, ammonia amino template remover to the primary filter cake obtained in step (3) to slurry, stir at 300 rpm for 20 min, then filter and wash with pure water until the conductivity is <0.8 mS / cm to obtain a secondary filter cake; wherein the mass ratio of the primary filter cake to the slurry water and the amino template remover is 1:4:0.1.

[0043] (5) Preparation of iron phosphate: dry and crush the secondary filter cake obtained in step (4) at 80°C for 10h to obtain a dried material, then sinter the dried material at 570°C for 2h to obtain anhydrous iron phosphate.

[0044] (6) Preparation of lithium iron phosphate Mix the anhydrous iron phosphate obtained in step 5 with the carbon source and lithium source in a molar ratio of 1:0.4:1.05, then add 50% of the total mass of water and mix, and perform sand grinding to a particle size D50 of 0.6μm, then perform spray drying, and finally perform calcination at 600°C for 7h at a heating rate of 5°C / min under a nitrogen atmosphere to obtain lithium iron phosphate.

[0045] Example 2 (1) Preparation of purified ferrous sulfate: add 70°C pure water to the titanium dioxide by-product ferrous sulfate, stir and dissolve to make the Fe% in the system 5%, add 25% ammonia water, stir at a speed of 200 rpm, and react until the pH is 4.0, then filter to obtain a purified ferrous sulfate solution; wherein the mass ratio is ferrous sulfate:25% ammonia water = 1:3%.

[0046] (2) Preparation of biomimetic multi-level pore structure composite reagent: ①Pre-wash the biological template agent silica with 4 times the mass of 0.8 mol / L hydrochloric acid by filtration, then wash with 2 times the mass of pure water by filtration; ②Mix the pretreated biomass-derived silica, lignosulfonate and epoxy resin in a ratio of 1:1:0.02, heat at 70°C and stir at 100 rpm for 80 min to obtain a biomimetic multi-level pore structure composite reagent.

[0047] (3) Preparation of primary filter cake: add phosphoric acid to the purified ferrous sulfate obtained in step (1) at a uniform speed for 15 min, add 20% hydrogen peroxide at a uniform speed for 60 min, add the biomimetic multi-level pore structure composite reagent at a uniform speed for 50 min, adjust the pH to 2.9 by adding 7% ammonia solution at a uniform speed, then incubate for 1.5h at a stirring rate of 250 rpm; wherein the molar ratio of purified ferrous sulfate: phosphorus source: oxidizing agent: biomimetic multi-level pore structure composite reagent is 1:0.6:0.6:0.04; after incubation, wash the obtained slurry with pure water by filtration until the conductivity is <5 mS / cm to obtain a primary filter cake.

[0048] (4) Preparation of secondary filter cake: The primary filter cake obtained in step (3) is slurried with pure water and an amino template remover. After stirring at 300 rpm for 20 min, the slurry is filtered and washed with pure water until the conductivity is <0.8 mS / cm, to obtain a secondary filter cake. The mass ratio of the primary filter cake to the slurry water and the amino template remover is 1:4:0.1.

[0049] (5) Preparation of iron phosphate: The secondary filter cake obtained in step (4) is dried at 80°C for 10 h and then ground to obtain a dried material. The dried material is sintered at 580°C for 2 h to obtain anhydrous iron phosphate.

[0050] (6) Preparation of lithium iron phosphate The anhydrous iron phosphate obtained in step (5) is mixed with a carbon source and a lithium source at a molar ratio of 1:0.4:1.05, and then 50% of the total mass of water is added for mixing. The mixture is sand ground to a particle size D50 of 0.6 μm, and then spray dried. Finally, the mixture is calcined at 600°C for 7 h at a heating rate of 5°C / min under a nitrogen atmosphere to obtain lithium iron phosphate.

[0051] Comparative Example 1 Compared with Example 1, the difference is that no biomimetic hierarchical porous structure composite reagent is added in step (3), and no amino template remover is added in step (4). The preparation steps of lithium iron phosphate are the same as those of Example 1.

[0052] Comparative Example 2 Compared with Example 1, the difference is that no biomimetic hierarchical porous structure composite reagent is added in step (3). The preparation steps of lithium iron phosphate are the same as those of Example 1.

[0053] Comparative Example 3 Compared with Example 1, the difference is that no amino template remover is added in step (4). The preparation steps of lithium iron phosphate are the same as those of Example 1.

[0054] The lithium iron phosphate prepared from the anhydrous iron phosphate obtained in the above Examples 1-2 and Comparative Examples 1 and 2 is detected for iron and phosphorus content, sulfur content, specific surface area, and electrochemical performance indicators of lithium iron phosphate by manual titration, carbon and sulfur analyzers, specific surface area and pore size analyzers, and compaction density instruments and blue electric test systems. The results are shown in Table 1: Table 1 Physicochemical indicators of anhydrous iron phosphate and electrochemical performance of lithium iron phosphate

[0055] Examples 1 and 2 were prepared according to the method of the claims, and the physical and chemical indicators and properties of the obtained products are shown in Table 1; in Comparative Example 1, without adding the biomimetic multi-level pore structure composite reagent and the amino template remover, under the same other conditions, the three-dimensional porous structure brought by the biomimetic multi-level pore structure composite reagent was lost, and its BET was greatly reduced. The amino group in the amino template remover was not 3+ Formation of a stable complex ([Fe(NH3)6] 3+ ) Adsorption of SO4 2- , its sulfur content becomes significantly higher, resulting in significantly worse iron-lithium compaction density and discharge capacity at the rear end; in comparative example 2, when the bionic multi-level pore structure composite reagent is not added and other conditions are the same, similarly, after losing the three-dimensional porous structure brought by the bionic multi-level pore structure composite reagent, its BET is greatly reduced, but due to the effect of the amino template remover, its sulfur content does not change, but due to the reduction of channels, its rear end iron-lithium compaction density and discharge capacity are reduced to a certain extent; in comparative example 3, when the amino template remover is not added and other conditions are the same, similarly, after losing the effect of the amino template remover on sulfur adsorption, its sulfur content becomes significantly higher. Although the bionic multi-level pore structure composite reagent can bring about a three-dimensional porous structure and uniformly distribute the conductive carbon material, there is no amino template remover to directionally remove the template, and a uniform three-dimensional pore channel cannot be presented, and its rear end iron-lithium compaction density and discharge capacity are also significantly reduced.

Claims

1. A method for preparing high specific surface area, high performance and low impurity ferric phosphate, characterized by: The following steps are involved: (1) Preparation of purified ferrous sulfate: dissolve the ferrous sulfate produced as a by-product of titanium dioxide in water to obtain a ferrous sulfate solution, then add an impurity remover, react and filter to obtain a purified ferrous sulfate solution; (2) Preparation of biomimetic multi-level pore structure composite reagent: the pretreated bio-template agent is mixed with a carbon source and a cross-linking agent to prepare a biomimetic multi-level pore structure composite reagent; (3) Preparation of a primary filter cake: adding a phosphorus source, an oxidant, a biomimetic multi-level pore structure composite reagent, and a pH regulator to the purified ferrous sulfate solution prepared in step (1) in sequence at a uniform rate, reacting to obtain a primary slurry, and washing with pure water and filtering to obtain a primary filter cake; (4) Preparation of secondary filter cake: add water to the primary filter cake prepared in step (2) to make a slurry, then add amino template remover at a uniform rate, after complete reaction, wash twice with pure water and filter to obtain a secondary filter cake; (5) Preparation of ferrophosphorus: The secondary filter cake prepared in step (3) is dried and sintered to obtain anhydrous ferric phosphate.

2. The method for preparing high specific surface area, high performance and low impurity ferric phosphate according to claim 1, characterized in that: The impurity remover in step (1) is any one of iron powder, ammonia water, sodium hydroxide and potassium hydroxide.

3. The method for preparing high specific surface area, high performance and low impurity ferric phosphate according to claim 1, characterized in that: The preparation method of the biomimetic multi-level pore structure composite reagent in step (2) is as follows: the pretreated biological template agent, the carbon source, and the cross-linking agent are mixed in a mass ratio of 1~2: 1~2: 0.01~0.02, and heated at 60℃-70℃ for 60 min-100 min to obtain the biomimetic multi-level pore structure composite reagent.

4. The method for preparing high specific surface area, high performance and low impurity ferric phosphate according to claim 3, characterized in that: The bio-template pretreatment method in step (2) is as follows: pre-washing the bio-template with an excess of 0.5-1 mol / L hydrochloric acid, and then washing with pure water; the bio-template comprises any one of diatomaceous earth and silica; the carbon source is any one of lignin sulfonate; and the cross-linking agent is any one of epoxy resin, silane coupling agent, and epichlorohydrin.

5. The method for preparing high specific surface area, high performance and low impurity ferric phosphate according to claim 4, characterized in that: In step (3), the molar ratio of the phosphorus source to the ferrous ions of the purified ferrous sulfate solution is 0.4-0.6:1; the molar ratio of the oxidant to the ferrous ions is 0.5-0.75:1; the mass ratio of the biomimetic multi-level pore structure composite reagent to the purified ferrous sulfate solution is 0.01-0.1:1; the pH regulator is added until the reaction pH end point is 2.8-3.0; and the product is washed with pure water once until the conductivity is less than 5mS / cm.

6. The method for preparing high specific surface area, high performance and low impurity ferric phosphate according to claim 1, characterized in that: In step (3), the phosphorus source is selected from one or more of phosphoric acid, sodium phosphate, sodium dihydrogen phosphate, or ammonium dihydrogen phosphate; the oxidant is any one of hydrogen peroxide, nitric acid, and sodium persulfate; and the pH adjuster is one or more of NaOH solution, ammonia water, and KOH solution.

7. The method for preparing high specific surface area, high performance and low impurity ferric phosphate according to claim 5, characterized in that: In the slurrying process of step (4), the mass ratio of water to the primary filter cake is 4-5:1; the mass ratio of the amino template remover to the primary filter cake is 0.05-0.1:1; the reaction time is 0.5-1 h, the reaction temperature is 40-60°C, and the stirring rate is 150-200 rpm; the product is washed twice with pure water until the conductivity is less than 0.8 mS / cm; the reaction amino template remover is ammonia water, ammonium carbonate, and ammonium dihydrogen carbonate.

8. The method for preparing high specific surface area, high performance and low impurity ferric phosphate according to claim 1, characterized in that: The drying temperature of the secondary filter cake in step (5) is 90-100°C, and the drying time is 10-12 h; the sintering temperature is 550-600°C, and the sintering time is 1-3 h.

9. High specific surface area, high performance and low impurity ferric phosphate, characterized by: Prepared by the method according to any one of claims 1 to 8, the specific surface area of ​​the iron phosphate is 46m 2 / g or above; sulfur content is less than 20ppm.

10. A lithium iron phosphate, characterized in that: It includes the high specific surface area, high performance and low impurity ferric phosphate as described in claim 9.

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