Ferric phosphate, preparation method therefor, and use thereof

Abstract

Ferric phosphate, a preparation method therefor, and the use thereof. The preparation method comprises the following steps: (1) performing corona discharge treatment on nanocellulose, and mixing same with water and an organic acid so as to obtain an esterified nanocellulose dispersion liquid; (2) mixing the esterified nanocellulose dispersion liquid with an oily solvent, and performing emulsification treatment to obtain an emulsion; (3) mixing a ferric salt solution with the emulsion, performing first stirring, adding a phosphate solution, adjusting the pH value of the mixed solution, performing second stirring, and performing sintering to obtain ferric phosphate. The present invention forms emulsion spheres from charged nanocellulose, directionally attaches metal cations to the surface of the nanocellulose, and finally reacts same with phosphate ions so as to obtain ferric phosphate crystals having good dispersity, thereby lowering the difficulty of crushing agglomerated ferric phosphate.

Description

Ferric phosphate and its preparation method and application Technical Field

[0001] The present disclosure belongs to the technical field of battery materials and relates to iron phosphate and a preparation method and application thereof. Background Art

[0002] As one of the core components of new energy vehicles, new energy batteries urgently need to develop rapidly to meet the urgent demand for their practical applications. The main cathode materials for lithium-ion batteries include lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, ternary materials, and lithium iron phosphate.

[0003] Lithium iron phosphate batteries are widely used due to their safety, long lifespan, and excellent high-temperature performance. They are also environmentally friendly, lightweight, and lack a memory effect. Iron phosphate, the precursor of the lithium iron phosphate cathode material, plays a crucial role in the electrochemical performance of the battery.

[0004] CN111704121A discloses a method for preparing iron phosphate and lithium iron phosphate, comprising the following steps: S1, preparing an iron source and a phosphorus source, dividing the iron source into two parts F1 and F2, and dividing the phosphorus source into two parts P1 and P2; S2, adding the phosphorus source P1 to the iron source F1, heating the mixture to 90-100°C, and keeping the temperature until the material turns white; S3, mixing the iron source F2 and the phosphorus source P2, and adding sulfuric acid to obtain a mixed solution; S4, adding the mixed solution obtained in step S3 to the material treated in step S2, reacting at 90-100°C for 1-3 hours, and washing and calcining the reaction product to obtain the iron phosphate.

[0005] CN116101993A discloses a method for preparing iron phosphate by a spray roasting method, and iron phosphate and lithium iron phosphate prepared by the method. The method for preparing iron phosphate comprises: mixing an iron salt solution and a phosphoric acid solution to obtain an iron-phosphorus mixed solution; atomizing the iron-phosphorus mixed solution to obtain atomized droplets; and roasting the atomized droplets at 500-800°C to obtain iron phosphate particles.

[0006] The particle size of iron phosphate has a great influence on the performance of lithium iron phosphate. The particle size of the iron phosphate precursor described in the above scheme is large, and the discharge capacity of the lithium iron phosphate battery produced is low, the cycle performance is poor, and the capacity decay is fast. Once the iron phosphate particles are produced, it is difficult to crush them by mechanical means.

[0007] Summary of the Invention

[0008] The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the claims.

[0009] The purpose of the present disclosure is to provide an iron phosphate and its preparation method and application. The present disclosure forms emulsion balls of charged nanocellulose, directionally adsorbs metal cations on the surface of nanocellulose, and finally reacts with phosphate ions to obtain iron phosphate crystals with good dispersion, thereby reducing the difficulty of breaking the agglomerated iron phosphate.

[0010] To achieve this purpose, the present disclosure adopts the following technical solutions:

[0011] In a first aspect, the present disclosure provides a method for preparing ferric phosphate, the preparation method comprising the following steps:

[0012] (1) treating the nanocellulose with corona discharge, and then mixing the nanocellulose with water and an organic acid to obtain an esterified nanocellulose dispersion;

[0013] (2) mixing the esterified nanocellulose dispersion with an oily solvent and performing emulsification treatment to obtain an emulsion;

[0014] (3) mixing the iron salt solution with the emulsion, performing one-step stirring, adding the phosphate solution, adjusting the pH of the mixed solution, performing two-step stirring, and sintering to obtain the iron phosphate.

[0015] The present invention performs a discharge treatment on the nanocellulose corona to make it charged, thereby generating attraction for metal cations, thereby directional adsorption, and forming a surface iron phosphate structure with an emulsion in the middle. The nanocellulose is treated by esterification to reduce the hydrophilicity of the nanocellulose, so that it forms more stable emulsified particles. The nanocellulose esterification removes the influence of hydroxyl groups in the nanocellulose, avoids the complexation reaction between hydroxyl groups and metal cations, and affects the formation of the final iron phosphate product, thereby obtaining iron phosphate particles with a hollow structure inside, and the iron phosphate can be easily broken into small particles of iron phosphate crystals.

[0016] In one embodiment, the mass ratio of the nanocellulose to water in step (1) is 1:(1-1000), for example, 1:1, 1:5, 1:10, 1:200 or 1:1000.

[0017] In one embodiment, the corona discharge voltage is 0.3-0.8 kV / cm, for example, 0.3 kV / cm, 0.4 kV / cm, 0.5 kV / cm, 0.7 kV / cm or 0.8 kV / cm.

[0018] In one embodiment, the discharge time of the corona discharge is 40 to 80 seconds, for example, 40 seconds, 50 seconds, 60 seconds, 70 seconds or 80 seconds.

[0019] In one embodiment, the organic acid includes any one of formic acid, oxalic acid, acetic acid or citric acid, or a combination of at least two thereof.

[0020] In one embodiment, the mass ratio of the nanocellulose to the organic acid is 1:(0.01-1), for example: 1:0.01, 1:0.05, 1:0.1, 1:0.6 or 1:1, etc.

[0021] In one embodiment, the mixing in step (1) comprises stirring and ultrasound.

[0022] In one embodiment, the power of the ultrasound in step (1) is 30% to 60%, for example, 30%, 35%, 40%, 50% or 60%.

[0023] In one embodiment, the ultrasonication time in step (1) is 3 to 20 minutes, for example, 3 minutes, 5 minutes, 10 minutes, 15 minutes or 20 minutes.

[0024] In one embodiment, the oily solvent in step (2) comprises any one of glycerol, diesel, liquid paraffin, n-heptane, toluene, xylene, edible oil, methyl methacrylate, butyl acrylate, dichloromethane or chloroform, or a combination of at least two thereof.

[0025] In one embodiment, the mass ratio of the oily solvent to water in the esterified nanocellulose dispersion is 1:(8-20), for example, 1:8, 1:10, 1:12, 1:15 or 1:20.

[0026] In one embodiment, the emulsification treatment in step (2) comprises ultrasound.

[0027] In one embodiment, the power of the ultrasound in step (2) is 30% to 60%, for example, 30%, 35%, 40%, 50% or 60%.

[0028] In one embodiment, the ultrasonication time in step (2) is 3 to 20 minutes, for example, 3 minutes, 5 minutes, 10 minutes, 15 minutes or 20 minutes.

[0029] In one embodiment, stirring is continued after the emulsification process.

[0030] In one embodiment, the stirring speed is 300-500 rpm, for example, 300 rpm, 350 rpm, 400 rpm, 450 rpm or 500 rpm.

[0031] In one embodiment, the concentration of the iron salt solution in step (3) is 0.1 to 0.3 mol / L, for example, 0.1 mol / L, 0.15 mol / L, 0.2 mol / L, 0.25 mol / L or 0.3 mol / L.

[0032] In one embodiment, the solute of the iron salt solution includes any one of ferric sulfate, ferric chloride, or ferric nitrate, or a combination of at least two thereof.

[0033] In one embodiment, the stirring time of the step is 3 to 8 minutes, for example, 3 minutes, 4 minutes, 5 minutes, 7 minutes or 8 minutes.

[0034] In one embodiment, the concentration of the phosphate solution is 0.1 to 0.3 mol / L, for example, 0.1 mol / L, 0.15 mol / L, 0.2 mol / L, 0.25 mol / L or 0.3 mol / L.

[0035] In one embodiment, the solute of the phosphate solution includes any one of phosphoric acid, ammonium hydrogen phosphate, or ammonium dihydrogen phosphate, or a combination of at least two thereof.

[0036] In one embodiment, the molar ratio of phosphate to iron ion in the mixed solution is (0.98-1.02):1, for example: 0.98:1, 0.99:1, 1:1, 1.01:1 or 1.02:1, etc.

[0037] In one embodiment, the regulator for regulating the pH of the mixed solution in step (3) comprises aqueous ammonia.

[0038] In one embodiment, the concentration of the ammonia water is 0.1 to 1 mol / L, for example, 0.1 mol / L, 0.2 mol / L, 0.5 mol / L, 0.8 mol / L or 1 mol / L.

[0039] In one embodiment, the pH of the mixed solution is adjusted to 1-2.2, for example, 1, 1.2, 1.5, 2 or 2.2.

[0040] In one embodiment, the second-step stirring time in step (3) is 1 to 2 hours, for example, 1 hour, 1.2 hours, 1.5 hours, 1.8 hours or 2 hours.

[0041] In one embodiment, a drying process is performed before sintering.

[0042] In one embodiment, the sintering temperature is 600-800°C, for example, 600°C, 650°C, 700°C, 750°C or 800°C.

[0043] In a second aspect, the present disclosure provides iron phosphate, which is prepared by the method described in the first aspect.

[0044] In a third aspect, the present disclosure provides a lithium iron phosphate, which is prepared by mixing and sintering the iron phosphate described in the second aspect and a lithium source.

[0045] Compared with the prior art, the present disclosure has the following beneficial effects:

[0046] (1) The present invention forms charged nanocellulose into emulsion balls, and directionally adsorbs metal cations on the surface of the nanocellulose, and finally reacts with phosphate ions to obtain iron phosphate crystals with good dispersibility. The iron phosphate has a hollow structure inside and can be easily broken into small iron phosphate particles by mechanical crushing.

[0047] (2) The iron phosphate particles prepared by the method disclosed in the present invention can reduce the difficulty of crushing, thereby reducing their particle size, increasing electrical conductivity and shortening the lithium ion transmission path, showing excellent rate performance.

[0048] Still other aspects will become apparent upon reading and understanding the accompanying drawings and detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] The accompanying drawings are used to provide a further understanding of the technical solution of this article and constitute a part of the specification. Together with the embodiments of this application, they are used to explain the technical solution of this article and do not constitute a limitation on the technical solution of this article.

[0050] FIG1 is a SEM image of ferric phosphate prepared in Example 1.

[0051] FIG2 is a SEM image of the iron phosphate prepared in Comparative Example 1. DETAILED DESCRIPTION

[0052] The technical solution of the present disclosure is further described below through specific implementation methods. Those skilled in the art should understand that the embodiments are only used to help understand the present disclosure and should not be regarded as specific limitations of the present disclosure.

[0053] Example 1

[0054] This embodiment provides a ferric phosphate, and the preparation method of the ferric phosphate is as follows:

[0055] (1) After the nanocellulose was subjected to corona discharge treatment at 0.5 kV / cm for 60 seconds, the cellulose and deionized water were mixed in a mass ratio of 1:100, and formic acid was added in a mass ratio of formic acid to nanocellulose of 1:0.2. After high-speed stirring, the mixture was treated with an ultrasonic processor at a power of 30% for 5 minutes to fully disperse the solution to obtain an esterified nanocellulose dispersion;

[0056] (2) Liquid paraffin and water of esterified nanocellulose dispersion were mixed in a mass ratio of 1:13 and treated with an ultrasonic processor at a power of 40% for 10 min to form stable nanocellulose-coated oil droplet particles. The liquid was then stirred at a stirring speed of 500 rpm.

[0057] (3) After adding 0.2 mol / L ferric chloride solution and stirring for 5 minutes, 0.2 mol / L ammonium hydrogen phosphate solution was added to ensure that the molar ratio of phosphate to trivalent iron ion was 1:1, and ammonia water was added to adjust the pH to 1.8. After stirring for 1.5 hours, the mixture was filtered, washed, dried at 80°C for 2.5 hours, and sintered at 700°C to obtain the ferric phosphate.

[0058] The SEM image of the iron phosphate is shown in FIG1 .

[0059] Example 2

[0060] This embodiment provides a ferric phosphate, and the preparation method of the ferric phosphate is as follows:

[0061] (1) After the nanocellulose was subjected to corona discharge treatment at 0.4 kV / cm for 72 seconds, the cellulose and deionized water were mixed in a mass ratio of 1:20, and formic acid was added in a mass ratio of formic acid to nanocellulose of 1:0.02. After high-speed stirring, the solution was treated with an ultrasonic processor at a power of 60% for 10 minutes to fully disperse the solution to obtain an esterified nanocellulose dispersion;

[0062] (2) Toluene and water of the esterified nanocellulose dispersion were mixed in a mass ratio of 1:8 and treated with an ultrasonic processor at a power of 30% for 20 min to form stable nanocellulose-coated oil droplet particles. The liquid was then stirred at a stirring speed of 500 rpm.

[0063] (3) After adding 0.1 mol / L ferric nitrate solution and stirring for 5 minutes, 0.1 mol / L phosphoric acid solution was added to ensure that the molar ratio of phosphate to trivalent iron ion was 1:1, and ammonia water was added to adjust the pH to 1.8. After stirring for 1.5 hours, the mixture was filtered, washed, dried at 80°C for 2.5 hours, and sintered at 600°C to obtain the ferric phosphate.

[0064] Example 3

[0065] This embodiment provides a ferric phosphate, and the preparation method of the ferric phosphate is as follows:

[0066] (1) After the nanocellulose was subjected to corona discharge treatment at 0.6 kV / cm for 50 seconds, the cellulose and deionized water were mixed in a mass ratio of 1:1000, and formic acid was added in a mass ratio of formic acid to nanocellulose of 1:0.8. After high-speed stirring, the mixture was treated with an ultrasonic processor at a power of 60% for 5 minutes to fully disperse the solution to obtain an esterified nanocellulose dispersion;

[0067] (2) Edible oil (soybean oil) and esterified nanocellulose dispersion were mixed in a mass ratio of 1:10 and treated with an ultrasonic processor at a power of 60% for 3 min to form stable nanocellulose-coated oil droplet particles. The liquid was then stirred at a stirring speed of 500 rpm.

[0068] (3) After adding 0.3 mol / L ferric chloride solution and stirring for 5 minutes, 0.3 mol / L ammonium dihydrogen phosphate solution was added to ensure that the molar ratio of phosphate to trivalent iron ion was 1:1, and ammonia water was added to adjust the pH to 1.8. After stirring for 1.5 hours, the mixture was filtered, washed, dried at 80°C for 2.5 hours, and sintered at 800°C to obtain the ferric phosphate.

[0069] Example 4

[0070] The only difference between this embodiment and embodiment 1 is that the mass ratio of the oily solvent to the water in the esterified nanocellulose dispersion is 1:8, and the other conditions and parameters are exactly the same as those in embodiment 1.

[0071] Example 5

[0072] The only difference between this embodiment and embodiment 1 is that the mass ratio of the oily solvent to the water in the esterified nanocellulose dispersion is 1:20, and the other conditions and parameters are exactly the same as those in embodiment 1.

[0073] Comparative Example 1

[0074] The only difference between this comparative example and Example 1 is that the nanocellulose is not subjected to corona discharge treatment, and the other conditions and parameters are exactly the same as those in Example 1. The SEM image of the obtained iron phosphate is shown in FIG2 .

[0075] Comparative Example 2

[0076] The only difference between this comparative example and Example 1 is that no organic acid is added for the esterification reaction, and the other conditions and parameters are exactly the same as those in Example 1.

[0077] Performance testing:

[0078] The iron phosphate precursor and Li2CO3 were loaded into a ball mill and wet-milled with anhydrous ethanol at a speed of 600 rpm for 5 hours; glucose, lithium carbonate and the prepared iron phosphate precursor in a ratio of 0.05:1.05:1.0 were calcined at 600°C under a nitrogen atmosphere to obtain lithium iron phosphate material.

[0079] The prepared lithium iron phosphate cathode material was mixed with a cyclohexane solution of acetylene black and polyvinylidene fluoride (PVDF) at room temperature and pressure to form a slurry (the weight ratio of cathode material: acetylene black: PVDF was 75:15:10). This slurry was evenly coated onto an aluminum foil substrate to serve as the positive electrode of a simulated battery. The negative electrode of the simulated battery used a lithium sheet, and the electrolyte consisted of 1 mol LiPF₆ dissolved in 1 L of a mixture of EC and DMC (1:1 by volume). The positive electrode, negative electrode, electrolyte, and separator were assembled in an argon-protected glove box to form a simulated battery. The simulated battery was rate-tested as follows: first, charge to 4.2 V at 30 mA / g, then discharge to 2.0 V at a rate current. The released capacity was the discharge capacity at that rate. After discharge, the battery was discharged again at 30 mA / g to 2.0 V. Testing at the next rate was then performed. The test results for this simulated battery are listed in Table 1.

[0080] Table 1

[0081] As can be seen from Table 1, from Examples 1-3, the 0.2C discharge capacity of the iron phosphate battery prepared by the method of the present disclosure can reach over 155 mAh / g, the 1C discharge capacity can reach over 140 mAh / g, the 3C discharge capacity can reach over 132 mAh / g, and the 10C discharge capacity can reach over 121 mAh / g. Different organic solvents affect the size of the emulsion droplets, while the addition of different phosphate and iron salt concentrations also affects the balling properties, thereby affecting the difficulty of the emulsion during the crushing process.

[0082] By comparing Example 1 and Examples 4-5, it can be seen that in the preparation process of the iron phosphate described in the present disclosure, the amount of oily solvent added will affect its performance. The mass ratio of the oily solvent to the water in the esterified nanocellulose dispersion is controlled at 1: (8 to 20), and the performance of the obtained iron phosphate is better. If the amount of oily solvent added is too large, the formed emulsion particles will stick together with the iron phosphate, affecting the crushing effect. If the amount of oily solvent added is too small, too few emulsion particles will be formed, resulting in a large amount of iron phosphate self-precipitation, which affects the crushing effect.

[0083] By comparing Example 1 and Comparative Example 1, it can be seen that the present invention performs corona discharge treatment on the nanocellulose to make it charged, generate attraction for metal cations, and directionally adsorb them to form a surface iron phosphate structure with an emulsion in the middle. If the nanocellulose is not subjected to corona discharge treatment, directional adsorption of trivalent iron cannot be formed, and the iron phosphate cannot be obtained.

[0084] By comparing Example 1 and Comparative Example 2, it can be seen that since the hydroxyl groups on the surface of the nanocellulose react with the trivalent iron, the hydrophilicity of the hydroxyl groups in the nanocellulose may also make it impossible to form stable emulsified particles during the continuous stirring reaction process. The present invention treats the nanocellulose by esterification to reduce the hydrophilicity of the nanocellulose, so that it forms more stable emulsified particles. Through the esterification of the nanocellulose, the influence of the hydroxyl groups in the nanocellulose is removed, and the complex reaction of the hydroxyl groups with the metal cations is avoided, which affects the formation of the final iron phosphate product, and obtains iron phosphate crystals that are easily broken into small particles.

Claims

1. A method for preparing ferric phosphate, comprising the following steps: (1) subjecting the nanocellulose to a corona discharge treatment and then mixing the nanocellulose with water and an organic acid to obtain an esterified nanocellulose dispersion; (2) mixing the esterified nanocellulose dispersion with an oily solvent and performing emulsification treatment to obtain an emulsion; (3) mixing the iron salt solution with the emulsion, performing one-step stirring, adding the phosphate solution, adjusting the pH value of the mixed solution, performing two-step stirring, and sintering to obtain the iron phosphate.

2. The preparation method according to claim 1, wherein The mass ratio of the nanocellulose to water in step (1) is 1:(1-1000).

3. The preparation method according to claim 1 or 2, wherein: The voltage of the corona discharge is 0.3-0.8 kV / cm.

4. The preparation method according to any one of claims 1 to 3, wherein The discharge time of the corona discharge is 40 to 80 seconds.

5. The preparation method according to any one of claims 1 to 4, wherein: The organic acid includes any one of formic acid, oxalic acid, acetic acid or citric acid, or a combination of at least two of them.

6. The preparation method according to any one of claims 1 to 5, wherein: The mass ratio of the nanocellulose to the organic acid is 1:(0.01-1).

7. The preparation method according to any one of claims 1 to 6, wherein: The mixing in step (1) includes stirring and ultrasound.

8. The preparation method according to any one of claims 1 to 7, wherein: The power of the ultrasound in step (1) is 30-60%; Optionally, the ultrasonication time is 3 to 20 minutes.

9. The preparation method according to any one of claims 1 to 8, wherein: The oily solvent in step (2) includes any one of glycerol, diesel, liquid paraffin, n-heptane, toluene, xylene, edible oil, methyl methacrylate, butyl acrylate, dichloromethane or chloroform, or a combination of at least two thereof.

10. The preparation method according to any one of claims 1 to 9, wherein: The mass ratio of the oily solvent to the water in the esterified nanocellulose dispersion is 1:(8-20).

11. The preparation method according to any one of claims 1 to 10, wherein: The emulsification treatment in step (2) includes ultrasound.

12. The preparation method according to any one of claims 1 to 11, wherein: The power of the ultrasound in step (2) is 30-60%; Optionally, the ultrasonication time is 3 to 20 minutes.

13. The preparation method according to any one of claims 1 to 4, wherein: After the emulsification treatment in step (2), stirring is continued; Optionally, the stirring speed is 300-500 rpm.

14. The preparation method according to any one of claims 1 to 13, wherein: The concentration of the iron salt solution in step (3) is 0.1 to 0.3 mol / L; Optionally, the solute of the iron salt solution includes any one of ferric sulfate, ferric chloride or ferric nitrate, or a combination of at least two thereof; Optionally, the stirring time of the step is 3 to 8 minutes; Optionally, the concentration of the phosphate solution is 0.1 to 0.3 mol / L; Optionally, the solute of the phosphate solution includes any one or a combination of at least two of phosphoric acid, ammonium hydrogen phosphate or ammonium dihydrogen phosphate; Optionally, the molar ratio of phosphate to iron ion in the mixed solution is (0.98-1.02):

1.

15. The preparation method according to any one of claims 1 to 14, wherein: The pH regulator of the mixed solution in step (3) comprises aqueous ammonia; Optionally, the concentration of the ammonia water is 0.1 to 1 mol / L; Optionally, the pH of the mixed solution is adjusted to 1-2.

2.

16. The preparation method according to any one of claims 1 to 15, wherein: The stirring time of the second step in step (3) is 1 to 2 hours; Optionally, a drying process is performed before sintering; Optionally, the sintering temperature is 600-800°C.

17. Iron phosphate obtained by the method according to any one of claims 1 to 16.

18. Lithium iron phosphate prepared by sintering the iron phosphate as claimed in claim 17 and a lithium source.

Images