Iron phosphate, its preparation method and application

Abstract

The application relates to a kind of ferric phosphate and its preparation method and application, the preparation method comprises the following steps: (1) after nanocellulose is treated by corona discharge, mixed with water and organic acid, esterified nanocellulose dispersion is obtained;(2) the esterified nanocellulose dispersion is mixed with oily solvent, and emulsion is obtained by emulsification treatment;(3) iron salt solution is mixed with the emulsion, one-step stirring is carried out, phosphate solution is added, the pH of mixed solution is adjusted, two-step stirring is carried out, and the ferric phosphate is obtained by sintering.The charged nanocellulose is formed into emulsion ball, and metal cation is directionally adsorbed on the surface of nanocellulose, finally reacts with phosphate ion to obtain ferric phosphate crystal with good dispersity, and the breaking difficulty of agglomerated ferric phosphate is reduced.

Description

TECHNICAL FIELD

[0001] The present disclosure belongs to the technical field of battery materials, and relates to a kind of iron phosphate and its preparation method and application. BACKGROUND

[0002] As one of the core components of new energy vehicles, new energy batteries urgently need rapid development to meet people's urgent demand for its practical application. The positive electrode material of lithium ion battery mainly includes lithium cobaltate, lithium manganate, lithium nickelate, ternary material and lithium iron phosphate.

[0003] Among them, lithium iron phosphate battery is widely used due to its high safety performance, long service life and good high temperature performance and many other characteristics. Meanwhile, lithium iron phosphate battery also has the advantages of environmental friendliness, light weight and no memory effect. As the precursor of lithium iron phosphate positive material, iron phosphate plays a crucial role in the electrochemical performance of the final lithium iron phosphate battery.

[0004] CN111704121A discloses a preparation method of iron phosphate and lithium iron phosphate, comprising the following steps: S1, preparing iron source and 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 phosphorus source P1 to iron source F1, heating to 90-100℃, and keeping the temperature until the material turns white;

[0005] S3, mixing iron source F2 with 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℃ for 1-3h, and then washing and calcining the reaction product to obtain the iron phosphate.

[0006] CN116101993A discloses a method for preparing iron phosphate by spray roasting, 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℃ to obtain iron phosphate particles.

[0007] 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 in the above scheme is large, and the discharge capacity of the prepared lithium iron phosphate battery is low, the cycle performance is poor, and the capacity decay is fast. Once the iron phosphate particles are prepared, it is difficult to crush them by mechanical means. SUMMARY

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

[0009] The purpose of the present disclosure is to provide a kind of ferric phosphate and its preparation method and application, the present disclosure is by forming emulsion ball to charged nanocellulose, and metal cation is adsorbed on the surface of nanocellulose, finally with phosphate ion reaction obtains the ferric phosphate crystal with better dispersity, reduces the difficulty of broken agglomerated ferric phosphate.

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

[0011] In a first aspect, the present disclosure provides a preparation method of ferric phosphate, which comprises the following steps:

[0012] (1) after corona discharge treatment to nanocellulose, mix with water and organic acid, to obtain esterified nanocellulose dispersion;

[0013] (2) mix the esterified nanocellulose dispersion with oil solvent, and obtain emulsion by emulsification treatment;

[0014] (3) mix ferric salt solution with the emulsion, stir for one step, add phosphate solution, adjust the pH of the mixed solution, stir for two steps, and sinter to obtain the ferric phosphate.

[0015] The present disclosure is by corona discharge treatment to nanocellulose, so it is charged, thus it has attraction to metal cation, thereby directional adsorption, forming the structure of surface ferric phosphate with emulsion in the middle, by esterification treatment to nanocellulose, reducing the hydrophilicity of nanocellulose, so that it forms more stable emulsion particles, by esterification of nanocellulose, removing the influence of hydroxyl in nanocellulose, avoiding complex reaction between hydroxyl and metal cation, affecting the formation of final ferric phosphate product, and then obtaining ferric phosphate particles with hollow structure inside, which can be easily broken into small particle ferric phosphate crystals.

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

[0017] In one embodiment, the voltage of corona discharge 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, etc.

[0018] In one embodiment, the discharge time of corona discharge is 40-80 s, for example: 40 s, 50 s, 60 s, 70 s or 80 s, etc.

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

[0020] In one embodiment, the mass ratio of the nanocellulose and 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 ultrasonication.

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

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

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

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

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

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

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

[0029] In one embodiment, the stirring is continuously performed after the emulsification treatment.

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

[0031] In one embodiment, the concentration of the iron salt solution in step (3) is 0.1-0.3 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, etc.

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

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

[0034] In one embodiment, the concentration of the phosphate solution is 0.1-0.3 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, etc.

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

[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 pH adjusting agent for adjusting the pH of the mixed solution in step (3) comprises ammonia water.

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

[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, etc.

[0040] In one embodiment, the time of the two-step stirring in step (3) is 1-2 h, for example, 1 h, 1.2 h, 1.5 h, 1.8 h or 2 h, etc.

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

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

[0043] In a second aspect, the disclosure provides a ferric phosphate prepared by the method of the first aspect.

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

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

[0046] (1) The present disclosure forms an emulsion ball by charging nanocellulose, and the metal cations are adsorbed on the surface of the nanocellulose in a directional manner, and finally reacts with phosphate ions to obtain a lithium iron phosphate crystal with good dispersity. The lithium iron phosphate has a hollow structure, which is easy to be broken into small particles by mechanical crushing.

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

[0048] Other aspects can be apparent after reading and understanding the accompanying drawings and detailed description. BRIEF DESCRIPTION OF DRAWINGS

[0049] The accompanying drawings are used to provide a further understanding of the technical solutions of the present disclosure, and constitute a part of the specification, and are used together with the embodiments of the present application to explain the technical solutions of the present disclosure, and do not constitute a limitation on the technical solutions of the present disclosure.

[0050] Figure 1 is an SEM image of the lithium iron phosphate prepared in Example 1.

[0051] Figure 2 is an SEM image of the lithium iron phosphate prepared in Comparative Example 1. DETAILED DESCRIPTION

[0052] The technical solutions of the present disclosure will be further described by specific embodiments. 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 a specific limitation on the present disclosure.

[0053] Example 1

[0054] The present embodiment provides a lithium iron phosphate, and the preparation method of the lithium iron phosphate is as follows:

[0055] (1) After the nanocellulose is subjected to corona discharge treatment at 0.5 kV / cm for 60 s, the nanocellulose is mixed with deionized water at a mass ratio of 1:100, formic acid is added, and the mass ratio of formic acid to nanocellulose is 1:0.2. After high-speed stirring, the solution is fully dispersed by an ultrasonic processor with a power of 30% for 5 min to obtain an esterified nanocellulose dispersion;

[0056] (2) liquid paraffin and water of the esterified nanocellulose dispersion liquid were mixed according to a mass ratio of 1:13, and an ultrasonic processor with a power of 40% was used to treat for 10 min to form stable nanocellulose-coated oil droplet particles, and then the liquid stirring speed was maintained at 500 rpm for continuous stirring;

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

[0058] The SEM image of the iron phosphate is shown in Figure 1 .

[0059] Example 2

[0060] This example provides an iron phosphate, and the preparation method thereof is as follows:

[0061] (1) After the nanocellulose was treated by corona discharge at 0.4 kV / cm for 72 s, the cellulose and deionized water were mixed according to a mass ratio of 1:20, formic acid was added, and the mass ratio of formic acid to nanocellulose was 1:0.02. After high-speed stirring, an ultrasonic processor with a power of 60% was used to treat for 10 min to fully disperse the solution, and an esterified nanocellulose dispersion liquid was obtained.

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

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

[0064] Example 3

[0065] This example provides an iron phosphate, and the preparation method thereof is as follows:

[0066] (1) the nanocellulose is treated by corona discharge at 0.6 kV / cm for 50 s, then mixed with deionized water at a mass ratio of 1:1000, formic acid is added, the mass ratio of formic acid to nanocellulose is 1:0.8, after high-speed stirring, the solution is fully dispersed by an ultrasonic processor with a power of 60% for 5 min, to obtain an esterified nanocellulose dispersion;

[0067] (2) the edible oil (soybean oil) is mixed with the esterified nanocellulose dispersion at a mass ratio of 1:10, and an ultrasonic processor with a power of 60% is used to treat for 3 min, to form stable nanocellulose-coated oil droplet particles, and then the liquid is continuously stirred at a stirring speed of 500 rpm;

[0068] (3) after adding 0.3 mol / L of ferric chloride solution and stirring for 5 min, 0.3 mol / L of ammonium dihydrogen phosphate solution is added, to ensure that the molar ratio of phosphate to trivalent iron ions is 1:1, ammonia water is added to adjust the pH to 1.8, and stirring is performed for 1.5 h, then filtration, washing, and drying at 80℃ for 2.5 h are performed, and the ferric phosphate is obtained by sintering at 800℃.

[0069] Example 4

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

[0071] Example 5

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

[0073] Comparative Example 1

[0074] The difference between this comparative example and Example 1 is only that the nanocellulose is not treated by corona discharge, and the other conditions and parameters are exactly the same as those in Example 1. The SEM image of the prepared ferric phosphate is shown in Figure 2 .

[0075] Comparative Example 2

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

[0077] Performance test:

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

[0079] The prepared lithium iron phosphate positive electrode material was mixed with acetylene black and a cyclohexane solution of polyvinylidene fluoride (PVDF) at room temperature and normal pressure to form a slurry (in a weight ratio of 75:15:10 of the positive electrode material:acetylene black:PVDF), and uniformly coated on an aluminum foil substrate as a positive electrode of a simulated battery. Lithium sheets were used as the negative electrode of the simulated battery, and the electrolyte was 1 mol LiPF6 dissolved in 1 L of a mixed solvent of EC and DMC (volume ratio 1:1). The positive electrode, negative electrode, electrolyte and separator were assembled into a simulated battery in an argon-protected glove box. The rate test procedure of the simulated battery was as follows: first charged at 30 mA / g to 4.2 V, then discharged at a rate current to 2.0 V, and the discharged capacity was the discharge capacity at the rate, and after the discharge ended, discharged at 30 mA / g to 2.0 V. Then the next rate test was performed. The test results of the simulated battery are shown in Table 1.

[0080] Table 1

[0081]

[0082]

[0083] As can be seen from Table 1, according to Examples 1-3, the 0.2C specific discharge capacity of the battery prepared from the lithium iron phosphate prepared by the method of the present disclosure can reach 155 mAh / g or more, the 1C specific discharge capacity can reach 140 mAh / g or more, the 3C specific discharge capacity can reach 132 mAh / g or more, and the 10C specific discharge capacity can reach 121 mAh / g or more. Different organic solvents affect the size of the emulsion droplets, and the addition of different phosphate and iron salt concentrations also affects the ball forming property, thereby affecting the difficulty of the breaking process.

[0084] As can be seen from the comparison of Example 1 and Examples 4-5, the amount of the oily solvent added in the preparation process of the iron phosphate according to the present disclosure affects the performance. When the mass ratio of the oily solvent to the esterified nanocellulose dispersion liquid is controlled to be 1:(8-20), the performance of the prepared iron phosphate is good. If the amount of the oily solvent is too large, the formed emulsion particles and the iron phosphate will stick together, affecting the breaking effect. If the amount of the oily solvent is too small, the formed emulsion particles are too few, causing a large amount of iron phosphate to self-precipitate, and affecting the breaking effect.

[0085] From the comparison of Example 1 and Comparative Example 1, it can be seen that the present disclosure carries out corona discharge treatment on nanocellulose to make it charged and have attraction to metal cations, so as to form a structure of surface iron phosphate emulsion. If the nanocellulose is not subjected to corona discharge treatment, it cannot form directional adsorption to ferric ions, and the iron phosphate cannot be obtained.

[0086] From the comparison of Example 1 and Comparative Example 2, it can be seen that the hydroxyl groups on the surface of nanocellulose can react with ferric ions, and the hydrophilicity of the hydroxyl groups can also make it impossible to form stable emulsion particles in the process of continuous stirring. The present disclosure reduces the hydrophilicity of nanocellulose by esterification treatment, so as to form more stable emulsion particles. Through the esterification of nanocellulose, the influence of the hydroxyl groups in nanocellulose is removed, so as to avoid the complex reaction of the hydroxyl groups with metal cations, affect the formation of the final iron phosphate product, and obtain iron phosphate crystals which are easy to break into small particles.

Claims

1. A method for preparing ferric phosphate, comprising the following steps: (1) After corona discharge treatment of nanocellulose, it is mixed with water and organic acid to obtain esterified nanocellulose dispersion; (2) The esterified nanocellulose dispersion is mixed with an oily solvent and then emulsified to obtain an emulsion; (3) Mix the iron salt solution with the emulsion, stir in one step, add phosphate solution, adjust the pH of the mixed solution, stir in two steps, and sinter to obtain the iron phosphate.

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

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

4. The preparation method according to claim 1, wherein, The corona discharge time is 40~80s.

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

6. The preparation method according to claim 1, wherein, The mass ratio of the nanocellulose to the organic acid is 1:(0.01~1).

7. The preparation method according to claim 1, wherein, The mixing in step (1) includes stirring and sonication.

8. The preparation method according to claim 7, wherein, The power of the ultrasound in step (1) is 30-60%.

9. The preparation method according to claim 7, wherein, The duration of the ultrasound is 3 to 20 minutes.

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

11. The preparation method according to claim 1, wherein, The mass ratio of the oily solvent to water in the esterified nanocellulose dispersion is 1:(8~20).

12. The preparation method according to claim 1, wherein, The emulsification process in step (2) includes ultrasound.

13. The preparation method according to claim 12, wherein, The power of the ultrasound in step (2) is 30-60%.

14. The preparation method according to claim 12, wherein, The duration of the ultrasound is 3 to 20 minutes.

15. The preparation method according to claim 1, wherein, After the emulsification process described in step (2), stirring is continued.

16. The preparation method according to claim 15, wherein, The stirring speed is 300~500 rpm.

17. The preparation method according to claim 1, wherein, The concentration of the iron salt solution in step (3) is 0.1~0.3 mol / L.

18. The preparation method according to claim 1, wherein, The solute in the iron salt solution includes any one or a combination of at least two of ferric sulfate, ferric chloride, or ferric nitrate.

19. The preparation method according to claim 1, wherein, The stirring time for this step is 3-8 minutes.

20. The preparation method according to claim 1, wherein, The concentration of the phosphate solution is 0.1~0.3 mol / L.

21. The preparation method according to claim 1, wherein, The solute in the phosphate solution includes any one or a combination of at least two of phosphoric acid, ammonium hydrogen phosphate, or ammonium dihydrogen phosphate.

22. The preparation method according to claim 1, wherein, The molar ratio of phosphate to iron ions in the mixed solution is (0.98~1.02):

1.

23. The preparation method according to claim 1, wherein, The pH adjuster for adjusting the mixed solution in step (3) includes ammonia.

24. The preparation method according to claim 23, wherein, The concentration of the ammonia water is 0.1~1 mol / L.

25. The preparation method according to claim 1, wherein, Adjust the pH of the mixed solution to 1~2.

2.

26. The preparation method according to claim 1, wherein, The stirring time for the two steps in step (3) is 1~2 hours.

27. The preparation method according to claim 1, wherein, The material undergoes a drying process before sintering.

28. The preparation method according to claim 1, wherein, The sintering temperature is 600~800℃.

29. A type of iron phosphate prepared by the method according to any one of claims 1-28.

30. A lithium iron phosphate prepared by sintering a mixture of iron phosphate and a lithium source as described in claim 29.

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