A kind of iron phosphate crystal and preparation method thereof

Abstract

The present invention relates to the field of iron phosphate technology, and in particular to an iron phosphate crystal and a preparation method thereof. The present application discloses an iron phosphate crystal, wherein the molar ratio of Fe to P in the iron phosphate crystal is 0.96-0.985; the preparation method of iron phosphate comprises the following steps: adding an iron salt solution, a monoammonium phosphate solution, and a hydrogen peroxide solution to a reactor, and the obtained mixed solution is subjected to a preliminary reaction at 90-100°C; after the preliminary reaction is completed, an external circulation reaction of the reactor is carried out at 85-90°C. The iron phosphate prepared by the present application with a molar ratio of Fe to P of 0.95-0.985 is beneficial to the preparation of high-performance lithium iron phosphate.

Description

Technical Field

[0001] The present invention relates to the technical field of iron phosphate, and in particular to an iron phosphate crystal and a preparation method thereof. Background Art

[0002] Iron phosphate is mainly used to manufacture lithium iron phosphate battery materials; it can also be used as a catalyst and in the manufacture of ceramics.

[0003] The color of high-purity ferric phosphate dihydrate is nearly white or light yellowish white powder. With the loss of crystal water, the color gradually turns yellow, and the pure anhydrous substance is yellowish white powder. When the phosphorus (P) in the ferric phosphate dihydrate exceeds the standard, the appearance is grayish white or dark grayish white, and when the iron exceeds the standard, it is dark yellow. The phosphorus-iron ratio is the most critical indicator for measuring the quality of ferric phosphate, and it is also the most critical factor in determining the quality of lithium iron phosphate.

[0004] If there is a large amount of divalent iron or sodium, potassium, sulfate, or ammonium ions in ferric phosphate, ferric phosphate dihydrate will appear dark black or grayish white.

[0005] To this end, the present invention provides an iron phosphate crystal with different molar ratios of Fe and P and a preparation method thereof. Summary of the invention

[0006] In order to overcome the deficiencies of the prior art, the present invention provides an iron phosphate crystal and its preparation method.

[0007] The technical solution adopted by the present invention to solve its technical problem is:

[0008] A ferric phosphate crystal, wherein the molar ratio of Fe to P in the ferric phosphate crystal is 0.95-0.985.

[0009] Preferably, the molar ratio of Fe to P in the iron phosphate crystals is 0.959-0.968.

[0010] Preferably, the weight content of Fe in the ferric phosphate crystals is ≥35.5%, and the weight content of P is ≥20.1%.

[0011] Preferably, the sum of the weight content of Fe and the weight content of PO4 in the iron phosphate crystals is >99%, and the pH of the iron phosphate crystals is 2.8-3.5.

[0012] The preparation method of the above-mentioned iron phosphate comprises the following steps:

[0013] Add iron salt solution, monoammonium phosphate solution and hydrogen peroxide into a reaction kettle, and conduct preliminary reaction of the obtained mixed solution at 90-100°C; after the preliminary reaction, conduct external circulation reaction at 85-90°C.

[0014] Preferably, the initial reaction time is 1.5-2h.

[0015] Preferably, the cyclic reaction time is 2-3 hours.

[0016] Preferably, the reactor is provided with a circulation pipeline, and a circulation pump is provided on the circulation pipeline; the mixed liquid reactor is transported to the circulation pipeline through the circulation pump, and then the mixed liquid is transported from the circulation pipeline to the reactor, forming a circulation to carry out an external circulation reaction.

[0017] Preferably, one end of the circulation pipeline is connected to the bottom of the reactor, and the other end of the circulation pipeline is connected to the top of the reactor. A circulation pump can be used to realize a circulation process in which the mixed liquid in the reactor flows out from the bottom of the reactor and the feed liquid enters the reactor from the top of the reactor.

[0018] Preferably, the stirring speed of the stirring paddle in the reactor is 800-900 r / min, and the conveying speed of the circulating pump is 50 m / min. 3 / h.

[0019] The beneficial effects of the present invention are:

[0020] The iron phosphate with a molar ratio of Fe to P of 0.95-0.985 described in the present invention is beneficial to the preparation of high-performance lithium iron phosphate. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0022] Figure 1-Figure 5 is an SE scanning diagram of the iron phosphate crystals in which the molar ratio of Fe to P is 0.968 according to the present invention;

[0023] Figure 6-Figure 11 is an SE scanning diagram of the iron phosphate crystals in which the molar ratio of Fe to P is 0.959 according to the present invention;

[0024] Fig.12 It is a powder diffraction pattern of the iron phosphate crystals in which the molar ratio of Fe to P is 0.968 according to the present invention. DETAILED DESCRIPTION

[0025] In order to facilitate the understanding of those skilled in the art, the present invention is further described below in conjunction with embodiments, and the contents mentioned in the implementation modes are not intended to limit the present invention.

[0026] As used herein, "and / or" includes the term of any and all combinations of one or more associated listed items. The terms used herein are only used to describe specific embodiments and are not intended to limit the present invention. As used herein, the singular forms "a", "an", "an" and "the" are also intended to include the plural forms, unless the context clearly indicates otherwise. It is further understood that "including", when used in this specification, specifies the stated features, integers, steps, operations, elements and / or compositions, but does not exclude the existence or addition of one or more other features, integers, steps, operations, elements, compositions and / or combinations thereof.

[0027] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention belongs. It is further understood that terms, such as defined in commonly used dictionaries, are interpreted in accordance with their meanings in the context of the relevant art and are not in an idealized or overly formal sense unless explicitly so defined herein.

[0028] The exemplary invention described herein may appropriately lack any one or more element limitations that are not specifically disclosed herein. Therefore, the terms "comprise", "include", "contain", etc. should be understood broadly and non-restrictively. In addition, the terminology used herein is used as a description, not a limitation, and it is unintentional to use these terminology expressions that do not include any equivalent characteristics, but only describe some of their characteristics, but various modifications are possible within the scope of the present invention according to the rights. Therefore, although the present invention has been specifically disclosed by preferred embodiments and optional features, the modifications disclosed herein to embody the changes of the present invention may be recorded by those skilled in the art, and such modifications and changes will be considered to be within the scope of the present invention.

[0029] The raw materials or reagents used in the embodiments of the present invention and the comparative examples are all purchased from mainstream manufacturers in the market. Those without indicating the manufacturer or the concentration are all analytically pure raw materials or reagents that can be routinely obtained, as long as they can play the expected role, there is no particular restriction. The instruments and equipment such as the reactor and rotary evaporator used in the present embodiment are all purchased from major manufacturers in the market, as long as they can play the expected role, there is no particular restriction. If specific techniques or conditions are not indicated in the present embodiment, the techniques or conditions described in the literature in this area or according to the product specification are carried out.

[0030] In the following embodiments, the feeding amount of the iron salt solution is 750 kg, and the weight content of ferrous sulfate heptahydrate in the iron salt solution is 21.7%; the feeding amount of the monoammonium phosphate solution is 445 kg, and the weight content of the monoammonium phosphate in the monoammonium phosphate solution is 19.6%; the feeding amount of ammonia water is 49 kg, and the concentration is 20%; the feeding amount of hydrogen peroxide is 60 kg.

[0031] Example 1

[0032] A method for preparing ferric phosphate comprises the following steps:

[0033] Iron salt solution, monoammonium phosphate solution and hydrogen peroxide were added to the reactor, and the obtained mixed solution was subjected to a preliminary reaction at 90°C for 1.5 hours. After the preliminary reaction, an external circulation reaction was carried out at 85°C for 2 hours.

[0034] The reactor is provided with a circulation pipeline, and a circulation pump is provided on the circulation pipeline. The mixed liquid reactor is transported to the circulation pipeline through the circulation pump, and then the mixed liquid is transported from the circulation pipeline to the reactor, forming a cycle to carry out an external circulation reaction. One end of the circulation pipeline is connected to the bottom of the reactor, and the other end of the circulation pipeline is connected to the top of the reactor. The circulation pump can be used to realize a circulation process in which the mixed liquid in the reactor flows out from the bottom of the reactor and the feed liquid enters the reactor from the top of the reactor. The stirring speed of the stirring paddle in the reactor is 800r / min, and the feed liquid conveying speed of the circulation pump is 50m / min. 3 / h.

[0035] Example 2

[0036] A method for preparing ferric phosphate comprises the following steps:

[0037] Iron salt solution, monoammonium phosphate solution and hydrogen peroxide are added to the reactor, and the obtained mixed solution is subjected to a preliminary reaction at 100°C for 2 hours. After the preliminary reaction, a circulation reaction outside the reactor is carried out at 90°C for 3 hours.

[0038] The reactor is provided with a circulation pipeline, and a circulation pump is provided on the circulation pipeline. The circulation pump is used to transport the mixed liquid from the reactor to the circulation pipeline, and then the mixed liquid is transported from the circulation pipeline to the reactor, forming a cycle to carry out an external circulation reaction. One end of the circulation pipeline is connected to the bottom of the reactor, and the other end of the circulation pipeline is connected to the top of the reactor. The circulation pump can be used to realize a circulation process in which the mixed liquid in the reactor flows out from the bottom of the reactor and the feed liquid enters the reactor from the top of the reactor. The stirring speed of the stirring paddle in the reactor is 900r / min, and the feed liquid conveying speed of the circulation pump is 50m / min. 3 / h.

[0039] Example 3

[0040] A method for preparing ferric phosphate comprises the following steps:

[0041] Iron salt solution, monoammonium phosphate solution and hydrogen peroxide were added to the reactor, and the obtained mixed solution was subjected to a preliminary reaction at 95°C for 1.8 hours. After the preliminary reaction, an external circulation reaction was carried out at 88°C for 2.5 hours.

[0042] The reactor is provided with a circulation pipeline, and a circulation pump is provided on the circulation pipeline. The circulation pump is used to transport the mixed liquid from the reactor to the circulation pipeline, and then the mixed liquid is transported from the circulation pipeline to the reactor, forming a cycle to carry out an external circulation reaction. One end of the circulation pipeline is connected to the bottom of the reactor, and the other end of the circulation pipeline is connected to the top of the reactor. The circulation pump can be used to realize a circulation process in which the mixed liquid in the reactor flows out from the bottom of the reactor and the feed liquid enters the reactor from the top of the reactor. The stirring speed of the stirring paddle in the reactor is 850r / min, and the feeding liquid conveying speed of the circulation pump is 50m / min. 3 / h.

[0043] Example 4

[0044] A method for preparing ferric phosphate comprises the following steps:

[0045] Iron salt solution, monoammonium phosphate solution and hydrogen peroxide are added to the reactor, and the obtained mixed solution is subjected to a preliminary reaction at 90°C for 2 hours. After the preliminary reaction, a circulation reaction outside the reactor is carried out at 85°C for 3 hours.

[0046] The reactor is provided with a circulation pipeline, and a circulation pump is provided on the circulation pipeline. The mixed liquid reactor is transported to the circulation pipeline through the circulation pump, and then the mixed liquid is transported from the circulation pipeline to the reactor, forming a cycle to carry out an external circulation reaction. One end of the circulation pipeline is connected to the bottom of the reactor, and the other end of the circulation pipeline is connected to the top of the reactor. The circulation pump can be used to realize a circulation process in which the mixed liquid in the reactor flows out from the bottom of the reactor and the feed liquid enters the reactor from the top of the reactor. The stirring speed of the stirring paddle in the reactor is 800r / min, and the feed liquid conveying speed of the circulation pump is 50m / min. 3 / h.

[0047] Example 5

[0048] A method for preparing ferric phosphate comprises the following steps:

[0049] Iron salt solution, monoammonium phosphate solution and hydrogen peroxide were added to the reactor, and the obtained mixed solution was subjected to a preliminary reaction at 100°C for 1.5 hours. After the preliminary reaction, an external circulation reaction was carried out at 90°C for 2 hours.

[0050] The reactor is provided with a circulation pipeline, and a circulation pump is provided on the circulation pipeline. The circulation pump is used to transport the mixed liquid from the reactor to the circulation pipeline, and then the mixed liquid is transported from the circulation pipeline to the reactor, forming a cycle to carry out an external circulation reaction. One end of the circulation pipeline is connected to the bottom of the reactor, and the other end of the circulation pipeline is connected to the top of the reactor. The circulation pump can be used to realize a circulation process in which the mixed liquid in the reactor flows out from the bottom of the reactor and the feed liquid enters the reactor from the top of the reactor. The stirring speed of the stirring paddle in the reactor is 900r / min, and the feed liquid conveying speed of the circulation pump is 50m / min. 3 / h.

[0051] For the above-mentioned Examples 1 to 5, the reaction liquid after the reaction is completed is post-processed: after the reaction is completed, the reaction liquid is filtered and washed for multiple times, the filter residue is sent to a slurry tank, pure water is added for high-speed dispersion washing, and the filter cake is filtered again to obtain an iron phosphate filter cake: after the iron phosphate filter cake is washed and qualified, the filter cake is sent to a flash dryer for flash evaporation to obtain dihydrated iron phosphate, the water content before drying is about 45%, and the water content after drying is 1%; the dihydrated iron phosphate after flash evaporation is sent to a rotary kiln for calcination to obtain anhydrous iron phosphate. The obtained iron phosphate is subjected to performance testing.

[0052] 1. Iron phosphate performance test

[0053]

[0054] The iron phosphate prepared above is mixed with phosphoric acid and lithium salt, and an ethanol solution is added for multi-stage mixing and grinding, and then spray-dried to obtain a precursor. The precursor is heat-treated under nitrogen protection to generate a lithium iron phosphate material.

[0055] The performance of the lithium iron phosphate prepared above is as follows:

[0056] 2. Lithium iron phosphate performance test

[0057]

[0058] 3. SE scanning detection of iron phosphate

[0059] from Figure 1-11 It can be seen that when the iron-phosphorus molar ratio is 0.959-0.968, the iron phosphate has high crystallinity, uniform particle dispersion and regular morphology.

[0060] 3. Powder diffraction of iron phosphate

[0061] from Fig.12 It can be seen that when the iron-phosphorus molar ratio is 0.968, the purity of the iron phosphate is high, the impurities are few, and the sharp peak position is slightly moved forward relative to the standard card. The characteristic peak clearly shows that the iron phosphate crystals prepared in the present application are of high purity and different from conventional iron phosphate (sharp peak).

[0062] The above embodiments are preferred implementation schemes of the present invention. In addition, the present invention may also be implemented in other ways. Any obvious replacement without departing from the concept of the present invention is within the protection scope of the present invention.

Claims

1. An iron phosphate crystal, characterized in that: The molar ratio of Fe to P in the iron phosphate crystals is 0.959-0.968; The method for preparing the iron phosphate crystals comprises the following steps: Add iron salt solution, monoammonium phosphate solution and hydrogen peroxide into a reaction kettle, and conduct preliminary reaction of the obtained mixed solution at 90-100°C; after the preliminary reaction, conduct external circulation reaction at 85-90°C.

2. The iron phosphate crystal according to claim 1, characterized in that: The weight content of Fe in the ferric phosphate crystals is ≥35.5%, and the weight content of P is ≥20.1%.

3. The iron phosphate crystal according to claim 1, characterized in that: The sum of the weight content of Fe and the weight content of PO4 in the iron phosphate crystals is greater than 99%, and the pH of the iron phosphate crystals is 2.8-3.

5.

4. A method for preparing iron phosphate crystals according to any one of claims 1 to 3, characterized in that: The following steps are involved: Add iron salt solution, monoammonium phosphate solution and hydrogen peroxide into a reaction kettle, and conduct preliminary reaction of the obtained mixed solution at 90-100°C; after the preliminary reaction, conduct external circulation reaction at 85-90°C.

5. The method for preparing iron phosphate crystals according to claim 4, characterized in that: The initial reaction time is 1.5-2h.

6. The method for preparing iron phosphate crystals according to claim 4, characterized in that: The cycle reaction time is 2-3 hours.

7. The method for preparing iron phosphate crystals according to claim 4, characterized in that: The reactor is provided with a circulation pipeline, and a circulation pump is provided on the circulation pipeline; the mixed liquid reactor is transported to the circulation pipeline through the circulation pump, and then the mixed liquid is transported from the circulation pipeline to the reactor, forming a cycle to perform an external circulation reaction.

8. The method for preparing iron phosphate crystals according to claim 4, characterized in that: One end of the circulation pipeline is connected to the bottom of the reactor, and the other end of the circulation pipeline is connected to the top of the reactor. A circulation pump can be used to realize a circulation process in which the mixed liquid in the reactor flows out from the bottom of the reactor and the feed liquid enters the reactor from the top of the reactor.

9. The method for preparing iron phosphate crystals according to claim 4, characterized in that: The stirring speed of the stirring paddle in the reactor is 800-900r / min, and the conveying speed of the circulating pump is 50m / min. 3 / h.

Images