A kind of lithium iron manganese phosphate precursor and preparation method of lithium iron manganese phosphate

Abstract

The present invention relates to a preparation method of a lithium iron manganese phosphate precursor and lithium iron manganese phosphate, and the preparation method of the lithium iron manganese phosphate precursor comprises the following steps: 1) preparing ferrous phosphate from ferrous sulfate produced as a byproduct of titanium dioxide in a sulfuric acid process, separating a mother liquor, and obtaining a first solution after the mother liquor is subjected to membrane treatment and MVR concentration treatment; 2) removing impurities from ferrous sulfate produced as a byproduct of titanium dioxide in a sulfuric acid process, obtaining a second solution; 3) mixing the first solution and the second solution to obtain a mixed salt solution; 4) simultaneously dropping the mixed salt solution and the ammonium phosphate salt solution into a reactor under an inert atmosphere to react, controlling the pH value of the solution in the reactor to 5-6, and controlling the reaction temperature to 50-80°C, performing solid-liquid separation after the reaction, and obtaining ammonium iron manganese phosphate. The present invention combines the ferrous mother liquor of titanium dioxide in a sulfuric acid process to prepare an iron phosphate process, and utilizes the comprehensive utilization of the iron phosphate reaction mother liquor to prepare ammonium iron manganese phosphate, with a high degree of resource utilization, and realizes the utilization of a large amount of Mn elements in the iron phosphate reaction mother liquor.

Description

Technical Field

[0001] The invention belongs to the technical field of titanium dioxide preparation, and in particular relates to a method for preparing lithium manganese iron phosphate by concentrating mother liquor in a ferric phosphate production process. Background Art

[0002] In recent years, lithium iron phosphate batteries have been widely used in UPS, power tools, electric vehicles, energy storage batteries and other fields. However, the relatively low voltage platform (3.4V) of lithium iron phosphate makes its energy density low, which limits its development and application. Lithium iron manganese phosphate has the same structure as lithium iron phosphate, but its discharge platform (4.1V) is higher, thus having a higher energy density. Therefore, ammonium manganese phosphate (NH4Mn x Fe (1-x) PO4, x = 0.5-0.8) as lithium manganese iron phosphate (LiMn x Fe (1-x) PO4, x = 0.5-0.8) and has attracted widespread attention.

[0003] Lithium manganese iron phosphate is currently mainly synthesized through solid-phase method or hydrothermal method. In the solid-phase method, the precursor contact is insufficient, the prepared sample particles are uneven in size, and the product consistency is poor. The hydrothermal method has high requirements for reaction equipment and needs to be operated in a high-temperature and high-pressure reactor, which is not easy to achieve industrialization.

[0004] At present, the preparation method of lithium manganese iron phosphate mostly adopts the method of mixing iron source, manganese source, lithium source and carbon source, and undergoing processes such as sand grinding, spray drying and sintering. The disadvantages are that it is impossible to achieve uniform mixing of manganese and iron at the atomic level, and it is impossible to achieve effective external wrapping of the carbon source. The prepared lithium manganese iron phosphate has poor charging constant voltage section and rate discharge performance, and trivalent manganese is prone to disproportionation reaction in the solution to generate divalent manganese and tetravalent manganese, and the purity of the product is not high.

[0005] Patent CN202210741388.5 discloses a method for preparing ammonium manganese iron phosphate, lithium manganese iron phosphate and its application. Ammonium manganese iron phosphate is first prepared as a precursor, and then mixed with a lithium source and a carbon source and calcined to prepare lithium manganese iron phosphate, so as to obtain a lithium manganese iron phosphate positive electrode material with a porous structure.

[0006] Similarly, patent CN202211455847.X also discloses a method for preparing a high-density lithium iron manganese phosphate precursor, a lithium iron manganese phosphate positive electrode material and a precursor. Ammonium iron manganese phosphate is first prepared as a precursor, and then mixed with a lithium source and a carbon source and calcined to prepare lithium iron manganese phosphate, which can improve the specific capacity of the positive electrode material.

[0007] In the above schemes, ammonium manganese iron phosphate is first prepared as a precursor, and then the precursor is mixed with a lithium source and a carbon source and calcined to prepare lithium manganese iron phosphate, which can improve the performance of lithium manganese iron phosphate. However, when preparing the precursor, iron salt and manganese salt are used to prepare the mixed phosphate, and the raw material cost is relatively high.

[0008] In the sulfuric acid process of titanium dioxide, a large amount of ferrous sulfate is produced as a by-product. The by-product ferrous sulfate contains a large amount of metal ions such as manganese, titanium, and magnesium, and has a low purity and low value. A part of the by-product ferrous sulfate is used to prepare ferric phosphate products. In the process of preparing ferric phosphate, a mother liquor containing ammonium sulfate and manganese sulfate is produced. In the prior art, the mother liquor is generally concentrated to recover the ammonium sulfate product, but the recovered ammonium sulfate product also has the problem of low value. Summary of the invention

[0009] In view of the above-mentioned defects in the prior art, the present invention provides a lithium iron manganese phosphate precursor and a method for preparing lithium iron manganese phosphate, and the specific scheme is:

[0010] A method for preparing a lithium iron manganese phosphate precursor comprises the following steps:

[0011] 1) preparing ferric phosphate from ferrous sulfate produced as a by-product of titanium dioxide produced by the sulfuric acid process, separating the mother liquor, and subjecting the mother liquor to membrane treatment and MVR concentration treatment to obtain a first solution;

[0012] 2) The ferrous sulfate produced as a by-product of the sulfuric acid process titanium dioxide is removed from impurities to obtain a second solution;

[0013] 3) mixing the first solution and the second solution to obtain a mixed salt solution;

[0014] 4) The mixed salt solution and the ammonium phosphate salt solution are simultaneously added dropwise to a reactor under inert atmosphere conditions for reaction, the pH value of the solution in the reactor is controlled to be 5-6, and the reaction temperature is controlled to be 50-80° C. After the reaction, solid-liquid separation is performed to obtain ammonium manganese iron phosphate.

[0015] In the present invention, ferrous sulfate produced as a byproduct of the sulfuric acid titanium dioxide process is used as a direct or indirect raw material to prepare ammonium manganese ferric phosphate, which can greatly reduce the cost of raw materials. Ferrous sulfate produced as a byproduct of the sulfuric acid titanium dioxide process contains manganese sulfate. The mother liquor generated in the process of preparing ferric phosphate from ferrous sulfate mainly contains ammonium sulfate, manganese sulfate, and ferrous sulfate. The mother liquor used to prepare ammonium manganese ferric phosphate can achieve complete recycling of iron, manganese, and ammonium elements, and has high economic benefits.

[0016] However, ferrous sulfate, a by-product of the sulfuric acid method titanium dioxide process, also contains impurity ions such as calcium, titanium, and magnesium. Lithium iron manganese phosphate, used as a positive electrode material, has high requirements for the content of impurity elements, generally required to be less than 50ppm.

[0017] Among them, calcium and titanium ions can be removed by neutralization precipitation during impurity removal, but magnesium ions are more difficult to remove by precipitation. If the process conditions in the prior art are used to prepare ammonium manganese iron phosphate, the magnesium content in the precursor exceeds the standard, affecting the quality of the final prepared lithium manganese iron phosphate.

[0018] In this scheme, this problem can be solved by controlling the pH value of 5-6 during the coprecipitation reaction. When the pH value is higher than 6, the magnesium ions in the mixed salt solution will also form a precipitate and mix into the ammonium manganese iron phosphate product, reducing the purity of the product. If the pH is controlled at 7 during the reaction, the magnesium content in the obtained product is above 200ppm, which cannot be used to prepare lithium manganese iron phosphate positive electrode materials. When the pH is controlled below 6, the magnesium content in the product is below 50ppm, which meets the requirements. When the pH value is controlled at 5-6, the ammonium manganese iron phosphate is not completely precipitated at room temperature, and the yield will be reduced. Therefore, the reaction temperature is correspondingly increased to 50-80°C, which ensures that the magnesium ions do not precipitate while ensuring the product yield.

[0019] Preferably, in step 3), the molar ratio of Mn / Fe in the mixed salt solution is adjusted to (1.0-4.0):1; the molecular formula of the ammonium manganese ferrous phosphate is NH4Mn x Fe (1-x) PO4, x = 0.5-0.8. The molar ratio of Mn / Fe in the mixed salt solution affects the ratio of manganese to iron in the final preparation of lithium manganese iron phosphate, and the selection of this ratio is closely related to the performance of the positive electrode material.

[0020] Preferably, the total solubility of manganese and iron ions in the mixed salt solution in step 3) is controlled at 30-100 g / L.

[0021] Preferably, the ammonium sulfate concentration of the first solution after the concentration treatment in step 1) is 15%-20%.

[0022] Preferably, the molar ratio of NH4:P in the ammonium phosphate solution in step 4) is (1.5-2.5):1; the molar ratio of P:(Mn+Fe) in the reaction vessel is (1.5-1.02):1.

[0023] A method for preparing lithium iron manganese phosphate comprises mixing the lithium iron manganese phosphate precursor obtained by the preparation method of the present invention with a lithium source and a carbon source in proportion, and calcining the mixture under an inert atmosphere to obtain the lithium iron manganese phosphate.

[0024] Preferably, the molar ratio of (Mn+Fe):Li:C in the mixture is 1:(1.0-1.15):(0.25-0.45).

[0025] Compared with the prior art, the present invention has the following innovations:

[0026] 1. The present invention combines the ferrous mother liquor (containing a large amount of Fe and Mn elements) of sulfuric acid titanium dioxide to prepare the ferric phosphate process, and then uses the ferric phosphate reaction mother liquor to comprehensively prepare (NH4Mn x Fe (1-x) PO4, x = 0.5-0.8), with a high degree of resource utilization, uniform crystal particles, high product value-added, and a closed chain formed to the greatest extent with the titanium dioxide method for preparing iron phosphate production workshop, realizing the comprehensive utilization of a large amount of Mn elements in the mother liquor of the iron phosphate reaction.

[0027] 2. Ammonium manganese iron phosphate is used as a precursor, in which iron and manganese are both divalent, and no further reduction is required during sintering, which reduces the use of carbon source. The ammonium ions are released in the form of ammonia gas, which is beneficial to the formation of a porous structure of the positive electrode material. The porous structure is beneficial to the infiltration of the positive electrode material and the electrolyte, and improves the efficiency of lithium ion deintercalation. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is the XRD diffraction pattern of the lithium iron manganese phosphate product in Example 1 of the present invention;

[0029] Figure 2 This is a SEM morphology of the lithium iron manganese phosphate product in Example 2 of the present invention. DETAILED DESCRIPTION

[0030] The present invention is clearly described below in conjunction with specific embodiments of the present invention. The description herein is only used to explain the present invention, but is not intended to limit the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work, any modifications, equivalent substitutions, improvements, etc., should be included in the protection scope of the present invention.

[0031] Example

[0032] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention.

[0033] Example 1

[0034] 1. Take a solution of the mother liquor after membrane treatment and MVR concentration treatment in the production process of ferric phosphate, the concentration of ammonium sulfate in the solution is controlled to 15%, and add ferrous sulfate and manganese sulfate solution purified from titanium dioxide byproducts under an inert atmosphere, and adjust the Mn / Fe molar ratio in the solution to a specified ratio, wherein Mn / Fe=4.0, and the solubility of metal ions (Mn, Fe) is controlled at 30 g / L to prepare a mixed salt solution (A);

[0035] 2. Add the mixed salt solution A and ammonium phosphate solution (phosphoric acid + ammonia water, where NH4:P=1.5) to the nitrogen environment reactor at the same time, control the pH value of the solution in the reactor to 5, the temperature in the reactor to 80°C, where the molar ratio of P:(Mn+Fe) is 1.5:1, and after reacting for 2 hours, manganese iron ammonium phosphate (NH4Mn x Fe (1-x) PO4, x = 0.8);

[0036] 3. Wash the synthesized ammonium manganese iron phosphate to neutrality, and dry it in a vacuum drying oven at 100°C for 9 hours to obtain ammonium manganese iron phosphate, the precursor of lithium manganese iron phosphate. The precursor and lithium carbonate, carbon source, etc. are measured in proportion, and lithium manganese iron phosphate, a positive electrode material for lithium-ion batteries, can be prepared through sand milling, spraying, sintering, crushing, post-treatment and other processes, wherein the molar ratio of (Mn+Fe): Li: carbon source is 1:1:0.25, and the carbon source is one, two or a mixture of three of glucose, sucrose and polyethylene glycol. The sintering process is: calcined at 700°C for 12 hours under a nitrogen atmosphere. XRD detection is performed on the obtained lithium manganese iron phosphate, and the detection results are as follows: Figure 1 As shown, it can be seen that the product has good crystallinity.

[0037] Example 2

[0038] 1. Take the solution of the mother liquor after membrane treatment and MVR concentration treatment in the process of ferric phosphate production, the ammonium sulfate concentration of the solution is controlled between 20%, and under an inert atmosphere, add the ferrous sulfate solution and manganese sulfate solution purified from titanium dioxide byproducts, adjust the Mn / Fe molar ratio in the solution to a specified ratio, wherein Mn / Fe=1.0, and the solubility of metal ions (Mn, Fe) is controlled at 100g / L, to prepare a mixed salt solution (A);

[0039] 2. Add the mixed salt solution A and ammonium phosphate solution (phosphoric acid + ammonia water, where NH4:P=2.5) to the nitrogen environment reactor at the same time, control the pH value of the solution in the reactor to 6, the temperature in the reactor to 50°C, where the molar ratio of P:(Mn+Fe) is 1.02:1, and after reacting for 3 hours, manganese iron ammonium phosphate (NH4Mn x Fe (1-x) PO4, x = 0.5;

[0040] 3. Wash the above synthesized ammonium manganese iron phosphate to neutrality, dry it in a vacuum drying oven at 120°C for 6 hours, and obtain the precursor of lithium manganese iron phosphate, ammonium manganese iron phosphate. The precursor and lithium carbonate, carbon source, etc. are measured in proportion, and lithium manganese iron phosphate, a positive electrode material for lithium-ion batteries, can be prepared through sand milling, spraying, sintering, crushing, post-treatment and other processes, wherein the molar ratio of (Mn+Fe): Li: carbon source is 1:1.15:0.45, and the carbon source is one, two or a mixture of three of glucose, sucrose and polyethylene glycol. The sintering process is: calcined at 850°C for 9 hours under a nitrogen atmosphere. The obtained lithium manganese iron phosphate was subjected to SEM detection, and the test results are as follows: Figure 2 As shown, it can be seen that the product crystal particles are uniform and have a multi-porous structure.

[0041] Example 3

[0042] 1. Take a solution of the mother liquor after membrane treatment and MVR concentration treatment in the production process of ferric phosphate, the ammonium sulfate concentration of the solution is controlled to 19%, and add ferrous sulfate solution and manganese sulfate solution purified from titanium dioxide byproducts under an inert atmosphere, and adjust the Mn / Fe molar ratio in the solution to a specified ratio, wherein Mn / Fe=1.5, and the solubility of metal ions (Mn, Fe) is controlled at 60g / L to prepare a mixed salt solution (A);

[0043] 2. Add the mixed salt solution A and ammonium phosphate solution (phosphoric acid + ammonia water, where NH4:P=2.0) to the nitrogen environment reactor at the same time, control the pH value of the solution in the reactor to 5.5, the temperature in the reactor to 65°C, where the molar ratio of P:(Mn+Fe) is 1.3:1, and after reacting for 2.5 hours, manganese iron ammonium phosphate (NH4Mn x Fe (1-x) PO4, x = 0.6);

[0044] 3. The ammonium manganese iron phosphate synthesized above is washed to neutrality, and dried in a vacuum drying oven at 110°C for 7h to obtain ammonium manganese iron phosphate, a precursor of lithium manganese iron phosphate. The precursor, lithium carbonate, carbon source, etc. are measured in proportion, and lithium manganese iron phosphate, a positive electrode material for lithium-ion batteries, can be prepared through sand milling, spraying, sintering, crushing, post-treatment and other processes, wherein the molar ratio of (Mn+Fe): Li: carbon source is 1:1.05:0.3, and the carbon source is one, two or a mixture of three of glucose, sucrose and polyethylene glycol. The sintering process is: calcined at 750°C for 10h under a nitrogen atmosphere.

[0045] Comparative Example 1

[0046] 1. Take a solution of the mother liquor after membrane treatment and MVR concentration treatment in the production process of ferric phosphate, the concentration of ammonium sulfate solution in the solution is controlled to 15%, and add ferrous sulfate solution and manganese sulfate solution purified from titanium dioxide byproducts under an inert atmosphere, and adjust the Mn / Fe molar ratio in the solution to a specified ratio, wherein Mn / Fe=4.0, and the solubility of metal ions (Mn, Fe) is controlled at 30 g / L, to prepare a mixed salt solution (A);

[0047] 2. Add the mixed salt solution A and ammonium phosphate solution (phosphoric acid + ammonia water, where NH4:P=1.5) to the nitrogen environment reactor at the same time, control the pH value of the solution in the reactor to 6.5, the temperature in the reactor to 80°C, where the molar ratio of P:(Mn+Fe) is 1.5:1, and after reacting for 2 hours, manganese iron ammonium phosphate (NH4Mn x Fe (1-x) PO4, x = 0.8);

[0048] 3. Wash the synthesized ammonium manganese ferric phosphate to neutrality, and dry it in a vacuum drying oven at 100° C. for 9 hours to obtain ammonium manganese ferric phosphate, a precursor of lithium manganese iron phosphate.

[0049] Comparative Example 2

[0050] 1. Take a solution of the mother liquor after membrane treatment and MVR concentration treatment in the production process of ferric phosphate, the concentration of ammonium sulfate solution in the solution is controlled to 15%, and add ferrous sulfate solution and manganese sulfate solution purified from titanium dioxide byproducts under an inert atmosphere, and adjust the Mn / Fe molar ratio in the solution to a specified ratio, wherein Mn / Fe=4.0, and the solubility of metal ions (Mn, Fe) is controlled at 30 g / L, to prepare a mixed salt solution (A);

[0051] 2. Add the mixed salt solution A and ammonium phosphate solution (phosphoric acid + ammonia water, where NH4:P=1.5) to the nitrogen environment reactor at the same time, control the pH value of the solution in the reactor to 7, the temperature in the reactor to 80°C, where the molar ratio of P:(Mn+Fe) is 1.5:1, and after reacting for 2 hours, manganese iron ammonium phosphate (NH4Mn x Fe (1-x) PO4, x = 0.8);

[0052] 3. Wash the synthesized ammonium manganese ferric phosphate to neutrality, and dry it in a vacuum drying oven at 100° C. for 9 hours to obtain ammonium manganese ferric phosphate, a precursor of lithium manganese iron phosphate.

[0053] Comparative Example 3

[0054] 1. Take a solution of the mother liquor after membrane treatment and MVR concentration treatment in the production process of ferric phosphate, the concentration of ammonium sulfate solution in the solution is controlled to 15%, and add ferrous sulfate solution and manganese sulfate solution purified from titanium dioxide byproducts under an inert atmosphere, and adjust the Mn / Fe molar ratio in the solution to a specified ratio, wherein Mn / Fe=4.0, and the solubility of metal ions (Mn, Fe) is controlled at 30 g / L, to prepare a mixed salt solution (A);

[0055] 2. Add the mixed salt solution A and ammonium phosphate solution (phosphoric acid + ammonia water, where NH4:P=1.5) to the nitrogen environment reactor at the same time, control the pH value of the solution in the reactor to 5, the temperature in the reactor to 20°C, where the molar ratio of P:(Mn+Fe) is 1.5:1, and after reacting for 2 hours, manganese iron ammonium phosphate (NH4Mn x Fe (1-x) PO4, x = 0.8);

[0056] 3. Wash the synthesized ammonium manganese ferric phosphate to neutrality, and dry it in a vacuum drying oven at 100° C. for 9 hours to obtain ammonium manganese ferric phosphate, a precursor of lithium manganese iron phosphate.

[0057] Comparative Example 4

[0058] 1. Take a solution of the mother liquor after membrane treatment and MVR concentration treatment in the production process of ferric phosphate, the concentration of ammonium sulfate solution in the solution is controlled to 15%, and add ferrous sulfate solution and manganese sulfate solution purified from titanium dioxide byproducts under an inert atmosphere, and adjust the Mn / Fe molar ratio in the solution to a specified ratio, wherein Mn / Fe=4.0, and the solubility of metal ions (Mn, Fe) is controlled at 30 g / L, to prepare a mixed salt solution (A);

[0059] 2. Add the mixed salt solution A and ammonium phosphate solution (phosphoric acid + ammonia water, where NH4:P=1.5) to the nitrogen environment reactor at the same time, control the pH value of the solution in the reactor to 5, the temperature in the reactor to 40°C, where the molar ratio of P:(Mn+Fe) is 1.5:1, and after reacting for 2 hours, manganese iron ammonium phosphate (NH4Mn x Fe (1-x) PO4, x = 0.8);

[0060] 3. Wash the synthesized ammonium manganese ferric phosphate to neutrality, and dry it in a vacuum drying oven at 100° C. for 9 hours to obtain ammonium manganese ferric phosphate, a precursor of lithium manganese iron phosphate.

[0061] According to Examples 1-3 and Comparative Examples 1-4, the magnesium ion content in the precursor ammonium manganese ferric phosphate obtained under different process conditions is compared, and the yield of ammonium manganese ferric phosphate is compared, as shown in the following table:

[0062]

[0063]

[0064] Comparing Example 1 with Comparative Examples 1-4, when the pH value was controlled at 5 during the reaction, the magnesium ion content in the precursor was low, and when the pH reached 7, the magnesium ion content in the precursor was too high. When the reaction temperature was controlled at 80°C, the yield was above 85%, and when the reaction temperature was lower, the yield was lower.

Claims

1. A method for preparing a lithium manganese iron phosphate precursor, characterized in that: The following steps are involved: 1) preparing ferric phosphate from ferrous sulfate produced as a by-product of titanium dioxide produced by the sulfuric acid process, separating the mother liquor, and subjecting the mother liquor to membrane treatment and MVR concentration treatment to obtain a first solution; 2) The ferrous sulfate produced as a by-product of the sulfuric acid process titanium dioxide is removed from impurities to obtain a second solution; 3) mixing the first solution and the second solution to obtain a mixed salt solution; 4) The mixed salt solution and the ammonium phosphate salt solution are simultaneously added dropwise to a reactor under inert atmosphere conditions for reaction, the pH value of the solution in the reactor is controlled to be 5-6, and the reaction temperature is controlled to be 50-80° C. After the reaction, solid-liquid separation is performed to obtain ammonium manganese iron phosphate.

2. The method for preparing a lithium iron manganese phosphate precursor according to claim 1, characterized in that: In step 3), the molar ratio of Mn / Fe in the mixed salt solution is adjusted to (1.0-4.0):1; the molecular formula of the ammonium manganese iron phosphate is NH4Mn x Fe (1-x) PO4, x = 0.5-0.

8.

3. The method for preparing a lithium iron manganese phosphate precursor according to claim 1, characterized in that: In step 3), the total solubility of manganese and iron ions in the mixed salt solution is controlled at 30-100 g / L.

4. The method for preparing a lithium iron manganese phosphate precursor according to claim 1, characterized in that: The ammonium sulfate concentration of the first solution after the concentration treatment in step 1) is 15%-20%.

5. The method for preparing a lithium iron manganese phosphate precursor according to claim 1, characterized in that: In step 4), the molar ratio of NH4:P in the ammonium phosphate solution is (1.5-2.5):1; the molar ratio of P:(Mn+Fe) in the reaction container is (1.5-1.02):

1.

6. A method for preparing lithium manganese iron phosphate, characterized in that: The lithium iron manganese phosphate precursor obtained by the preparation method as claimed in claim 1 is mixed with a lithium source and a carbon source in proportion, and the mixture is calcined in an inert atmosphere to obtain lithium iron manganese phosphate.

7. The method for preparing lithium manganese iron phosphate according to claim 6, characterized in that: The molar ratio of (Mn+Fe):Li:C in the mixture is 1:(1.0-1.15):(0.25-0.45).

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