A method for preparing ammonium manganese iron phosphate and lithium manganese iron phosphate

Abstract

The present invention relates to the technical field of lithium battery electrode materials, and specifically to a method for preparing ammonium iron manganese phosphate and lithium iron manganese phosphate. The preparation steps of ammonium iron manganese phosphate include: (1) preparing an iron source solution, a manganese source solution and an ammonium salt solution; (2) mixing reaction; (3) filtering and washing; (4) adding phosphorus reaction; the preparation method of lithium iron manganese phosphate is: adding water, a lithium source and a carbon source to the ammonium iron manganese phosphate, and then sequentially performing sand milling, spray drying and high-temperature calcination to obtain lithium iron manganese phosphate. The ammonium iron manganese phosphate of the present invention has low production cost, high production efficiency, good product consistency and repeatability; the lithium iron manganese phosphate product prepared using ammonium iron manganese phosphate has high compaction density and good electrical properties.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium battery electrode materials, and specifically relates to a preparation method of ammonium iron manganese phosphate and lithium iron manganese phosphate. Background Art

[0002] In the existing lithium-ion battery industry, lithium iron phosphate batteries are widely used as power batteries and energy storage batteries for electric vehicles due to their advantages such as high energy density, environmental friendliness, and high safety. However, in the existing technology, the capacity of lithium iron phosphate batteries has approached their theoretical capacity, and the tap density has also approached the limit, making it difficult to further improve the energy density of lithium iron phosphate batteries. Lithium iron manganese phosphate battery is a lithium battery prepared by using the emerging material lithium iron manganese phosphate (LiFe （1−x） Mn x PO4, 0 < x < 1, abbreviated as LFMP) as the battery electrode material. It has the same theoretical capacity and tap density as lithium iron phosphate batteries, but its discharge voltage is higher than that of lithium iron phosphate batteries. Therefore, lithium iron manganese phosphate batteries have a higher energy density than lithium iron phosphate batteries and have broad development prospects.

[0003] The main production raw materials of lithium iron manganese phosphate are lithium source, carbon source, and iron manganese phosphate precursor. As the core raw material, the quality of the iron manganese phosphate precursor has a crucial impact on the performance of lithium iron manganese phosphate. Ammonium iron manganese phosphate is an ideal iron manganese phosphate precursor. Therefore, how to prepare a high-quality ammonium iron manganese phosphate with low energy consumption is an important topic in the lithium-ion battery industry.

[0004] The existing preparation process of ammonium iron manganese phosphate is generally set with reference to the preparation process of lithium iron phosphate precursor. The steps are generally to mix the raw materials and then heat them to react to form a solid, filter and wash the solid, and then carry out high-temperature calcination for purification. The existing preparation process of ammonium iron manganese phosphate has high energy consumption, high production cost, and low production efficiency. The quality of the prepared ammonium iron manganese phosphate product is unstable, which in turn leads to the tap density and electrical properties of the lithium iron manganese phosphate product not being guaranteed, and has an adverse impact on the performance of lithium iron manganese phosphate batteries. Summary of the Invention

[0005] Aiming at the technical problems of high production energy consumption, high production cost, and low efficiency of the existing ammonium iron manganese phosphate, and the unstable quality of ammonium iron manganese phosphate products affecting the performance of lithium iron manganese phosphate products, the present invention provides a preparation method of ammonium iron manganese phosphate and lithium iron manganese phosphate. The production cost of ammonium iron manganese phosphate is low, the production efficiency is high, and the product consistency and repeatability are good; the lithium iron manganese phosphate product prepared by using ammonium iron manganese phosphate has a high tap density and good electrical properties.

[0006] In the first aspect, the present invention provides a preparation method of ammonium iron manganese phosphate, and the steps include:

[0007] (1) preparing an iron source solution, a manganese source solution and an ammonium salt solution, wherein the iron source, the manganese source and the ammonium salt are dissolved in water to prepare the iron source solution, the manganese source solution and the ammonium salt solution, respectively, wherein the iron source is selected from at least one of ferrous sulfate, ferrous chloride, ferrous nitrate and ferrous oxalate; the manganese source is selected from at least one of manganese sulfate, manganese chloride, manganese nitrate and manganese acetate; and the ammonium salt solution is ammonium bicarbonate solution or ammonium carbonate solution;

[0008] (2) mixing reaction, mixing the iron source solution and the manganese source solution to obtain a mixed solution; first adding the ammonium salt solution to the reaction kettle, and then adding the mixed solution to the reaction kettle at room temperature and under stirring to obtain a first slurry;

[0009] (3) filtering and washing, filtering and washing the first slurry to obtain a filter cake;

[0010] (4) Phosphorus addition reaction: water is added to the filter cake to prepare a second slurry, and then phosphoric acid and monoammonium phosphate are added to the second slurry to react at room temperature. The product after the reaction is filtered, washed, and dried to obtain an ammonium iron manganese phosphate product.

[0011] Furthermore, in the mixed solution of step (2), the molar ratio of manganese to iron is (6-9):(1-4); and the molar amount of ammonium ion in the first slurry is greater than the sum of the molar amounts of manganese and iron.

[0012] Furthermore, in step (2), the stirring speed in the reactor is 200-500 rpm, and the feeding time of the mixed solution is 2-4 h.

[0013] Furthermore, in step (3), the washing endpoint of the first slurry is that the slurry conductivity is less than 3000 μS / cm.

[0014] Furthermore, the mass concentration of phosphoric acid used in step (4) is 85%; the reaction time after adding phosphoric acid and monoammonium phosphate to the second slurry is 1-2 hours; stirring is performed during the reaction at a stirring speed of 200-500 rpm; the drying temperature of the product after the reaction is 100-120° C., and the drying time is 3-5 hours.

[0015] Furthermore, the monoammonium phosphate is agricultural grade monoammonium phosphate or industrial grade monoammonium phosphate.

[0016] Furthermore, the ratio of the sum of the molar amounts of manganese and iron in the second slurry of step (4) to the sum of the molar amounts of phosphorus in phosphoric acid and monoammonium phosphate is 10:(10-13).

[0017] In a second aspect, the present invention provides a method for preparing lithium iron manganese phosphate, wherein ammonium iron manganese phosphate is prepared using the above preparation method, water, a lithium source and a carbon source are added to the ammonium iron manganese phosphate, and then sand milling, spray drying and high-temperature calcination are performed in sequence to obtain lithium iron manganese phosphate; the lithium source is at least one of lithium hydroxide, lithium carbonate and lithium phosphate; and the carbon source is carbon-containing organic matter.

[0018] Furthermore, the particle size of the material after sand milling is 200-500nm, the high-temperature calcination temperature is 700-900°C, and the high-temperature calcination time is 15-24h.

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

[0020] 1. The preparation method of ammonium iron manganese phosphate provided by the present invention comprises the following steps: using ammonium bicarbonate or ammonium carbonate to react with an iron source and a manganese source, filtering and washing, and then reacting with a phosphorus source; filtering, washing, and drying the product after the reaction to obtain an ammonium iron manganese phosphate product; the reaction process does not require heating or high-temperature calcination process; the production cost of ammonium iron manganese phosphate is low, the production efficiency is high, and the product consistency and repeatability are good; the lithium iron manganese phosphate product prepared using ammonium iron manganese phosphate has high compaction density and good electrical properties.

[0021] 2. The present invention can use the production equipment for preparing iron phosphate to prepare ammonium iron manganese phosphate, and use the production equipment for preparing lithium iron phosphate to prepare lithium iron manganese phosphate, which can further save the equipment cost for producing lithium iron manganese phosphate and improve economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0023] Figure 1 It is the XRD analysis chart and PDF standard card spectrum of the ammonium manganese iron phosphate prepared in Example 1.

[0024] Figure 2 This is a SEM scan of the ammonium manganese iron phosphate prepared in Example 1, with a scale of 20 μm.

[0025] Figure 3 It is the XRD analysis chart and PDF standard card spectrum of the lithium iron manganese phosphate prepared in Example 6.

[0026] Figure 4 This is a SEM scan of the lithium iron manganese phosphate prepared in Example 6, with a scale of 20 μm.

[0027] Figure 5This is a SEM scan of the lithium iron manganese phosphate prepared in Example 6, with a scale of 500 nm.

[0028] Figure 6 It is the XRD analysis diagram and PDF standard card spectrum of the iron manganese phosphate precursor prepared in Comparative Example 1.

[0029] Figure 7 This is a SEM scan of the iron manganese phosphate precursor prepared in Comparative Example 1, with a scale of 20 μm.

[0030] Figure 8 It is the XRD analysis chart and PDF standard card spectrum of lithium iron manganese phosphate prepared in comparative example 2.

[0031] Fig. 9 This is a SEM scan of the lithium iron manganese phosphate prepared in Comparative Example 2, with a scale of 20 μm.

[0032] Fig.10 This is a SEM scan of the lithium iron manganese phosphate prepared in Comparative Example 2, with a scale of 500 nm. DETAILED DESCRIPTION

[0033] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0034] Example 1

[0035] A method for preparing ammonium manganese iron phosphate, comprising the steps of:

[0036] (1) Prepare 5 L of 0.25 mol / L ferrous sulfate solution, 5 L of 1 mol / L manganese sulfate solution, and 5 L of 1.5 mol / L ammonium bicarbonate solution;

[0037] (2) The ferrous sulfate solution and the manganous sulfate solution in step (1) are mixed to prepare 10 L of a mixed solution; an ammonium bicarbonate solution is added to a reactor, and then the mixed solution is added to the reactor under stirring at room temperature to obtain 15 L of a first slurry; the stirring speed in the reactor is 400 rpm, and the feeding time of the mixed solution is 2 h;

[0038] (3) filtering and washing the first slurry, wherein the washing end point is that the slurry conductivity is less than 3000 μS / cm, to obtain a filter cake;

[0039] (4) Add water to the filter cake to prepare a second slurry to obtain 5 L of the second slurry, then add 87.9 g of phosphoric acid with a mass concentration of 85% and 179 g of industrial-grade monoammonium phosphate powder with a purity of 99% to the second slurry, and react at room temperature for 1 h. Stirring is performed during the reaction at a speed of 400 rpm. The product after the reaction is filtered and washed. The washing end point is that the slurry conductivity is <2000 μS / cm. Then, the remaining solid is dried at a drying temperature of 100°C for a drying time of 3 h to obtain an ammonium iron manganese phosphate product.

[0040] The ammonium manganese iron phosphate product obtained in Example 1 was subjected to XDR analysis and SEM scanning. The XDR analysis results are as follows: Figure 1 The SEM scanning results are shown in Figure 2 shown.

[0041] according to Figure 1 It can be seen from the XDR analysis results that the ammonium manganese iron phosphate product prepared in Example 1 presents the phase of ammonium manganese iron phosphate; Figure 2 It can be seen from the SEM scanning results that the ammonium iron manganese phosphate product prepared in Example 1 is in the form of flakes under the microscope, the diameter of the flake ammonium iron manganese phosphate is 10-20 μm, and the thickness of the flake ammonium iron manganese phosphate is 1-5 μm.

[0042] Example 2

[0043] A method for preparing ammonium manganese iron phosphate, comprising the steps of:

[0044] (1) Prepare 30 L of 0.25 mol / L ferrous sulfate solution, 30 L of 1 mol / L manganese sulfate solution, and 30 L of 1.27 mol / L ammonium carbonate solution;

[0045] (2) The ferrous sulfate solution and the manganous sulfate solution in step (1) are mixed to prepare 60 L of a mixed solution; an ammonium carbonate solution is added to a reactor, and then the mixed solution is added to the reactor under stirring at room temperature to obtain 90 L of a first slurry; the stirring speed in the reactor is 400 rpm, and the feeding time of the mixed solution is 3 h;

[0046] (3) filtering and washing the first slurry, wherein the washing end point is that the slurry conductivity is less than 2000 μS / cm, to obtain a filter cake;

[0047] (4) Add water to the filter cake to prepare a second slurry to obtain 30 L of the second slurry, then add 29.5 g of 85% phosphoric acid and 961.20 g of 20% monoammonium phosphate solution to the second slurry, and react at room temperature for 1 h. Stirring is performed during the reaction at a speed of 400 rpm. The product after the reaction is filtered and washed. The washing end point is that the slurry conductivity is <4000 μS / cm. Then, the remaining solid is dried at a drying temperature of 100°C for 3 h to obtain an ammonium iron manganese phosphate product.

[0048] Example 3

[0049] A method for preparing ammonium manganese iron phosphate, comprising the steps of:

[0050] (1) Prepare 1000 L of 0.25 mol / L ferrous sulfate solution, 1000 L of 1 mol / L manganese sulfate solution, and 1000 L of 1.5 mol / L ammonium bicarbonate solution;

[0051] (2) The ferrous sulfate solution and the manganous sulfate solution in step (1) are mixed to prepare 2000 L of a mixed solution; an ammonium bicarbonate solution is added to a reactor, and then the mixed solution is added to the reactor under stirring at room temperature to obtain 3000 L of a first slurry; the stirring speed in the reactor is 400 rpm, and the feeding time of the mixed solution is 4 hours;

[0052] (3) filtering and washing the first slurry, wherein the washing end point is that the slurry conductivity is less than 2500 μS / cm, to obtain a filter cake;

[0053] (4) Add water to the filter cake to prepare a second slurry of 1000 L, then add 4.3 kg of phosphoric acid with a mass concentration of 85% and 13.5 kg of industrial-grade monoammonium phosphate powder with a purity of 99% to the second slurry, and react at room temperature for 1 hour. Stirring is performed during the reaction at a speed of 400 rpm. The product after the reaction is filtered and washed. The washing end point is that the slurry conductivity is <2000 μS / cm. Then, the remaining solid is dried at a drying temperature of 100°C for 3 hours to obtain an ammonium iron manganese phosphate product.

[0054] Example 4

[0055] A method for preparing lithium manganese iron phosphate, using the ammonium manganese iron phosphate of Example 1 as a raw material, adding deionized water, lithium carbonate and glucose to the ammonium manganese iron phosphate to prepare a mixture, and then sand-milling the mixture, wherein the particle size of the material after sand milling is 350nm; spray drying the sand-milled material, and then calcining it at 720°C in a nitrogen atmosphere for 20h to obtain a lithium manganese iron phosphate product.

[0056] Example 5

[0057] A method for preparing lithium manganese iron phosphate, using the ammonium manganese iron phosphate of Example 2 as a raw material, and the preparation steps of the lithium manganese iron phosphate are the same as those of Example 4.

[0058] Example 6

[0059] A method for preparing lithium manganese iron phosphate, using the ammonium manganese iron phosphate of Example 3 as a raw material, and the preparation steps of the lithium manganese iron phosphate are the same as those of Example 4.

[0060] The lithium iron manganese phosphate prepared in Example 6 was sent for XRD and SEM testing, and the results were as follows: Figure 3-5 As shown. Among them, Figure 3 This is the XRD pattern of lithium manganese iron phosphate obtained in Example 6, Figure 4-5 This is a SEM image of the lithium manganese iron phosphate obtained in Example 6. Figure 6 It can be seen that the prepared lithium iron manganese phosphate is in very good agreement with the standard card, indicating that the prepared lithium iron manganese phosphate is pure phase and has high crystallinity. Figure 4 It can be seen that the prepared lithium iron manganese phosphate is a spherical agglomerate with a high sphericity, which is beneficial to improve the compaction density. Figure 5 It can be seen that the primary particles are spherical with a diameter of 200-400nm, which is conducive to the insertion and extraction of lithium ions during charging and discharging, and improves the charging and discharging capacity.

[0061] Comparative Example 1

[0062] A method for preparing a lithium manganese iron phosphate precursor, comprising the following steps:

[0063] (1) Prepare 1000 L of 0.25 mol / L ferrous sulfate solution, 1000 L of 1 mol / L manganese sulfate solution, and 1000 L of 1.5 mol / L ammonium bicarbonate solution;

[0064] (2) The ferrous sulfate solution and the manganous sulfate solution in step (1) are mixed to prepare 2000 L of a mixed solution; an ammonium bicarbonate solution is added to a reactor, and then the mixed solution is added to the reactor under stirring at room temperature to obtain 3000 L of a first slurry; the stirring speed in the reactor is 400 rpm, and the feeding time of the mixed solution is 4 hours;

[0065] (3) filtering and washing the first slurry, wherein the washing end point is that the slurry conductivity is less than 2500 μS / cm, to obtain a filter cake;

[0066] (4) Add water to the filter cake to prepare a second slurry of 1000 L, then add 4.3 kg of phosphoric acid with a mass concentration of 85% and 13.5 kg of industrial-grade monoammonium phosphate powder with a purity of 99% to the second slurry, and react at 90-100° C. for 1 h. Stirring is performed during the reaction at a speed of 400 rpm. The product after the reaction is filtered and washed. The washing end point is that the slurry conductivity is <2000 μS / cm. Then, the remaining solid is dried at a drying temperature of 100° C. for 3 h. The dried material is sintered at 550° C. for 2 h to obtain a lithium iron manganese phosphate precursor product.

[0067] Comparing Comparative Example 1 with Example 3, it can be seen that step (4) of Comparative Example 1 needs to react at 90-100° C., and the reaction product needs to be sintered at high temperature after drying. Therefore, Comparative Example 1 has higher energy consumption than Example 3.

[0068] The lithium iron manganese phosphate precursor product prepared in Comparative Example 1 was sent for XRD and SEM testing, and the results showed Figure 6 and Figure 7 In. From Figure 6 From the XRD results, the lithium iron manganese phosphate precursor prepared in Comparative Example 1 contains not only iron phosphate and manganese phosphate phases, but also an impurity phase, namely, manganese pyrophosphate phase. Figure 7 From the SEM results, the lithium iron manganese phosphate precursor prepared in Comparative Example 1 contains not only lamellar morphology but also smaller granular morphology.

[0069] Comparative Example 2

[0070] A method for preparing lithium iron manganese phosphate, using the lithium iron manganese phosphate precursor of comparative example 1 as a raw material, adding deionized water, lithium carbonate and glucose to the lithium iron manganese phosphate precursor to prepare a mixture, wherein the mass ratio of the lithium iron manganese phosphate precursor, water, lithium carbonate and glucose is 1:3:0.250:0.10, and then sand-milling the mixture, wherein the particle size of the material after sand-milling is 350nm; spray-drying the sand-milled material, and then calcining it at 720°C in a nitrogen atmosphere for 20 hours to obtain a lithium iron manganese phosphate product.

[0071] The lithium iron manganese phosphate product prepared in Comparative Example 2 was sent for XRD and SEM testing, and the results showed Figure 8-10 In. From Figure 8 From the XRD results, the lithium iron manganese phosphate prepared in Comparative Example 2 contains not only two phases of lithium iron phosphate and lithium iron manganese phosphate, but also a small amount of lithium phosphate and manganese dioxide impurity phases. The presence of these impurity phases may affect the electrical properties of the material and reduce the charge and discharge capacity of the material. Figure 9-10 From the SEM results, the lithium iron manganese phosphate prepared in Comparative Example 2 is Fig. 9), the low sphericity of the agglomerated particles may lead to a low compaction density; at high magnification ( Fig.10 ), abnormal crystal growth and uneven carbon coating may lead to low charge and discharge capacity.

[0072] The lithium iron manganese phosphate prepared in Examples 4-6 and Comparative Example 2 was made into button-type batteries under the same conditions according to a conventional method, and then its electrical properties were tested under the same conditions. The electrical properties test results are shown in Table 1.

[0073] Table 1 Electrical performance test results

[0074]

[0075] According to the test results in Table 1, it can be seen that the lithium iron manganese phosphate prepared in Examples 4-6 has higher electrical properties and compaction density than the lithium iron manganese phosphate prepared in Comparative Example 2. The compaction density of Examples 4-6 is 0.2-0.3 g / cc higher than that of Comparative Example 2, which may be due to its high spherical particle morphology ( Figure 4 ), the friction between spherical particles is small, the fluidity is better, and it is easier to compact when compacted to obtain a higher compaction density. The charging capacity of Example 4-6 is 8-10 mAh / g higher than that of Comparative Example 2, and the discharge capacity is 10-16 mAh / g higher. This is mainly because the lithium iron manganese phosphate prepared in Example 4-6 is a pure phase product with high crystallinity ( Figure 3 ), while the lithium iron manganese phosphate prepared in the comparative example contains a small amount of impurity phases such as lithium phosphate and manganese dioxide, and has a low crystallinity ( Figure 8 ). In addition, the lithium iron manganese phosphate prepared in Comparative Example 2 has abnormal crystal growth resulting in uneven carbon coating, further reducing its charge and discharge capacity.

[0076] Although the present invention has been described in detail with reference to the accompanying drawings and in combination with the preferred embodiments, the present invention is not limited thereto. Without departing from the spirit and essence of the present invention, a person of ordinary skill in the art may make various equivalent modifications or substitutions to the embodiments of the present invention, and these modifications or substitutions shall be within the scope of the present invention. Any person of ordinary skill in the art may easily think of changes or substitutions within the technical scope disclosed by the present invention, and these shall be within the scope of protection of the present invention.

Claims

1. A method for preparing ammonium manganese iron phosphate, characterized in that the steps include: (1) dissolving an iron source, a manganese source and an ammonium salt in water to prepare an iron source solution, a manganese source solution and an ammonium salt solution, respectively, wherein the iron source is selected from at least one of ferrous sulfate, ferrous chloride, ferrous nitrate and ferrous oxalate; the manganese source is selected from at least one of manganese sulfate, manganese chloride, manganese nitrate and manganese acetate; and the ammonium salt solution is an ammonium bicarbonate solution or an ammonium carbonate solution; (2) mixing the iron source solution and the manganese source solution to prepare a mixed solution, wherein the molar ratio of manganese element to iron element in the mixed solution is (6-9):(1-4); Firstly, an ammonium salt solution is added to the reaction kettle, and then, under room temperature and stirring, the mixed solution is added to the reaction kettle to react to obtain a first slurry, wherein the molar amount of ammonium radicals in the first slurry is greater than the sum of the molar amounts of manganese and iron; (3) filtering and washing the first slurry to obtain a filter cake; (4) adding water to the filter cake to prepare a second slurry, then adding phosphoric acid and monoammonium phosphate to the second slurry, reacting at room temperature, the ratio of the sum of the molar amounts of manganese and iron in the second slurry to the sum of the molar amounts of phosphorus in phosphoric acid and monoammonium phosphate being 10:(10-13), filtering, washing and drying the reaction product to obtain an ammonium manganese iron phosphate product; The mass concentration of phosphoric acid used in step (4) is 85%; the reaction time after adding phosphoric acid and monoammonium phosphate to the second slurry is 1-2 hours; stirring is performed during the reaction at a stirring speed of 200-500 rpm; the drying temperature of the product after the reaction is 100-120° C. and the drying time is 3-5 hours.

2. The preparation method according to claim 1, characterized in that In step (2), the stirring speed in the reactor is 200-500 rpm, and the feeding time of the mixed solution is 2-4 h.

3. The preparation method according to claim 1, characterized in that: In step (3), the washing end point of the first slurry is that the slurry conductivity is less than 3000 μS / cm.

4. The preparation method according to claim 1, characterized in that: The monoammonium phosphate used in step (4) is agricultural grade monoammonium phosphate or industrial grade monoammonium phosphate.

5. A method for preparing lithium manganese iron phosphate, characterized in that: Ammonium iron manganese phosphate is prepared using the preparation method as described in claim 1, water, a lithium source and a carbon source are added to the ammonium iron manganese phosphate, and then sand milling, spray drying and high-temperature calcination are carried out in sequence to obtain lithium iron manganese phosphate; the lithium source is at least one of lithium hydroxide, lithium carbonate and lithium phosphate; and the carbon source is carbon-containing organic matter.

6. The preparation method according to claim 5, characterized in that: The particle size of the material after sand grinding is 200-500nm, the high-temperature calcination temperature is 700-900℃, and the high-temperature calcination time is 15-24h.

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