Process for producing lithium iron manganese phosphate

Abstract

The application discloses a production process of lithium manganese iron phosphate, and belongs to the technical field of electrode materials. The application adopts two different forms of iron phosphate to be mixed as an iron source, and is matched with manganese dioxide and manganese carbonate, so that the optimal proportion of the use amount is obtained, a lithium manganese iron phosphate material with more uniform particle size is prepared, the obtained product has smaller crystal grain size, the particle morphology is more regular, and the compaction density is higher, so that the use performance and safety of a prepared battery can be effectively improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electrode materials, and particularly relates to a production process of lithium manganese iron phosphate. BACKGROUND

[0002] Lithium manganese iron phosphate (LMFP) is considered as an upgraded version of lithium iron phosphate in the industry, and has better thermal stability, chemical stability and economy than ternary materials, and is also higher in energy density than lithium iron phosphate. However, lithium manganese iron phosphate has problems such as poor conductivity, poor rate performance and poor cycle performance. At present, most enterprises on the market improve the performance of lithium manganese iron phosphate by nanocrystallization. Nanocrystallization reduces the crystal grain size of the material by mechanical ball milling and controlling the calcination temperature, so as to shorten the lithium ion diffusion path, improve the lithium ion migration efficiency, and further improve the rate performance of the material. At the same time of reducing the crystal grain size, the specific surface area of the material is improved, so as to increase the contact interface with the electrolyte, reduce the electrode interface impedance, and further improve the electrochemical performance.

[0003] However, the single nanocrystallization method for reducing the particle size of primary particles to improve the electrochemical performance of the material will cause the material to lack the support of large particles, the product compaction density is low, and the energy density is reduced. SUMMARY

[0004] In view of the problems in the background art, the purpose of the present application is to provide a production process of lithium manganese iron phosphate. The present application uses two different forms of iron phosphate as iron sources, and cooperates with manganese dioxide and manganese carbonate to optimize the proportion of the use amount, so as to prepare a lithium manganese iron phosphate material with more uniform particle size, which is high in uniformity and good in overall performance.

[0005] The technical scheme of the present application is as follows:

[0006] A production process of lithium manganese iron phosphate, comprising the following steps:

[0007] Step one: mixing flaky iron phosphate and spherical iron phosphate as iron sources, and taking lithium source, manganese source, carbon source and additives respectively for drying;

[0008] Step two: adding lithium source, manganese source, iron source, additives and carbon source into deionized water in sequence, continuously stirring and dispersing during the adding process, grinding the obtained slurry, and then spray drying;

[0009] Step three: sintering the spray-dried material at 750-820 DEG C under a protective gas atmosphere, and crushing the sintered material to obtain lithium manganese iron phosphate.

[0010] Further, the lithium source in step one is lithium dihydrogen phosphate and lithium carbonate.

[0011] Further, the manganese source in step one is composed of manganese dioxide and manganese carbonate, and the molar ratio of manganese in the manganese dioxide and manganese carbonate is (0.5-2):1.

[0012] Further, the carbon source in step one is PEG and glucose.

[0013] Further, the additive in step one is magnesium oxide and titanium dioxide.

[0014] Further, the drying in step one is carried out at 80-120℃ for 2-6 h.

[0015] Further, the addition amount of each raw material in step two satisfies the molar ratio of manganese / iron of 1-4, the molar ratio of (manganese+iron) / phosphorus of 0.94-0.99, and the molar ratio of lithium / (manganese+iron) of 1.01-1.08.

[0016] Further, the addition amount of the carbon source in step two is 10%-15% of the total mass of the iron source and the manganese source; the addition amount of the additive is 0.8%-1.5% of the total mass of the iron source and the manganese source, wherein the addition amount of magnesium oxide is 0.5%-1.0% of the total mass of the iron source and the manganese source, and the addition amount of titanium dioxide is 0.3%-0.5% of the total mass of the iron source and the manganese source.

[0017] Further, the solid content of the slurry in step two is 30%-50%, the particle size of the ground slurry is controlled to D50 of 0.25-0.4 μm, and the pH is controlled to 6-9.

[0018] Further, the inlet air temperature of the spray drying in step two is 190-220℃, and the outlet air temperature is 80-100℃.

[0019] Further, the protective gas atmosphere in step three is at least one of nitrogen atmosphere and argon atmosphere.

[0020] Further, the sintering heating rate in step three is 1.5℃ / min, and the holding time is 8-12 h.

[0021] Further, the crushing after sintering in step three adopts air flow crushing, and the particle size after crushing is controlled to D50 of 0.5-2 μm.

[0022] The flaky iron phosphate can form a crystal with a larger particle size at high temperature, and the spherical iron phosphate can form a crystal with a smaller particle size at the same temperature, the crystal particle size of the lithium manganese iron phosphate material prepared by mixing the two kinds of iron phosphate tends to be intermediate size, and the crystal morphology tends to be regular shape, thereby the compaction density of the material can be increased, the battery capacity and energy density can be improved, and the conductivity, ion transport and cycle stability of the battery material can be improved. When only one kind of iron phosphate is used, the crystal morphology of manganese dioxide and manganese carbonate also reaches the above effect of the iron phosphate at high temperature, so that the particle size of the prepared lithium manganese iron phosphate material is more uniform, the product uniformity is higher, and the overall performance is improved.

[0023] The process of the present application adopts the mixing mode of multiple iron phosphates and multiple manganese sources, utilizes the different morphology and reactivity of different iron and manganese, and in the sintering process, different nucleation and grain growth processes are experienced, so that the lithium manganese iron phosphate with a large number of small particles and a small amount of large particles can be obtained by preparation with a suitable ratio, and the compaction density and electrochemical performance are improved.

[0024] The present application has the following beneficial effects:

[0025] 1. The raw material sources of the preparation method are wide, the main raw materials can be selectively more, and the preparation cost is low.

[0026] 2. The product obtained by the present application has smaller crystal particle size, more regular particle morphology, higher compaction density, and can effectively improve the use performance and safety of the prepared battery. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 The SEM picture (magnification 20000) of the lithium manganese iron phosphate prepared in Example 1 of the present application. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical scheme and advantages of the present application clearer, the technical scheme of the present application will be described clearly and completely in combination with examples. If the specific conditions are not specified in the examples, the conventional conditions or the conditions recommended by the manufacturer are used. If the reagents or instruments used are not specified by the manufacturer, they are all conventional products that can be purchased on the market.

[0029] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description of the present application is only for the purpose of describing specific embodiments and is not intended to limit the present application. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0030] The experimental raw materials of the application are all from the market, wherein the purity of the flaky iron phosphate and the spheroidal iron phosphate is 97%, the purity of the manganese dioxide is 90%, the purity of the manganese carbonate is 99.5%, the purity of the lithium dihydrogen phosphate is 99.8%, and the purity of the lithium carbonate is 99.8%.

[0031] Example 1

[0032] A production process of lithium manganese iron phosphate, comprising:

[0033] 1. Take 1 kg of flaky iron phosphate, 1 kg of spheroidal iron phosphate, 0.567 kg of manganese dioxide, 1.587 kg of manganese carbonate, 2.078 kg of lithium dihydrogen phosphate, 0.516 kg of lithium carbonate, 0.03 kg of magnesium oxide, 0.015 kg of titanium dioxide, 0.3312 kg of PEG, 0.3888 kg of glucose, and 18.36 kg of deionized water after drying (80℃, 4 h) for standby.

[0034] 2. Slowly add lithium carbonate (dispersed for 20 min), lithium dihydrogen phosphate (first dissolved in water and then added, dispersed for 20 min), manganese carbonate, manganese dioxide, two kinds of iron phosphate (dispersed for 30 min), magnesium oxide, glucose, and PEG (dispersed for 40 min) into the deionized water in sequence to obtain a slurry, and then grind, control the solid content of the slurry to be 40%, the particle size D50=0.32 μm, and the pH value to be 7.5.

[0035] 3. Take the obtained slurry to perform spray drying (the inlet air temperature is 210℃, and the outlet air temperature is 90℃) to obtain a material with a moisture content of 1.2%; put the spray-dried material into a kiln to perform sintering (the sintering temperature is 800℃, the heating rate is 1.5℃ / min, and the holding time is 10 h), and the oxygen content is controlled to be 1-3 PPM during the whole sintering process; the sintered product is lithium manganese iron phosphate, which is crushed to D50=1-1.5 μm and packaged to obtain the finished product.

[0036] The SEM picture of the lithium manganese iron phosphate prepared in the example is shown in Figure 1 .

[0037] Refer to the step parameters of Example 1 to design Examples 2-7 and Comparative Examples 1-4, and the dosages of the raw materials are shown in Table 1.

[0038] The raw materials and dosages of the above examples and comparative examples are shown in the following table.

[0039] Table 1 Dosage of raw materials (unit: kg)

[0040]

[0041] The performance of the lithium manganese iron phosphate samples prepared in the above examples and comparative examples is detected, and the results are as follows.

[0042] Table 2 Compaction density and electrochemical performance test results

[0043]

[0044] From the above, the carbon source, additive amount and other preparation processes of Comparative Examples 1 to 4 are consistent with the examples, and the difference lies in that the manganese iron source raw material uses a single manganese source and a single iron phosphate. As can be seen from the data results in the table, the use of different iron sources and different manganese sources together can improve the compaction density and electrochemical performance of the material. Different phosphoric acid iron and different manganese sources are selected in the present application, and different grain nucleation and growth processes exist in the sintering process, and different proportions are adjusted, which can achieve more excellent particle size grading effect, retain a large number of small particles while obtain sufficient large particles, effectively improve the compaction density and electrical performance.

[0045] The above-described embodiments only express several preferred embodiments of the present application, which are described in detail and specifically, but are not used to limit the present application. It should be pointed out that the present application can also have various changes and modifications for those skilled in the art, and any modification, equivalent replacement, improvement, etc. made within the concept and principle of the present application should be included in the protection scope of the present application.

Claims

1. A production process for lithium manganese iron phosphate, characterized in that, Includes the following steps: Step 1: Mix flake ferric phosphate with spherical ferric phosphate as an iron source, and simultaneously take lithium source, manganese source, carbon source and additives, and dry them separately for later use. The lithium source is lithium dihydrogen phosphate and lithium carbonate, and the manganese source is composed of manganese dioxide and manganese carbonate, with a molar ratio of manganese element in manganese dioxide and manganese carbonate of (0.5-2):

1. Step 2: Add lithium source, manganese source, iron source, additive and carbon source to deionized water in sequence, stirring and dispersing continuously during the addition process. Grind the resulting slurry and then spray dry it. Step 3: The spray-dried material is sintered in a protective atmosphere at 750-820℃, and then crushed to obtain lithium manganese iron phosphate.

2. The production process of lithium manganese iron phosphate according to claim 1, characterized in that, The carbon source mentioned in step one is PEG and glucose.

3. The production process of lithium manganese iron phosphate according to claim 1, characterized in that, The additives mentioned in step one are magnesium oxide and titanium dioxide.

4. The production process of lithium manganese iron phosphate according to claim 1, characterized in that, In step two, the amount of each raw material added should meet the following requirements: the manganese / iron molar ratio is 1~4, the (manganese + iron) / phosphorus molar ratio is 0.94~0.99, and the lithium / (manganese + iron) molar ratio is 1.01~1.

08.

5. The production process of lithium manganese iron phosphate according to claim 1, characterized in that, In step two, the amount of carbon source added is 10%-15% of the total mass of iron and manganese sources; the amount of additives added is 0.8%-1.5% of the total mass of iron and manganese sources, of which the amount of magnesium oxide added is 0.5%-1.0% of the total mass of iron and manganese sources and the amount of titanium dioxide added is 0.3%-0.5% of the total mass of iron and manganese sources.

6. The production process of lithium manganese iron phosphate according to claim 1, characterized in that, Step 2: Grind the slurry to a particle size of D50 of 0.25-0.4 μm and control the pH to 6-9.

7. The production process of lithium manganese iron phosphate according to claim 1, characterized in that, In step two, the inlet air temperature for spray drying is 190-220℃, and the outlet air temperature is 80-100℃.

8. The production process of lithium manganese iron phosphate according to claim 1, characterized in that, The sintering heating rate in step three is 1.5℃ / min, and the holding time is 8-12 h.

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