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

Abstract

The present invention relates to the technical field of lithium battery electrode materials, and in particular to a preparation method of a lithium iron manganese phosphate precursor and lithium iron manganese phosphate. The main component of the lithium iron manganese phosphate precursor is ammonium iron manganese phosphate, and the preparation steps include: (1) preparing an iron source solution, a manganese source solution and a phosphorus source solution; (2) mixing reaction; (3) filtering and washing; (4) adding phosphorus reaction; the preparation method of lithium iron manganese phosphate is to add water, a lithium source and a carbon source to the lithium iron manganese phosphate precursor, and then sequentially perform sand milling, spray drying and high-temperature calcination 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. The ammonium iron manganese phosphate in the lithium iron manganese phosphate precursor prepared by the present invention is mainly single crystal dispersed large particles, and the lithium iron manganese phosphate product prepared using the lithium iron manganese phosphate precursor as a raw material has high compaction density, high capacitance, strong stability and good cycle performance.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium battery electrode materials, and particularly relates to a preparation method of lithium iron manganese phosphate precursor 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 relatively 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 using the emerging material lithium iron manganese phosphate (LiFe （1−x） Mn x PO 4 , 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 lithium iron manganese phosphate precursor. As the core raw material, the quality of the lithium iron manganese phosphate precursor has a crucial impact on the performance of lithium iron manganese phosphate. The lithium iron manganese phosphate precursor mainly composed of ammonium iron manganese phosphate is a commonly used lithium iron manganese phosphate precursor. Therefore, how to prepare a high-quality lithium iron manganese phosphate precursor mainly composed of ammonium iron manganese phosphate with low energy consumption is an important topic in the lithium-ion battery industry.

[0004] On a microscopic scale, ammonium iron manganese phosphate has a crystal structure. When the traditional co-precipitation method is used to prepare the lithium iron manganese phosphate precursor, generally, a slurry is used as the base, and then an acid (usually phosphoric acid) is added for crystallization co-precipitation reaction. Due to using a slurry as the base, there are many crystal nuclei during crystallization precipitation, the supersaturation is high, the nucleation of crystals is many, the growth rate is fast, the primary particles of the generated lithium iron manganese phosphate precursor are small, and the primary particles agglomerate to form spherical secondary particles, constituting a polycrystalline structure. Compared with the single crystal structure, the polycrystalline structure of the lithium iron manganese phosphate precursor has poor framework firmness. During the compaction and charge-discharge cycles, especially under high-voltage charge-discharge, it is easy to cause the material to crack and break due to the continuous expansion and contraction of the particles, resulting in a lower tap density, poor stability, high-temperature resistance performance, and cycle performance of the lithium iron manganese phosphate battery prepared based on the existing lithium iron manganese phosphate precursor, and a shorter service life. Summary of the Invention

[0005] Aiming at the technical problem that the existing lithium iron manganese phosphate precursor products with ammonium iron manganese phosphate as the main component are mostly polycrystalline structures, and the lithium iron manganese phosphate batteries processed and prepared on the basis of the products have low compaction density, poor stability, high temperature resistance and cycle performance, and short service life. The present invention provides a preparation method of a lithium iron manganese phosphate precursor and lithium iron manganese phosphate, wherein the ammonium iron manganese phosphate in the prepared lithium iron manganese phosphate precursor is mainly single crystal dispersed large particles, and the lithium iron manganese phosphate product prepared with the lithium iron manganese phosphate precursor as the raw material has high compaction density, high capacitance, strong stability and good cycle performance.

[0006] In a first aspect, the present invention provides a method for preparing a lithium iron manganese phosphate precursor, wherein the main component of the lithium iron manganese phosphate precursor is ammonium iron manganese phosphate, and the preparation steps include:

[0007] (1) preparing an iron source solution, a manganese source solution and a phosphorus source solution, dissolving the iron source, the manganese source and the phosphorus source in water to prepare the iron source solution, the manganese source solution and the phosphorus source 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, manganese acetate and manganese carbonate; and the phosphorus source is selected from at least one of monoammonium phosphate, diammonium phosphate, triammonium phosphate, monosodium phosphate, disodium phosphate and trisodium phosphate;

[0008] (2) mixing reaction, first adding water into the reaction kettle, then simultaneously adding the iron source solution, the manganese source solution and the phosphorus source solution into the reaction kettle, stirring and reacting to obtain a reaction solution;

[0009] The reaction equation involved in step (2) is:

[0010] Fe 2+ +Mn 2+ +PO4 3- →(FeMn) 3 (PO 4 ) 2 ;

[0011] Product (FeMn) 3 (PO 4 ) 2 It is an amorphous, non-crystalline solid;

[0012] (3) filtering and washing, filtering and washing the reaction solution to obtain a filter cake, and then adding water to the filter cake to prepare a slurry;

[0013] (4) Phosphorus addition reaction: a strong acid and an ammonium phosphate solution are mixed and heated to 60-70°C, and then the slurry is added dropwise, reacted at 60-70°C, and then filtered, washed, and dried to obtain a lithium iron manganese phosphate precursor;

[0014] The lithium iron manganese phosphate precursor obtained in step (4) is a single crystal particle. The mechanism of generating the single crystal particle is as follows: This scheme uses a strong acid + ammonium phosphate solution as a primer, and a large amount of H + ,PO 4 3- NH 4 + Then, the slurry containing amorphous manganese iron phosphate is added to the primer by dripping. Since the addition method is dripping, the slurry concentration in the primer is low during the reaction, and the crystal nucleation is small. In addition, because there is a large amount of NH 4 + Adsorbed on the surface of the crystal nucleus, hindering the growth of the crystal, so the growth rate of the crystal nucleus is slow. The number of crystal nuclei in the primer is small, the crystal growth rate is slow, and it is not easy for the particles to agglomerate. In addition, due to the NH 4 + The adsorption effect changes the supersaturation of the crystal nucleus surface, thereby affecting the growth of the crystal and ultimately affecting the final morphology of the crystal, thus forming dispersed single crystal large particles.

[0015] Furthermore, the molar ratio of manganese to iron in the reaction solution of step (2) is (6-9):(1-4); and the ratio of the sum of the molar amounts of manganese and iron to the molar amount of phosphorus in the reaction solution is 10:(10-13).

[0016] Furthermore, in step (2), the stirring speed in the reactor is 200-500 rpm, and the feeding time of the iron source solution, the manganese source solution and the phosphorus source solution is 3-5 h.

[0017] Furthermore, in step (3), the washing endpoint of the reaction solution is that the conductivity of the washing solution is less than 1000 μS / cm.

[0018] Furthermore, the strong acid in step (4) is at least one of sulfuric acid, nitric acid and hydrochloric acid, and the ammonium phosphate salt is at least one of monoammonium phosphate, diammonium phosphate and triammonium phosphate;

[0019] When the strong acid is sulfuric acid and the ammonium phosphate salt is diammonium phosphate, the reaction equation of sulfuric acid and diammonium phosphate is:

[0020] H 2 SO 4 +(NH 4 ) 2 HPO 4 →H 3 PO 4 +(NH4) 2 SO 4 ;

[0021] The overall reaction equation involved in step (4) is:

[0022] (FeMn) 3 (PO 4 ) 2 +H 2 SO 4 +(NH4) 2 HPO 4

[0023] →NH 4 MnPO 4 ·H 2 O+NH 4 (Fe 2 (PO4) 2 )OH·2H 2 O+(NH4) 2 SO 4 .

[0024] Furthermore, in step (4), the slurry is added for 3-5 hours, the reaction time is 2-4 hours, the drying temperature is 100-120°C, and the drying time is 3-5 hours.

[0025] In a second aspect, the present invention provides a method for preparing lithium iron manganese phosphate, using the lithium iron manganese phosphate precursor prepared by the aforementioned preparation method as a raw material, adding water, a lithium source and a carbon source to the lithium iron manganese phosphate precursor, and then sequentially performing sand milling, spray drying, and high-temperature calcination to obtain lithium iron manganese phosphate; the lithium source is at least one of lithium hydroxide, lithium carbonate, and lithium phosphate; the carbon source is carbon-containing organic matter;

[0026] When the lithium source is lithium carbonate and the carbon source is glucose, the reaction equation involved is:

[0027] NH 4 MnPO 4 ·H2O+NH 4 (Fe 2 (PO4) 2 )OH·2H 2 O+Li 2 CO 3 +C 6 H 12 O 6

[0028] →LiMnFePO 4 +NH 3 +CO 2 +H 2 O.

[0029] Furthermore, the mass ratio of the lithium iron manganese phosphate precursor, water, lithium source and carbon source is: 1: (2-4): (0.250-0.255): (0.08-0.10).

[0030] Furthermore, the particle size of the material after sand milling is 200-500nm, the high temperature calcination temperature is 600-900°C, and the high temperature calcination time is 15-24h.

[0031] The beneficial effects of the present invention are:

[0032] The preparation method of the lithium iron manganese phosphate precursor provided by the present invention utilizes the simultaneous feeding reaction of an iron source, a manganese source and a phosphorus source, and the reaction product is then reacted under acidic conditions to obtain a lithium iron manganese phosphate precursor whose main component is ammonium iron manganese phosphate. The process flow is simple, the reaction process temperature is low, and the reaction product does not require high-temperature calcination. The energy consumption in the production process is low and the production efficiency is high. The ammonium iron manganese phosphate in the obtained lithium iron manganese phosphate precursor is mainly single crystal dispersed large particles. The lithium iron manganese phosphate product prepared using the lithium iron manganese phosphate precursor of this scheme as a raw material has high compaction density, high capacitance, strong stability and good cycle performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] 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.

[0034] Figure 1 This is the XRD analysis diagram of the amorphous manganese iron phosphate in the slurry prepared in step (3) of Example 1.

[0035] Figure 2 This is the XRD analysis diagram of the lithium manganese iron phosphate precursor prepared in Example 1.

[0036] Figure 3 This is a SEM scan of the lithium manganese iron phosphate precursor prepared in Example 1, with a scale of 5 μm.

[0037] Figure 4 This is a SEM scan of the lithium manganese iron phosphate precursor prepared in Example 1, with a scale of 500 nm.

[0038] Figure 5 This is the XRD analysis diagram of the lithium manganese iron phosphate precursor prepared in Example 3.

[0039] Figure 6 This is a SEM scan of the lithium manganese iron phosphate precursor prepared in Example 3, with a scale of 5 μm.

[0040] Figure 7 This is a SEM scan of the lithium manganese iron phosphate precursor prepared in Example 3, with a scale of 500 nm.

[0041] Figure 8 This is a SEM scan of the selected area of ​​the EDS spectrum of the lithium manganese iron phosphate precursor prepared in Example 3, with a scale of 500 nm.

[0042] Fig. 9 This is the distribution diagram of the Fe element in the selected area of ​​the EDS spectrum of the lithium manganese iron phosphate precursor prepared in Example 3.

[0043] Fig.10 This is the distribution diagram of the Mn element in the selected area of ​​the EDS spectrum of the lithium manganese iron phosphate precursor prepared in Example 3.

[0044] Fig.11 This is the distribution diagram of the P element in the selected area of ​​the EDS energy spectrum of the lithium manganese iron phosphate precursor prepared in Example 3.

[0045] Fig.12 This is the distribution diagram of the O element in the selected area of ​​the EDS spectrum of the lithium manganese iron phosphate precursor prepared in Example 3.

[0046] Fig.13 This is the total spectrum of the selected area of ​​the EDS spectrum of the lithium manganese iron phosphate precursor prepared in Example 3.

[0047] Fig.14 This is the XRD analysis diagram of the lithium manganese iron phosphate precursor prepared in Comparative Example 1.

[0048] Fig.15 This is a SEM scan of the lithium manganese iron phosphate precursor prepared in Comparative Example 1, with a scale of 40 μm.

[0049] Fig.16 This is a SEM scan of the lithium manganese iron phosphate precursor prepared in Comparative Example 1, with a scale of 400 nm.

[0050] Fig.17 This is a SEM scan of a selected area of ​​the EDS spectrum of the lithium manganese iron phosphate precursor prepared in Comparative Example 1, with a scale of 1 μm.

[0051] Fig.18 This is the distribution diagram of Fe, Mn, P, and O elements in the selected area of ​​the EDS spectrum of the lithium iron manganese phosphate precursor prepared in Comparative Example 1.

[0052] Fig.19 This is the XRD analysis diagram of the lithium manganese iron phosphate precursor prepared in Comparative Example 2.

[0053] Fig. 20 This is a SEM scan of the lithium manganese iron phosphate precursor prepared in Comparative Example 2, with a scale of 40 μm.

[0054] Fig.21 This is a SEM scan of the lithium manganese iron phosphate precursor prepared in Comparative Example 2, with a scale of 400 nm.

[0055] Fig. 22 This is a SEM scan of the selected area of ​​the EDS spectrum of the lithium manganese iron phosphate precursor prepared in Comparative Example 2, with a scale of 1 μm.

[0056] Fig.23 This is the distribution diagram of Fe, Mn, P, and O elements in the selected area of ​​the EDS spectrum of the lithium manganese iron phosphate precursor prepared in Comparative Example 2.

[0057] Fig.24 This is the XRD analysis diagram of the lithium iron manganese phosphate prepared in Example 6, and the standard spectrum of lithium iron manganese phosphate PDF: 00-011-0455 is attached.

[0058] Fig.25 This is a SEM scan of the lithium iron manganese phosphate prepared in Example 6, with a scale of 5 μm.

[0059] Fig.26 This is a SEM scan of the lithium iron manganese phosphate prepared in Example 6, with a scale of 5 μm.

[0060] Fig. 27 This is the XRD analysis diagram of the lithium iron manganese phosphate prepared in Comparative Example 4, and the standard spectrum of lithium iron manganese phosphate PDF: 00-011-0455 is attached.

[0061] Fig.28 This is a SEM scan of the lithium iron manganese phosphate prepared in Comparative Example 4, with a scale of 10 μm.

[0062] Fig.29 This is a SEM scan of the lithium iron manganese phosphate prepared in Comparative Example 4, with a scale of 3 μm. DETAILED DESCRIPTION

[0063] 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.

[0064] Example 1

[0065] A method for preparing a lithium iron manganese phosphate precursor, wherein the main component of the lithium iron manganese phosphate precursor is ammonium iron manganese phosphate, and the preparation steps include:

[0066] (1) Prepare 5 L of 0.25 mol / L ferrous oxalate solution, 5 L of 1 mol / L manganous acetate solution, and 5 L of 1.5 mol / L trisodium phosphate solution;

[0067] (2) first add water to the reactor until the water can be stirred up by the paddle, then add the ferrous oxalate solution, manganous acetate solution and trisodium phosphate solution in step (1) to the reactor at the same time, set the stirring rate to 200 rpm, stir and react to obtain a reaction solution, and the feeding time of the ferrous oxalate solution, manganous acetate solution and trisodium phosphate solution is 3 hours;

[0068] (3) Filter and wash the reaction liquid to obtain a filter cake. The washing end point of the reaction liquid is that the conductivity of the washing liquid is less than 1000 μS / cm. Then, water is added to the filter cake to prepare a slurry to obtain 5 L of slurry.

[0069] Take a small amount of slurry, filter, wash and dry it, and then perform XRD analysis. The XRD analysis results are as follows: Figure 1 As shown, from the XRD results, the slurry is an amorphous iron manganese phosphate slurry.

[0070] (4) 287.9 ​​g of 85% sulfuric acid was mixed with 1 L of 0.5 mol / L diammonium phosphate solution, and then the temperature was raised to 65°C. The slurry was then added dropwise while stirring at a stirring rate of 200 rpm. The reaction was carried out at 65°C. The slurry addition time was 10 h and the reaction time was 2 h. The lithium iron manganese phosphate precursor was then obtained after filtration, washing and drying. The washing end point was that the conductivity of the washing liquid was <2000 μS / cm. The drying temperature was 100°C and the drying time was 3 h.

[0071] The lithium iron manganese phosphate precursor product prepared in Example 1 was subjected to XRD analysis and SEM scanning. The XRD analysis results are as follows: Figure 2 The SEM scanning results are shown in Figure 3-Figure 4 shown.

[0072] according to Figure 2 It can be seen from the XRD analysis results that the lithium iron manganese phosphate precursor product prepared in Example 1 presents the phase of ammonium iron manganese phosphate; Figure 3-Figure 4 It can be seen from the SEM scanning results that the lithium manganese iron phosphate precursor product prepared in Example 1 presents a single crystal dispersed octahedral morphology under the microscopic level, and the particle size is 250-300nm.

[0073] Example 2

[0074] A method for preparing a lithium iron manganese phosphate precursor, wherein the main component of the lithium iron manganese phosphate precursor is ammonium iron manganese phosphate, and the preparation steps include:

[0075] (1) Prepare 30 L of 0.4 mol / L ferrous chloride solution, 30 L of 0.6 mol / L manganous nitrate solution, and 30 L of 1.15 mol / L diammonium phosphate solution;

[0076] (2) first add water to the reactor until the water can be stirred by the paddle, then add the ferrous chloride solution, manganous nitrate solution and diammonium phosphate solution in step (1) to the reactor at the same time, set the stirring rate to 450 rpm, stir and react to obtain a reaction solution, and the feeding time of the ferrous chloride solution, manganous nitrate solution and diammonium phosphate solution is 5 hours;

[0077] (3) Filter and wash the reaction liquid to obtain a filter cake. The washing end point of the reaction liquid is that the conductivity of the washing liquid is less than 1000 μS / cm. Then, water is added to the filter cake to prepare a slurry to obtain 30 L of slurry.

[0078] (4) 35 g of 98% sulfuric acid and 961.20 g of 50% monoammonium phosphate solution were mixed and heated to 65°C. The slurry was then added dropwise while stirring at a stirring rate of 500 rpm. The mixture was reacted at 65°C. The slurry addition time was 7 h and the reaction time was 3 h. The lithium iron manganese phosphate precursor was then obtained after filtration, washing and drying. The washing end point was that the conductivity of the washing liquid was <4000 μS / cm. The drying temperature was 100°C and the drying time was 3 h.

[0079] Example 3

[0080] A method for preparing a lithium iron manganese phosphate precursor, wherein the main component of the lithium iron manganese phosphate precursor is ammonium iron manganese phosphate, and the preparation steps include:

[0081] (1) Prepare 100 L of 0.3 mol / L ferrous sulfate solution, 100 L of 0.7 mol / L manganous sulfate solution, and 100 L of 1.3 mol / L monoammonium phosphate solution;

[0082] (2) first add water to the reactor until the water can be stirred up by the paddle, then add the ferrous sulfate solution, manganous sulfate solution and monoammonium phosphate solution in step (1) to the reactor at the same time, set the stirring rate to 350 rpm, stir and react to obtain a reaction solution, and the feeding time of the ferrous sulfate solution, manganous sulfate solution and monoammonium phosphate solution is 5 hours;

[0083] (3) Filtering and washing the reaction liquid to obtain a filter cake, wherein the washing end point of the reaction liquid is when the conductivity of the washing liquid is less than 1000 μS / cm; then adding water to the filter cake to prepare a slurry to obtain 100 L of slurry;

[0084] (4) 1.23 kg of 98% sulfuric acid and 0.78 kg of 10% triammonium phosphate solution were mixed and heated to 65°C. The slurry was then added dropwise while stirring at a stirring rate of 450 rpm. The mixture was reacted at 65°C. The slurry addition time was 9 h and the reaction time was 4 h. The lithium iron manganese phosphate precursor was then obtained after filtration, washing and drying. The washing end point was that the conductivity of the washing solution was <2000 μS / cm. The drying temperature was 100°C and the drying time was 3 h.

[0085] The lithium iron manganese phosphate precursor product prepared in Example 3 was subjected to XRD analysis, SEM scanning and EDS energy spectrum analysis. The XRD analysis results are as follows: Figure 5 The SEM scanning results are shown in Figure 6-Figure 7 As shown, the EDS spectrum analysis results are as follows Figure 8-Figure 13 shown.

[0086] according to Figure 5 It can be seen from the XRD analysis results that the lithium iron manganese phosphate precursor product prepared in Example 3 presents the phase of ammonium iron manganese phosphate; Figure 6-Figure 7 The SEM scanning results show that the lithium iron manganese phosphate precursor product prepared in Example 3 presents a single crystal dispersed octahedron morphology under the microscopic view, and the particle size is 250-300nm; Figure 8-Figure 13 It can be seen from the EDS energy spectrum analysis results that in the single crystal particles of the lithium iron manganese phosphate precursor product obtained in Example 3, the iron, manganese, phosphorus and oxygen elements are evenly distributed, indicating that the manganese and iron elements in the iron manganese phosphate particles are evenly distributed without segregation, and manganese and iron achieve uniform mutual solubility at the atomic or molecular level, which is beneficial to the performance of electrical properties.

[0087] Example 4

[0088] A method for preparing lithium iron manganese phosphate, comprising: using the lithium iron manganese phosphate precursor prepared in 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 source and carbon source is: 1: (2-4): (0.250-0.255): (0.08-0.10), and then sand-milling the mixture, wherein the particle size of the material after sand-milling is 350 nm; 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.

[0089] Example 5

[0090] A method for preparing lithium iron manganese phosphate, using the lithium iron manganese phosphate precursor prepared in Example 2 as a raw material, and the preparation steps of the lithium iron manganese phosphate are the same as those in Example 4.

[0091] Example 6

[0092] A method for preparing lithium iron manganese phosphate, using the lithium iron manganese phosphate precursor prepared in Example 3 as a raw material, and the preparation steps of the lithium iron manganese phosphate are the same as those in Example 4.

[0093] The lithium iron manganese phosphate prepared in Example 6 was subjected to XRD analysis and SEM scanning. The XRD analysis results are as follows: Fig.24 The SEM scanning results are shown in Figure 25-26 shown.

[0094] according to Fig.24 It can be seen from the XRD analysis results that the XRD pattern of the lithium iron manganese phosphate prepared in Example 6 is 100% consistent with the standard spectrum, indicating that the product of Example 6 is a pure phase lithium iron manganese phosphate product, does not contain other impurities, and has high crystallinity; Figure 25-26 It can be seen from the SEM scanning results that the primary particles of lithium iron manganese phosphate prepared in Example 6 are spherical with a size of 100-200nm. The primary particles agglomerate to form spherical secondary agglomerates, and the secondary agglomerates have a gradation of large and small particles, which is beneficial to the improvement of compaction density.

[0095] Comparative Example 1

[0096] A method for preparing a lithium iron manganese phosphate precursor, wherein the main component of the lithium iron manganese phosphate precursor is ammonium iron manganese phosphate, and the preparation steps include:

[0097] (1) Prepare 100 L of 0.3 mol / L ferrous sulfate solution, 100 L of 0.7 mol / L manganous sulfate solution, and 100 L of 1.3 mol / L monoammonium phosphate solution;

[0098] (2) firstly adding the ferrous sulfate solution and manganous sulfate solution in step (1) into the reactor as a primer solution, and then adding the monoammonium phosphate solution in step (1) into the reactor, setting the stirring rate to 350 rpm, stirring and reacting to obtain a reaction solution, and the feeding time of the monoammonium phosphate solution is 5 hours;

[0099] (3) Filtering and washing the reaction liquid to obtain a filter cake, wherein the washing end point of the reaction liquid is when the conductivity of the washing liquid is less than 1000 μS / cm; then adding water to the filter cake to prepare a slurry to obtain 100 L of slurry;

[0100] (4) 1.23 kg of 98% sulfuric acid and 0.78 kg of 10% triammonium phosphate solution were mixed and heated to 65°C. The slurry was then added dropwise while stirring at a stirring rate of 350 rpm. The mixture was reacted at 65°C. The slurry addition time was 9 h and the reaction time was 4 h. The lithium iron manganese phosphate precursor was then obtained after filtration, washing and drying. The washing end point was that the conductivity of the washing solution was <2000 μS / cm. The drying temperature was 100°C and the drying time was 3 h.

[0101] The lithium iron manganese phosphate precursor product prepared in Comparative Example 1 was subjected to XRD analysis, SEM scanning and EDS energy spectrum analysis. The XRD analysis results are as follows: Fig.14 The SEM scanning results are shown in Figure 15-16 As shown, the EDS spectrum analysis results are as follows Figure 17-Figure 18 shown.

[0102] according to Fig.14 It can be seen from the XRD analysis results that the lithium iron manganese phosphate precursor product prepared in Comparative Example 1 presents the phase of ammonium iron manganese phosphate; Figure 15-16 The SEM scanning results show that the primary particles of the lithium iron manganese phosphate precursor prepared in Comparative Example 1 are small and the secondary agglomerates are spherical; Figure 17-Figure 18 It can be seen from the EDS energy spectrum analysis results that there are uneven distributions of Mn and Fe elements and segregation of Mn elements in the single crystal particles of the lithium iron manganese phosphate precursor product prepared in Comparative Example 1.

[0103] Comparative Example 2

[0104] A method for preparing a lithium iron manganese phosphate precursor, wherein the main component of the lithium iron manganese phosphate precursor is ammonium iron manganese phosphate, and the preparation steps include:

[0105] (1) Prepare 100 L of 0.3 mol / L ferrous sulfate solution, 100 L of 0.7 mol / L manganous sulfate solution, and 100 L of 1.3 mol / L monoammonium phosphate solution;

[0106] (2) first add water to the reactor until the water can be stirred up by the paddle, then add the ferrous sulfate solution, manganous sulfate solution and monoammonium phosphate solution in step (1) to the reactor at the same time, set the stirring rate to 450 rpm, stir and react to obtain a reaction solution, and the feeding time of the ferrous sulfate solution, manganous sulfate solution and monoammonium phosphate solution is 5 hours;

[0107] (3) Filtering and washing the reaction liquid to obtain a filter cake, wherein the washing end point of the reaction liquid is when the conductivity of the washing liquid is less than 1000 μS / cm; then adding water to the filter cake to prepare a slurry to obtain 100 L of slurry;

[0108] (4) The slurry was added to the reactor as a primer, the stirring rate was set to 350 rpm and the temperature was raised to 65°C, and then 1.23 kg of 98% sulfuric acid and 0.78 kg of 10% diammonium phosphate solution were added to the reactor. The addition time was 9 hours and the reaction time was 4 hours. The lithium iron manganese phosphate precursor was then obtained after filtration, washing and drying. The washing end point was that the conductivity of the washing liquid was <2000 μS / cm, the drying temperature was 100°C, and the drying time was 3 hours.

[0109] The lithium iron manganese phosphate precursor product prepared in Comparative Example 2 was subjected to XRD analysis, SEM scanning and EDS energy spectrum analysis. The XRD analysis results are as follows: Fig.19 The SEM scanning results are shown in Figure 20-21 As shown, the EDS spectrum analysis results are as follows Figure 22-Figure 23 shown.

[0110] according to Fig.19 It can be seen from the XRD analysis results that the lithium iron manganese phosphate precursor product prepared in Comparative Example 2 presents the phase of ammonium iron manganese phosphate; Figure 20-21 The SEM scanning results show that the primary particles of the lithium iron manganese phosphate precursor prepared in Comparative Example 2 are small and the secondary agglomerates are spherical; Figure 22-Figure 23 It can be seen from the EDS energy spectrum analysis results that there is obvious Mn element segregation in the single crystal particles of the lithium iron manganese phosphate precursor product prepared in Comparative Example 2.

[0111] Comparative Example 3

[0112] A method for preparing lithium iron manganese phosphate, using the lithium iron manganese phosphate precursor prepared in Comparative Example 1 as a raw material, and the preparation steps of the lithium iron manganese phosphate are the same as those in Example 4.

[0113] Comparative Example 4

[0114] A method for preparing lithium iron manganese phosphate, using the lithium iron manganese phosphate precursor prepared in Comparative Example 2 as a raw material, and the preparation steps of the lithium iron manganese phosphate are the same as those in Example 4.

[0115] The lithium iron manganese phosphate prepared in Comparative Example 4 was subjected to XRD analysis and SEM scanning. The XRD analysis results are as follows: Fig. 27 The SEM scanning results are shown in Figure 28-29 shown.

[0116] according to Fig. 27 The XRD analysis results show that the XRD pattern of the lithium iron manganese phosphate prepared in Comparative Example 4 is compared with the standard spectrum. In addition to the main component of the lithium iron manganese phosphate phase, it also contains a small amount of Li 3 PO 4 and H 2 Mn 5 (PO 4 ) 4 (H 2 O) 4 The two impurity phases may be due to the segregation of manganese in the ammonium iron manganese phosphate precursor prepared in Comparative Example 2 (such as Fig.23 As shown in the figure, when reacting with lithium carbonate to synthesize lithium iron manganese phosphate, the reaction is uneven and an impurity phase is produced. The presence of the impurity phase may affect the electrical properties of the positive electrode material and reduce the capacity; according to Figure 28-29It can be seen from the SEM scanning results that the lithium iron manganese phosphate prepared in Comparative Example 4 has abnormal crystal growth. The reason for the abnormal crystal growth is that the manganese element is segregated in the lithium iron manganese phosphate precursor, which causes the manganese-rich area crystals to grow abnormally when the lithium iron manganese phosphate precursor reacts with lithium carbonate at high temperature. These abnormally grown crystals will hinder the compaction of the powder when it is made into an electrode sheet, thereby reducing the compaction density of the positive electrode material. At the same time, due to the abnormal growth of the crystals, the carbon coating effect of the lithium iron manganese phosphate is poor and the carbon coating is uneven, which will also reduce the discharge capacity of the positive electrode material.

[0117] The lithium iron manganese phosphate prepared in Examples 4-6 and Comparative Examples 3-4 were made into button-type batteries under the same conditions according to a conventional method, and then their electrical properties were tested under the same conditions. The electrical property test results are shown in Table 1.

[0118] Table 1 Electrical performance test results

[0119]

[0120] According to the test results in Table 1, it can be seen that compared with Comparative Examples 3-4, the compaction density of the lithium iron manganese phosphate prepared in Example 4-6 is 0.3-0.4g / cc higher, the discharge voltage is 0.3-0.35V higher, and the discharge capacity is 15-20mAh / g higher. The electrical properties and compaction density of the lithium iron manganese phosphate prepared in Example 4-6 are significantly higher than those of Comparative Examples 3-4. The high compaction density and discharge capacity are due to the fact that the lithium iron manganese phosphate precursor used as the raw material has a single crystal structure, high crystallinity, dense growth, and uniform distribution of manganese and iron elements. The lithium iron manganese phosphate crystals prepared using the lithium iron manganese phosphate precursor with a single crystal structure grow uniformly, and the secondary particles are spherical with a particle size distribution, which is conducive to improving compaction. At the same time, the crystals have no abnormal growth, the carbon coating is uniform, and the electrical properties are also better. However, the distribution of manganese element in the ammonium iron manganese phosphate precursor in Comparative Example 1-2 is uneven, resulting in impurity phase when reacting with lithium carbonate to synthesize lithium iron manganese phosphate, abnormal growth of crystals, resulting in a decrease in compaction density when pressed into electrodes, and also resulting in low discharge capacity.

[0121] 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 a lithium iron manganese phosphate precursor, wherein the main component of the lithium iron manganese phosphate precursor is ammonium iron manganese phosphate, characterized in that: The preparation steps include: (1) dissolving an iron source, a manganese source and a phosphorus source in water to prepare an iron source solution, a manganese source solution and a phosphorus source 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, manganese acetate and manganese carbonate; and the phosphorus source is selected from at least one of monoammonium phosphate, diammonium phosphate, triammonium phosphate, monosodium phosphate, disodium phosphate and trisodium phosphate; (2) first adding water into the reaction kettle, then simultaneously adding the iron source solution, the manganese source solution and the phosphorus source solution into the reaction kettle, stirring and reacting to obtain a reaction solution; In the reaction solution, the molar ratio of manganese to iron is (6-9):(1-4); In the reaction solution, the ratio of the sum of the molar amounts of manganese and iron to the molar amount of phosphorus is 10:(10-13); (3) filtering and washing the reaction solution to obtain a filter cake, and then adding water to the filter cake to prepare a slurry; (4) After mixing a strong acid and an ammonium phosphate solution, the temperature is raised to 60-70°C, and then the slurry is added dropwise. The slurry is added for 3-5 hours. The mixture is reacted at 60-70°C for 2-4 hours. The mixture is then filtered, washed, and dried to obtain a lithium iron manganese phosphate precursor. The drying temperature 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 iron source solution, the manganese source solution and the phosphorus source solution is 3-5 hours.

3. The preparation method according to claim 1, characterized in that: In step (3), the washing end point of the reaction solution is that the conductivity of the washing solution is less than 1000 μS / cm.

4. The preparation method according to claim 1, characterized in that: The strong acid in step (4) is at least one of sulfuric acid, nitric acid and hydrochloric acid, and the ammonium phosphate salt is at least one of monoammonium phosphate, diammonium phosphate and triammonium phosphate.

5. A method for preparing lithium manganese iron phosphate, characterized in that: Using the lithium iron manganese phosphate precursor obtained by the preparation method as described in claim 1 as a raw material, adding water, a lithium source and a carbon source to the lithium iron manganese phosphate precursor, and then sequentially performing sand milling, spray drying, and high-temperature calcination 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 mass ratio of lithium iron manganese phosphate precursor, water, lithium source and carbon source is: 1: (2-4): (0.250-0.255): (0.08-0.10).

7. 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 600-900℃, and the high-temperature calcination time is 15-24h.

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