A preparation method of a doped manganese iron phosphate precursor

Abstract

The application provides a preparation method of a doped manganese iron phosphate precursor and belongs to the field of preparation of positive electrode material precursors. The method comprises the following steps: (1) mixing and grinding raw materials: manganese source, iron source, dopant, phosphorus source and dispersant are mixed and wet-ground; (2) high-temperature aging crystallization of the mixed slurry: the ground slurry is subjected to high-temperature aging crystallization to obtain a manganese iron phosphate suspension, and the suspension is subjected to solid-liquid separation, washing and drying to obtain the manganese iron phosphate precursor. The technical scheme for preparing the doped manganese iron phosphate precursor provided by the application has the characteristics of simplicity and high efficiency, simple process control and easy industrialization.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical energy storage of lithium-ion battery cathode materials, and particularly relates to a method for preparing a doped manganese iron phosphate precursor material. Background Technology

[0002] Lithium manganese iron phosphate (LMP) is expected to replace lithium iron phosphate and become the ideal choice for the next generation of low-cost, high-voltage cathode materials due to its good safety performance, high voltage platform, and low cost (basically on par with lithium iron phosphate). It has already been applied in small areas in portable mobile energy storage, two-wheeled electric vehicles, and some electric vehicle models. In the long run, LMP has huge potential for practical applications.

[0003] Currently, the preparation processes of lithium manganese iron phosphate (LFP) are mainly divided into two categories: solid-phase methods and liquid-phase methods. Solid-phase methods include high-temperature solid-phase methods and carbothermal reduction methods. The process mainly involves mixing and grinding raw materials such as manganese, iron, phosphorus, dopants, and carbon sources; slurry drying; powder sintering; and crushing and packaging of the black material. While current solid-phase processes have advantages such as simple operation, a large process window, and ease of industrialization, they also suffer from drawbacks such as uneven mixing due to the variety of raw materials, the inability to achieve atomic-level fusion of manganese and iron, and uneven carbon coating. These drawbacks often result in LFP products with large specific surface area, low compaction, and poor processing performance. On the other hand, liquid-phase methods mainly include sol-gel methods, hydrothermal-solvothermal methods, and co-precipitation. Among these, sol-gel methods and hydrothermal-solvothermal methods face greater difficulties in industrialization due to high raw material costs, high energy consumption, and poor stability, and are typically used for laboratory-scale preparation. The coprecipitation method is commonly used in the preparation of lithium manganese iron phosphate precursors by coprecipitating divalent manganese iron ions with soluble carbonate (such as Chinese invention patent CNCN104752719A) or oxalate (such as Chinese invention patent CN104752715A, CN103887491A) solutions. However, it also faces technical challenges such as complicated process flow, harsh reaction conditions, and many limitations on reaction technology.

[0004] In summary, while there are numerous existing technologies for preparing lithium iron phosphate (LFP), most are still immature, and the resulting LFP cathode materials face several pressing issues in practical applications. These include low conductivity and ion diffusion coefficient, low capacity, low compaction density, large specific surface area, and high-voltage plateau decay due to manganese leaching. Referring to the development history of the LFP industry, LFP prepared by adding lithium carbonate to iron phosphate not only has a simple preparation process but also offers significant advantages in cost, performance, and production consistency. Therefore, developing a precursor for LFP preparation using iron manganese phosphate not only simplifies the process but also provides advantages such as uniform element mixing, high product capacity, and good processing performance. Thus, developing an efficient and simple precursor for LFP preparation is of great significance to the development of LFP production. Summary of the Invention

[0005] The purpose of this invention is to provide a simple and efficient precursor preparation technology for ferromanganese phosphate, which aims to simplify the production process of ferromanganese phosphate and improve the shortcomings of lithium manganese phosphate such as poor kinetic behavior, low compaction, and large specific surface area through precursor technology.

[0006] This invention achieves the preparation of lithium manganese iron phosphate precursor through the following technical solution:

[0007] A method for preparing a manganese iron phosphate precursor, the method comprising the following steps;

[0008] (1) Mix the manganese source, iron source, dopant, phosphorus source and dispersant and perform wet grinding;

[0009] (2) The ground slurry was aged and crystallized at high temperature to obtain a suspension of manganese iron phosphate. The suspension was then subjected to solid-liquid separation, washing, and drying to obtain the precursor of manganese iron phosphate.

[0010] The manganese source is one or more of metallic manganese, manganese monoxide, manganese dioxide, manganese trioxide, manganese tetroxide, manganese carbonate, manganese oxalate, and manganese dihydrogen phosphate; the iron source is one or more of iron powder, ferric oxide, ferric oxide, ferric tetroxide, ferric phosphate dihydrate, and ferric phosphate; the phosphorus source is one or more of phosphoric acid, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate.

[0011] When the raw materials contain divalent manganese or iron, an oxidant is added during the high-temperature aging and crystallization step. The oxidant is selected from one or more of ammonium persulfate, hydrogen peroxide, nitric acid, sodium hypochlorite, oxygen, ozone, and ammonium nitrate.

[0012] The dopant is one or more of soluble titanium salts, soluble vanadium salts, and soluble magnesium salts.

[0013] The soluble titanium salt is selected from titanium tetrachloride, titanium oxysulfate, titanium tetraiodide, and titanium tetrabromide.

[0014] The soluble vanadium salt is selected from vanadium oxalate, vanadium sulfate, ammonium metavanadate, and vanadium dichloride.

[0015] The soluble magnesium salt is selected from magnesium nitrate, magnesium chloride, and magnesium sulfate.

[0016] The dispersant is diisopropyl di(triethanolamine) titanate or polyethylene glycol lauric acid.

[0017] In this invention, the dispersant contains both anchoring and hydrophilic groups, effectively achieving the grinding and dispersion of solid substances. This solves the problems of agglomeration and coarsening caused by increased surface tension during slurry grinding and dispersion. During grinding, the anchoring groups in the dispersant are firmly anchored to the solid surface, and the solids are dispersed due to the repulsive force between the dispersants, preventing agglomeration. Simultaneously, the hydrophilic groups in the dispersant allow for dissolution and dispersion in water. This dual hydrophilic and anchoring property of the dispersant achieves highly efficient dispersion and grinding of solid substances. Thanks to this efficient dispersing effect, the dispersant provides efficient and uniform mixing of manganese, iron, and phosphorus sources and dopants, providing more uniform reaction conditions for subsequent high-temperature aging and crystallization reactions.

[0018] The solid content of the slurry is 30-50%.

[0019] The grinding method is selected from one or both of ball milling and sand milling, and the particle size of the mixture after grinding is controlled to be 50 nm ≤ D. 50 ≤800 nm.

[0020] The high-temperature aging method is selected from one or more of water bath heating, oil bath heating, electric heating, and coil heating.

[0021] The solid-liquid separation and washing method is one or more of vacuum filtration, centrifugation, and pressure filtration. After washing, the conductivity of the filtrate is controlled to be ≤500 μs / cm.

[0022] Another technical solution of the present invention is to provide a manganese iron phosphate precursor, wherein the molecular formula of the manganese iron phosphate precursor is Mn x Fe 1-x-y M y PO4•(2-x)H2O, wherein 0.5≤x≤1 and 0.01≤y≤0.1, is prepared using the method described above.

[0023] The gain effect of this invention is:

[0024] (1) The preparation process of manganese iron phosphate provided by the present invention is simple and efficient, and easy to scale up for industrial production;

[0025] (2) The production and preparation of lithium manganese iron phosphate using the precursor of manganese iron phosphate provided by the invention can effectively simplify the production and preparation process of lithium manganese iron phosphate, improve production efficiency, and reduce costs and increase efficiency.

[0026] (3) The lithium manganese iron phosphate prepared by the precursor provided by the present invention can effectively improve the uniformity of the mixing of various elements, and the product has more advantages in terms of electrical performance and processing performance. Attached Figure Description

[0027] Figure 1 is the XRD pattern of the doped manganese iron phosphate precursor prepared in Example 1 of the present invention.

[0028] Figure 2 is a SEM image of the doped manganese iron phosphate precursor prepared in Example 1 of the present invention. Detailed Implementation

[0029] Example 1

[0030] The molecular formula of the doped manganese iron phosphate precursor prepared in this embodiment is Mn. 0.6 Fe 0.38 Ti 0.02 The specific preparation method for PO4•1,4H2O is as follows: Weigh 0.3 mol of Mn2O3, 0.19 mol of Fe2O3, 0.02 mol of TiO2, and 1 mol of H3PO4 to prepare a suspension with a solid content of 40%, and then perform sand milling. At the beginning of milling, add 0.5 g of diisopropyl di(triethanolamine)titanate as a dispersant. When the particle size D of the mixture slurry during sand milling... 50 After reaching a particle size ≤500 nm, the slurry was removed and transferred to a jacketed reactor for oil bath crystallization at 83 ℃. The temperature of the slurry in the reactor was monitored, and timing began when the slurry temperature reached 80 ℃. The crystallization process was completed after 2 hours of constant temperature. Afterward, the manganese ferric phosphate was removed and repeatedly filtered and washed until the conductivity of the filtrate was less than 450 μs / cm, at which point the washing process was terminated. The washed filter cake was then placed in a forced-air drying oven and dried at 80 ℃ for 12 hours to obtain the product with the molecular formula Mnn in Example 1. 0.6 Fe 0.38 Ti 0.02 The target precursor product of PO4•1.4H2O.

[0031] Example 2

[0032] This embodiment is basically the same as Example 1, except that it is prepared with the molecular formula Mn 0.6 Fe 0.38 Ti 0.02The manganese source used in the preparation of the doped manganese iron phosphate precursor PO4•1.4H2O is different. The specific preparation method is as follows: 0.2 mol of Mn3O4, 0.19 mol of Fe2O3, 0.02 mol of TiO2 and 1 mol of H3PO4 are weighed and prepared into a suspension with a solid content of 40%, which is then subjected to sand milling. At the beginning of the milling, 0.5 g of diisopropyl di(triethanolamine)titanate is added as a dispersant. The sand milling process and the detection of process quantities are consistent with those in Example 1. After the slurry is taken out, it is transferred to a jacketed reactor for oil bath heating and crystallization. The oil bath temperature is also set to 83 ℃. Since the manganese source Mn3O4 used in this example contains Mn 2+ For Mn ions, an oxidant needs to be added during high-temperature crystallization. 2+ Transform into Mn 3+ Therefore, 0.1 mol of NaClO manganese oxide source needs to be added before the crystallization isothermal timer for the slurry. The subsequent preparation process is consistent with that in Example 1. After the preparation process is completed, the molecular formula of Example 2 is also Mn. 0.6 Fe 0.38 Ti 0.02 The target precursor product of PO4•1.4H2O.

[0033] Example 3

[0034] This embodiment is basically the same as Example 1, except that it is prepared with the molecular formula Mn 0.6 Fe 0.38 Ti 0.02 The iron source used in the preparation of the doped manganese iron phosphate precursor PO4•1.4H2O is different. The specific preparation method is as follows: 0.3 mol of Mn2O3, 0.38 mol of FeO, 0.02 mol of TiO2 and 1 mol of H3PO4 are weighed and prepared into a suspension with a solid content of 40%, which is then subjected to sand milling. At the beginning of the milling, 0.5 g of diisopropyl di(triethanolamine)titanate is added as a dispersant. The sand milling process and the detection of process quantities are consistent with those in Example 1. After the slurry is taken out, it is transferred to a jacketed reactor for oil bath heating and crystallization. The oil bath temperature is also set to 83 ℃. Since the FeO iron source used in this example contains Fe 2+ For ions, an oxidizing agent needs to be added during high-temperature crystallization to neutralize Fe. 2+ Converted to Fe 3+ Therefore, 0.1 mol of NaClO iron oxide source needs to be added before the crystallization isothermal timer for the slurry. The subsequent preparation process is consistent with that in Example 1. After the preparation process is completed, the molecular formula of Example 3 is also Mn. 0.6 Fe 0.38 Ti 0.02 The target precursor product of PO4•1.4H2O.

[0035] Example 4

[0036] This embodiment is basically the same as Example 1, except that it is prepared with the molecular formula Mn 0.6 Fe 0.38 Ti 0.02 The manganese and iron sources used in the preparation of the doped manganese iron phosphate precursor PO4•1.4H2O are different. The specific preparation method is as follows: 0.2 mol of Mn3O4, 0.38 mol of FeO, 0.02 mol of TiO2 and 1 mol of H3PO4 are weighed and prepared into a suspension with a solid content of 40%, which is then milled. At the beginning of milling, 0.5 g of diisopropyl di(triethanolamine)titanate is added as a dispersant. The milling process and the detection of process quantities are consistent with those in Example 1. After the slurry is taken out, it is transferred to a jacketed reactor for oil bath heating and crystallization. The oil bath temperature is also set to 83 ℃. Since the manganese source Mn3O4 used in this example contains Mn 2+ The iron source FeO used contains Fe ions. 2+ An oxidant needs to be added during high-temperature crystallization to neutralize Mn. 2+ Transform into Mn 3+ , to Fe 2+ Converted to Fe 3+ Therefore, 0.2 mol of NaClO manganese oxide source and iron source need to be added before the crystallization isothermal timer for the slurry. The subsequent preparation process is consistent with that in Example 1. After the preparation process is completed, the molecular formula of Example 4 is also Mn. 0.6 Fe 0.38 Ti 0.02 The target precursor product of PO4•1.4H2O.

[0037] Example 5

[0038] This embodiment is basically the same as Example 1, except that it is prepared with the molecular formula Mn 0.6 Fe 0.38 Ti 0.02 The phosphorus source used in the preparation of the doped manganese iron phosphate precursor PO4•1.4H2O is different. The specific preparation method is as follows: 0.3 mol of Mn2O3, 0.19 mol of Fe2O3, 0.02 mol of TiO2 and 1 mol of NH4H2PO4 are weighed and prepared into a suspension with a solid content of 40%, which is then subjected to sand milling. At the beginning of the milling, 0.5 g of diisopropyl di(triethanolamine)titanate is added as a dispersant. All subsequent preparation processes are consistent with those in Example 1. After the preparation process is completed, the molecular formula of Example 5, which is also Mn, is obtained. 0.6 Fe 0.38 Ti 0.02 The target precursor product of PO4•1.4H2O.

[0039] Example 6

[0040] This embodiment is basically the same as Example 1, except that the molecular formula and the dopant used are different. The precursor prepared in this embodiment has the molecular formula Mn. 0.6 Fe 0.38 Mg 0.02 The specific preparation method for PO4•1.4H2O is as follows: 0.3 mol of Mn2O3, 0.19 mol of Fe2O3, 0.02 mol of MgO, and 1 mol of H3PO4 are weighed and prepared into a suspension with a solid content of 40%. The suspension is then milled. At the beginning of the milling process, 0.5 g of diisopropyl di(triethanolamine)titanate is added as a dispersant. All subsequent preparation processes are consistent with those in Example 1. After the preparation process is completed, the molecular formula of Example 5, Mn2O3, is obtained. 0.6 Fe 0.38 Mg 0.02 The target precursor product of PO4•1.4H2O.

[0041] Example 7

[0042] This embodiment is basically the same as Example 1, except that the dispersant used in the preparation is different. The precursor prepared in this embodiment has the molecular formula Mn. 0.6 Fe 0.38 Ti 0.02 The specific preparation method for PO4•1.4H2O is as follows: 0.3 mol of Mn2O3, 0.19 mol of Fe2O3, 0.02 mol of TiO2, and 1 mol of H3PO4 are weighed and prepared into a suspension with a solid content of 40%. The suspension is then milled. At the beginning of the milling process, 0.5 g of polyethylene glycol lauric acid is added as a dispersant. All subsequent preparation processes are consistent with those in Example 1. After the preparation process is completed, the molecular formula of Example 7, Mn2O3, is obtained. 0.6 Fe 0.38 Ti 0.02 The target precursor product of PO4•1.4H2O.

[0043] Comparative Example 1

[0044] This embodiment is basically the same as Example 1, except that the dispersant used is different. The precursor prepared in this embodiment has the molecular formula Mn. 0.6 Fe 0.38 Ti 0.02 The specific preparation method for PO4•1.4H2O is as follows: 0.3 mol of Mn2O3, 0.19 mol of Fe2O3, 0.02 mol of TiO2, and 1 mol of H3PO4 were weighed and prepared into a suspension with a solid content of 40%. The suspension was then milled. At the beginning of the milling process, 0.5 g of polyethylene glycol was added as a dispersant. All subsequent preparation processes were consistent with those in Example 1. After the preparation process was completed, the molecular formula of Comparative Example 1, Mn2O3, was obtained. 0.6 Fe0.38 Mg 0.02 The target precursor product of PO4•1.4H2O.

[0045] Comparative Example 2

[0046] This embodiment is basically the same as Example 1, except that this comparative example does not use a dispersant, and the precursor prepared in this embodiment has the molecular formula Mn. 0.6 Fe 0.38 Ti 0.02 The specific preparation method for PO4•1,4H2O is as follows: 0.3 mol of Mn2O3, 0.19 mol of Fe2O3, 0.02 mol of TiO2, and 1 mol of H3PO4 are weighed and prepared into a suspension with a solid content of 40%. The suspension is then milled. No dispersant is added at the beginning of the milling process. All subsequent preparation processes are consistent with those in Example 1. After the preparation process is completed, the molecular formula of Comparative Example 2, Mn2O3, is obtained. 0.6 Fe 0.38 Ti 0.02 The target precursor product of PO4•1.4H2O.

[0047] Application examples

[0048] The doped iron manganese phosphate precursors prepared in Examples 1-7 and Comparative Examples 1-2 were used to prepare lithium iron manganese phosphate cathode materials. The specific preparation steps are as follows:

[0049] (1) Weigh 100 g of manganese iron phosphate precursor, 21.04 g of lithium carbonate, 9.13 g of glucose, and 273 g of pure water and mix and mill them. When the particle size D of the mixed slurry is... 50 Once the nanometer size reaches ≤350 nm, the sand milling step is terminated.

[0050] (2) After removing the slurry from the sand milling step, spray dry it, adjust the outlet air temperature of the spray dryer to 80-85℃, and control the moisture content of the dried powder to be less than 2%;

[0051] (3) The spray-dried powder was sintered at high temperature under an inert atmosphere. The sintering temperature was 750 °C and the holding time was set to 10 h.

[0052] (4) The sintered black material is pulverized to obtain the finished lithium manganese iron phosphate cathode material prepared from the precursor, wherein the particle size of the pulverized powder is controlled to be 0.78μm≤D 50 ≤1.5μm.

[0053] Comparative Example 3

[0054] This comparative example provides a method for directly preparing lithium manganese iron phosphate without precursors. The specific method is as follows:

[0055] (1) Mix 47.37 g of Mn2O3, 30.34 g of Fe2O3, 1.60 g of TiO2, 13.70 g of glucose monohydrate, 115.03 g of NH4H2PO4 and 410 g of water and then perform sand milling. When the particle size D50 of the mixed slurry is ≤350 nm, the sand milling step is ended.

[0056] (2) After removing the slurry from the sand milling step, spray dry it, adjust the outlet air temperature of the spray dryer to 80-85℃, and control the moisture content of the dried powder to be less than 2%;

[0057] (3) The spray-dried powder was sintered at high temperature under an inert atmosphere. The sintering temperature was 750 °C and the holding time was set to 10 h.

[0058] (4) The sintered black material is pulverized to obtain the finished lithium manganese iron phosphate cathode material prepared from the precursor, wherein the particle size of the pulverized powder is controlled to be 0.78μm≤D 50 ≤1.5μm.

[0059] The lithium manganese iron phosphate coin cells prepared using Examples 1-6 as precursors and Comparative Example 1 were tested, and compaction, specific surface area, and XRD tests were performed. The results are shown in Table 1 below:

[0060] Table 1. Performance comparison of lithium manganese iron phosphate prepared using Examples 1-7 and Comparative Examples 1-2 as precursors and lithium manganese iron phosphate prepared using Comparative Example 3.

[0061]

[0062] By comparing the electrochemical performance and physical characterization test results of Examples 1-7 and Comparative Examples 1-3 in Table 1, it can be found that the lithium manganese iron phosphate cathode material prepared with the precursor provided by the present invention has significant advantages over the pure solid-phase process without a precursor in terms of electrochemical performance, product compaction density, and processing performance.

Claims

1. A method for preparing a doped manganese iron phosphate precursor, characterized in that, The preparation method includes the following steps; (1) The manganese source, iron source, dopant, phosphorus source and dispersant are mixed and wet-milled, wherein the dispersant is diisopropyl di(triethanolamine) titanate; (2) The ground slurry was aged and crystallized at high temperature to obtain a suspension of manganese iron phosphate. The suspension was then subjected to solid-liquid separation, washing, and drying to obtain the precursor of manganese iron phosphate.

2. The method for preparing the manganese iron phosphate precursor according to claim 1, characterized in that, The manganese source is one or more of metallic manganese, manganese monoxide, manganese dioxide, manganese trioxide, manganese tetroxide, manganese carbonate, manganese oxalate, and manganese dihydrogen phosphate; the iron source is one or more of iron powder, ferric oxide, ferric oxide, ferric tetroxide, ferric phosphate dihydrate, and ferric phosphate; the phosphorus source is one or more of phosphoric acid, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate.

3. The method for preparing the manganese iron phosphate precursor according to claim 1, characterized in that, When the raw materials contain divalent manganese or iron, an oxidant is added during the high-temperature aging and crystallization step. The oxidant is selected from one or more of ammonium persulfate, hydrogen peroxide, nitric acid, sodium hypochlorite, oxygen, ozone, and ammonium nitrate.

4. The method for preparing the manganese iron phosphate precursor according to claim 1, characterized in that, The dopant is one or more of soluble titanium salts, soluble vanadium salts, and soluble magnesium salts.

5. The method for preparing the manganese iron phosphate precursor according to claim 1, characterized in that, The solid content of the slurry is 30-50%.

6. The method for preparing the manganese iron phosphate precursor according to claim 1, characterized in that, The grinding method is selected from one or both of ball milling and sand milling, and the particle size of the mixture after grinding is controlled to be 50 nm ≤ D. 50 ≤800 nm.

7. The method for preparing the manganese iron phosphate precursor according to claim 1, characterized in that, The high-temperature aging method is selected from one or more of water bath heating, oil bath heating, electric heating, and coil heating.

8. The method for preparing manganese iron phosphate precursor according to claim 1, wherein the solid-liquid separation and washing method is one or more of vacuum filtration, centrifugation, and pressure filtration, and the conductivity σ of the filtrate is controlled to be ≤500 μs / cm after washing.

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