Preparation method of manganous ferric phosphate

Abstract

The invention discloses a preparation method of manganous ferric phosphate, and belongs to the technical field of battery positive electrode material manufacturing. Manganese element doping is mainly carried out in the aging stage, an oxidizing agent is not used, and the crystallization property and the iron-phosphorus ratio of the material are improved through secondary calcination. According to the invention, divalent manganese ions can be prevented from being oxidized into trivalent manganese ions when the divalent iron ions are oxidized in the synthesis stage, disproportionation and co-ion effect of the trivalent manganese ions are avoided, so that the divalent manganese ions stably exist in the product, the low-temperature discharge performance of the battery is improved, and meanwhile, the preparation cost is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of battery positive electrode material manufacturing, and specifically relates to a method for preparing manganese ferrous phosphate. Background Art

[0002] Lithium iron phosphate batteries have gradually surpassed ternary batteries and become the main power battery for electric vehicles due to their advantages such as low cost, high safety, abundant resources and no pollution. According to statistics, the output of ternary materials in 2024 will be 992,300 tons, while the output of lithium iron phosphate will be 2.4449 million tons, which has received widespread attention in recent years. Current research shows that the appropriate amount of doping with lithium iron phosphate can effectively improve its electronic conductivity and low-temperature performance, thereby improving electrochemical performance and low-temperature discharge performance. However, the high-temperature solid-phase preparation method of lithium iron phosphate has certain limitations, especially when doping modification is carried out in the solid-phase reaction stage, there may be problems with uneven doping elements or failure to effectively embed into the lattice. Introducing doping elements into the precursor preparation stage and using chemical precipitation method can theoretically make the doping elements evenly mixed at the atomic and molecular levels, thereby better improving the performance of lithium iron phosphate.

[0003] At present, doping modification is carried out in the preparation process of iron phosphate precursor, mainly focusing on the three stages of iron phosphate preparation: synthesis, aging and impregnation after aging. However, the existing technology has poor universality, high energy consumption, long reaction time, and cannot guarantee the stability of the product. At the same time, a large amount of oxidant is also wasted. 3+ The disproportionation and common ion effect can easily convert it into Mn 2+ and Mn 4+ , and cannot exist stably in the product. The charging and discharging mechanism of manganese ions in lithium iron phosphate is similar to that of iron ions. Both achieve charging and discharging through the conversion between high-valent ions gaining and losing electrons and low-valent ions. Due to differences in the crystallization properties of the precursor iron phosphate, its iron-phosphorus ratio is usually lower than the theoretical value of 1, generally between 0.95-0.98, which affects the performance of iron phosphate in the preparation process of lithium iron phosphate. Especially after element doping modification, part of the iron element may be replaced by the doping element, resulting in a further decrease in the iron-phosphorus ratio and crystallization performance. Therefore, there are still some problems that need to be solved in the process of iron phosphate element doping modification. Summary of the invention

[0004] The purpose of the present invention is to provide a method for preparing manganese ferrous phosphate, by doping manganese element in the aging stage, preventing divalent manganese ions from being oxidized to trivalent manganese ions when oxidizing divalent iron ions in the synthesis stage, avoiding the disproportionation effect and common ion effect of trivalent manganese ions, making the divalent manganese ions stably exist in the product, and improving the low-temperature discharge performance of the battery; at the same time, the method can reduce costs and improve production efficiency.

[0005] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] A method for preparing manganous ferrous phosphate comprises the following steps:

[0007] 1) preparing an iron source solution, a manganese source solution and a phosphorus source solution;

[0008] 2) adding an oxidant to the phosphorus source solution to prepare a phosphorus-oxygen solution;

[0009] 3) adding the iron source solution into the reaction kettle as the base liquid, and then adding hot pure water to make the volume constant, stirring for a period of time; then adding the phosphorus-oxygen solution while stirring, stirring for a period of time after adding, and washing and filtering after completion to obtain a solid water-containing filter cake;

[0010] 4) transferring the filter cake obtained in step 3) to a pulping reactor, adding hot pure water and controlling the solid content, then adding phosphoric acid, stirring to pulp and heating for a period of time;

[0011] 5) transferring the slurried material to an aging reactor, adding a manganese source solution and stirring evenly, then heating the aging reactor for a period of time, washing and filtering after completion to obtain a solid water-containing filter cake;

[0012] 6) drying and secondary calcining the filter cake obtained in step 5) at high temperature to obtain manganese ferrous phosphate product.

[0013] Furthermore, the step of configuring the iron source solution in step 1) includes: dissolving the iron source in pure water or acid, removing impurities and filtering, adjusting the pH value to 0.5-3.5, and obtaining an iron source solution with a concentration of 20-100 g / L; wherein the iron source is selected from one of ferrous sulfate, ferrous oxalate, ferrous nitrate, ferrous greening, iron powder, ferric oxide, ferrophosphate tetroxide, ferrophosphorus slag, and lithium iron phosphate recovered black powder; the acid is selected from one of phosphoric acid, sulfuric acid, and hydrochloric acid, or a mixed acid of phosphoric acid and sulfuric acid.

[0014] Furthermore, the step of preparing a manganese source solution in step 1) comprises: dissolving a manganese source in pure water, filtering and removing impurities to obtain a manganese source solution with a concentration of 0-10000 ppm; wherein the manganese source is selected from one or more of manganese sulfate, manganese carbonate, manganese acetate, manganese nitrate, manganese acetate, manganese oxalate, manganese chloride, and manganese phosphate.

[0015] Furthermore, the manganese source in step 1) contains one or more of the doping elements Ni, Co, Mn, Cr, Zr, Nb, Cu, V, Ti, Zn, Al, Ga, Mg, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc, and Y.

[0016] Furthermore, the step of preparing a phosphorus source solution in step 1) includes: dissolving the phosphorus source in pure water, filtering and removing impurities, adjusting the pH value of the solution to 3.0-8.5, and obtaining a phosphorus source solution with a concentration of 20-80 g / L; wherein the phosphorus source is selected from one or more of diammonium dihydrogen phosphate, monoammonium dihydrogen phosphate, sodium monohydrogen phosphate, and sodium dihydrogen phosphate.

[0017] Furthermore, in step 2), the oxidant is selected from one or more of hydrogen peroxide, potassium permanganate, nitric acid, and ammonium persulfate.

[0018] Furthermore, in step 2), the mass percentage of the oxidant in the phosphorus-oxygen solution is 2.5%-5.5%.

[0019] Furthermore, in step 3), the mass fractions of iron source solution, hot pure water and phosphorus-oxygen solution added are 2-15 parts, 0.2-2.5 parts and 2-10 parts respectively, the stirring time during volume adjustment is 5-60min, and the stirring speed is 100-350r / min; the flow rate of phosphorus-oxygen solution addition is 7-20L / min, and the stirring time after addition is 30-120min; the conductivity of washing water used for washing is ≤3500μs / cm.

[0020] Furthermore, in step 4), the solid content is 5%-20%, the P / Fe molar ratio of phosphoric acid is 0.15-1.2, the stirring speed is 150-400 r / min, the heating temperature is 35-75° C., and the insulation time is 30-60 min.

[0021] Furthermore, in step 5), the mass fraction of the manganese source solution added is 0.1-0.9 parts, the heating temperature is 85-100° C., the heating time is 60-180 min, and the conductivity of the washing water is ≤500 μs / cm.

[0022] Furthermore, in step 6), the drying temperature is 80-120°C; the high-temperature secondary calcination conditions are: the primary calcination temperature is 650-750°C, and the secondary calcination temperature is 550-650°C.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1. The present invention aims at the special properties of trivalent manganese ions and chooses to add manganese elements in the aging stage, so that when oxidizing divalent iron ions in the synthesis stage, the divalent manganese ions can be effectively prevented from being oxidized to trivalent manganese ions, thereby avoiding the disproportionation and common ion effect of trivalent manganese ions, thereby ensuring the stable existence of divalent manganese ions in the final product.

[0025] 2. The present invention selects manganese doping to occur during the aging stage, and does not use an oxidant, which can effectively maintain the low valence state of manganese. This not only reduces the amount of oxidant used, but also saves the manufacturing cost of the iron phosphate precursor. In addition, since manganese ions maintain a low valence state in the precursor, there is no need to use an additional reducing agent for reduction during the preparation of lithium iron phosphate, thereby achieving a double reduction in production costs.

[0026] 3. The present invention adopts a secondary calcination process to significantly improve the crystallization performance and iron-phosphorus ratio of manganese-doped iron phosphate, thereby optimizing the preparation process of lithium iron phosphate. This method helps to improve the electrochemical performance of iron manganese phosphate materials, especially during battery discharge, improves its performance stability and low-temperature discharge capability, and ultimately enables the prepared iron manganese phosphate composite material to play a better role in application. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a SEM image of amorphous iron phosphate in the synthesis stage in Example 1;

[0028] Figure 2 is the XRD pattern of manganese ferrous phosphate dihydrate in the drying stage in Example 1;

[0029] Figure 3 is a SEM image of manganese ferrous phosphate dihydrate in the drying stage of Example 1;

[0030] Figure 4 is the EPMA graph of manganese ferrous phosphate dihydrate in the drying stage in Example 1;

[0031] Figure 5 is the XRD pattern of anhydrous manganese ferrous phosphate in the calcination stage in Example 1;

[0032] Figure 6 is a SEM image of anhydrous manganese ferrous phosphate in the calcination stage in Example 1;

[0033] Figure 7 This is the EPMA diagram of anhydrous manganese ferrous phosphate in the calcination stage in Example 1. DETAILED DESCRIPTION

[0034] In order to make the various technical features and advantages or technical effects in the above technical solutions of the present invention more obvious and easy to understand, they are described in detail below in conjunction with embodiments.

[0035] Example 1

[0036] 1. Prepare a ferrous sulfate solution with a pH value of 2 and a concentration of 65 g / L, a 5000 ppm manganese sulfate solution, and a diammonium phosphate solution with a pH value of 7 and a concentration of 60 g / L.

[0037] 2. Add hydrogen peroxide to the diammonium phosphate solution to prepare a phosphorus-oxygen solution with a pH value of 7 and a concentration of 50 g / L, of which the mass proportion of hydrogen peroxide is 3.5%.

[0038] 3. Add 8 kg of ferrous sulfate solution to the reactor as the base liquid, then add 1.8 kg of 75°C hot pure water to the reactor to make up the volume, and continue stirring for 10 minutes at a stirring speed of 200 r / min. Then add 5.5 kg of phosphorus-oxygen solution to the reactor at a flow rate of 10 L / min, and the stirring speed of the reactor during the addition process is 200 r / min. After the addition of phosphorus-oxygen solution is completed, continue the synthesis reaction for 60 minutes. After the synthesis reaction is completed, wash and filter, and the conductivity of the washing water used is 3000 μs / cm to obtain a solid water-containing filter cake (i.e., amorphous iron phosphate).

[0039] 4. Transfer the filter cake to the pulping reactor, add hot pure water 3 times the weight of the filter cake, and control the solid content of the reactant to 15%. Then add phosphoric acid with a P / Fe molar ratio of 0.8 to the slurry, stir at 300r / min, keep the reaction at 55°C, and continue the reaction for 60min.

[0040] 5. The slurried material was transferred to the aging reactor, and 0.393 kg of manganese sulfate solution was added to the aging reactor at a flow rate of 0.1 L / min, the stirring speed was 300 r / min, and the stirring was continued for 60 min. Then the temperature was raised to 95 ° C and the reaction was continued for 180 min. After the reaction was completed, the material was washed and filtered, and the conductivity of the washing water used was 300 μs / cm to obtain a solid water-containing filter cake.

[0041] 6. Dry the filter cake at 105°C to obtain ferric phosphate dihydrate. Then calcine the ferric phosphate dihydrate at 700°C once and 600°C twice to finally obtain anhydrous manganese ferric phosphate product.

[0042] Example 2

[0043] 1. Prepare a ferrous sulfate solution with a pH value of 1 and a concentration of 20 g / L, a 6000 ppm Mn-containing manganese sulfate solution, and a diammonium phosphate solution with a pH value of 3 and a concentration of 20 g / L.

[0044] 2. Add hydrogen peroxide to the diammonium phosphate solution to prepare a phosphorus-oxygen solution with a pH value of 7 and a concentration of 50 g / L, of which the mass proportion of hydrogen peroxide is 2.5%.

[0045] 3. Add 2kg of ferrous sulfate solution to the reactor as the base liquid, then add 0.5kg of 60℃ hot pure water to the reactor to make it constant, and continue stirring for 30min at a stirring speed of 100r / min. Then add 2kg of phosphorus-oxygen solution to the reactor at a flow rate of 7L / min, and the stirring speed of the reactor during the addition process is 100r / min. After the addition of phosphorus-oxygen solution is completed, continue the synthesis reaction for 30min. After the synthesis reaction is completed, wash and filter, and the conductivity of the washing water used is 3000μs / cm to obtain a solid water-containing filter cake (i.e., amorphous iron phosphate).

[0046] 4. Transfer the filter cake to the pulping reactor, add hot pure water 3 times the weight of the filter cake, and control the solid content of the reactant to 5%. Then add phosphoric acid with a P / Fe molar ratio of 0.2 to the slurry, stir at a speed of 150r / min, keep the reaction at 35°C, and continue the reaction for 30 minutes.

[0047] 5. The slurried material was transferred to the aging reactor, and 0.150 kg of manganese sulfate solution was added to the aging reactor at a flow rate of 0.1 L / min, the stirring speed was 150 r / min, and the stirring was continued for 100 min. Then the temperature was raised to 85 ° C and the reaction was continued for 60 min. After the reaction was completed, the material was washed and filtered, and the conductivity of the washing water used was 300 μs / cm to obtain a solid water-containing filter cake.

[0048] 6. Dry the filter cake at 80°C to obtain dihydrated ferric phosphate. Then, calcine the dihydrated ferric phosphate once at 650°C and twice at 550°C to finally obtain anhydrous manganese ferric phosphate product.

[0049] Example 3

[0050] 1. Prepare a ferrous sulfate solution with a pH value of 3.5 and a concentration of 100 g / L, a 10,000 ppm Co-containing manganese sulfate solution, and a diammonium phosphate solution with a pH value of 8 and a concentration of 80 g / L.

[0051] 2. Add hydrogen peroxide to the diammonium phosphate solution to prepare a phosphorus-oxygen solution with a pH value of 7 and a concentration of 50 g / L, of which the mass proportion of hydrogen peroxide is 5.5%.

[0052] 3. Add 15kg of ferrous sulfate solution to the reactor as the base liquid, then add 2.5kg of 90°C hot pure water to the reactor to make up the volume, and continue stirring for 60min at a stirring speed of 300r / min. Then add 10kg of phosphorus-oxygen solution to the reactor at a flow rate of 20L / min, and the stirring speed of the reactor during the addition process is 300r / min. After the addition of phosphorus-oxygen solution is completed, continue the synthesis reaction for 120min. After the synthesis reaction is completed, wash and filter, and the conductivity of the washing water used is 3000μs / cm to obtain a solid water-containing filter cake (i.e., amorphous iron phosphate).

[0053] 4. Transfer the filter cake to the pulping reactor, add hot pure water 3 times the weight of the filter cake, and control the solid content of the reactant to 20%. Then add an appropriate amount of phosphoric acid with a P / Fe molar ratio of 1.2 to the slurry, stir at 400r / min, keep the reaction at 75℃, and continue the reaction for 50min.

[0054] 5. The slurried material was transferred to the aging reactor, and 0.845 kg of manganese sulfate solution was added to the aging reactor at a flow rate of 0.1 L / min, the stirring speed was 400 r / min, and the stirring was continued for 180 min. Then the temperature was raised to 100 ° C and the reaction was continued for 120 min. After the reaction was completed, the material was washed and filtered, and the conductivity of the washing water used was 300 μs / cm to obtain a solid water-containing filter cake.

[0055] 6. Dry the filter cake at 120°C to obtain ferric phosphate dihydrate. Then calcine the ferric phosphate dihydrate at 750°C once and 650°C twice to obtain anhydrous manganese ferric phosphate.

[0056] The intermediate products in the preparation process of Example 1, i.e., amorphous ferric phosphate in the synthesis stage, manganese ferric phosphate dihydrate in the drying stage, and the final product, i.e., anhydrous manganese ferric phosphate in the calcination stage, were characterized. Figures 1 to 7 .

[0057] Figure 1 This is the SEM picture of amorphous iron phosphate in the synthesis stage. It can be seen that the amorphous iron phosphate in the synthesis stage is composed of ellipsoidal primary particles agglomerated and self-assembled.

[0058] Figure 2 This is the XRD diagram of manganese ferrous phosphate dihydrate in the drying stage. The corresponding standard card is 76-0447. It can be seen that the crystallinity of manganese ferrous phosphate dihydrate is high.

[0059] Figure 3 This is the SEM image of manganese ferrous phosphate dihydrate in the drying stage. It can be seen that the ferric phosphate dihydrate is assembled from ellipsoidal primary particles into a secondary lamellar structure, and then the lamellar structure self-assembles into a flower cluster structure.

[0060] Figure 4 This is the EPMA diagram of manganese ferrous phosphate dihydrate in the drying stage. From the element distribution in this diagram, it can be seen that the manganese element doped in the manganese phosphate dihydrate is uniform.

[0061] Figure 5 This is the XRD diagram of anhydrous manganese ferric phosphate in the calcination stage. The corresponding standard card is 77-0094. It can be seen that the anhydrous ferric phosphate has high crystallinity.

[0062] Figure 6 This is the SEM image of anhydrous manganese ferric phosphate in the calcination stage. It can be seen that the anhydrous ferric phosphate is a block structure.

[0063] Figure 7 This is the EPMA diagram of anhydrous manganese ferric phosphate during the calcination stage. From the element distribution in this diagram, it can be seen that the manganese element doped in the anhydrous manganese phosphate is uniform.

[0064] Although the present invention has been disclosed as above by way of embodiments, it is not intended to limit the present invention. Appropriate modifications or equivalent substitutions of the technical solutions of the present invention made by ordinary technicians in the field should all be included in the protection scope of the present invention. The protection scope of the present invention shall be based on what is defined in the claims.

Claims

1. A method for preparing manganous ferrous phosphate, characterized in that: The steps include: 1) preparing an iron source solution, a manganese source solution and a phosphorus source solution; 2) adding an oxidant to the phosphorus source solution to prepare a phosphorus-oxygen solution; 3) adding the iron source solution into the reaction kettle as the base liquid, and then adding hot pure water to make the volume constant, stirring for a period of time; then adding the phosphorus-oxygen solution while stirring, stirring for a period of time after adding, and washing and filtering after completion to obtain a solid water-containing filter cake; 4) transferring the filter cake obtained in step 3) to a pulping reactor, adding hot pure water and controlling the solid content, then adding phosphoric acid, stirring to pulp and heating for a period of time; 5) transferring the slurried material to an aging reactor, adding a manganese source solution and stirring evenly, then heating the aging reactor for a period of time, washing and filtering after completion to obtain a solid water-containing filter cake; 6) drying and secondary calcining the filter cake obtained in step 5) at high temperature to obtain manganese ferrous phosphate product.

2. The preparation method according to claim 1, characterized in that The step of preparing the iron source solution in step 1) comprises: dissolving the iron source in pure water or acid, removing impurities and filtering, adjusting the pH value to 0.5-3.5, and obtaining an iron source solution with a concentration of 20-100 g / L; wherein the iron source is selected from one of ferrous sulfate, ferrous oxalate, ferrous nitrate, ferrous greening, iron powder, ferric oxide, ferroferric oxide, ferrophosphorus slag, and lithium iron phosphate recovered black powder; and the acid is selected from one of phosphoric acid, sulfuric acid, and hydrochloric acid, or a mixed acid of phosphoric acid and sulfuric acid.

3. The preparation method according to claim 1, characterized in that: The step of preparing a manganese source solution in step 1) comprises: dissolving a manganese source in pure water, filtering and removing impurities to obtain a manganese source solution with a concentration of 0-10000 ppm; wherein the manganese source is selected from one or more of manganese sulfate, manganese carbonate, manganese acetate, manganese nitrate, manganese acetate, manganese oxalate, manganese chloride, and manganese phosphate.

4. The preparation method according to claim 3, characterized in that: In step 1), the manganese source contains one or more of the doping elements Ni, Co, Mn, Cr, Zr, Nb, Cu, V, Ti, Zn, Al, Ga, Mg, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc, and Y.

5. The preparation method according to claim 1, characterized in that: The step of preparing the phosphorus source solution in step 1) comprises: dissolving the phosphorus source in pure water, filtering and removing impurities, adjusting the pH value of the solution to 3.0-8.5, and obtaining a phosphorus source solution with a concentration of 20-80 g / L; wherein the phosphorus source is selected from one or more of diammonium dihydrogen phosphate, monoammonium dihydrogen phosphate, sodium monohydrogen phosphate, and sodium dihydrogen phosphate.

6. The preparation method according to claim 1, characterized in that: In step 2), the oxidant is selected from one or more of hydrogen peroxide, potassium permanganate, nitric acid, and ammonium persulfate; the mass percentage of the oxidant in the phosphorus-oxygen solution is 2.5%-5.5%.

7. The preparation method according to claim 1, characterized in that: In step 3), the mass fractions of iron source solution, hot pure water and phosphorus-oxygen solution added are 2-15 parts, 0.2-2.5 parts and 2-10 parts respectively, the stirring time during volume adjustment is 5-60min, and the stirring speed is 100-350r / min; the flow rate of phosphorus-oxygen solution addition is 7-20L / min, and the stirring time after addition is 30-120min; the conductivity of washing water for washing is ≤3500μs / cm.

8. The preparation method according to claim 1, characterized in that: In step 4), the solid content is 5%-20%, the P / Fe molar ratio of phosphoric acid is 0.15-1.2, the stirring speed is 150-400r / min, the heating temperature is 35-75°C, and the insulation time is 30-60min.

9. The preparation method according to claim 1, characterized in that: In step 5), the mass fraction of the manganese source solution added is 0.1-0.9 parts, the heating temperature is 85-100° C., the heating time is 60-180 min, and the conductivity of the washing water used for washing is ≤500 μs / cm.

10. The preparation method according to claim 1, characterized in that: In step 6), the drying temperature is 80-120°C; the high-temperature secondary calcination conditions are: the primary calcination temperature is 650-750°C, and the secondary calcination temperature is 550-650°C.

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