A method for preparing nanoparticle iron phosphate

Abstract

This specification discloses a method for preparing nanoparticle iron phosphate. The method involves obtaining an amorphous iron phosphate slurry; mixing the iron phosphate slurry with an acid to obtain a mixture, wherein the acid includes phosphoric acid and ammonium sulfate, and the molar ratio of the phosphoric acid to ammonium sulfate is between 1:0.1 and 1:0.2; placing the mixture in a reactor, heating to the reaction temperature, and carrying out an aging reaction to obtain a solid product; washing the solid product and calcining it in a muffle furnace to obtain nanoparticle iron phosphate, wherein the particle size of the nanoparticle iron phosphate is between 100 nm and 200 nm, thereby improving the primary particle size of iron phosphate and enhancing particle dispersion performance, thus improving the ion transport rate of lithium iron phosphate prepared using this iron phosphate as a precursor and enhancing its electrical performance.

Description

Technical Field

[0001] This specification relates to the field of lithium-ion battery materials technology, and in particular to a method for preparing nanoparticle iron phosphate. Background Technology

[0002] In commercial battery cells, most LiFePO4 products currently exhibit an activation capacity of 155 mAh / g at room temperature and 0.1C during the first week of cycling, but only reach 130 mAh / g at 1C rate during room temperature cycling, far below the theoretical capacity. Therefore, it is necessary to improve the kinetic properties of LiFePO4 materials to increase their capacity at different charge / discharge rates. The kinetic properties of cathode materials depend on the electron and Li ion transport rates within the material. Research indicates that nano-sizing of the material particles is crucial for improving the Li diffusion rate, and the degree of nano-sizing of LiFePO4 materials is directly and positively correlated with the nano-sizing degree of its precursor, iron phosphate.

[0003] Therefore, a method for preparing highly dispersed nanoparticle iron phosphate is needed. Summary of the Invention

[0004] This specification provides a method for preparing nanoparticle iron phosphate to solve the following technical problem: the need for a method for preparing highly dispersed nanoparticle iron phosphate.

[0005] To solve the above-mentioned technical problems, the embodiments in this specification are implemented as follows:

[0006] In a first aspect, embodiments of this specification provide a method for preparing nanoparticle iron phosphate, comprising:

[0007] Amorphous ferric phosphate slurry is obtained; the ferric phosphate slurry is mixed with an acid to obtain a mixture, wherein the acid comprises phosphoric acid and ammonium sulfate, and the molar ratio of the phosphoric acid and ammonium sulfate is between 1:0.1 and 1:0.2; the mixture is placed in a reactor, heated to the reaction temperature, and aged to obtain a solid product; the solid product is washed and calcined in a muffle furnace to obtain nanoparticle ferric phosphate, wherein the particle size of the nanoparticle ferric phosphate is between 100 nm and 200 nm, and the particle size D50 is 2-3 μm.

[0008] In a second aspect, an embodiment of this specification provides a method for preparing lithium iron phosphate, comprising: mixing iron phosphate with lithium carbonate, a composite carbon source, and water, and performing a stirring and milling process, wherein the iron phosphate is prepared based on the method of the first aspect; spray-drying the milled mixture, and then calcining the dried material at high temperature under a protective atmosphere; and obtaining lithium iron phosphate after gas crushing.

[0009] The above-described at least one technical solution adopted in one or more embodiments of this specification can achieve the following beneficial effects: by obtaining an amorphous iron phosphate slurry; mixing the iron phosphate slurry with an acid to obtain a mixed solution, wherein the acid includes phosphoric acid and ammonium sulfate, wherein the molar ratio of the phosphoric acid and ammonium sulfate is between 1:0.1 and 1:0.2; placing the mixed solution into a reaction vessel, heating it to the reaction temperature, and carrying out an aging reaction to obtain a solid product; washing the solid product and calcining it in a muffle furnace to obtain iron phosphate nanoparticles, wherein the particle size of the iron phosphate nanoparticles is between 100 nm and 200 nm, and the particle size D50 is 2-3 μm, thereby improving the primary particle size of iron phosphate and improving the particle dispersion performance, thereby improving the ion transport rate of lithium iron phosphate prepared using this iron phosphate as a precursor and improving its electrical performance. Attached Figure Description

[0010] To more clearly illustrate the technical solutions in the embodiments or prior art of this specification, the drawings used in the description of the embodiments or prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this specification. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0011] Figure 1 A schematic flowchart illustrating a method for preparing nanoparticle iron phosphate provided in the embodiments of this specification;

[0012] Figure 2 An electron microscope schematic diagram of a nano-sized iron phosphate provided in an embodiment of this application;

[0013] Figure 3 An electron microscope schematic diagram of another nano-sized iron phosphate provided in an embodiment of this application;

[0014] Figure 4 An electron microscope schematic diagram of a comparative example of nano-sized iron phosphate provided in this application;

[0015] Figure 5 This is an electron microscope schematic diagram of another comparative example of nano-sized iron phosphate provided in this application. Detailed Implementation

[0016] This specification provides a method for preparing nanoparticle iron phosphate.

[0017] To enable those skilled in the art to better understand the technical solutions in this specification, the technical solutions in the embodiments of this specification will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this specification, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this application.

[0018] Figure 1 This is a schematic flowchart illustrating a method for preparing nanoparticle iron phosphate, as provided in the embodiments of this specification.

[0019] Figure 1 The process may include the following steps:

[0020] S102: Obtain amorphous ferric phosphate slurry.

[0021] The term "amorphous" here refers to the fact that the ferric phosphate in the ferric phosphate slurry has not yet crystallized, and its characteristic is that it cannot produce a diffraction effect on X-rays.

[0022] Amorphous ferric phosphate slurry can be prepared using the following method:

[0023] Ferrous salt solution F1 was prepared by using ferrous sulfate and deionized water; phosphate salt solution was prepared by using monoammonium phosphate and deionized water, and hydrogen peroxide was added to the phosphate salt solution to obtain phosphate salt mixture L1; ferrous salt solution F1, phosphate salt mixture L1 and ammonia water were pumped into a reaction vessel to react and generate amorphous ferric phosphate slurry.

[0024] Specifically, when iron salt solution F1, phosphate salt mixture L1 and ammonia water are pumped into the reactor for reaction, amorphous iron phosphate material H1 can be obtained. At this time, ammonia water can be added to adjust the pH value of the iron phosphate material. The pH value of the resulting amorphous iron phosphate slurry is about 2.4. It can be washed with pure water, and the pH value of the resulting iron phosphate slurry is about 2.4 to 2.6.

[0025] During the preparation process, the iron salt solution F1 and the phosphate salt mixture L1 have the same molar concentration and are pumped into the reactor in a volume ratio of 1:1. The feeding rate of the iron salt solution F1 and the mixture L1 is 0.2 L / min, and the feeding rate of the ammonia water is 0.03 L / min.

[0026] S104, the ferric phosphate slurry is mixed with the acid material to obtain a mixture, wherein the acid material includes phosphoric acid and ammonium sulfate, and the molar ratio of the phosphoric acid and ammonium sulfate is between 1:0.1 and 1:0.2.

[0027] S106, the mixture is placed in a reactor, heated to the reaction temperature, and aged to obtain a solid product.

[0028] The reaction temperature is 90 to 100 degrees Celsius, and the aging reaction lasts for about 2 hours.

[0029] S108, the solid product is washed and calcined in a muffle furnace to obtain nanoparticles of iron phosphate.

[0030] The calcination temperature in the muffle furnace is 550℃ to 600℃, and the calcination time is 4 hours. The resulting iron phosphate nanoparticles have a particle size between 100nm and 200nm, and the prepared iron phosphate also has the characteristics of being highly dispersed secondary aggregates that are not easily agglomerated from primary particles. This characteristic also affects its electrical properties.

[0031] Amorphous iron phosphate slurry is obtained; the iron phosphate slurry is mixed with an acid to obtain a mixture, wherein the acid includes phosphoric acid and ammonium sulfate, and the molar ratio of the phosphoric acid and ammonium sulfate is between 1:0.1 and 1:0.3; the mixture is placed in a reactor, heated to the reaction temperature, and aged to obtain a solid product; the solid product is washed and calcined in a muffle furnace to obtain iron phosphate nanoparticles, wherein the particle size of the iron phosphate nanoparticles is between 100 nm and 200 nm, thereby improving the primary particle size of iron phosphate and improving the particle dispersion performance, thereby improving the ion transport rate of lithium iron phosphate prepared using this iron phosphate as a precursor and improving its electrical performance.

[0032] To make the solution of this application clearer, several specific embodiments and comparative examples are provided below for illustration.

[0033] Example 1

[0034] S1. Preparation of ferrous salt solution: Take ferrous sulfate and add it to deionized water to prepare 10L of ferrous sulfate solution F1 with a concentration of 1.5mol / L.

[0035] S2. Prepare a mixed solution of phosphate salt and hydrogen peroxide: Take monoammonium phosphate and add it to deionized water to prepare a phosphate salt solution with a concentration of 1.5 mol / L, totaling 10 L. Then add 9 mol of hydrogen peroxide to the phosphate salt solution and mix well to obtain a mixed solution of phosphate salt and hydrogen peroxide, L1.

[0036] S3. Take 10L of ferrous sulfate solution F1; take 10L of a mixed solution of phosphate salt and hydrogen peroxide L1; take 1.5L of ammonia water, and pump them into the reactor using a peristaltic pump. The feeding rate of ferrous salt solution F1 and mixed solution L1 is 0.2L / min, and the feeding rate of ammonia water is 0.03L / min.

[0037] S4. After the reaction is complete, amorphous iron phosphate material H1 is obtained. The pH value of iron phosphate material H1 is adjusted to 2.4 using ammonia water.

[0038] S5. After washing the ferric phosphate material H1 with pure water, it is pulped to obtain ferric phosphate slurry J1, wherein the pulping volume is 12L.

[0039] S6. Mix ferric phosphate slurry J1 with acid material, wherein the acid material is a mixed solution of phosphoric acid and ammonium sulfate, and the molar ratio of phosphoric acid to ammonium sulfate is 1:0.1.

[0040] S7. After mixing evenly, add to the reaction vessel and carry out crystallization at 94℃ for 2 hours.

[0041] S8. After the reaction is complete, the material is washed and sintered in a muffle furnace at 570°C for 4 hours to obtain the iron phosphate.

[0042] The resulting ferric phosphate electron microscopy morphology is as follows: Figure 2 As shown, Figure 2 The image shown is an electron microscope schematic diagram of a nano-sized iron phosphate provided in the embodiment of this application. It can be seen that the size of the primary particles under the electron microscope is relatively small, ranging from 100nm to 200nm. The particle size D50 is measured to be 2.25um by a particle size analyzer.

[0043] Example 2:

[0044] Compared with Example 1, the formulation in Example 2 includes ammonium sulfate added at a ratio of 1:0.2, comprising the following steps:

[0045] S1. Preparation of ferrous salt solution: Take ferrous sulfate and add it to deionized water to prepare 10L of ferrous sulfate solution F1 with a concentration of 1.5mol / L.

[0046] S2. Prepare a mixed solution of phosphate salt and hydrogen peroxide: Take monoammonium phosphate and add it to deionized water to prepare a phosphate salt solution with a concentration of 1.5 mol / L, totaling 10 L. Then add 9 mol of hydrogen peroxide to the phosphate salt solution and mix well to obtain a mixed solution of phosphate salt and hydrogen peroxide, L1.

[0047] S3. Take 10L of ferrous sulfate solution F1; take 10L of a mixed solution of phosphate salt and hydrogen peroxide L1; take 1.5L of ammonia water, and pump them into the reactor using a peristaltic pump. The feeding rate of ferrous salt solution F1 and mixed solution L1 is 0.2L / min, and the feeding rate of ammonia water is 0.03L / min.

[0048] S4. After the reaction is complete, amorphous iron phosphate material H1 is obtained. The pH value of iron phosphate material H1 is adjusted to 2.4 using ammonia water.

[0049] S5. After washing the ferric phosphate material H1 with pure water, it is pulped to obtain ferric phosphate slurry J1, wherein the pulping volume is 12L.

[0050] S6. Mix ferric phosphate slurry J1 with acid material, wherein the acid material is a mixed solution of phosphoric acid and ammonium sulfate, and the stoichiometric ratio of the substances is 1:0.2.

[0051] S7. After mixing evenly, add to the reaction vessel and carry out crystallization at 94℃ for 2 hours.

[0052] S8. After the reaction is complete, the material is washed and sintered in a muffle furnace at 570°C for 4 hours to obtain the iron phosphate.

[0053] The resulting ferric phosphate electron microscopy morphology is as follows: Figure 3 As shown, Figure 3 This is an electron microscope schematic diagram of another nano-sized iron phosphate provided in an embodiment of this application. It can also be seen that the obtained nano-sized iron phosphate particles are between 100 nm and 200 nm, and their particle size D50 is measured to be 2.50 μm by a particle size analyzer.

[0054] Comparative Example 1:

[0055] Compared with Example 1, ammonium sulfate was added to the formulation at a ratio of 1:0.3, including the following steps:

[0056] S1. Preparation of ferrous salt solution: Take ferrous sulfate and add it to deionized water to prepare 10L of ferrous sulfate solution F1 with a concentration of 1.5mol / L.

[0057] S2. Prepare a mixed solution of phosphate salt and hydrogen peroxide: Take monoammonium phosphate and add it to deionized water to prepare a phosphate salt solution with a concentration of 1.5 mol / L, totaling 10 L. Then add 9 mol of hydrogen peroxide to the phosphate salt solution and mix well to obtain a mixed solution of phosphate salt and hydrogen peroxide, L1.

[0058] S3. Take 10L of ferrous sulfate solution F1; take 10L of a mixed solution of phosphate salt and hydrogen peroxide L1; take 1.5L of ammonia water, and pump them into the reactor using a peristaltic pump. The feeding rate of ferrous salt solution F1 and mixed solution L1 is 0.2L / min, and the feeding rate of ammonia water is 0.03L / min.

[0059] S4. After the reaction is complete, amorphous iron phosphate material H1 is obtained. The pH value of iron phosphate material H1 is adjusted to 2.4 using ammonia water.

[0060] S5. After washing the ferric phosphate material H1 with pure water, it is pulped to obtain ferric phosphate slurry J1, wherein the pulping volume is 12L.

[0061] S6. Mix ferric phosphate slurry J1 with acid material, wherein the acid material is a mixed solution of phosphoric acid and ammonium sulfate, and the stoichiometric ratio of the substances is 1.0:0.3.

[0062] S7. After mixing evenly, add to the reaction vessel and carry out crystallization at 94℃ for 2 hours.

[0063] S8. After the reaction is complete, the material is washed and sintered in a muffle furnace at 570°C for 4 hours to obtain the iron phosphate.

[0064] The resulting ferric phosphate electron microscopy morphology is as follows: Figure 4 As shown, Figure 4 This is an electron microscope schematic diagram of a comparative example of nano-sized iron phosphate provided in this application. It can be seen that the grain size of the iron phosphate obtained at this time is about 400nm-700nm, and the primary particle size is much larger than that of the iron phosphate in Examples 1 and 2. The particle size D50 is measured to be 3.27um by a particle size analyzer.

[0065] Comparative Example 2:

[0066] Comparative examples, where ammonium sulfate is not added, include the following steps:

[0067] S1. Preparation of ferrous salt solution: Take ferrous sulfate and add it to deionized water to prepare 10L of ferrous sulfate solution F1 with a concentration of 1.5mol / L.

[0068] S2. Prepare a mixed solution of phosphate salt and hydrogen peroxide: Take monoammonium phosphate and add it to deionized water to prepare a phosphate salt solution with a concentration of 1.5 mol / L, totaling 10 L. Then add 9 mol of hydrogen peroxide to the phosphate salt solution and mix well to obtain a mixed solution of phosphate salt and hydrogen peroxide, L1.

[0069] S3. Take 10L of ferrous sulfate solution F1; take 10L of a mixed solution of phosphate salt and hydrogen peroxide L1; take 1.5L of ammonia water, and pump them into the reactor using a peristaltic pump. The feeding rate of ferrous salt solution F1 and mixed solution L1 is 0.2L / min, and the feeding rate of ammonia water is 0.03L / min.

[0070] S4. After the reaction is complete, amorphous iron phosphate material H1 is obtained. The pH value of iron phosphate material H1 is adjusted to 2.4 using ammonia water.

[0071] S5. After washing the ferric phosphate material H1 with pure water, it is pulped to obtain ferric phosphate slurry J1, wherein the pulping volume is 12L.

[0072] S6. Mix ferric phosphate slurry J1 with acid material, wherein the acid material is phosphoric acid, and the stoichiometric ratio of the substances is 1.0.

[0073] S7. After mixing evenly, add to the reaction vessel and carry out crystallization at 94℃ for 2 hours.

[0074] S8. After the reaction is complete, the material is washed and sintered in a muffle furnace at 570°C for 4 hours to obtain the iron phosphate.

[0075] The resulting ferric phosphate electron microscopy morphology is as follows: Figure 5 As shown, Figure 5 This is an electron microscope schematic diagram of another comparative example of nano-sized iron phosphate provided in this application. As can be seen, the iron phosphate prepared by this method has a grain size of approximately 100 nm-200 nm, and its particle size D50 is 8.42 μm as measured by a particle size analyzer.

[0076] In a second aspect, embodiments of this specification also provide a method for preparing lithium iron phosphate, comprising:

[0077] Ferric phosphate is mixed with lithium carbonate, a composite carbon source, and water, and then subjected to stirring and sand milling. The ferric phosphate is prepared based on the method described in the first aspect. The mixture after sand milling is spray-dried, and then the dried material is calcined at high temperature under a protective atmosphere. After gas crushing, lithium iron phosphate is obtained.

[0078] The iron phosphate prepared using Examples 1 and 2 and Comparative Examples 1 and 2 described above was used to prepare lithium iron phosphate using the same method described above. The preparation method of lithium iron phosphate is as follows: 1. Lithium carbonate, a composite carbon source, and water were added to the prepared iron phosphate, followed by stirring and sand milling. 2. The mixture after sand milling was spray-dried, and then the dried material was placed in a protective atmosphere and calcined at 745°C for 8 hours. After air crushing, lithium iron phosphate was obtained. The lithium iron phosphate was assembled into coin cells using conventional methods, and its charge-discharge performance under 1C conditions was measured using conventional methods in the art. The test results of the examples and comparative examples are shown in Table 1 below.

[0079] Table 1. Performance Comparison of Lithium Iron Phosphate Prepared in Examples and Comparative Examples

[0080]

[0081]

[0082] As can be seen from Table 1 above, the highly dispersed nanoparticle iron phosphate (Examples 1 and 2) prepared using the scheme of this application have 1C charge-discharge performance of over 150 mAh / g and higher discharge specific capacity. The average 1C charge-discharge performance of Comparative Example 1 is only 126 mAh / g. Combined with its particle size and SEM morphology, it can be seen that the sample with nano-sized primary particles has better electrical performance when the secondary agglomerates are smaller. This indicates that there is a suitable range for the proportion of ammonium sulfate in the second synthesis reaction, that is, the molar ratio of phosphoric acid to ammonium sulfate is between 1:0.1 and 1:0.2.

[0083] The morphology of ferric phosphate changes with the proportion of ammonium sulfate added; only when it forms a shape like... Figure 1 and Figure 2 Only iron phosphate with nano-sized primary particles can exhibit high rate performance in lithium iron phosphate. Comparative Example 2 also has nano-sized primary particles, but its 1C charge / discharge performance is worse than Examples 1 and 2 when the D50 size is larger than that of Examples 1 / 2 / 3. This indicates that large agglomerates reduce the rate performance of the material. Only lithium iron phosphate prepared with both nano-sized primary particles and highly dispersed, non-agglomerated secondary agglomerates can possess excellent rate performance.

[0084] The foregoing has described specific embodiments of this specification. Other embodiments are within the scope of the appended claims. In some cases, the actions or steps recited in the claims may be performed in a different order than that shown in the embodiments and may still achieve the desired result. Furthermore, the processes depicted in the drawings do not necessarily require the specific or sequential order shown to achieve the desired result. In some embodiments, multitasking and parallel processing are possible or may be advantageous.

[0085] The above description is merely one or more embodiments of this specification and is not intended to limit this specification. Various modifications and variations can be made to the one or more embodiments of this specification by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principle of one or more embodiments of this specification should be included within the scope of the claims of this specification.

Claims

1. A method for preparing nanoparticle iron phosphate, comprising: Ferrous salt solution F1 was prepared by using ferrous sulfate and deionized water; A phosphate salt solution was prepared by using monoammonium phosphate and deionized water, and hydrogen peroxide was added to the phosphate salt solution to obtain a phosphate salt mixture L1. Iron salt solution F1, phosphate salt mixture L1 and ammonia water are pumped into a reaction vessel to generate an amorphous iron phosphate slurry with a pH value between 2.4 and 2.

6. The ferric phosphate slurry is mixed with an acid to obtain a mixture, wherein the acid comprises phosphoric acid and ammonium sulfate, and the molar ratio of the phosphoric acid to ammonium sulfate is between 1:0.1 and 1:0.

2. The mixture is placed in a reaction vessel, heated to the reaction temperature, and aged to obtain a solid product. The solid product is washed and calcined in a muffle furnace to obtain iron phosphate nanoparticles, wherein the particle size of the iron phosphate nanoparticles is between 100 nm and 200 nm, and the particle size D50 is 2-3 μm.

2. The method as described in claim 1, wherein, The iron salt solution F1 and the phosphate salt mixture L1 have the same molar concentration and are pumped into the reactor in a volume ratio of 1:

1. The feed rate ratio of the iron salt solution F1, the mixture L1, and the ammonia water is 20:20:

3.

3. The method as described in claim 1, wherein, The reaction temperature is 90 to 100 degrees Celsius, and the aging reaction lasts for 2 hours.

4. The method of claim 1, wherein, The calcination temperature in the muffle furnace is 550℃ to 600℃, and the calcination time is 4 hours.

5. The method of claim 1, wherein, The washing process is terminated when the conductivity of the wash water is <500 uS / cm.

6. The method of claim 1, wherein, The concentrations of ferric phosphate slurry and acid were 1.25 mol / L and 25 mol / L, respectively, with a volume ratio of 1:0.

05.

7. A method for preparing lithium iron phosphate, comprising: Ferric phosphate is mixed with lithium carbonate, a composite carbon source, and water, and then subjected to stirring and sand milling. The ferric phosphate is prepared according to the method of claim 1. The mixture after sand milling is spray dried, and then the dried material is calcined at high temperature under a protective atmosphere; Lithium iron phosphate is obtained after gas crushing.

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