Nano-ferric phosphate, preparation method thereof, nano-lithium ferric phosphate cathode material, preparation method and application thereof
By using co-precipitation and surfactants, nano-sized lithium iron phosphate cathode materials were prepared, solving the problems of uneven particle size and large particle size of lithium iron phosphate materials. This improved the uniformity and conductivity of the materials, thereby enhancing the electrochemical performance of lithium-ion batteries.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- FOSHAN DYNANONIC
- Filing Date
- 2023-11-24
- Publication Date
- 2026-05-12
AI Technical Summary
Existing lithium iron phosphate materials suffer from problems such as uneven particle size, large particle size, and small specific surface area, resulting in low volumetric capacity and poor electrochemical performance of batteries.
Nano-sized iron phosphate was prepared by co-precipitation. By adding surfactants such as citric acid, polyethylene glycol, hexadecyltrimethylammonium bromide and sodium hexadecylbenzenesulfonate, and controlling the pH value and stirring and heating conditions, uniform nano-sized iron phosphate particles were formed. During the mixing and sintering process with lithium source and carbon source, the surfactants acted as carbon sources and were distributed inside the nano-sized lithium iron phosphate cathode material.
A uniform and fine-particle lithium iron phosphate cathode material was prepared, which improved conductivity and stability and enhanced the electrochemical performance of lithium-ion batteries.
Smart Images
Figure CN117602603B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of lithium battery materials technology, and more specifically, to a nano-iron phosphate and its preparation method, a nano-lithium iron phosphate cathode material and its preparation method and application. Background Technology
[0002] Lithium iron phosphate (LFP) is an important cathode material for lithium-ion batteries, possessing advantages such as high structural stability, good safety performance, moderate operating voltage, good plateau characteristics, and large theoretical capacity. However, current LFP materials suffer from problems such as uneven particle size, large particle size, and small specific surface area. This results in batteries with low volumetric capacity and poor electrochemical performance. Summary of the Invention
[0003] The purpose of this invention is to overcome the defects of the prior art by providing a nano-iron phosphate and its preparation method, a nano-lithium iron phosphate cathode material and its preparation method and application.
[0004] The technical problem solved by this invention is achieved by the following technical solution.
[0005] This invention provides a method for preparing nano-ferric phosphate, comprising: preparing a first precursor slurry by co-precipitation of an iron source and a phosphorus source; adding a surfactant; and, under stirring and heating conditions, adding a precipitant to control the pH value to obtain a second precursor slurry; and post-processing the second precursor slurry to obtain nano-ferric phosphate, wherein the surfactant includes at least one selected from citric acid, polyethylene glycol, hexadecyltrimethylammonium bromide, and sodium hexadecylbenzenesulfonate.
[0006] The present invention also provides a nano-iron phosphate prepared by the above preparation method, wherein the primary particle size of the nano-iron phosphate is 50-150 nm and the morphology of the nano-iron phosphate is spherical or near-spherical.
[0007] The present invention also provides a method for preparing nano-lithium iron phosphate cathode material, which includes: sintering the nano-iron phosphate, lithium source and carbon source prepared above under an inert gas atmosphere to obtain nano-lithium iron phosphate cathode material.
[0008] The present invention also provides a nano-lithium iron phosphate cathode material prepared by the above preparation method, wherein the primary particle size of the nano-lithium iron phosphate cathode material is 150-250 nm, and the morphology of the nano-lithium iron phosphate cathode material is spherical or near-spherical.
[0009] The present invention also provides a lithium-ion battery comprising the above-mentioned nano-lithium iron phosphate cathode material.
[0010] The present invention has the following beneficial effects:
[0011] This invention provides a nano-iron phosphate and its preparation method, a nano-lithium iron phosphate cathode material and its preparation method, and its application. The preparation method of the nano-iron phosphate includes: preparing a first precursor slurry by co-precipitation of an iron source and a phosphorus source; adding a surfactant; and adding a precipitant to control the pH value under stirring and heating conditions to obtain a second precursor slurry. The second precursor slurry is then post-treated to obtain nano-iron phosphate. The surfactant includes at least one selected from citric acid, polyethylene glycol, hexadecyltrimethylammonium bromide, and sodium hexadecylbenzenesulfonate. In the preparation process of nano-iron phosphate, the first precursor slurry is prepared by co-precipitation, and then the surfactant is added. On the one hand, the surfactant can inhibit the growth of crystal nuclei in the precipitated product, resulting in more uniform nano-iron phosphate particles. On the other hand, during the sintering of nano-iron phosphate with lithium and carbon sources to prepare nano-lithium iron phosphate cathode materials, the surfactant can also act as a partial carbon source distributed within the nano-lithium iron phosphate cathode material, improving the conductivity and ionization conductivity of the finished nano-lithium iron phosphate cathode material. This method is unique and effective, producing nano-lithium iron phosphate cathode materials with uniform morphology and fine particles, exhibiting spherical or near-spherical shapes, while also demonstrating good conductivity and high stability. Attached Figure Description
[0012] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.
[0013] Figure 1 SEM image of the nano-iron phosphate prepared in Example 1;
[0014] Figure 2 SEM image of the nano-lithium iron phosphate cathode material prepared in Example 1;
[0015] Figure 3 SEM image of the nano-iron phosphate prepared in Example 2;
[0016] Figure 4 SEM image of the nano-lithium iron phosphate cathode material prepared in Example 2;
[0017] Figure 5 SEM image of the nano-iron phosphate prepared in Example 3;
[0018] Figure 6 SEM image of the nano-lithium iron phosphate cathode material prepared in Example 3;
[0019] Figure 7SEM image of the nano-iron phosphate prepared for Comparative Example 1;
[0020] Figure 8 SEM image of the nano-lithium iron phosphate cathode material prepared for Comparative Example 1. Detailed Implementation
[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.
[0022] The following provides a detailed description of a nano-iron phosphate and its preparation method, a nano-lithium iron phosphate cathode material and its preparation method, and its application, provided by embodiments of the present invention.
[0023] In a first aspect, embodiments of the present invention provide a method for preparing nano-ferric phosphate, comprising: preparing a first precursor slurry by co-precipitation of an iron source and a phosphorus source; adding a surfactant; and, under stirring and heating conditions, adding a precipitant to control the pH value to obtain a second precursor slurry; and post-processing the second precursor slurry to obtain nano-ferric phosphate, wherein the surfactant comprises at least one selected from citric acid, polyethylene glycol, hexadecyltrimethylammonium bromide, and sodium hexadecylbenzenesulfonate.
[0024] This invention provides a method for preparing nano-sized iron phosphate. First, a first precursor slurry is obtained by explosive nucleation in solution using a co-precipitation method. Then, a surfactant is added to the first precursor slurry. The surfactant improves interfacial adsorption and reduces the surface energy of the iron phosphate crystals through affinity, thereby effectively inhibiting the crystal growth process. Then, by controlling the reaction temperature and pH value of the solution, the crystals in the solution are stably grown to obtain a second precursor slurry. The second precursor slurry is then post-processed to obtain nano-sized iron phosphate.
[0025] In an optional embodiment, the method includes the following steps: adjusting the pH of the mixture of iron source and phosphorus source to 1-2, and then co-precipitating it with an oxidant to obtain a first precursor slurry; then mixing the first precursor slurry with a surfactant evenly, and adding a precipitant under stirring and heating conditions to maintain the pH of the reaction at 1-2, and after the reaction is completed, obtaining a second precursor slurry; and aging, washing and calcining the second precursor slurry to obtain nano-iron phosphate.
[0026] In an optional embodiment, the preparation of the first precursor slurry includes: mixing an iron source solution and a phosphorus source solution to obtain a mixed solution, adjusting the pH of the mixed solution to 1-2, and then adding an excess of oxidant solution to carry out a co-precipitation reaction to obtain the first precursor slurry.
[0027] Preferably, the iron source includes at least one of ferrous sulfate and iron powder, and the phosphorus source includes at least one of phosphoric acid, ammonium phosphate, and ammonium dihydrogen phosphate. The concentration of the iron source solution is 1-3 mol / L, and the concentration of the phosphorus source solution is 1-3 mol / L.
[0028] Preferably, the pH of the mixture is adjusted to 1-2 using a sulfuric acid solution, the concentration of which is 1-3 mol / L.
[0029] Preferably, the oxidant is hydrogen peroxide, the molar ratio of the iron source to the hydrogen peroxide is 1:(0.55-0.75), and the concentration of the oxidant solution is 1-4 mol / L;
[0030] Preferably, the coprecipitation reaction is carried out at a temperature of 80–90°C for 1–3 hours.
[0031] In the preparation process of the first precursor slurry, the iron source solution and the phosphorus source solution need to be mixed to obtain a mixed solution. Then the pH of the mixed solution is adjusted to 1-2. If the pH is above 2, the solubility product of ferric hydroxide will lead to the formation of ferric hydroxide impurities. Therefore, it is necessary to control the pH of the mixed solution to be adjusted to 1-2.
[0032] In an optional embodiment, the preparation of the second precursor slurry includes: mixing the first precursor slurry with a surfactant until uniform, adding a precipitant dropwise under stirring and heating conditions and controlling the pH of the reaction to be 1 to 2, thereby obtaining the second precursor slurry.
[0033] Preferably, the surfactant includes at least one selected from citric acid, polyethylene glycol, hexadecyltrimethylammonium bromide, and sodium hexadecylbenzenesulfonate, more preferably citric acid;
[0034] Preferably, the surfactant content in the second precursor slurry is 0.2–1 g / 500 ml, the stirring speed is 400–700 rpm, and the heating temperature is 80–90 °C.
[0035] Preferably, the precipitant includes at least one of sodium hydroxide solution and ammonia water, and the concentration of the precipitant is 1-4 mol / L;
[0036] Preferably, the total dropping time of the precipitant is controlled to be 20-40 minutes, and the pH of the final solution is 1-2 after the dropping of the precipitant is finished.
[0037] In the preparation of the second precursor slurry, the first precursor slurry is mixed evenly with a surfactant. Under stirring and heating conditions, a precipitant is added dropwise in stages, and the pH of the reaction is controlled at 1-2. Stirring and heating are used to enhance the affinity between the grains and the surfactant, leveraging the surfactant's ability to inhibit grain growth. Stirring also inhibits the formation of large particles. Furthermore, during the co-precipitation reaction of the iron and phosphorus source mixture with the oxidant, the following reaction occurs: 2Fe 2+ +2H2PO4 - +H₂O₂=2FePO₄ + 2H₂O + 2H + The entire reaction process is accompanied by H + The formation of H+ occurs initially with the addition of phosphoric acid and an oxidizing agent, making the reaction quite acidic. As stirring and heating continue, the reaction becomes increasingly acidic. A precipitant can be used to absorb the large amount of H+ generated during the reaction. + This stabilizes the pH at 1–2. By controlling the reaction temperature and pH of the first precursor slurry, uniformly sized nano-iron phosphate particles can be continuously and stably generated.
[0038] In an optional embodiment, the preparation of nano-ferric phosphate includes: filtering and washing the second precursor slurry, adding it to a phosphoric acid solution for aging and crystallization, filtering and washing it again, and calcining it to obtain nano-ferric phosphate.
[0039] Preferably, during the aging and crystallization process, the stirring speed is 300-700 rpm, the heating temperature is 80-90℃, and the aging time is 2-4 hours;
[0040] Preferably, the concentration of the phosphoric acid solution is 1–3 mol / L;
[0041] Preferably, the calcination temperature is 550–650°C and the time is 4–6 hours.
[0042] In the above preparation process of nano-iron phosphate, the second precursor slurry is filtered and washed and then added to a phosphoric acid solution for aging and crystallization. Aging and crystallization not only removes impurity ions and adjusts the iron-phosphorus ratio, but also obtains a more complete crystal form, which lays the foundation for the subsequent growth of a better nano-lithium iron phosphate crystal structure. In order to promote the crystal transformation, aging and crystallization is carried out under stirring and heating conditions. If heating is not carried out, the crystal form of nano-iron phosphate cannot be changed.
[0043] Secondly, embodiments of the present invention also provide a nano-iron phosphate prepared by the above preparation method, wherein the primary particle size of the nano-iron phosphate is 50-150 nm, and the morphology of the nano-iron phosphate is spherical or near-spherical.
[0044] Thirdly, embodiments of the present invention also provide a method for preparing nano-lithium iron phosphate cathode material, which includes: sintering the nano-iron phosphate, lithium source and carbon source prepared above under an inert gas atmosphere to obtain nano-lithium iron phosphate cathode material.
[0045] In an optional embodiment, nano-iron phosphate, lithium source and carbon source are mixed and ground to obtain nano-lithium iron phosphate precursor, and then the nano-lithium iron phosphate precursor is sintered and cooled to obtain nano-lithium iron phosphate cathode material.
[0046] Preferably, nano-iron phosphate, lithium source and carbon source are mixed in a molar ratio of (2-2.5):(1-1.50):(0.2-0.4) and then ball-milled at 200-400 rpm for 4-6 hours to obtain nano-lithium iron phosphate precursor;
[0047] Preferably, the carbon source includes at least one of glucose, sucrose, and polyacrylol;
[0048] Preferably, the sintering includes one-stage sintering, two-stage sintering, and three-stage sintering. The first-stage sintering involves heating from room temperature to a first sintering temperature at a first heating rate and holding for a first sintering time. The second-stage sintering involves heating from the first sintering temperature to a second sintering temperature at a second heating rate and holding for a second sintering time. The third-stage sintering involves heating from the second sintering temperature to a third sintering temperature at a third heating rate and holding for a third sintering time.
[0049] More preferably, the first sintering temperature is 30-50°C and the first sintering time is 1-2 hours; the second sintering temperature is 550-600°C and the second sintering time is 3-4 hours; the third sintering temperature is 700-750°C and the third sintering time is 7-10 hours.
[0050] More preferably, the first heating rate is 10℃ / min, the second heating rate is 5℃ / min, and the third heating rate is 2℃ / min.
[0051] In the above-described preparation process of nano-lithium iron phosphate cathode material, the nano-iron phosphate, lithium source, and carbon source prepared above are mixed and sintered under an inert gas atmosphere. During the preparation of nano-iron phosphate, surfactants are used to inhibit grain growth. During calcination, the surfactants can also act as a carbon source, distributing within the nano-lithium iron phosphate, thus improving the conductivity and ionization conductivity of the finished nano-lithium iron phosphate cathode material. Furthermore, the overall sintering temperature is relatively low during the subsequent sintering process, resulting in nanoscale spherical lithium iron phosphate cathode material with good particle distribution. Simultaneously, in this embodiment of the invention, a carbon source is added during the preparation of the nano-lithium iron phosphate cathode material. After high-temperature calcination, the carbon source can generate a continuous or discontinuous carbon coating layer on the surface of the nano-lithium iron phosphate cathode material, or generate carbon particles within the gaps between the nano-lithium iron phosphate cathode material, further improving the conductivity of the nano-lithium iron phosphate cathode material.
[0052] Fourthly, embodiments of the present invention also provide a nano-lithium iron phosphate cathode material prepared by the above-described preparation method, wherein the primary particle size of the nano-lithium iron phosphate cathode material is 150-250 nm, and the morphology of the nano-lithium iron phosphate cathode material is spherical or near-spherical.
[0053] The morphological differences between the nano-iron phosphate and nano-lithium iron phosphate cathode materials provided in the embodiments of the present invention are small; that is, the morphology and volume corresponding to the conversion from nano-iron phosphate to nano-lithium iron phosphate cathode materials do not change significantly. This proves that it is feasible to control the morphology of nano-lithium iron phosphate cathode materials using surfactants. It is evident that the embodiments of the present invention mainly solve the problems of nano-lithium iron phosphate particle size and morphology by controlling the particle morphology of nano-iron phosphate, providing a nano-spherical lithium iron phosphate cathode material. This nano-lithium iron phosphate cathode material also has advantages such as uniform particle size, small particle size, large specific surface area, and low resistivity.
[0054] Fifthly, embodiments of the present invention provide a lithium-ion battery, the lithium-ion battery comprising the above-mentioned nano-lithium iron phosphate cathode material.
[0055] The features and performance of the present invention will be further described in detail below with reference to embodiments.
[0056] Example 1
[0057] A method for preparing a lithium iron phosphate cathode material includes the following steps:
[0058] (1) Weigh out ferrous sulfate, hydrogen peroxide, sodium hydroxide, phosphoric acid and sulfuric acid, dissolve them in water respectively, and prepare ferrous sulfate solution, hydrogen peroxide solution, sodium hydroxide solution, phosphoric acid solution and sulfuric acid solution with a concentration of 1 mol / L.
[0059] (2) Mix ferrous sulfate and phosphoric acid in a 1:1 ratio to obtain 500 mL of solution. Add sulfuric acid solution to adjust the pH to 1. Then add excess hydrogen peroxide solution (the molar ratio of iron source to hydrogen peroxide is 1:0.55). After reacting for 1 hour, the first precursor slurry is obtained.
[0060] (3) Weigh 0.2g of citric acid, add it to the first precursor slurry and stir to dissolve. Then stir and heat at 80℃ and 400rpm, add sodium hydroxide solution dropwise in steps, and finish the addition within 20min. The final solution pH is 1, and the second precursor slurry is obtained. Filter and wash to obtain solid.
[0061] (4) Wash the solid thoroughly, then add phosphoric acid solution and age and crystallize at 90°C for 2 hours, then wash the solid thoroughly.
[0062] (5) The aged solid was calcined at 550°C for 4 hours to dehydrate it, and finally spherical or near-spherical nano-iron phosphate was obtained.
[0063] (6) The nano-iron phosphate prepared above is mixed with lithium source and glucose in a molar ratio of 2:1.03:0.3 and ground to obtain nano-lithium iron phosphate precursor;
[0064] The nano-lithium iron phosphate precursor prepared above was sintered under an inert gas atmosphere. The sintering was carried out in three stages: the first sintering temperature was 30℃ and the first sintering time was 1 hour; the second sintering temperature was 550℃ and the second sintering time was 3 hours; the third sintering temperature was 700℃ and the third sintering time was 7 hours; after cooling, nano-sized spherical or near-spherical lithium iron phosphate cathode materials were obtained.
[0065] Figure 1 , Figure 2 The images show scanning electron microscope (SEM) images of the nano-iron phosphate and nano-lithium iron phosphate cathode materials prepared in Example 1. It can be seen that the particles in both images are spherical or near-spherical, with iron phosphate particles having a diameter of 90 nm and lithium iron phosphate particles having a diameter of 160 nm. The overall particle distribution is uniform and the morphology is regular; the morphology and volume do not change significantly when converting from iron phosphate to lithium iron phosphate.
[0066] Example 2
[0067] A method for preparing a lithium iron phosphate cathode material includes the following steps:
[0068] (1) Weigh out ferrous sulfate, hydrogen peroxide, sodium hydroxide, phosphoric acid and sulfuric acid, dissolve them in water respectively, and prepare ferrous sulfate solution with a concentration of 2 mol / L, hydrogen peroxide solution with a concentration of 2 mol / L, sodium hydroxide solution with a concentration of 2 mol / L, phosphoric acid solution with a concentration of 2 mol / L and sulfuric acid solution with a concentration of 2 mol / L.
[0069] (2) Ferrous sulfate and phosphoric acid were mixed in a 1:1 ratio to obtain 500 mL of solution. Sulfuric acid solution was added to adjust the pH to 1.5. Then, excess hydrogen peroxide solution was added (the molar ratio of iron source to hydrogen peroxide was 1:0.55). After reacting for 2 hours, the first precursor slurry was obtained.
[0070] (3) Weigh 0.5g of citric acid, add it to the first precursor slurry and stir to dissolve. Then stir and heat at 85℃ and 550rpm, add sodium hydroxide solution dropwise in steps, and finish the addition within 30min. The final solution pH is 1.5, and the second precursor slurry is obtained. Filter and wash to obtain solid.
[0071] (4) Wash the solid thoroughly, then add phosphoric acid solution and age and crystallize at 90°C for 2 hours at 500 rpm, then wash the solid thoroughly.
[0072] (5) The aged solid was calcined at 600°C for 5 hours to dehydrate it, and finally spherical or near-spherical nano-iron phosphate was obtained.
[0073] (6) The nano-iron phosphate prepared above is mixed with lithium source and glucose in a molar ratio of 2:1.03:0.3 and ground to obtain nano-lithium iron phosphate precursor;
[0074] The nano-lithium iron phosphate precursor prepared above was sintered under an inert gas atmosphere. The sintering was carried out in three stages: the first sintering temperature was 40℃ and the first sintering time was 1 hour; the second sintering temperature was 550℃ and the second sintering time was 4 hours; the third sintering temperature was 700℃ and the third sintering time was 8 hours; after cooling, nano-sized spherical or near-spherical lithium iron phosphate was obtained.
[0075] Figure 3 , Figure 4 The images show scanning electron microscope (SEM) images of the nano-iron phosphate and nano-lithium iron phosphate cathode materials prepared in Example 2. It can be seen that the particles in both images are spherical or near-spherical, with iron phosphate particles having a diameter of 80 nm and lithium iron phosphate particles having a diameter of 150 nm. The overall particle distribution is uniform and the morphology is regular; the morphology and volume do not change significantly when converting from iron phosphate to lithium iron phosphate.
[0076] Example 3
[0077] A method for preparing a lithium iron phosphate cathode material includes the following steps:
[0078] (1) Weigh out ferrous sulfate, hydrogen peroxide, sodium hydroxide, phosphoric acid and sulfuric acid, dissolve them in water respectively, and prepare ferrous sulfate solution with a concentration of 3 mol / L, hydrogen peroxide solution with a concentration of 4 mol / L, sodium hydroxide solution with a concentration of 4 mol / L, phosphoric acid solution with a concentration of 3 mol / L and sulfuric acid solution with a concentration of 3 mol / L.
[0079] (2) Mix ferrous sulfate and phosphoric acid in a 1:1 ratio to obtain 500 mL of solution. Add sulfuric acid solution to adjust the pH to 2. Then add excess hydrogen peroxide solution (the molar ratio of iron source to hydrogen peroxide is 1:0.55). After reacting for 2 hours, the first precursor slurry is obtained.
[0080] (3) Weigh 0.2g of citric acid, add it to the first precursor slurry and stir to dissolve. Then stir and heat at 80℃ and 400rpm, and add sodium hydroxide solution dropwise in steps. The addition is completed within 30min. The final solution pH is 1.5, and the second precursor slurry is obtained. Filter and wash to obtain solid.
[0081] (4) Wash the solid thoroughly, then add phosphoric acid solution and age and crystallize at 90°C for 2 hours at 500 rpm, then wash the solid thoroughly.
[0082] (5) The aged solid was calcined at 500°C for 4 hours to dehydrate it, and finally spherical or near-spherical nano-iron phosphate was obtained.
[0083] (6) The nano-iron phosphate prepared above is mixed with lithium source and glucose in a molar ratio of 2:1.03:0.3 and ground to obtain nano-lithium iron phosphate precursor;
[0084] The nano-lithium iron phosphate precursor prepared above was sintered under an inert gas atmosphere. The sintering was carried out in three stages: the first sintering temperature was 30℃ and the first sintering time was 1 hour; the second sintering temperature was 550℃ and the second sintering time was 4 hours; the third sintering temperature was 700℃ and the third sintering time was 7 hours; after cooling, nano-sized spherical or near-spherical lithium iron phosphate was obtained.
[0085] Figure 5 , Figure 6 The images show scanning electron microscope (SEM) images of the nano-iron phosphate and nano-lithium iron phosphate cathode materials prepared in Example 3. It can be seen that the particles in both images are spherical or near-spherical, with iron phosphate particles having a diameter of 125 nm and lithium iron phosphate particles having a diameter of 250 nm. The overall particle distribution is uniform and the morphology is regular; the morphology and volume do not change significantly when converting from iron phosphate to lithium iron phosphate.
[0086] Comparative Example 1
[0087] A method for preparing a lithium iron phosphate cathode material includes the following steps:
[0088] (1) Weigh out ferrous sulfate, hydrogen peroxide, sodium hydroxide, phosphoric acid and sulfuric acid, dissolve them in water respectively, and prepare ferrous sulfate solution with a concentration of 1 mol / L, hydrogen peroxide solution with a concentration of 1 mol / L, sodium hydroxide solution with a concentration of 3 mol / L, phosphoric acid solution with a concentration of 1 mol / L and sulfuric acid solution with a concentration of 1 mol / L.
[0089] (2) Mix ferrous sulfate and phosphoric acid in a 1:1 ratio to obtain 500 mL of solution. Add sulfuric acid solution to adjust the pH to 1. Then add excess hydrogen peroxide solution (the molar ratio of iron source to hydrogen peroxide is 1:0.55). After reacting for 2 hours, the first precursor slurry is obtained.
[0090] (3) Stir and heat the first precursor slurry at 80℃ and 400rpm, add sodium hydroxide solution dropwise to it in steps, and finish the addition within half an hour. The final solution pH is 1.5. Filter and wash to obtain solid.
[0091] (4) Wash the solid thoroughly, then add phosphoric acid solution and age and crystallize at 90°C for 2 hours at 500 rpm, then wash the solid thoroughly.
[0092] (5) The aged solid was calcined at 500°C for 4 hours to dehydrate it, and finally nano-iron phosphate was obtained.
[0093] (6) The nano-iron phosphate prepared above is mixed with lithium source and glucose in a molar ratio of 2:1.03:0.3 and ground to obtain nano-lithium iron phosphate precursor;
[0094] The nano-sized lithium iron phosphate precursor prepared above was sintered under an inert gas atmosphere. The sintering was carried out in three stages: the first sintering temperature was 30℃ and the first sintering time was 1 hour; the second sintering temperature was 550℃ and the second sintering time was 4 hours; the third sintering temperature was 700℃ and the third sintering time was 7 hours; after cooling, nano-sized lithium iron phosphate was obtained.
[0095] Comparative Example 1 did not contain the surfactant citric acid, and the concentration varied, which affected the spherical morphology, such as agglomeration and non-spherical shapes. Figure 7 , Figure 8 The images show scanning electron microscope (SEM) images of the nano-iron phosphate and nano-lithium iron phosphate cathode materials prepared in Comparative Example 1. The iron phosphate particles have a diameter of 400 nm, while the lithium iron phosphate particles have a diameter of 800 nm. The overall particle distribution is uneven and the morphology is irregular.
[0096] Table 1
[0097] Example 1 Example 2 Example 3 Comparative Example 1 Nano-sized iron phosphate D50 particle size (nm) 1.59 1.43 1.82 2.13 Nano-sized lithium iron phosphate D50 particle size (nm) 1.94 1.73 2.11 2.31
[0098] As can be seen from Table 1, the lithium iron phosphate cathode material particles prepared by the method provided by this invention are all in the nanoscale range. Compared with the comparative example, the morphology difference between lithium iron phosphate and iron phosphate particles prepared by this method is small, proving that it is feasible to control the morphology of lithium iron phosphate by surfactant.
[0099] Table 2
[0100]
[0101] As can be seen from Table 2 above, compared with Comparative Example 1, the lithium iron phosphate cathode material particles prepared by the preparation method provided in this invention have a larger specific surface area and extremely low resistivity. This is because the lithium iron phosphate cathode material prepared in this invention has a smaller particle size and its morphology is mostly spherical or near-spherical, thus having a larger specific surface area. Simultaneously, the nano-lithium iron phosphate particles prepared in this invention have a regular and uniform morphology, further indicating good uniformity of carbon coating on the surface of the nano-lithium iron phosphate particles, resulting in lower resistivity of the prepared nano-lithium iron phosphate cathode material. All of these factors indicate that the conductivity and reactivity of this type of material are greatly improved. Applying it to lithium batteries can further improve the electrochemical performance of lithium-ion batteries.
[0102] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.
Claims
1. A method for preparing nano-ferric phosphate, characterized in that, Includes the following steps: The pH of the mixture of iron and phosphorus sources is adjusted to 1-2, and then a co-precipitation reaction is carried out with an oxidant. Nucleation occurs in the solution to obtain a first precursor slurry. The co-precipitation reaction temperature is 80-90℃ and the time is 1-3h. Then, the first precursor slurry is mixed evenly with a surfactant. Under stirring and heating conditions, a precipitant is added to maintain the pH of the reaction at 1-2. After the reaction is completed, a second precursor slurry is obtained. The surfactant content in the second precursor slurry is 0.2-1g / 500ml. The stirring speed is 400-700rpm and the heating temperature is 80-90℃. The second precursor slurry is aged, washed and calcined to obtain nano-ferric phosphate. The surfactant includes at least one of citric acid, polyethylene glycol, hexadecyltrimethylammonium bromide and sodium hexadecylbenzenesulfonate. The primary particle size of the obtained nano-ferric phosphate is 50-150 nm, and the morphology of the nano-ferric phosphate is spherical or near-spherical.
2. The preparation method according to claim 1, characterized in that, The preparation of the first precursor slurry includes: mixing an iron source solution and a phosphorus source solution to obtain a mixed solution, adjusting the pH of the mixed solution to 1-2, and then adding an excess of oxidant solution to carry out a co-precipitation reaction to obtain the first precursor slurry.
3. The preparation method according to claim 2, characterized in that, The iron source includes at least one of ferrous sulfate and iron powder, and the phosphorus source includes at least one of phosphoric acid, ammonium phosphate, and ammonium dihydrogen phosphate. The concentration of the iron source solution is 1~3 mol / L, and the concentration of the phosphorus source solution is 1~3 mol / L.
4. The preparation method according to claim 2, characterized in that, The pH of the mixture is adjusted to 1-2 using a sulfuric acid solution with a concentration of 1-3 mol / L.
5. The preparation method according to claim 2, characterized in that, The oxidant is hydrogen peroxide, the molar ratio of the iron source to the hydrogen peroxide is 1:(0.55~0.75), and the concentration of the oxidant solution is 1~4 mol / L.
6. The preparation method according to claim 1, characterized in that, The preparation of the second precursor slurry includes: mixing the first precursor slurry with a surfactant until uniform, adding a precipitant dropwise under stirring and heating conditions, and controlling the pH of the reaction to be 1~2, thereby obtaining the second precursor slurry.
7. The preparation method according to claim 6, characterized in that, The surfactant includes at least one of citric acid, polyethylene glycol, hexadecyltrimethylammonium bromide, and sodium hexadecylbenzenesulfonate.
8. The preparation method according to claim 7, characterized in that, The surfactant is citric acid.
9. The preparation method according to claim 6, characterized in that, The precipitant includes at least one of sodium hydroxide solution and ammonia water, and the concentration of the precipitant is 1~4 mol / L.
10. The preparation method according to claim 6, characterized in that, The total dropping time of the precipitant is controlled to be 20-40 minutes, and the pH of the final solution is 1-2 after the dropping of the precipitant is finished.
11. The preparation method according to claim 1, characterized in that, The preparation of the nano-ferric phosphate includes: filtering and washing the second precursor slurry, adding it to a phosphoric acid solution for aging and crystallization, filtering and washing it again, and calcining it to obtain nano-ferric phosphate.
12. The preparation method according to claim 11, characterized in that, During the aging and crystallization process, the stirring speed is 300~700 rpm, the heating temperature is 80~90℃, and the aging time is 2~4 hours.
13. The preparation method according to claim 11, characterized in that, The concentration of the phosphoric acid solution is 1~3 mol / L.
14. The preparation method according to claim 11, characterized in that, The calcination temperature is 550~650℃, and the time is 4~6 hours.
15. A method for preparing a nano-lithium iron phosphate cathode material, characterized in that, It includes: Under an inert gas atmosphere, nano-iron phosphate, lithium source and carbon source are mixed and sintered to obtain nano-lithium iron phosphate cathode material, wherein the nano-iron phosphate is nano-iron phosphate prepared by the preparation method according to any one of claims 1 to 14.
16. The preparation method according to claim 15, characterized in that, The nano-sized iron phosphate, lithium source, and carbon source are mixed and ground to obtain a nano-sized lithium iron phosphate precursor. The nano-sized lithium iron phosphate precursor is then sintered and cooled to obtain a nano-sized lithium iron phosphate cathode material.
17. The preparation method according to claim 16, characterized in that, Nano-sized iron phosphate, lithium source and carbon source are mixed in a molar ratio of (2~2.5):(1~1.50):(0.2~0.4) and then ball-milled at 200~400 rpm for 4~6 hours to obtain nano-sized lithium iron phosphate precursor.
18. The preparation method according to claim 16, characterized in that, The carbon source includes at least one of glucose, sucrose, and polyacrylol.
19. The preparation method according to claim 16, characterized in that, The sintering process includes first-stage sintering, second-stage sintering, and third-stage sintering. The first-stage sintering involves heating from room temperature to a first sintering temperature at a first heating rate and holding for a first sintering time. The second-stage sintering involves heating from the first sintering temperature to a second sintering temperature at a second heating rate and holding for a second sintering time. The third-stage sintering involves heating from the second sintering temperature to a third sintering temperature at a third heating rate and holding for a third sintering time.
20. The preparation method according to claim 19, characterized in that, The first sintering temperature is 30~50℃, and the first sintering time is 1~2 hours; The second sintering temperature is 550~600℃, and the second sintering time is 3~4 hours; The third sintering temperature is 700~750℃, and the third sintering time is 7~10 hours.
21. The preparation method according to claim 19, characterized in that, The first heating rate is 10℃ / min, the second heating rate is 5℃ / min, and the third heating rate is 2℃ / min.
22. A nano-lithium iron phosphate cathode material prepared by the preparation method according to any one of claims 15-21, characterized in that, The primary particle size of the nano-lithium iron phosphate cathode material is 150~250 nm, and the morphology of the nano-lithium iron phosphate cathode material is spherical or near-spherical.
23. A lithium-ion battery, characterized in that, The lithium-ion battery includes the nano-lithium iron phosphate cathode material as described in claim 22.