Preparation method and application of nanosheet-shaped lithium iron phosphate particles
By controlling the ratio of hydrothermal reaction raw materials and the concentration of lithium source slurry, nanosheet-shaped lithium iron phosphate particles were synthesized using a microwave hydrothermal method. This solved the problems of high cost and environmental pollution associated with the hydrothermal method, and enabled the efficient preparation of nanosheet-shaped lithium iron phosphate particles with excellent electrochemical performance, which are suitable for lithium-ion battery cathode materials.
Patent Information
- Application Number
- CN202511967511.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-24
- Publication Date
- 2026-03-03
AI Technical Summary
Existing hydrothermal methods for preparing nanosheet-shaped lithium iron phosphate particles suffer from high costs, environmental pollution, and difficulties in large-scale production.
Nanosheet-shaped lithium iron phosphate particles were prepared by controlling the molar ratio of hydrothermal reaction raw materials and the mass percentage of lithium hydroxide monohydrate in the lithium source slurry. The synthesis was carried out using a microwave hydrothermal method without the introduction of morphology guiding agents and in a high-pressure reactor.
Nanosheet-shaped lithium iron phosphate particles with (010) preferred growth crystal planes were obtained. These particles have short lithium-ion diffusion distances, excellent electrochemical performance, simple equipment, controllable cost, and are easy to industrialize.
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Figure CN121591189A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of lithium battery cathode material technology, specifically to a method for preparing and applying nanosheet-like lithium iron phosphate particles. Background Technology
[0002] Since the commercialization of lithium-ion batteries, cathode materials have been a hot research area. Among them, lithium iron phosphate (LiFePO4) with an olivine structure has a theoretically high specific capacity (170 mAh g⁻¹). -1 With advantages such as stable charging and discharging platform, high charging and discharging voltage (3.4V), low price, environmental friendliness, and non-toxicity and non-polluting properties, it has been widely used in the cathode material of lithium-ion batteries. As the cathode material of energy storage batteries, it has been applied in new energy vehicles, ships, communication base stations, special medical devices and other fields.
[0003] The unique olivine-type structure of LiFePO4 results in a low lithium-ion diffusion coefficient (1×10⁻⁶). -14 cm 2 / s) and electronic conductivity (1×10 -9 The inherent defects of lithium iron phosphate (LFP) batteries (S / cm) and the fact that lithium ions can only be transported along the one-dimensional channel
[010] crystal orientation lead to a decrease in the rate performance of LFP batteries, thus limiting their practical application as power batteries.
[0004] To address the aforementioned defects of lithium iron phosphate (poor intrinsic conductivity and slow lithium-ion diffusion), researchers have employed various methods, including ion doping, morphology control, and interface modification. Studies have shown that lithium iron phosphate with a nanosheet structure and a preferred (010) growth crystal plane can significantly shorten the lithium-ion insertion / extraction path, while simultaneously increasing the specific surface area and enhancing electrochemical activity.
[0005] The hydrothermal method is a wet chemical method for directly synthesizing crystals in a closed, high-temperature, and high-pressure aqueous solution. Its principle is to utilize the high-temperature, high-pressure aqueous environment to cause precursor substances to react and directly crystallize the target product. This method has attracted much attention in the field of LFP battery cathode materials because it can precisely control the morphology and crystal form of the product by adjusting parameters such as reaction temperature, pressure, solution concentration, and additives. However, existing hydrothermal methods require the introduction of morphology-directing agents (surfactants, template agents, organic acids, etc.) to control the morphology of lithium iron phosphate, which has drawbacks of sacrificing environmental friendliness and increasing costs. Microwave hydrothermal synthesis of lithium iron phosphate can shorten the reaction time and optimize the product morphology, but it is limited by equipment costs and scalability bottlenecks. Summary of the Invention
[0006] In view of this, the purpose of this invention is to provide a method for preparing nanosheet lithium iron phosphate particles and its application, aiming to solve the problems of high cost, environmental pollution and difficulty in large-scale production of existing hydrothermal methods for preparing nanosheet lithium iron phosphate particles.
[0007] To achieve the above objectives, the present invention provides the following technical solution.
[0008] In a first aspect, the present invention provides a method for preparing nanosheet-like lithium iron phosphate particles, which includes the following steps: Step 1: Weigh the lithium source, iron source, and phosphorus source for the hydrothermal preparation of lithium iron phosphate according to the molar ratio of Li:Fe:P = 3:1:1; the lithium source is selected from lithium hydroxide monohydrate. Step 2: Add lithium hydroxide monohydrate to pure water and mix evenly to obtain lithium source slurry, controlling the mass percentage of lithium hydroxide monohydrate in the lithium source slurry to be 30%-35%; Step 3: Add the phosphorus source to the lithium source slurry until the reaction is complete to obtain lithium phosphate slurry; Step 4: Add the iron source to the lithium phosphate slurry obtained in step 3 under a nitrogen atmosphere for pre-reaction for 3-9 hours to obtain the hydrothermal precursor slurry; Step 5: Transfer the hydrothermal precursor slurry to a hydrothermal reactor for hydrothermal reaction to obtain lithium iron phosphate slurry. The hydrothermal reaction temperature is 150-210℃ and the holding time is 1-12h. Step 6: After the hydrothermal reaction is completed, the lithium iron phosphate slurry is separated, washed, and dried to obtain the nano-sheet lithium iron phosphate particles.
[0009] Furthermore, step 6 also includes a process of carbon coating the hydrothermally reacted lithium iron phosphate slurry. Carbon coating of lithium iron phosphate can further improve its electrochemical performance.
[0010] Furthermore, the carbon coating method involves adding 7% glucose by mass of lithium iron phosphate to the lithium iron phosphate slurry, followed by ball milling, spraying, calcination at 700°C under a nitrogen atmosphere, and crushing to obtain carbon-coated nanosheet-like lithium iron phosphate particles.
[0011] Furthermore, the iron source includes ferrous sulfate, ferrous chloride, and ferrous nitrate.
[0012] Furthermore, the phosphorus source includes phosphoric acid, diammonium hydrogen phosphate, and diammonium dihydrogen phosphate.
[0013] This invention prepares nanosheet-like lithium iron phosphate (LFP) particles by controlling the molar ratio of the hydrothermal reaction raw materials and the mass percentage of lithium hydroxide monohydrate in the lithium source slurry. Existing research has verified that when the molar amount of Li is greater than or less than 3%, the pH of the hydrothermal precursor slurry is greater than 6.5 or less than 5.0. At excessively high pH values, the LFP particles synthesized hydrothermally are too fine and contain impurities; at excessively low pH values, the LFP particles synthesized hydrothermally are too large, resulting in excessively long lithium ion transport paths within the particles and significantly reduced charge-discharge performance. When n(Li), n(Fe), n(P) = 3∶1∶1, the pH of the hydrothermal precursor slurry is in the range of 5.0-6.5, and the LFP synthesized under this pH condition consists of pure-phase nanoscale particles.
[0014] The key point of this invention lies in the mass percentage of lithium hydroxide monohydrate in the lithium source slurry. Through research, the inventors discovered that when the mass percentage of lithium hydroxide monohydrate in the lithium source slurry is 30%-35%, a portion of insoluble lithium hydroxide monohydrate exists in the slurry. The lithium phosphate prepared by reacting with the phosphorus source consists of micron-sized bulk particles and nanoparticles. The hydrothermal precursors obtained by pre-reacting the iron source with lithium phosphate of different particle sizes exhibit different morphologies. The hydrothermal precursor prepared with large lithium phosphate particles exhibits a two-dimensional planar morphology, while the precursor prepared entirely with nanoparticles exhibits a three-dimensional morphology. The lithium iron phosphate prepared from the two-dimensional planar precursor exhibits a sheet-like morphology, while the lithium iron phosphate prepared from the three-dimensional precursor exhibits a rod-like morphology. This invention, by controlling the mass percentage of lithium hydroxide monohydrate in the lithium source slurry to 30%-35%, prepares sheet-like lithium iron phosphate.
[0015] Secondly, it is understood that the application of the preparation method of nanosheet lithium iron phosphate particles provided by this invention in the cathode material of lithium iron phosphate batteries should fall within the protection scope of this invention.
[0016] Compared with the prior art, the present invention has the following beneficial effects: The method for preparing nanosheet-shaped lithium iron phosphate particles provided by this invention only requires adjusting the molar ratio of raw materials and the mass percentage of lithium hydroxide monohydrate in the lithium source slurry to obtain a hydrothermal precursor with a two-dimensional planar morphology, thereby preparing nanosheet-shaped lithium iron phosphate particles with a (010) preferred growth crystal plane. These particles have a shorter lithium ion diffusion distance and excellent electrochemical performance. This invention does not introduce additional additives such as morphology guiding agents during the entire reaction process, and there is no large amount of impurity ions introduced to contaminate the product. This invention uses a high-pressure reactor for synthesis, which is simple, cost-controllable, and easy to industrialize.
[0017] In summary, this invention has the advantages of simple equipment, easy operation, controllable cost, environmental friendliness, and ease of industrialization, making it suitable for widespread application. Attached Figure Description
[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.
[0019] Figure 1 This is a process flow diagram for preparing lithium iron phosphate particles in the embodiments and comparative examples of the present invention; Figure 2 The images show SEM images of the lithium phosphate slurry prepared in the embodiments and comparative examples of the present invention (in the images, EHT=1.00kV / WD=5.0mm / Mag=30.00KX / Signal A=SE2 / 300nm). Figure 3 SEM images of the hydrothermal precursor slurries prepared in the embodiments and comparative examples of the present invention (in the figures, EHT=1.00kV / WD=5.0mm / Mag=10.00KX / Signal A=SE2 / 1μm). Figure 4 The images show SEM images of lithium iron phosphate powder prepared in the embodiments and comparative examples of the present invention (in the images, EHT=1.00kV / WD=5.0mm / Mag=30.00KX / Signal A=SE2 / 300nm). Figure 5 The XRD pattern of lithium iron phosphate powder prepared in an embodiment of the present invention; Figure 6 This is a TEM image of the lithium iron phosphate powder prepared in an embodiment of the present invention. Specific implementation methods
[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0021] Example:
[0022] A type of lithium iron phosphate granules, according to Figure 1 The process described is prepared according to the following method.
[0023] The raw materials were industrial-grade lithium hydroxide monohydrate, food-grade 85% phosphoric acid, and ferrous sulfate solution. The raw materials were weighed according to a molar ratio of n(Li):n(Fe):n(P) = 3:1:1.
[0024] Lithium hydroxide monohydrate powder was dissolved in pure water, maintaining the mass percentage of lithium hydroxide monohydrate within the range of 30%-35%. Then, 85% phosphoric acid was added dropwise to the lithium hydroxide solution to complete the preparation of lithium phosphate. The final pH of the lithium phosphate slurry was controlled to 10.5, and its morphology was observed using a scanning electron microscope (SEM). After the lithium phosphate reaction, ferrous sulfate solution was added to the lithium phosphate slurry under a nitrogen atmosphere for pre-reaction to obtain a hydrothermal precursor slurry. The reaction time was 3-9 hours, and the pH of the hydrothermal precursor slurry was controlled within the range of 5.0-6.5. The morphology of the hydrothermal precursor slurry was observed using SEM. After the pre-reaction, the hydrothermal precursor slurry was transferred to a hydrothermal reactor for hydrothermal reaction at a temperature of 150℃-210℃ for 1-12 hours. After the hydrothermal reaction, a portion of the lithium iron phosphate slurry was separated and washed to obtain lithium iron phosphate powder, which was used for SEM morphology observation, TEM structural observation, and XRD analysis. The remaining portion of lithium iron phosphate slurry was mixed with 7% glucose by mass of lithium iron phosphate, and then ball-milled, spray-dried, calcined at 700°C under a nitrogen atmosphere, and crushed to obtain carbon-coated lithium iron phosphate material, which was used to assemble experimental batteries for electrochemical performance testing.
[0025] Comparative Example 1: The same example was used to prepare lithium iron phosphate particles, except that the mass percentage of lithium hydroxide monohydrate was 9%-11%.
[0026] Comparative Example 2: The same example was used to prepare lithium iron phosphate particles, except that the mass percentage of lithium hydroxide monohydrate was 18%-20%.
[0027] The solubility of lithium hydroxide monohydrate at 20°C is 12.8 g / 100 g H2O, corresponding to a mass percentage concentration of 11.3% for a saturated solution. Therefore, in Examples and Comparative Example 2, lithium hydroxide monohydrate cannot be completely dissolved at the corresponding mass percentages, while lithium hydroxide monohydrate in Comparative Example 1 can be completely dissolved at a mass percentage of 9%-11%.
[0028] from Figure 2It is evident that when the mass percentage of lithium hydroxide monohydrate in the lithium source slurry is 30%-35%, the lithium hydroxide monohydrate in the slurry is divided into two parts (undissolved and dissolved). The undissolved lithium hydroxide monohydrate reacts with phosphoric acid to prepare 1μm-sized blocky particles. Therefore, the lithium phosphate slurry obtained in the examples consists of 1μm-sized blocky particles and 60nm-sized small particles. In contrast, in Comparative Example 1, when the mass percentage of lithium hydroxide monohydrate is 9%-11%, the lithium hydroxide monohydrate is completely dissolved, and the lithium source slurry is actually a lithium source solution. The lithium phosphate slurry obtained by reacting with phosphoric acid consists entirely of 60nm-sized small particles, with no large particles present. In Comparative Example 2, the lithium hydroxide monohydrate concentration is 18%-20%. Although there is insoluble lithium hydroxide monohydrate in the slurry, the content is small, and the proportion of 1μm-sized blocky particles in the prepared lithium phosphate slurry is extremely small. Based on the above three lithium phosphate slurries, ferrous sulfate solution is added for pre-reaction, resulting in... Figure 3 As can be seen, the hydrothermal precursor prepared in the examples exhibits a two-dimensional planar morphology, while the precursors prepared in Comparative Examples 1 and 2 have a three-dimensional morphology. The hydrothermal precursor slurry was added to a hydrothermal reactor for reaction, yielding two lithium iron phosphate products with significantly different morphologies. See [link to relevant documentation]. Figure 4 As shown, lithium iron phosphate prepared from a two-dimensional planar precursor exhibits a sheet-like morphology, while lithium iron phosphate prepared from a three-dimensional precursor exhibits a rod-like morphology. Figure 5 XRD analysis of the test sample (lithium iron phosphate powder from the example) was compared with the ICDD standard database. It was found that it highly matched the standard card numbered 83-2092. This card corresponds to a synthetically produced lithium iron phosphate (LiFePO4) substance with the same crystal structure as the natural Triphylite mineral. Figure 5 XRD analysis results showed that the powder sample of the example was pure phase lithium iron phosphate. Figure 6 TEM data confirmed that the lithium iron phosphate product of the examples had obvious (020) crystal plane exposure. Therefore, the (010) crystal plane of the lamellar lithium iron phosphate prepared in the examples is the preferred growth plane, which shortens the lithium ion transport distance, facilitates rapid lithium ion transport, and enhances the electrochemical performance of the material.
[0029] Table 1 shows the electrochemical performance data of lithium iron phosphate materials with different morphologies prepared in Examples 1 and 2.
[0030] Table 1. Performance Comparison of Lithium Iron Phosphate Batteries
[0031] As can be seen from Table 1 above, thanks to the (020) preferred growth crystal face, the capacity of the sheet-like lithium iron phosphate in the examples is higher than that of the bar-like lithium iron phosphate in Comparative Examples 1 and 2 at different rates.
[0032] In summary, the method for preparing nanosheet-shaped lithium iron phosphate particles provided by the present invention only requires adjusting the molar ratio of raw materials and the mass percentage of lithium hydroxide monohydrate in the lithium source slurry to obtain a hydrothermal precursor with a two-dimensional planar morphology, and to prepare nanosheet-shaped lithium iron phosphate particles with a (010) preferred growth crystal plane. These particles have a shorter lithium ion diffusion distance and better electrochemical performance.
[0033] The above are merely preferred embodiments of the present invention. It should be noted that the above preferred embodiments should not be considered as limitations on the present invention, and the scope of protection of the present invention should be determined by the scope defined in the claims. For those skilled in the art, any improvements and modifications made to the technical solutions of the present invention without departing from the spirit and scope of the present invention should be considered within the scope of protection of the present invention.
Claims
1. A method for preparing nanosheet-like lithium iron phosphate particles, characterized in that: Includes the following steps: Step 1: Weigh the lithium source, iron source, and phosphorus source for the hydrothermal preparation of lithium iron phosphate according to the molar ratio of Li:Fe:P = 3:1:1; the lithium source is selected from lithium hydroxide monohydrate. Step 2: Add lithium hydroxide monohydrate to pure water and mix evenly to obtain lithium source slurry, controlling the mass percentage of lithium hydroxide monohydrate in the lithium source slurry to be 30%-35%; Step 3: Add the phosphorus source to the lithium source slurry until the reaction is complete to obtain lithium phosphate slurry; Step 4: Add the iron source to the lithium phosphate slurry obtained in step 3 under a nitrogen atmosphere for pre-reaction for 3-9 hours to obtain the hydrothermal precursor slurry; Step 5: Transfer the hydrothermal precursor slurry to a hydrothermal reactor for hydrothermal reaction to obtain lithium iron phosphate slurry. The hydrothermal reaction temperature is 150-210℃ and the holding time is 1-12h. Step 6: After the hydrothermal reaction is completed, the lithium iron phosphate slurry is separated, washed, and dried to obtain the nano-sheet lithium iron phosphate particles.
2. The preparation method according to claim 1, characterized in that: Step 6 also includes a process of carbon coating the hydrothermally reacted lithium iron phosphate slurry.
3. The preparation method according to claim 2, characterized in that: The carbon coating method involves adding 7% glucose (by mass fraction of lithium iron phosphate) to the lithium iron phosphate slurry, followed by ball milling, spraying, calcination at 700°C under a nitrogen atmosphere, and crushing to obtain carbon-coated nanosheet-like lithium iron phosphate particles.
4. The preparation method according to claim 1, characterized in that: The iron source includes ferrous sulfate, ferrous chloride, and ferrous nitrate.
5. The preparation method according to claim 1, characterized in that: The phosphorus source includes phosphoric acid, diammonium hydrogen phosphate, and ammonium dihydrogen phosphate.
6. The application of the preparation method according to any one of claims 1 to 5 in the cathode material of lithium iron phosphate batteries.