Preparation method of nitrogen-boron-doped high-compaction lithium iron phosphate positive electrode material
By constructing a gradient carbon framework structure through nitrogen-boron doping, the problems of insufficient compaction density and conductivity of lithium iron phosphate cathode materials in the prior art are solved, and high compaction density and efficient electron conduction of the material are achieved.
Patent Information
- Application Number
- CN202511305510.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-09-12
- Publication Date
- 2025-12-16
AI Technical Summary
In existing technologies, the double sintering process is difficult to improve the compaction density, rate performance and conductivity of lithium iron phosphate cathode materials at the same time. Traditional carbon source doping methods result in incomplete conductive networks, low crystal structure stability and low electronic conduction efficiency.
By employing nitrogen-boron doping, lithium, iron, phosphorus, carbon, and nitrogen sources are mixed through ultrasonic dispersion and ball milling to form a CN bond structure. In the secondary sintering process, a boron source is introduced to form BC bonds, thereby constructing a gradient carbon skeleton with an outer boron-rich outer layer and an inner nitrogen-rich inner layer, thus optimizing the particle morphology and electronic conduction pathway.
It significantly improves the compaction density and electronic conductivity of the material, enhances the charge/discharge specific capacity, first-efficiency performance, and rate capability, and ensures the structural stability and lithium-ion transport kinetics of lithium iron phosphate.
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Figure CN121134718A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The application relates to the technical field of preparation of lithium ion battery positive electrode materials, in particular to a preparation method of nitrogen-boron-doped high-compaction lithium iron phosphate positive electrode material. BACKGROUND
[0002] As a lithium ion battery positive electrode material, lithium iron phosphate is widely used in the field of power batteries due to its high safety, long cycle life and low cost, and with the continuous improvement of battery performance requirements, high-performance lithium iron phosphate batteries have higher standards for the compaction density of positive electrode materials, and the high compaction density directly affects the volume energy density of the battery.
[0003] At present, the mainstream process for producing high-compaction lithium iron phosphate is a secondary sintering process. The process is to optimize the microstructure of the material by adopting two sintering steps at different temperatures or in different atmospheres during preparation, promote grain growth and densification, and thus improve the crystallinity, density and compaction density of the material, and improve its electrochemical performance. However, the secondary sintering process has significant technical challenges in practical application:
[0004] On the one hand, in order to achieve particle densification, high-temperature sintering needs to be controlled, but small particles are prone to excessive adhesion to form large particles at high temperatures, resulting in a longer ion diffusion path and reducing the rate performance of the material;
[0005] On the other hand, if the temperature is too low, the densification effect cannot be achieved, so there are still challenges to achieve high compaction density requirements;
[0006] Therefore, the traditional secondary sintering process needs to further optimize and improve the capacity, rate performance and particle densification degree of lithium iron phosphate, in addition, simply relying on the temperature and atmosphere adjustment of secondary sintering cannot fundamentally improve the conductivity and ion transport dynamics of the material.
[0007] In the traditional process, the single addition of carbon source easily leads to an incomplete conductive network, and the material without effective doping modification has low crystal structure stability and electronic conduction efficiency, which further restricts the synergistic improvement of compaction density and electrochemical performance. Therefore, it has become a research hotspot and urgent need in the current field to develop a lithium iron phosphate preparation method that can combine process optimization and doping modification to simultaneously improve the capacity, rate performance and structural stability of the material while ensuring high compaction density. SUMMARY
[0008] The purpose of the present application is to provide a preparation method of nitrogen-boron-doped high-compaction lithium iron phosphate positive electrode material, which solves the technical problem of further improving the compaction density and electronic conduction efficiency of the lithium iron phosphate positive electrode material in the prior art.
[0009] The objective of this invention can be achieved through the following technical solution: a method for preparing a nitrogen-boron-doped high-pressure lithium iron phosphate cathode material, comprising the following steps:
[0010] S1. Add lithium source, iron source, phosphorus source, carbon source and nitrogen source to deionized water, ultrasonically disperse at 20-30℃ for 30-50 min, then transfer to ball mill for ball milling. After ball milling to the first predetermined particle size, transfer to spray dryer for spray drying, and then transfer the spray-dried product to tube furnace for pre-sintering under inert atmosphere to obtain nitrogen-doped pre-sintered material.
[0011] Reaction principle:
[0012] Ultrasonic dispersion and ball milling enable the carbon and nitrogen sources to be uniformly embedded in the interparticle gaps. During the pre-sintering stage in an inert atmosphere, the carbon source pyrolyzes to generate an amorphous carbon network, and the nitrogen source decomposes to generate N-containing active species. These N-containing active species react chemically with the unsaturated carbon atoms in the carbon network through diffusion, replacing some C atom positions to form CN covalent bonds. At the same time, high temperature promotes the initial formation of the lithium iron phosphate crystal phase, and the carbon-nitrogen complex grows directionally at the grain boundaries to obtain nitrogen-doped pre-sintered material.
[0013] S2. Add the nitrogen-doped pre-burned material, carbon source, and boron source to deionized water, ultrasonically disperse for 20-40 minutes, and then transfer it to a ball mill for ball milling. After ball milling to the second predetermined particle size, transfer it to a spray dryer for spray drying. Then transfer the spray-dried product to a tube furnace and sinter it under an inert atmosphere to obtain nitrogen- and boron-doped high-pressure lithium iron phosphate cathode material.
[0014] Reaction principle:
[0015] After ultrasonic dispersion, the boron and carbon sources are preferentially adsorbed on the particle surface, while the nitrogen-doped carbon layer is retained inside. During sintering, the boron source decomposes to generate intermediates such as B2O3, which react with the pyrolysis products of the outer carbon source to form BC bonds. Nitrogen is difficult to diffuse outward due to its high-temperature stability, ultimately forming a gradient structure with a boron-rich outer layer and a nitrogen-rich inner layer.
[0016] Furthermore, in step S1, the lithium source is lithium carbonate; the iron and phosphorus sources are iron phosphate; the carbon source is at least one of glucose, sucrose, fructose, and polyethylene glycol; and the nitrogen source is at least one of melamine, urea, polyaniline, and polyvinylpyrrolidone.
[0017] Furthermore, in step S1, the ratio of the amount of lithium source, iron source, phosphorus source, carbon source, nitrogen source and deionized water is 3.7-4.0g:15.2g:0.9-1.1g:0.05-0.12g:60mL.
[0018] Furthermore, in step S1, the first predetermined particle size is 0.35-0.5μm, the pre-sintering temperature is 500-700℃, and the sintering time is 3-5h.
[0019] Furthermore, in step S2, the boron source is boric acid, and the carbon source is at least one of glucose, sucrose, fructose, and polyethylene glycol.
[0020] Furthermore, in step S2, the ratio of the nitrogen-doped pre-calcined material, carbon source, boron source, and deionized water is 100g:3-4g:0.2-0.6g:300mL.
[0021] Furthermore, in step S2, the second predetermined particle size is 0.5-0.8 μm, the sintering temperature is 800-900℃, and the sintering time is 8-10 h.
[0022] The present invention has the following beneficial effects:
[0023] 1. In this invention, the addition of nitrogen and boron significantly improves the compaction density of the material. Nitrogen doping stabilizes the crystal structure of lithium iron phosphate by forming CN bonds with the carbon network during the pre-sintering stage, reducing defects and pores inside the crystal. Boron doping reacts with the outer carbon source during the secondary sintering to form BC bonds, optimizing the morphology and particle size distribution of the particles and promoting close packing between particles. The synergistic effect of the two makes the material particles more compact, effectively improving the packing efficiency of the material and greatly increasing the compaction density of the material.
[0024] 2. In this invention, carbon sources are supplemented in two separate sintering processes. By introducing carbon sources step by step, a more complete conductive carbon chain skeleton network is constructed, which broadens the electron conduction path between particles and significantly improves the electron conduction efficiency. At the same time, the coating layer formed by the carbon source at high temperature can effectively inhibit excessive grain growth and overheating of the material during high-temperature calcination, reduce structural collapse and increased porosity caused by overheating, and ensure the stability of the lithium iron phosphate olivine structure.
[0025] 3. In the first sintering stage, nitrogen doping is introduced. The nitrogen-containing active species generated by the decomposition of the nitrogen source combine with the carbon network to form a stable CN bond structure, providing more channels for lithium-ion transport and significantly improving the lithium-ion transport kinetics. In the second sintering stage, boron doping is introduced. The decomposition products of the boron source promote interparticle melting, ultimately forming a composite carbon framework structure with a gradient distribution of "boron doping on the outside and nitrogen doping on the inside". Nitrogen and boron work synergistically to build efficient electron transport channels in the conductive carbon network, greatly improving the electrochemical performance of the material, such as charge / discharge specific capacity, first-efficiency performance, and rate performance. Attached Figure Description
[0026] 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 or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0027] Figure 1 This is a SEM image of the lithium iron phosphate cathode material prepared in Example 3 of the present invention;
[0028] Figure 2 The charge-discharge curves of the lithium iron phosphate cathode material prepared in Example 3 of this invention are shown. Detailed Implementation
[0029] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. 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.
[0030] In this invention, polyethylene glycol is selected from Nanjing Zhiyuan International Trade Co., Ltd., with CAS number 25322-68-3, an effective ingredient content of 99%, and a model of PEG200;
[0031] In this invention, the melamine is selected from Wuhan Bontesway Chemical Products Co., Ltd., CAS No. 108-78-1, and the content of active ingredient is 99.5%;
[0032] In this invention, polyaniline is selected from Wuhan Shuer Biotechnology Co., Ltd., with CAS number 5612-44-2 and model number shuer632;
[0033] In this invention, polyvinylpyrrolidone is selected from Shandong Xindongneng Chemical Co., Ltd., with CAS number 9003-39-8 and an effective ingredient content of 99%;
[0034] Example 1
[0035] This embodiment provides a method for preparing a nitrogen-boron-doped high-pressure lithium iron phosphate cathode material, including the following steps:
[0036] S1. Preparation of nitrogen-doped pre-calcined material
[0037] Weigh out 3.7g lithium carbonate, 15.2g ferric phosphate, 0.9g glucose and 0.05g melamine and add them to 60mL deionized water. Disperse the mixture ultrasonically at 20℃ for 30min, then transfer it to a ball mill and ball mill at 200rpm. When the particle size is 0.35μm, transfer it to a spray dryer for spray drying. Then transfer the spray-dried product to a tube furnace and pre-sinter it at 500℃ under an inert atmosphere for 3h to obtain nitrogen-doped pre-sintered material.
[0038] S2. Preparation of nitrogen- and boron-doped high-pressure lithium iron phosphate cathode materials
[0039] Weigh out 100g of nitrogen-doped pre-calcined material, 3g of glucose and 0.2g of boric acid and add them to 300mL of deionized water. Disperse the mixture ultrasonically for 20min, then transfer it to a ball mill for ball milling at 180rpm. When the particle size is 0.5μm, transfer it to a spray dryer for spray drying. Then transfer the spray-dried product to a tube furnace and pre-sinter it at 800℃ in an inert atmosphere for 8h to obtain nitrogen-boron-doped high-pressure lithium iron phosphate cathode material.
[0040] Example 2
[0041] This embodiment provides a method for preparing a nitrogen-boron-doped high-pressure lithium iron phosphate cathode material, including the following steps:
[0042] S1. Preparation of nitrogen-doped pre-calcined material
[0043] Weigh out 3.8g lithium carbonate, 15.2g ferric phosphate, 1g sucrose and 0.08g polyaniline and add them to 60mL deionized water. Disperse the mixture ultrasonically at 30℃ for 40min, then transfer it to a ball mill and ball mill at 200rpm. When the particle size is 0.45μm, transfer it to a spray dryer for spray drying. Then transfer the spray-dried product to a tube furnace and pre-sinter it at 600℃ under an inert atmosphere for 4h to obtain nitrogen-doped pre-sintered material.
[0044] S2. Preparation of nitrogen- and boron-doped high-pressure lithium iron phosphate cathode materials
[0045] Weigh out 100g of nitrogen-doped pre-calcined material, 3.5g of polyethylene glycol, and 0.4g of boric acid and add them to 300mL of deionized water. Disperse the mixture ultrasonically for 30min, then transfer it to a ball mill for ball milling at 180rpm. When the particle size is 0.65μm, transfer it to a spray dryer for spray drying. Then transfer the spray-dried product to a tube furnace and pre-sinter it at 850℃ in an inert atmosphere for 9h to obtain nitrogen-boron-doped high-pressure lithium iron phosphate cathode material.
[0046] Example 3
[0047] This embodiment provides a method for preparing a nitrogen-boron-doped high-pressure lithium iron phosphate cathode material, including the following steps:
[0048] S1. Preparation of nitrogen-doped pre-calcined material
[0049] Weigh out 4.0g lithium carbonate, 15.2g ferric phosphate, 1.1g fructose and 0.12g polyvinylpyrrolidone and add them to 60mL deionized water. Disperse the mixture ultrasonically at 30℃ for 50min, then transfer it to a ball mill and ball mill at 200rpm. When the particle size is 0.5μm, transfer it to a spray dryer for spray drying. Then transfer the spray-dried product to a tube furnace and pre-sinter it at 00℃ under an inert atmosphere for 5h to obtain nitrogen-doped pre-sintered material.
[0050] S2. Preparation of nitrogen- and boron-doped high-pressure lithium iron phosphate cathode materials
[0051] Weigh out 100g of nitrogen-doped pre-calcined material, 4g of fructose, and 0.6g of boric acid and add them to 300mL of deionized water. Disperse the mixture ultrasonically for 40min, then transfer it to a ball mill for ball milling at 180rpm. When the particle size is 0.8μm, transfer it to a spray dryer for spray drying. Then transfer the spray-dried product to a tube furnace and pre-sinter it at 900℃ in an inert atmosphere for 10h to obtain nitrogen-boron-doped high-pressure lithium iron phosphate cathode material.
[0052] Comparative Example 1
[0053] The difference between this comparative example and Example 3 is that the nitrogen source was removed in S1.
[0054] Comparative Example 2
[0055] The difference between this comparative example and Example 3 is that the boron source was omitted in S2.
[0056] Comparative Example 3
[0057] The difference between this comparative example and Example 3 is that the addition of a nitrogen source in S1 is omitted, and the addition of a boron source in S2 is also omitted.
[0058] Performance testing:
[0059] Lithium iron phosphate, PVDF, and conductive carbon black were mixed in a mass ratio of 8:1:1. The mixture was coated onto aluminum foil, dried, and then pressed to form an electrode sheet. A lithium metal foil was used as the negative electrode, a polypropylene membrane as the separator, and 1M LiPF6 / (PC+DMC) = 1:1 was used as the electrolyte to assemble a battery for charge-discharge testing. The voltage range was 2.5-3.9V. Specific data are shown in the table below.
[0060]
[0061] Data Analysis:
[0062] Comparative analysis of the data in Table 1 above shows that in the preparation method of the nitrogen-boron-doped high-pressure lithium iron phosphate cathode material of the present invention, nitrogen and boron doping are introduced during the preparation process. Nitrogen doping stabilizes the crystal structure and reduces crystal defects by forming CN bonds with the carbon network during the pre-sintering stage, while boron doping optimizes the particle morphology and packing by forming BC bonds with the outer carbon source during secondary sintering. The two work synergistically, resulting in a powder compaction density of 2.612-2.650 g / cm³ in Examples 1-3. 3 Significantly higher than the 2.324 g / cm³ of the undoped nitrogen-boron comparative example 3. 3 It is also higher than the 2.455 g / cm³ of Comparative Example 1, which is doped with only nitrogen or boron. 3 Compared with Comparative Example 2, 2.403 g / cm³ 3 This fully demonstrates that nitrogen-boron synergistic doping can significantly improve the compaction density of materials;
[0063] Because the present invention supplements the carbon source in two sintering processes, it constructs a more complete conductive carbon chain framework network step by step. At the same time, the carbon source coating layer inhibits excessive grain growth and overburning, ensuring structural stability. Therefore, the 0.1C charging specific capacity of Examples 1-3 (160.34-161.54 mAh / g) and the discharge specific capacity (157.04-159.20 mAh / g) are higher than those of Comparative Examples 1-3, and the first-time efficiency (97.92-98.55%) is even better, demonstrating the role of a complete conductive network and stable structure in improving capacity and first-time efficiency.
[0064] Because the first sintering of this invention introduces nitrogen doping to form stable CN bonds and improve lithium-ion transport kinetics, and the second sintering introduces boron doping to form a gradient carbon framework of "boron doping on the outside and nitrogen doping on the inside" to construct an efficient electron transport channel, the nitrogen and boron synergistically optimize the ion and electron transport performance. Therefore, the 1C discharge specific capacity of Examples 1-3 (138.76-141.41 mAh / g) is higher than that of Comparative Examples 1-3. Among them, the 141.41 mAh / g of Example 3 is significantly higher than that of Comparative Example 3 (136.01 mAh / g), indicating that the synergistic effect of nitrogen and boron can effectively improve the rate performance of the material.
[0065] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to specific implementations. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.
Claims
1. A method for preparing a nitrogen-boron-doped high-pressure lithium iron phosphate cathode material, characterized in that, Includes the following steps: S1. Add lithium source, iron source, phosphorus source, carbon source and nitrogen source to deionized water, ultrasonically disperse at 20-30℃ for 30-50 min, then transfer to ball mill for ball milling. After ball milling to the first predetermined particle size, transfer to spray dryer for spray drying, and then transfer the spray-dried product to tube furnace for pre-sintering under inert atmosphere to obtain nitrogen-doped pre-sintered material. S2. Add the nitrogen-doped pre-burned material, carbon source, and boron source to deionized water, ultrasonically disperse for 20-40 minutes, and then transfer it to a ball mill for ball milling. After ball milling to the second predetermined particle size, transfer it to a spray dryer for spray drying. Then transfer the spray-dried product to a tube furnace and sinter it under an inert atmosphere to obtain nitrogen- and boron-doped high-pressure lithium iron phosphate cathode material.
2. The method for preparing a nitrogen-boron-doped high-pressure lithium iron phosphate cathode material according to claim 1, characterized in that, In step S1, the lithium source is lithium carbonate; the iron and phosphorus sources are iron phosphate; the carbon source is at least one of glucose, sucrose, fructose, and polyethylene glycol; and the nitrogen source is at least one of melamine, urea, polyaniline, and polyvinylpyrrolidone.
3. The method for preparing a nitrogen-boron-doped high-pressure lithium iron phosphate cathode material according to claim 1, characterized in that, In step S1, the ratio of lithium source, iron source, phosphorus source, carbon source, nitrogen source and deionized water is 3.7-4.0g:15.2g:0.9-1.1g:0.05-0.12g:60mL.
4. The method for preparing a nitrogen-boron-doped high-pressure lithium iron phosphate cathode material according to claim 1, characterized in that, In step S1, the ball milling speed is 200 rpm, the first predetermined particle size is 0.35-0.5 μm, the pre-sintering temperature is 500-700℃, and the sintering time is 3-5 h.
5. The method for preparing a nitrogen-boron-doped high-pressure lithium iron phosphate cathode material according to claim 1, characterized in that, In step S2, the boron source is boric acid, and the carbon source is at least one of glucose, sucrose, fructose, and polyethylene glycol.
6. The method for preparing a nitrogen-boron-doped high-pressure lithium iron phosphate cathode material according to claim 1, characterized in that, In step S2, the ratio of the nitrogen-doped pre-burned material, carbon source, boron source and deionized water is 100g:3-4g:0.2-0.6g:300mL.
7. The method for preparing a nitrogen-boron-doped high-pressure lithium iron phosphate cathode material according to claim 1, characterized in that, In step S2, the ball milling speed is 180 rpm, the second predetermined particle size is 0.5-0.8 μm, the sintering temperature is 800-900℃, and the sintering time is 8-10 h.