Processing method of high-conductivity ultra-thin carbon layer high-compacted lithium iron phosphate
By constructing lithium iron phosphate materials with ultrathin carbon layers and Ti-N doped structures, the problems of low compaction density and difficulty in achieving both conductivity caused by excessive carbon coating were solved, resulting in high compaction density and excellent electrochemical performance, while reducing energy consumption and production cycle.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- YUNNAN YINGHE NEW ENERGY MATERIALS CO LTD
- Filing Date
- 2026-01-29
- Publication Date
- 2026-05-26
AI Technical Summary
Existing lithium iron phosphate materials have low compaction density due to excessive carbon coating, and it is difficult to balance conductivity and compaction density. Traditional production processes are energy-intensive, have long cycles, and require strict control of sintering temperature and atmosphere.
Porous carbon sources were prepared by wet ball milling and combined with an in-situ doping system. By constructing an ultrathin carbon layer and a Ti-N doped structure, a conductive framework rich in mesopores was formed, which shortened the lithium-ion diffusion path and optimized the crystal structure.
It achieves high compaction density and excellent electrochemical performance with low carbon content, reduces energy consumption and production costs, shortens the production cycle, and maintains high conductivity.
Smart Images
Figure CN122079102A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of lithium-ion battery material preparation technology, specifically relating to a high-conductivity ultrathin carbon layer high-pressure lithium iron phosphate processing method. Background Technology
[0002] Lithium iron phosphate (LiFePO4, LFP) has become one of the mainstream cathode materials in the lithium-ion battery market due to its excellent thermal stability, safety, long cycle life, and wide availability of raw materials. Currently, the main production process for high-impact-density lithium iron phosphate is the "iron phosphate method," which involves solid-state sintering using iron phosphate, lithium source, and carbon source as the main raw materials.
[0003] However, lithium iron phosphate materials have inherent defects such as low electronic conductivity and small lithium-ion diffusion coefficient. To overcome this problem, the industry usually adopts a carbon coating strategy to construct a conductive network. Existing mainstream processes usually require the addition of 1.3%-1.5% organic carbon source by mass to meet the industry's requirements for conductivity.
[0004] However, this high-carbon-content coating strategy has drawbacks: due to the low true density of amorphous carbon materials and their extremely low compaction density (1.8 g / cm³),... 3 -2.0g / cm 3 Excessive carbon layers coating the surface of lithium iron phosphate particles can form a "cushion"-like coating, reducing the compaction density of the material. In addition, the traditional iron phosphate method for producing high-compact materials uses a two-sintering process, which has high energy consumption, a long production cycle, and strict requirements for sintering temperature and atmosphere control.
[0005] Therefore, developing a lithium iron phosphate processing method that can significantly reduce carbon content while maintaining high conductivity, thereby achieving high solid density, is a technical challenge that the industry urgently needs to solve. Summary of the Invention
[0006] To overcome the problems in the background technology, this invention develops a high-conductivity ultrathin carbon layer high-compact lithium iron phosphate processing method, which solves the technical problems of low compaction density caused by excessive carbon coating in existing lithium iron phosphate cathode materials, and the difficulty in balancing conductivity and compaction density. By constructing a special pore structure and in-situ doping system, excellent electrochemical performance is achieved at extremely low carbon content.
[0007] To achieve the above objectives, the present invention is implemented through the following technical solution: A method for processing high-conductivity, ultrathin carbon layer, high-pressure lithium iron phosphate includes the following steps: S1. Asphalt, phenolic resin and sodium chloride are mixed in ethanol by wet ball milling, and then carbonized at 750°C. The product is washed with water to remove sodium chloride and dried to obtain the first carbon source. S2. Mix iron phosphate, lithium source, phosphorus source, second carbon source and dispersant to obtain a first iron-containing precursor mixture, wherein the second carbon source includes at least titanium citrate, and the iron-to-phosphorus ratio of the iron phosphate raw material is 0.965 and the D50 is 1.0-5.0µm. S3. The pH value of the first iron-containing precursor mixture prepared in S2 is adjusted to a preset alkaline pH value using an alkaline solution to obtain the second iron-containing precursor mixture, wherein the preset alkaline pH value is 8-10. S4. The second iron-containing precursor mixture prepared in S3 is added to the first carbon source prepared in S1 for grinding and drying to obtain an iron-containing precursor mixture, wherein the particle size of the iron-containing precursor mixture is 0.4µm≤D50≤1.5µm. S5. The iron-containing precursor prepared in S4 is sintered and pulverized in an inert gas atmosphere to obtain lithium iron phosphate cathode material.
[0008] Furthermore, in step S1, the mass ratio of asphalt, phenolic resin, and sodium chloride is 1:2:3, and the mixing time is 12 hours.
[0009] Furthermore, the second carbon source added in step S2 also includes 0.1% (by mass) of iron phthalocyanine iron phosphate. As a highly conductive carbon source, its central Fe²⁺ / Fe³⁺ redox pair is electrochemically active and can act as an "electron transfer station," promoting charge transfer reactions during charging and discharging. More importantly, it may catalyze the redox reaction on the lithium iron phosphate surface, lowering the energy barrier for lithium ion extraction / intercalation, thereby accelerating the diffusion of lithium ions at the solid-liquid interface and within the solid phase.
[0010] Further, in step S2, the mass ratio of the second carbon source to the iron phosphate mixture is (0.002-0.05):1.
[0011] Further, in step S2, the amount of dispersant added is 0.5%-2.0% of the total weight of ferric phosphate, and the dispersant is selected from at least one of polyethylene glycol, citric acid, succinic acid, tripropyl phosphate, dibutyl phosphate, polyamide silicone oil, methylcyclosiloxane, sodium dodecylbenzenesulfonate, and sodium octylbenzenesulfonate.
[0012] Furthermore, in step S4, the mass ratio of the first carbon source to the second precursor mixture is 0.01:1.
[0013] Furthermore, in step S5, the sintering includes a first sintering stage and a second sintering stage: First sintering stage: Heat to 500℃ at 2℃ / min and hold for 2h to ensure perfect carbonization of the carbon layer. Heat to 800℃ at a rate of 5℃ / min and hold for 6h to form the main crystalline phase. Second sintering stage: carbon layer annealing and lattice repair are carried out at a temperature of 650℃ for 3 hours, followed by furnace cooling.
[0014] A lithium iron phosphate cathode material prepared by a high-conductivity ultrathin carbon layer high-pressure lithium iron phosphate processing method is disclosed. The material has a porous conductive framework formed by pore formation using sodium chloride template, as well as lattice titanium doping achieved by pH-controlled release of titanium citrate and nitrogen doping structure achieved by resin and pitch carbonization.
[0015] The beneficial effects of this invention are: 1. This invention constructs an ultrathin carbon layer by significantly reducing the amount of carbon source added, effectively avoiding the cushioning effect caused by thick carbon layers, thereby improving the compaction density of the material. Despite the ultrathin carbon layer, this invention ensures excellent conductivity through a dual carbon source + dual doping strategy: the first carbon source uses NaCl template to create pores, forming a three-dimensional conductive framework rich in mesopores, which shortens the solid-phase diffusion path of lithium ions. Nitrogen (N) doping is introduced by using phenolic resin / asphalt, and titanium (Ti) doping is introduced by using pH-controlled excited titanium citrate. The Ti-N dual doping produces a synergistic effect, which not only improves the intrinsic electronic conductivity of LFP, but also optimizes the crystal structure and broadens the ion channels.
[0016] 2. Compared with the traditional two-sintering process, the low-carbon content formula of this invention makes it possible to use one-sintering, thereby reducing energy consumption and production costs and shortening the production cycle. Attached Figure Description
[0017] To clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments are explained.
[0018] Figure 1 This is a transmission electron microscope (TEM) image (10 nm) of the lithium iron phosphate carbon coating layer in Example 1 of the present invention. Figure 2 This is a transmission electron microscope (TEM) image (10 nm) of the carbon coating layer of lithium iron phosphate in Example 2 of the present invention. Figure 3 This is a transmission electron microscope (TEM) image (10 nm) of the lithium iron phosphate carbon coating layer in Example 3 of the present invention. Figure 4 This is a transmission electron microscope (TEM) image (10 nm) of the lithium iron phosphate carbon coating layer of Comparative Example 3 of the present invention. Detailed Implementation
[0019] To make the objectives, technical solutions, and beneficial effects of the present invention clearer, the preferred embodiments of the present invention will be described in detail below to facilitate understanding by those skilled in the art.
[0020] I. Implementation Examples Example 1 S1, Preparation of porous first carbon source Weigh the asphalt, phenolic resin, and sodium chloride (NaCl) according to a mass ratio of 1:2:3. Add the above raw materials to an appropriate amount of ethanol solvent, place them in a ball mill jar and wet ball mill for 12 hours at a speed of 300 rpm to make the materials evenly mixed; The mixed slurry was dried to remove the solvent and placed in a tube furnace. Under nitrogen protection, the temperature was increased to 750°C at 5°C / min and held for 4 hours for carbonization. After cooling to room temperature, the carbonized product was dispersed in deionized water and washed repeatedly until no chloride ions were detected in the filtrate or the filtrate was neutral. The filter cake was then vacuum dried to obtain the first carbon source. S2, precursor mixture Iron phosphate with an iron-to-phosphorus ratio of 0.965 and a D50 of 2.0 µm was selected; Lithium carbonate was selected as the lithium source. Phosphoric acid was selected as the phosphorus source; Titanium citrate was selected, and 0.1% by mass of iron phthalocyanine phosphate was added as a second carbon source; Polyethylene glycol was selected as the dispersant, and the amount of dispersant added was 0.8% of the total weight of ferric phosphate. The mass ratio of the second carbon source to the iron phosphate mixture is 0.01:1; Iron phosphate, lithium source, phosphorus source, second carbon source and dispersant are mixed to obtain the first iron-containing precursor mixture; S3, pH adjustment The pH of the first iron-containing precursor mixture prepared by S2 was adjusted. During the stirring process, ammonia or lithium hydroxide solution was added dropwise to adjust the pH of the slurry to 9 to obtain the second iron-containing precursor mixture. At this time, the alkaline environment caused the titanium citrate chelate structure to dissociate, and the released titanium species were uniformly adsorbed on the surface of the iron phosphate particles. S4, Preparation of iron-containing precursor mixture The second iron-containing precursor mixture prepared in S3 was added to the first carbon source prepared in S1 and ground. The mass ratio of the first carbon source to the second iron-containing precursor mixture was 0.01:1. The D50 of the solid particles in the slurry was controlled to be 1.0 µm to obtain the iron-containing precursor mixture. The precursor powder was obtained by granulation and drying using a spray drying tower. S5, Sintering The precursor is placed in a roller kiln, protected with nitrogen, and sintered using a segmented sintering process. First sintering stage: Heat to 500℃ at 2℃ / min and hold for 2h to ensure perfect carbonization of the carbon layer. Heat to 800℃ at a rate of 5℃ / min and hold for 6h to form the main crystalline phase. Second sintering stage: carbon layer annealing and lattice repair are carried out at a temperature of 650℃ for 3 hours, followed by furnace cooling.
[0021] Finished product: LFP material is obtained after air jet pulverization, demagnetization, and sieving.
[0022] Example 2 S1, Preparation of porous first carbon source Weigh the asphalt, phenolic resin, and sodium chloride (NaCl) according to a mass ratio of 1:2:3. Add the above raw materials to an appropriate amount of ethanol solvent, place them in a ball mill jar and wet ball mill for 12 hours at a speed of 300 rpm to make the materials evenly mixed; The mixed slurry was dried to remove the solvent and placed in a tube furnace. Under nitrogen protection, the temperature was increased to 750°C at 5°C / min and held for 4 hours for carbonization. After cooling to room temperature, the carbonized product was dispersed in deionized water and washed repeatedly until no chloride ions were detected in the filtrate or the filtrate was neutral. The filter cake was then vacuum dried to obtain the first carbon source. S2, precursor mixture Iron phosphate with an iron-to-phosphorus ratio of 0.965 and a D50 of 1.0µm was selected; Lithium carbonate was selected as the lithium source. Phosphoric acid was selected as the phosphorus source; Titanium citrate was selected, and 0.1% by mass of iron phthalocyanine phosphate was added as a second carbon source; PEG was selected as the dispersant, and the amount of dispersant added was 0.5% of the total weight of ferric phosphate. The mass ratio of the second carbon source to the iron phosphate mixture is 0.002:1; Iron phosphate, lithium source, phosphorus source, second carbon source and dispersant are mixed to obtain the first iron-containing precursor mixture; S3, pH adjustment The pH of the first iron-containing precursor mixture prepared by S2 was adjusted. During the stirring process, ammonia or lithium hydroxide solution was added dropwise to adjust the pH of the slurry to 8 to obtain the second iron-containing precursor mixture. At this time, the alkaline environment caused the titanium citrate chelate structure to dissociate, and the released titanium species were uniformly adsorbed on the surface of the iron phosphate particles. S4, Preparation of iron-containing precursor mixture The second iron-containing precursor mixture prepared in S3 was added to the first carbon source prepared in S1 and ground. The mass ratio of the first carbon source to the second iron-containing precursor mixture was 0.01:1. The D50 of the solid particles in the slurry was controlled to be 0.4µm to obtain the iron-containing precursor mixture. The precursor powder was obtained by granulation and drying using a spray drying tower. S5, Sintering The precursor is placed in a roller kiln, protected with nitrogen, and sintered using a segmented sintering process. First sintering stage: Heat to 500℃ at 2℃ / min and hold for 2h to ensure perfect carbonization of the carbon layer. Heat to 800℃ at a rate of 5℃ / min and hold for 6h to form the main crystalline phase. Second sintering stage: carbon layer annealing and lattice repair are carried out at a temperature of 650℃ for 3 hours, followed by furnace cooling.
[0023] Finished product: LFP material is obtained after air jet pulverization, demagnetization, and sieving.
[0024] Example 3 S1, Preparation of porous first carbon source Weigh the asphalt, phenolic resin, and sodium chloride (NaCl) according to a mass ratio of 1:2:3. Add the above raw materials to an appropriate amount of ethanol solvent, place them in a ball mill jar and wet ball mill for 12 hours at a speed of 300 rpm to make the materials evenly mixed; The mixed slurry was dried to remove the solvent and placed in a tube furnace. Under nitrogen protection, the temperature was increased to 750°C at 5°C / min and held for 4 hours for carbonization. After cooling to room temperature, the carbonization product was dispersed in deionized water and washed repeatedly until no chloride ions were detected in the filtrate or the filtrate was neutral. The filter cake was vacuum dried to obtain nitrogen-doped porous carbon material with rich mesoporous / macroporous structure, i.e., the first carbon source. S2, precursor mixture Iron phosphate with an iron-to-phosphorus ratio of 0.965 and a D50 of 5µm was selected; Lithium hydroxide was selected as the lithium source; Ammonium phosphate was selected as the phosphorus source; Titanium citrate was selected, and 0.1% by mass of iron phthalocyanine phosphate was added as a second carbon source; Polyethylene glycol was selected as the dispersant, and the amount of dispersant added was 2.0% of the total weight of ferric phosphate. The mass ratio of the second carbon source to the iron phosphate mixture is 0.05:1; Iron phosphate, lithium source, phosphorus source, second carbon source and dispersant are mixed to obtain the first iron-containing precursor mixture; S3, pH adjustment The pH of the first iron-containing precursor mixture prepared by S2 was adjusted. During the stirring process, ammonia or lithium hydroxide solution was added dropwise to adjust the pH of the slurry to 10 to obtain the second iron-containing precursor mixture. At this time, the alkaline environment caused the titanium citrate chelate structure to dissociate, and the released titanium species were uniformly adsorbed on the surface of the iron phosphate particles. S4, Preparation of iron-containing precursor mixture The second iron-containing precursor mixture prepared in S3 was added to the first carbon source prepared in S1 and ground. The mass ratio of the first carbon source to the second iron-containing precursor mixture was 0.01:1. The D50 of the solid particles in the slurry was controlled to be 1.5µm to obtain the iron-containing precursor mixture. The precursor powder was obtained by granulation and drying using a spray drying tower. S5, Sintering The precursor is placed in a roller kiln, protected with nitrogen, and sintered using a segmented sintering process. First sintering stage: Heat to 500℃ at 2℃ / min and hold for 2h to ensure perfect carbonization of the carbon layer. Heat to 800℃ at a rate of 5℃ / min and hold for 6h to form the main crystalline phase. Second sintering stage: carbon layer annealing and lattice repair are carried out at a temperature of 650℃ for 3 hours, followed by furnace cooling.
[0025] Finished product: LFP material is obtained after air jet pulverization, demagnetization, and sieving.
[0026] II. Proportional Setting Comparative Example 1 (without a hole-forming template) The only difference from Example 1 is that sodium chloride (NaCl) is not added during the preparation of the first carbon source. The asphalt and phenolic resin are directly mixed and carbonized. Objective: To verify the effect of salt template pore formation on ion diffusion rate and rate performance.
[0027] Comparative Example 2 (without pH adjustment) The only difference from Example 1 is that no pH adjustment is performed during the mixing process, and the natural pH of the slurry is maintained (usually weakly acidic or neutral). Objective: To verify the effect of pH control on titanium source release, doping effect and final conductivity.
[0028] Comparative Example 3 (Traditional High-Carbon Coating) The only difference from Example 1 is that: instead of using a first carbon source and titanium citrate, glucose with a mass fraction of 1.5% is directly added as a single carbon source, and pH adjustment is not performed.
[0029] Objective: To simulate traditional processes and compare and verify the advantages of this invention in achieving high compaction and high conductivity under low carbon content.
[0030] Comparative Example 4 (without added iron phthalocyanine) The only difference from Example 1 is that titanium citrate is selected as the second carbon source, and 0.1% by mass of iron phthalocyanine is not added as the second carbon source; Objective: To verify the effect of iron phthalocyanine on doping effect and final conductivity.
[0031] III. Performance Testing 1. Test parameters and methods Compacted density: Tested using a powder compaction density meter. Test instrument: Sansi Zongheng UTM7305, pressure 30 KN, mold inner diameter 13 mm.
[0032] Electrochemical performance: The material was assembled into a 2032 coin cell and tested using a LAND CT3002C / CT3002A instrument at an ambient temperature of 25±2℃ and a voltage range of 2.0~3.75V.
[0033] Resistivity: Tested using an ST24742B powder resistivity meter at a pressure of 12 MPa.
[0034] 2. Test Results Table 1: Test results of physical properties of each group of samples Table 2: Electrochemical performance test results of each group of samples (25℃, 2.0-3.75V) Results Analysis and Conclusions As can be seen from the data in Tables 1 and 2, the lithium iron phosphate materials prepared in Examples 1-3 still maintain excellent conductivity and rate performance (5C retention rate reached 95.48% in Example 1) even with extremely low total carbon content. This is due to the synergistic effect of the porous structure of the first carbon source and Ti-N dual doping. In contrast, although Comparative Example 3 maintained basic conductivity by increasing carbon content, its compaction density was significantly lower than that of Example 1 (by about 0.16 g / cm³).
[0035] IV. Morphological Observation The structure and thickness of the carbon coating layer on the material surface were observed using a high-resolution transmission electron microscope with an accelerating voltage of 200 kV.
[0036] Morphological analysis Figures 1 to 3The images are transmission electron microscope (TEM) images of Examples 1-3. It can be clearly observed from the images that the lithium iron phosphate particles prepared in this invention are coated with a uniform, continuous and extremely thin amorphous carbon layer with a thickness of about 2 nm. This ultrathin structure ensures that electrons can penetrate the carbon layer for rapid transport while minimizing the volume ratio of inactive carbon materials, enabling the particles to be tightly packed together, thereby eliminating the cushioning effect caused by traditional thick carbon layers. In comparison, Figure 4 (Comparative Example 3, Traditional High-Carbon Coating) The carbon layer on the particle surface is significantly thicker, about 5 nm, and unevenly distributed. Some areas show a thicker amorphous carbon accumulation. Although this excessively thick carbon layer provides a conductive path, it also acts as a loose medium, hindering the dense contact between lithium iron phosphate particles, directly leading to a significant reduction in its compaction density.
[0037] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made to it in form and detail without departing from the scope defined by the claims of the present invention.
Claims
1. A high-conductivity ultra-thin carbon layer high-compaction lithium iron phosphate processing method, characterized in that, The method comprises the following steps: S1, mixing asphalt, phenolic resin and sodium chloride in ethanol by a wet ball milling method, and then carbonizing at 750°C, and after removing sodium chloride by water washing and drying, a first carbon source is obtained; S2, mixing iron phosphate, lithium carbonate, phosphoric acid, a second carbon source and a dispersant to obtain a first iron-containing precursor mixture, wherein the second carbon source at least contains titanium citrate, the iron-phosphorus ratio of the iron phosphate raw material is 0.965, and the D50 is 1.0-5.0 µm; S3, adjusting the pH value of the first iron-containing precursor mixture prepared in S2 to a preset alkaline pH value by using lithium hydroxide or ammonia water to obtain a second iron-containing precursor mixture, wherein the preset alkaline pH value is 8-10; S4, grinding and drying the second iron-containing precursor mixture prepared in S3 in the first carbon source prepared in S1 to obtain an iron-containing precursor mixture, wherein the particle size of the iron-containing precursor mixture is 0.4 µm≤D50≤1.5 µm; S5, sintering and crushing the iron-containing precursor prepared in S4 in an inert gas atmosphere to obtain a lithium iron phosphate positive electrode material.
2. The method of claim 1, wherein the high conductivity ultra-thin carbon layer high-compactness lithium iron phosphate is processed by the following steps: In the step S1, the mass ratio of asphalt, phenolic resin and sodium chloride is 1:2:3, and the mixing time is 12 hours. 3. The high-conductivity ultrathin carbon layer high-pressure lithium iron phosphate processing method according to claim 1, characterized in that: The second carbon source in the step S2 further comprises 0.1% of iron phthalocyanine based on the mass of the iron phosphate.
4. The high-conductivity ultrathin carbon layer high-pressure lithium iron phosphate processing method according to claim 1, characterized in that: In the step S2, the mass ratio of the second carbon source to the iron phosphate mixture is (0.002-0.05):
1.
5. The high-conductivity ultrathin carbon layer high-pressure lithium iron phosphate processing method according to claim 1, characterized in that: In the step S2, the dispersant is added in an amount of 0.5%-2.0% based on the total weight of the iron phosphate, and the dispersant is at least one selected from polyethylene glycol, citric acid, succinic acid, tripropyl phosphate, dibutyl phosphate, polyamide silicone oil, methylcyclosiloxane, sodium dodecylbenzenesulfonate and sodium octylbenzenesulfonate.
6. The high-conductivity ultrathin carbon layer high-pressure lithium iron phosphate processing method according to claim 1, characterized in that: In the step S4, the mass ratio of the first carbon source to the second precursor mixture is 0.01:
1.
7. The high-conductivity ultrathin carbon layer high-pressure lithium iron phosphate processing method according to claim 1, characterized in that: In the step S5, the sintering comprises a first sintering stage and a second sintering stage: First sintering stage: heating to 500°C at a rate of 2°C / min, holding for 2h to ensure perfect carbonization of the carbon layer, heating at a rate of 5°C / min to a temperature of 800°C, and holding for 6h to form the main crystal phase; Second sintering stage: temperature 650°C, holding time 3h for carbon layer annealing and lattice repair, and cooling in the furnace.
8. The lithium iron phosphate cathode material prepared according to the method of any one of claims 1-7, characterized in that: The material has a porous conductive framework formed by sodium chloride templating, and lattice titanium doping achieved by pH-regulated release of titanium citrate and nitrogen-doped structure achieved by carbonization of resin and asphalt.