Phosphate positive electrode material and carbon coating method of phosphate positive electrode material
By using a spray drying and sintering technology that mixes cationic emulsions with anionic precursor slurries, a uniform carbon coating layer is formed, which solves the conductivity and stability problems of lithium iron phosphate and lithium manganese iron phosphate, and improves electronic conductivity and discharge capacity.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- DEYANG CHUANFA LONGMANG NEW MATERIAL CO LTD
- Filing Date
- 2026-03-18
- Publication Date
- 2026-05-12
AI Technical Summary
Existing carbon coating technologies for lithium iron phosphate and lithium manganese iron phosphate suffer from difficulties in controlling the uniformity and continuity of the carbon layer, resulting in low electronic conductivity. Furthermore, carbon layer shedding and increased contact resistance are prone to occur under high-rate and long-cycle conditions. In particular, the structural instability caused by manganese leaching further highlights the urgency of optimizing the coating.
A method of spray drying and sintering by mixing cationic emulsion with anionic precursor slurry is adopted. A dense organic coating film is formed on the surface of phosphate-based cathode material. The electrostatic adsorption of latex particles in solvent by potential difference is used to form a uniform carbon coating layer. Combined with carbon sources such as PEG and glucose, a carbon layer with high electronic conductivity is formed at high temperature.
The conductivity and discharge capacity of lithium iron phosphate and lithium manganese iron phosphate cathode materials have been improved, the resistivity has been reduced to below 10 Ω·cm, the 1C discharge capacity has reached more than 145 mAh/g, and the carbon coating layer on the particle surface is smooth and not easy to fall off.
Smart Images
Figure CN122010081A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of battery materials technology, specifically relating to a phosphate-based cathode material and a method for carbon coating the phosphate-based cathode material. Background Technology
[0002] Lithium iron phosphate (LiFePO4) and lithium manganese iron phosphate (LFP) are common phosphate cathode materials. LiFePO4 (LFP), with its excellent thermal stability, low cost, and environmentally friendly properties, has become the mainstream choice for lithium-ion battery cathode materials, widely used in power batteries and energy storage. As an important evolution of LFP, lithium manganese iron phosphate (LiMn)... x Fe 1-x PO4 (LMFP) significantly improves operating voltage and energy density by introducing manganese, and is considered a strong contender for the next generation of high-performance, cost-effective cathode materials.
[0003] However, both LFP and LMFP face inherent technical bottlenecks: their olivine crystal structure causes FeO6 octahedra to be isolated by PO4 tetrahedra, preventing the formation of a continuous conductive network and resulting in extremely low electronic conductivity (approximately 10). -9 The electron conduction efficiency (ECE) of lithium iron phosphate (LFP) and lithium manganese iron phosphate (LFP) is severely limited by its high-rate charge-discharge performance. To overcome this bottleneck, carbon coating technology has been widely adopted. By constructing a conductive network on the particle surface, it can effectively improve electron conduction efficiency. However, in existing technologies, carbon coating of LFP / LFP mainly involves simply mixing with a carbon source, drying the residue, and then sintering it at high temperature to form a carbon layer. This limits the effectiveness of carbon coating due to the difficulty in controlling the uniformity, continuity, and thickness of the carbon layer: traditional single carbon layers struggle to balance conductivity and compaction density, and under high-rate and long-cycle conditions, problems such as carbon layer detachment and increased contact resistance easily occur, leading to electrochemical performance degradation. For LFP, carbon coating also needs to address the structural instability challenge caused by manganese leaching, further highlighting the urgency and necessity of optimizing coating technology. Summary of the Invention
[0004] To address the problem of poor carbon coating effect in existing phosphate-based cathode materials, this invention provides a phosphate-based cathode material and a method for carbon coating the phosphate-based cathode material.
[0005] The technical solution adopted in this invention is as follows:
[0006] A method for carbon coating of a phosphate-based cathode material includes the following steps:
[0007] S1: Synthesize cationic emulsions containing cationic latex particles;
[0008] S2: Preparation of anionic precursor slurry for phosphate-based cathode materials;
[0009] S3: Mix the cationic emulsion and the anionic precursor slurry according to the specified ratio to obtain a mixture.
[0010] S4: Spray dry the mixture to remove solvent and demulsify, and obtain the demulsified solid material;
[0011] S5: The demulsified solid material is sintered under an inert atmosphere to obtain carbon-coated phosphate cathode material;
[0012] S1 and S2 are not in any particular order.
[0013] Preferably, in step S2, the raw materials for preparing phosphate-based cathode materials are ground to a set particle size to obtain an anionic precursor slurry, and the alcohol-to-water ratio of the solvent added during grinding is 1:3~6.
[0014] When using this technical solution, if the alcohol-to-water ratio of the anionic precursor slurry is too low, the particle dispersion is poor, and the latex particles become fused together after sintering. If the alcohol-to-water ratio of the anionic precursor slurry is too high, the potential difference between the latex particles and the particle surface is small, the electrostatic adsorption force decreases, and the surface coating layer is easily detached.
[0015] Preferably, the alcohol in the added solvent is ethanol.
[0016] Preferably, the solid content of the anionic precursor slurry is 20-50%.
[0017] Preferably, the particle size after grinding is 0.35~0.40 μm.
[0018] Preferably, in step S3, the anionic precursor slurry is first stirred, and then the cationic emulsion is added to the anionic precursor slurry according to a mass ratio of 100:5~20 of solid content of anionic precursor slurry to solid content of cationic emulsion. After reacting in a water bath at 25~50℃ for 0.1~2h, the precursor coated with latex particles (demulsification) is obtained by spray drying.
[0019] Preferably, the raw materials used in S2 for preparing phosphate-based cathode materials include: lithium source, iron source, manganese source, phosphorus source, and carbon source;
[0020] The lithium source is one or more combinations of lithium dihydrogen phosphate, lithium monohydrogen phosphate, lithium phosphate, lithium carbonate, lithium hydroxide, lithium oxalate, and lithium acetate.
[0021] The iron source is one or more of the following: ferrous oxalate, ferrous acetate, ferric oxide, ferric phosphate, ferric hydroxide, ferric carbonate, ferric citrate, and ferric acetate.
[0022] The manganese source is one or more of the following: manganese tetroxide, manganese dioxide, manganese monoxide, manganese carbonate, manganese oxalate, and manganese acetate.
[0023] The phosphorus source is one or more of phosphoric acid, diammonium hydrogen phosphate, and ammonium dihydrogen phosphate;
[0024] The carbon source is one or more of the following: glucose, PEG, PVP, citric acid, sodium dodecylbenzenesulfonate, ethylenediaminetetraacetic acid, isooctanol ether phosphate, and sodium secondary alkyl sulfonate.
[0025] Preferably, carbon-coated phosphate-based cathode material is obtained by sintering S5 at 350~500℃ for 2~4h and then at 600~750℃ for 6~10h. The carbon-coated phosphate-based cathode material obtained by sintering at this temperature has the characteristics of good coating uniformity and low resistivity.
[0026] Preferably, the method for preparing the cationic emulsion in S1 includes:
[0027] S101. Preparation of Solution A: Styrene, butyl methacrylate, allyl hexanoate, ethylene glycol dimethacrylate, hexadecyltrimethylammonium chloride, and deionized water are mixed in a mass ratio of 10~30:5~20:1~15:1~10:0.5~5:100 and pre-emulsified.
[0028] S102. Prepare solution B: Mix 2,2-azo(2-methylpropylimidazolium) dihydrochloride with deionized water at a mass ratio of 1~10:100;
[0029] S103. Preparation of Solution C: Pre-emulsify by mixing butyl acrylate, ethylene glycol dimethacrylate, hexadecyltrimethylammonium chloride, 2,2-azo(2-methylpropylimidazolium) dihydrochloride and deionized water at a mass ratio of 10~50:2~20:0.5~10:0.05~2:100;
[0030] S104. Remove the oxygen from solution A, and heat solution A and solution B to 20~50℃. Then slowly add solution B to solution A. The mass ratio of solution A to solution B is 100:1~20.
[0031] S105. The mixed solution obtained in S104 is heated to 40℃~70℃, and then solution C is slowly added to the mixed solution to obtain the cationic emulsion. The mass ratio of solution A to solution C is 100:25~100.
[0032] After adopting this technical solution, the prepared latex particles are of the "hard core and soft shell" type. The hard core is conducive to improving the mechanical strength of the latex particles, while the soft shell is conducive to improving the film-forming properties of the latex particles.
[0033] Preferably, styrene, butyl methacrylate, allyl hexanoate, ethylene glycol dimethacrylate, hexadecyltrimethylammonium chloride, and deionized water are mixed in a mass ratio of 18:15:12:5:3:100 for pre-emulsification.
[0034] After adopting this technical solution, the copolymer of styrene, butyl methacrylate and allyl hexanoate has a higher glass transition temperature, which can enhance the mechanical properties of latex particles. However, adding too much styrene will result in poor film-forming properties of the latex particles.
[0035] Preferably, 2,2-azo(2-methylpropylimidazolium) dihydrochloride is mixed with deionized water at a mass ratio of 5:100.
[0036] After adopting this technical solution, mixing at this mass ratio can promote monomer polymerization. If the ratio is too large, the local reaction concentration will be too high, which will easily lead to explosive polymerization. If the ratio is too small, the reaction rate will be too slow and the preparation cycle will be long.
[0037] Preferably, butyl acrylate, ethylene glycol dimethacrylate, hexadecyltrimethylammonium chloride, 2,2-azo(2-methylpropylimidazolium) dihydrochloride and deionized water are mixed in a mass ratio of 30:15:5:0.2:100 for pre-emulsification.
[0038] After adopting this technical solution, the copolymer of butyl acrylate and ethylene glycol dimethacrylate has a lower glass transition temperature, which can increase the film-forming properties of latex particles. Too low a dosage will result in poor film-forming properties of the latex particles adsorbed on the particle surface by the polymer emulsion, while too high a dosage makes it difficult to control the film-forming properties under room temperature conditions.
[0039] Preferably, the mass ratio of solution A to solution B is 100:10.
[0040] The reason for the above settings after adopting this technical solution is that if the mass ratio is too high, the reaction will be insufficient, and if the ratio is too low, the latex particles will easily agglomerate.
[0041] Preferably, the mass ratio of solution A to solution C is 100:50.
[0042] The reason for this setting is that if the mass ratio is too high, the latex particles will have poor film-forming properties, and if it is too low, the latex particles will have poor mechanical properties.
[0043] Preferably, nitrogen gas is introduced into S104 to remove oxygen from the solution, and solution B is slowly added to solution A over 10-60 minutes.
[0044] Preferably, in step S105, the solution is heated to 60°C, and solution C is slowly added to the mixed solution within 30 to 120 minutes (preferably 60 minutes) to obtain the cationic emulsion.
[0045] Preferably, the cationic latex particles in S1 have a diameter of <100nm, a core-shell structure, and a solid content of 5%~40%.
[0046] After adopting this technical solution, the cationic latex particles synthesized in this way have good mechanical properties and film-forming properties.
[0047] A phosphate-based cathode material obtained by the carbon coating method of the aforementioned phosphate-based cathode material.
[0048] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:
[0049] 1. This invention utilizes the difference in potential between the surface of the phosphate cathode material and the latex particles in the solvent, causing the latex particles to be adsorbed onto the surface of the phosphate cathode material. Then, through heat drying, a dense organic coating film is formed on the surface of the phosphate cathode material. After sintering, the organic coating film is carbonized to form a uniformly carbon-coated lithium iron phosphate / lithium manganese iron phosphate cathode material. The appearance morphology of the obtained lithium iron phosphate / lithium manganese iron phosphate cathode material shows that the organic coating film used in this invention achieves a good carbon coating effect.
[0050] 2. The polystyrene in the latex particles of this invention readily forms a graphite-like carbon layer after pyrolysis. The carbon layer formed synergistically with carbon sources such as PEG and glucose at high temperatures exhibits higher electronic conductivity. From the obtained lithium iron phosphate / lithium manganese iron phosphate cathode materials and their conductivity data and Raman spectral ID / IG values, it can be seen that the organic coating of the latex particles in this invention facilitates the graphitization of the carbon layer of lithium iron phosphate / lithium manganese iron phosphate. Moreover, the formed carbon coating layer is smooth, resulting in rounded and uniformly sized particles. The carbon coating layer is not easily detached, which allows the battery resistivity to be reduced to below 10 Ω·cm after the application of the phosphate-based cathode material in the battery, and the 1C discharge capacity to reach above 145 mAh / g. This indicates that this invention effectively improves the discharge capacity while improving the conductivity of the phosphate-based cathode material. Attached Figure Description
[0051] Figure 1 TEM image of the latex particles synthesized in Example 1;
[0052] Figure 2 The images show SEM characterization (a) and Raman characterization (b) of the phosphate-based cathode material obtained in Example 1.
[0053] Figure 3 The images show SEM (a) and Raman (b) characterizations of the phosphate-based cathode material obtained in Example 2.
[0054] Figure 4The image shows the SEM characterization of the phosphate-based cathode material obtained in Comparative Example 1.
[0055] Figure 5 The image shows the SEM characterization of the phosphate-based cathode material obtained in Comparative Example 2.
[0056] Figure 6 The image shows the SEM characterization of the phosphate-based cathode material obtained in Comparative Example 3.
[0057] Figure 7 The image shows the SEM characterization of the phosphate-based cathode material obtained in Comparative Example 4.
[0058] Figure 8 The image shows the SEM characterization of the phosphate-based cathode material obtained in Comparative Example 5.
[0059] Figure 9 The image shows the SEM characterization of the phosphate-based cathode material obtained in Comparative Example 6.
[0060] Figure 10 The image shows the SEM characterization of the phosphate-based cathode material obtained in Comparative Example 7.
[0061] Figure 11 The image shows the SEM characterization of the phosphate-based cathode material obtained in Comparative Example 8. Detailed Implementation
[0062] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments.
[0063] Example 1
[0064] A method for carbon coating of a phosphate-based cathode material includes the following steps:
[0065] S1: Synthesize cationic emulsions containing cationic latex particles;
[0066] Methods for preparing cationic emulsions include:
[0067] S101. Preparation of Solution A: Styrene (Aladdin Reagent S110376), butyl methacrylate (Aladdin Reagent B110902), allyl hexanoate (Aladdin Reagent A109767), ethylene glycol dimethacrylate (Aladdin Reagent E106223), hexadecyltrimethylammonium chloride (Aladdin Reagent H105309), and deionized water are mixed in a mass ratio of 18:15:12:5:3:100 for pre-emulsification;
[0068] S102. Prepare solution B: Mix 2,2-azo(2-methylpropylimidazolium) dihydrochloride (Aladdin Reagent A101386) with deionized water at a mass ratio of 5:100;
[0069] S103, Preparation of Solution C: Pre-emulsify by mixing butyl acrylate (Aladdin Reagent B100035), ethylene glycol dimethacrylate (Aladdin Reagent E106223), hexadecyltrimethylammonium chloride (Aladdin Reagent H105309), 2,2-azo(2-methylpropylimidazolium) dihydrochloride (Aladdin Reagent A101386) and deionized water at a mass ratio of 30:15:5:0.2:100;
[0070] S104. Nitrogen gas is introduced into solution A while stirring to remove oxygen from the solution. Solution A and solution B are heated to 30°C. Then, solution B is slowly added to solution A over 30 minutes. The mass ratio of solution A to solution B is 100:10.
[0071] S105. The mixed solution obtained in S104 is heated to 60°C, and then solution C is slowly added to the mixed solution over 60 minutes to obtain the cationic emulsion. The mass ratio of solution A to solution C is 100:50. In this embodiment, the solid content of the cationic emulsion obtained is 35%. Figure 1 It can be seen that the cationic latex particles obtained in this embodiment have a diameter of <100nm and a core-shell structure;
[0072] S2: Weigh lithium carbonate (Aladdin Reagent L1455823), ferric phosphate (Aladdin Reagent F188971), manganese oxalate (Aladdin Reagent M304253), and ammonium dihydrogen phosphate (Aladdin Reagent A141011) in a molar ratio of 0.5:0.4:0.6:0.6. Based on the total mass of the above mixture, weigh 2% PEG (polyethylene glycol) (Aladdin Reagent P103725) and 6% glucose (Aladdin Reagent D274366) by mass fraction, and add them to an ethanol aqueous solution. Grind to obtain an anionic precursor slurry. The alcohol-to-water ratio of the solvent added during grinding is 2:8. In this embodiment, the solid content of the anionic precursor slurry is 30%, and the particle size after grinding is 0.35~0.40um.
[0073] S3: First, stir the anionic precursor slurry at a stirring speed of 100~400 rpm. Then, add the cationic emulsion to the anionic precursor slurry according to the mass ratio of solid content of anionic precursor slurry to solid content of cationic emulsion of 100:10. After reacting in a water bath at 35℃ for 1 hour, the precursor coated with latex particles is obtained by spray drying.
[0074] S4: Spray dry the mixture to remove the solvent and demulsify (60~90℃, vacuum degree 0.05~0.09MPa) to obtain the demulsified solid material;
[0075] S5: The demulsified solid material was sintered at 450°C for 3 hours and then at 650°C for 8 hours under an inert atmosphere to obtain carbon-coated lithium manganese iron phosphate cathode material. The SEM characterization image (a) and Raman characterization image (b) of the lithium manganese iron phosphate cathode material obtained in this embodiment are shown below. Figure 2 As shown, due to the moderate adsorption force between the latex particles and the precursor particles, there is less adhesion between the particles after adsorption, resulting in rounded and uniformly sized particles after sintering. By comparing the ID / IG values, the introduction of latex particles leads to a higher degree of graphitization in the carbon coating layer. The resistivity of the lithium manganese iron phosphate cathode material obtained in this embodiment is 9.7 Ω·m.
[0076] Example 2
[0077] A method for carbon coating of a phosphate-based cathode material includes the following steps:
[0078] S1: Synthesize cationic emulsions containing cationic latex particles;
[0079] Methods for preparing cationic emulsions include:
[0080] S101. Preparation of Solution A: Styrene (Aladdin Reagent S110376), butyl methacrylate (Aladdin Reagent B110902), allyl hexanoate (Aladdin Reagent A109767), ethylene glycol dimethacrylate (Aladdin Reagent E106223), hexadecyltrimethylammonium chloride (Aladdin Reagent H105309), and deionized water are mixed in a mass ratio of 18:15:12:5:3:100 for pre-emulsification;
[0081] S102. Prepare solution B: Mix 2,2-azo(2-methylpropylimidazolium) dihydrochloride (Aladdin Reagent A101386) with deionized water at a mass ratio of 5:100;
[0082] S103, Preparation of Solution C: Pre-emulsify by mixing butyl acrylate (Aladdin Reagent B100035), ethylene glycol dimethacrylate (Aladdin Reagent E106223), hexadecyltrimethylammonium chloride (Aladdin Reagent H105309), 2,2-azo(2-methylpropylimidazolium) dihydrochloride (Aladdin Reagent A101386) and deionized water at a mass ratio of 30:15:5:0.2:100;
[0083] S104. Nitrogen gas is introduced into solution A while stirring to remove oxygen from the solution. Solution A and solution B are heated to 30°C. Then, solution B is slowly added to solution A over 30 minutes. The mass ratio of solution A to solution B is 100:10.
[0084] S105. The mixed solution obtained in S104 is heated to 60°C, and then solution C is slowly added to the mixed solution over 60 minutes to obtain the cationic emulsion. The mass ratio of solution A to solution C is 100:50. In this embodiment, the solid content of the cationic emulsion obtained is 35%. Figure 1 It can be seen that the diameter of the cationic latex particles obtained in this embodiment is <100nm, which is a core-shell structure;
[0085] S2: Weigh lithium carbonate (Aladdin reagent L1455823), ferric phosphate (Aladdin reagent F188971), and phosphoric acid (Aladdin reagent P112024) in a molar ratio of 0.5:0.97:0.03. Based on the total mass of the above mixture, weigh 2% PEG (polyethylene glycol) (Aladdin reagent P103725) and 5% glucose (Aladdin reagent D274366) by mass fraction, and add them to an ethanol aqueous solution. Grind to obtain an anionic precursor slurry. The alcohol-to-water ratio of the solvent added during grinding is 2:8. In this embodiment, the solid content of the anionic precursor slurry is 35%, and the particle size after grinding is 0.35~0.40um.
[0086] S3: First, stir the anionic precursor slurry at a stirring speed of 100~400 rpm. Then, add the cationic emulsion to the anionic precursor slurry according to the mass ratio of solid content of anionic precursor slurry to solid content of cationic emulsion of 100:12. After reacting in a water bath at 35℃ for 1 hour, the precursor coated with latex particles is obtained by spray drying.
[0087] S4: Spray dry the mixture to remove the solvent and demulsify (60~90℃, vacuum degree 0.05~0.09MPa) to obtain the demulsified solid material;
[0088] S5: The demulsified solid material was sintered at 450°C for 3 hours and then at 700°C for 8 hours under an inert atmosphere to obtain carbon-coated lithium iron phosphate cathode material. The SEM characterization image (a) and Raman characterization image (b) of the lithium iron phosphate cathode material obtained in this embodiment are shown below. Figure 3 As shown, from Figure 3 It can be seen that the adsorption force between the latex particles and the precursor particles is moderate, and the particles are round and uniform in size. By comparing the ID / IG values, the introduction of latex particles results in a higher degree of graphitization of the carbon coating layer.
[0089] Example 3
[0090] A method for carbon coating of a phosphate-based cathode material includes the following steps:
[0091] S1: Synthesize cationic emulsions containing cationic latex particles;
[0092] Methods for preparing cationic emulsions include:
[0093] S101. Preparation of Solution A: Styrene (Aladdin Reagent S110376), butyl methacrylate (Aladdin Reagent B110902), allyl hexanoate (Aladdin Reagent A109767), ethylene glycol dimethacrylate (Aladdin Reagent E106223), hexadecyltrimethylammonium chloride (Aladdin Reagent H105309), and deionized water are mixed in a mass ratio of 20:15:10:5:3:100 for pre-emulsification;
[0094] S102. Prepare solution B: Mix 2,2-azo(2-methylpropylimidazolium) dihydrochloride (Aladdin Reagent A101386) with deionized water at a mass ratio of 5:100;
[0095] S103, Preparation of Solution C: Pre-emulsify by mixing butyl acrylate (Aladdin Reagent B100035), ethylene glycol dimethacrylate (Aladdin Reagent E106223), hexadecyltrimethylammonium chloride (Aladdin Reagent H105309), 2,2-azo(2-methylpropylimidazolium) dihydrochloride (Aladdin Reagent A101386) and deionized water at a mass ratio of 28:17:5:0.2:100;
[0096] S104. Nitrogen gas is introduced into solution A while stirring to remove oxygen from the solution. Solution A and solution B are heated to 30°C. Then, solution B is slowly added to solution A over 30 minutes. The mass ratio of solution A to solution B is 100:10.
[0097] S105. The mixed solution obtained in S104 is heated to 60°C, and then solution C is slowly added to the mixed solution over 60 minutes to obtain the cationic emulsion. The mass ratio of solution A to solution C is 100:50. In this embodiment, the solid content of the cationic emulsion obtained is 30%.
[0098] S2: Weigh lithium carbonate, iron phosphate, and phosphoric acid in a molar ratio of 0.5:0.97:0.03. Based on the total mass of the mixture, weigh 2% PEG (polyethylene glycol) and 5% glucose by mass fraction, and add an ethanol aqueous solution. Grind to obtain an anionic precursor slurry. The alcohol-to-water ratio of the solvent added during grinding is 2:8. In this embodiment, the solid content of the anionic precursor slurry is 30%, and the particle size after grinding is 0.35~0.40um.
[0099] S3: First, stir the anionic precursor slurry at a stirring speed of 100~400 rpm. Then, add the cationic emulsion to the anionic precursor slurry according to the mass ratio of solid content of anionic precursor slurry to solid content of cationic emulsion of 100:15. After reacting in a water bath at 35℃ for 1 hour, the precursor coated with latex particles is obtained by spray drying.
[0100] S4: Spray dry the mixture to remove the solvent and demulsify (60~90℃, vacuum degree 0.05~0.09MPa) to obtain the demulsified solid material;
[0101] S5: The demulsified solid material is sintered at 450℃ for 3 hours and 700℃ for 8 hours under an inert atmosphere to obtain carbon-coated lithium iron phosphate cathode material.
[0102] Example 4
[0103] A method for carbon coating of a phosphate-based cathode material includes the following steps:
[0104] S1: Synthesize cationic emulsions containing cationic latex particles;
[0105] Methods for preparing cationic emulsions include:
[0106] S101. Preparation of Solution A: Styrene, butyl methacrylate, allyl hexanoate, ethylene glycol dimethacrylate, hexadecyltrimethylammonium chloride, and deionized water are mixed in a mass ratio of 20:15:10:5:3:100 and pre-emulsified.
[0107] S102. Prepare solution B: Mix 2,2-azo(2-methylpropylimidazolium) dihydrochloride with deionized water at a mass ratio of 5:100;
[0108] S103, Preparation of Solution C: Pre-emulsify by mixing butyl acrylate, ethylene glycol dimethacrylate, hexadecyltrimethylammonium chloride, 2,2-azo(2-methylpropylimidazolium) dihydrochloride and deionized water at a mass ratio of 28:17:5:0.2:100;
[0109] S104. Nitrogen gas is introduced into solution A while stirring to remove oxygen from the solution. Solution A and solution B are heated to 30°C. Then, solution B is slowly added to solution A over 30 minutes. The mass ratio of solution A to solution B is 100:10.
[0110] S105. The mixed solution obtained in S104 is heated to 60°C, and then solution C is slowly added to the mixed solution over 60 minutes to obtain the cationic emulsion. The mass ratio of solution A to solution C is 100:50. In this embodiment, the solid content of the cationic emulsion obtained is 35%. Figure 1 It can be seen that the diameter of the cationic latex particles obtained in this embodiment is <100nm, which is a core-shell structure;
[0111] S2: Weigh lithium carbonate, iron phosphate, manganese oxalate, and ammonium dihydrogen phosphate in a molar ratio of 0.5:0.4:0.6:0.6. Based on the total mass of the mixture, weigh 2% PEG (polyethylene glycol) and 6% glucose by mass fraction, and add an ethanol aqueous solution. Grind to obtain an anionic precursor slurry. The alcohol-to-water ratio of the solvent added during grinding is 2:8. In this embodiment, the solid content of the anionic precursor slurry is 30%, and the particle size after grinding is 0.35~0.40um.
[0112] S3: First, stir the anionic precursor slurry at a stirring speed of 100~400 rpm. Then, add the cationic emulsion to the anionic precursor slurry according to the mass ratio of solid content of anionic precursor slurry to solid content of cationic emulsion of 100:10. After reacting in a water bath at 35℃ for 1 hour, the precursor coated with latex particles is obtained by spray drying.
[0113] S4: Spray dry the mixture to remove the solvent and demulsify (60~90℃, vacuum degree 0.05~0.09MPa) to obtain the demulsified solid material;
[0114] S5: The demulsified solid material is sintered at 450℃ for 3 hours and 650℃ for 8 hours under an inert atmosphere to obtain carbon-coated lithium manganese iron phosphate cathode material.
[0115] Comparative Example 1
[0116] This comparative example is basically the same as Example 1, except that the alcohol-to-water ratio in S2 is 1:9. The SEM characterization image of the lithium manganese iron phosphate cathode material obtained in this comparative example is shown below. Figure 4 As shown, from Figure 4 It can be seen that a low alcohol-to-water ratio results in strong adsorption of latex particles, leading to the sharing of latex particles between particles, which in turn causes local agglomeration after sintering. The resistivity of the lithium manganese iron phosphate cathode material obtained in this comparative example is 48.0 Ω·m.
[0117] Comparative Example 2
[0118] This comparative example is basically the same as Example 1, except that the alcohol-to-water mass ratio is 3:7. The SEM characterization image of the lithium manganese iron phosphate cathode material obtained in this comparative example is shown below. Figure 5 As shown, from Figure 5 It can be seen that an excessively high alcohol-to-water ratio results in weak adsorption of latex particles, leading to carbon shedding after sintering. The resistivity of the lithium manganese iron phosphate cathode material obtained in this comparative example is 20.5 Ω·m.
[0119] Comparative Example 3
[0120] This comparative example is basically the same as Example 1, except that no cationic emulsion is added. The SEM characterization image of the lithium manganese iron phosphate cathode material obtained in this comparative example is shown below. Figure 6 As shown, from Figure 6 It can be seen that the particles sintered without latex particle coating are uneven in size and partially agglomerated, indicating uneven carbon coating and severe adhesion between particles. The resistivity of the lithium manganese iron phosphate cathode material obtained in this comparative example is 151.0 Ω·m.
[0121] Comparative Example 4
[0122] This comparative example is basically the same as Example 1, except that 2% PEG (polyethylene glycol) and 6% glucose are not added, and the ratio of cationic emulsion used is increased to 100:30 to ensure sufficient carbon source for the sintering reaction. The SEM characterization image of the lithium manganese iron phosphate cathode material obtained in this comparative example is shown below. Figure 7 As shown, from Figure 7 It can be seen that using only cationic emulsion as a carbon source for coating results in lithium manganese iron phosphate cathode materials with different particle sizes. This indicates that cationic latex ions only have a strong adsorption effect on areas with potential points in the precursor. In areas with weak or no potential, the adsorption effect is weak, and carbon coating cannot be effectively formed. This results in low growth resistance and the growth of non-spherical irregular particles.
[0123] Comparative Example 5
[0124] This comparative example is basically the same as Example 1, except that: S101, preparing solution A: styrene, butyl methacrylate, allyl hexanoate, ethylene glycol dimethacrylate, hexadecyltrimethylammonium chloride, and deionized water were mixed in a mass ratio of 40:3:2:5:3:100 and pre-emulsified. The SEM characterization of the lithium manganese iron phosphate cathode material obtained in this comparative example is as follows: Figure 8 As shown, from Figure 8It can be seen that the carbon coating layer on the surface of lithium manganese iron phosphate particles is relatively rough. This is because the styrene ratio is too high, resulting in a large proportion of rigid benzene ring structure in the latex particles. The organic coating film after the latex particles are demulsified has poor fluidity, which in turn leads to a rough carbon coating.
[0125] Comparative Example 6
[0126] This comparative example is basically the same as Example 1, except that: in S103, butyl acrylate, ethylene glycol dimethacrylate, hexadecyltrimethylammonium chloride, 2,2-azo(2-methylpropylimidazolium) dihydrochloride, and deionized water are mixed in a mass ratio of 60:30:10:0.4:100 for pre-emulsification. The SEM characterization of the lithium manganese iron phosphate cathode material obtained in this comparative example is as follows: Figure 9 As shown, from Figure 9 It can be seen that the proportion of film-forming components in latex particles is too high. During the stirring and adsorption process, some latex particles collide, crosslink, and agglomerate, resulting in uneven carbon distribution and uneven particle size after sintering.
[0127] Comparative Example 7
[0128] This comparative example is basically the same as Example 1, except that the mass ratio of solution A to solution B in S104 is 100:50. The SEM characterization of the lithium manganese iron phosphate cathode material obtained in this comparative example is as follows: Figure 10 As shown, from Figure 10 It can be seen that the result is similar to that of Comparative Example 6, both of which have an excessively high proportion of film-forming components in the latex particles, resulting in uneven carbon distribution on the particle surface after sintering and local agglomeration.
[0129] Comparative Example 8
[0130] This comparative example is basically the same as Example 1, except that the mass ratio of the solid content of the anionic precursor slurry to the solid content of the cationic emulsion is 100:50. The SEM characterization of the lithium manganese iron phosphate cathode material obtained in this comparative example is as follows: Figure 11 As shown, from Figure 11 It can be seen that, due to the limited adsorption sites on the precursor surface, too many latex particles remain free between the particles, causing the particles to sinter together and become large particles.
[0131] Table 1
[0132]
[0133] As can be seen from Examples 1-4 in Table 1, applying the technical solution of this application to the preparation of lithium manganese iron phosphate can yield a resistivity of about 10 Ω·cm, a 1C discharge capacity of over 140 mAh / g, a 1C median voltage of over 3.75 V, a 0.1C discharge capacity of over 150 mAh / g, and a 0.1C median voltage of over 3.95 V; applying the technical solution of this application to the preparation of lithium iron phosphate can yield a resistivity of 6~7 Ω·cm, a 1C discharge capacity of about 145 mAh / g, and a 0.1C discharge capacity of over 155 mAh / g.
[0134] As shown in Table 1, Examples 1 and Comparative Examples 1-2 demonstrate that when the alcohol-to-water ratio of the anionic precursor slurry is too low, the particle dispersibility is poor, and the latex particles become fused together after sintering. When the alcohol-to-water ratio of the anionic precursor slurry is too high, the potential difference between the cationic emulsion and the particle surface is small, the electrostatic adsorption force decreases, and the surface coating layer is easily detached. Therefore, the alcohol-to-water ratio needs to be controlled at 1:3~6.
[0135] Examples 1 and 3 show that using cationic emulsions for carbon coating can effectively prevent particle adhesion and improve carbon coating uniformity, thus effectively improving the carbon coating effect.
[0136] As shown in Table 1, in the anionic phosphate precursor slurry, a layer of latex particles is adsorbed on the precursor surface through the electrostatic adsorption of cationic latex particles. After demulsification and sintering, the resulting lithium iron phosphate / lithium manganese iron phosphate has a smoother carbon coating layer, and the particles are more rounded and uniform in size. Simultaneously, its discharge capacity is significantly improved, and its resistivity is significantly reduced. Therefore, the cationic latex particles in this invention can improve the carbon coating effect of phosphate-based cathode materials, thereby controlling the discharge capacity and resistivity.
[0137] The embodiments described above merely illustrate specific implementation methods of this application, and while the descriptions are detailed and specific, they should not be construed as limiting the scope of protection of this application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the technical solution of this application, and these modifications and improvements all fall within the scope of protection of this application.
Claims
1. A method for carbon coating of a phosphate-based cathode material, characterized in that: Includes the following steps: S1: Synthesize cationic emulsions containing cationic latex particles; S2: Preparation of anionic precursor slurry for phosphate-based cathode materials; S3: Mix the cationic emulsion and the anionic precursor slurry according to the specified ratio to obtain a mixture. S4: Spray dry the mixture to remove solvent and demulsify, and obtain the demulsified solid material; S5: The demulsified solid material is sintered under an inert atmosphere to obtain carbon-coated phosphate cathode material; S1 and S2 are not in any particular order.
2. The carbon coating method for a phosphate-based cathode material according to claim 1, characterized in that: In S2, the raw materials for preparing phosphate-based cathode materials are ground to a set particle size to obtain an anionic precursor slurry. The alcohol-to-water ratio of the solvent added during grinding is 1:3~6.
3. The carbon coating method for a phosphate-based cathode material according to claim 2, characterized in that: The solid content of the anionic precursor slurry is 20-50%.
4. The carbon coating method for a phosphate-based cathode material according to claim 2, characterized in that: The particle size after grinding is 0.35~0.40um.
5. A method for carbon coating of a phosphate-based cathode material according to any one of claims 1-4, characterized in that: In step S3, the anionic precursor slurry is first stirred, and then the cationic emulsion is added to the anionic precursor slurry according to a mass ratio of 100:5~20 of solid content of anionic precursor slurry to solid content of cationic emulsion. After reacting in a water bath at 25~50℃ for 0.1~2h, the precursor coated with latex particles is obtained by spray drying.
6. A method for carbon coating of a phosphate-based cathode material according to any one of claims 1-4, characterized in that: The raw materials for preparing phosphate-based cathode materials in S2 include: lithium source, iron source, manganese source, phosphorus source, and carbon source; The lithium source is one or more combinations of lithium dihydrogen phosphate, lithium monohydrogen phosphate, lithium phosphate, lithium carbonate, lithium hydroxide, lithium oxalate, and lithium acetate. The iron source is one or more of the following: ferrous oxalate, ferrous acetate, ferric oxide, ferric phosphate, ferric hydroxide, ferric carbonate, ferric citrate, and ferric acetate. The manganese source is one or more of the following: manganese tetroxide, manganese dioxide, manganese monoxide, manganese carbonate, manganese oxalate, and manganese acetate. The phosphorus source is one or more of phosphoric acid, diammonium hydrogen phosphate, and ammonium dihydrogen phosphate; The carbon source is one or more of the following: glucose, PEG, PVP, citric acid, sodium dodecylbenzenesulfonate, ethylenediaminetetraacetic acid, isooctanol ether phosphate, and sodium secondary alkyl sulfonate.
7. A method for carbon coating of a phosphate-based cathode material according to any one of claims 1-4, characterized in that: Carbon-coated phosphate-based cathode materials are obtained by sintering S5 at 350~500℃ for 2~4h and 600~750℃ for 6~10h.
8. A method for carbon coating of a phosphate-based cathode material according to any one of claims 1-4, characterized in that: The preparation methods of cationic emulsions in S1 include: S101. Preparation of Solution A: Styrene, butyl methacrylate, allyl hexanoate, ethylene glycol dimethacrylate, hexadecyltrimethylammonium chloride, and deionized water are mixed in a mass ratio of 10~30:5~20:1~15:1~10:0.5~5:100 and pre-emulsified. S102. Prepare solution B: Mix 2,2-azo(2-methylpropylimidazolium) dihydrochloride with deionized water at a mass ratio of 1~10:100; S103. Preparation of Solution C: Pre-emulsify by mixing butyl acrylate, ethylene glycol dimethacrylate, hexadecyltrimethylammonium chloride, 2,2-azo(2-methylpropylimidazolium) dihydrochloride and deionized water at a mass ratio of 10~50:2~20:0.5~10:0.05~2:100; S104. Remove the oxygen from solution A, and heat solution A and solution B to 20~50℃. Then slowly add solution B to solution A. The mass ratio of solution A to solution B is 100:1~20. S105. The mixed solution obtained in S104 is heated to 40℃~70℃, and then solution C is slowly added to the mixed solution to obtain the cationic emulsion. The mass ratio of solution A to solution C is 100:25~100.
9. A method for carbon coating of a phosphate-based cathode material according to claim 8, characterized in that: The cationic latex particles in S1 have a diameter of less than 100 nm, a core-shell structure, and a solid content of 5% to 40%.
10. A phosphate-based cathode material obtained by the carbon coating method of the phosphate-based cathode material according to any one of claims 1-9.