Colloidal mixed slurry and method for preparing sodium-ion battery cathode material
By preparing a clear and transparent colloidal mixed slurry, the problem of slurry deposition and layering in sodium-ion battery cathode materials was solved, improving the quality and electrochemical performance of the finished product and enabling low-cost large-scale production.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- WUHAN BISIDI BATTERY MATERIAL CO LTD
- Filing Date
- 2024-05-30
- Publication Date
- 2026-07-31
AI Technical Summary
Existing sodium-ion battery cathode material, sodium iron pyrophosphate suspension, is prone to deposition and stratification, resulting in uneven finished product quality and affecting electrochemical performance.
A carbon source containing citric acid and a trivalent iron source were premixed and milled to control the particle size to 0.6 μm, forming a clear and transparent colloidal slurry. After adding a sodium source, milling was continued until the reaction endpoint. Na4Fe3(PO4)2P2O7/C composite cathode material was prepared by spray drying and sintering.
This solved the problem of slurry deposition and stratification, improved the quality and electrochemical performance of the finished product, reduced the content of magnetic materials, and enabled low-cost, easily scaled-up production.
Smart Images
Figure CN118495497B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of sodium-ion battery technology, and more specifically, relates to a colloidal mixed slurry and a method for preparing sodium-ion battery cathode materials. Background Technology
[0002] In recent years, sodium-ion batteries have gradually become a research hotspot in the energy storage field due to their abundant resources and low cost. The cathode materials for sodium-ion batteries mainly include oxides, polyanionic materials, and Prussian blue materials. Common polyanionic cathode materials mainly include phosphates, pyrophosphates, sulfates, silicates, borates, and mixed polyanionic materials. Sodium iron pyrophosphate, as a type of mixed polyanionic material, has received widespread attention due to its structural stability and environmental friendliness.
[0003] Most existing sodium iron pyrophosphate (Na4Fe3(PO4)2P2O7) cathode materials are synthesized using a liquid-phase method. This involves mixing iron, phosphorus, carbon, and sodium sources to form a slurry. This slurry is typically in a suspension state. During storage and transportation to the next process, the slurry is prone to solid deposition and stratification, leading to scaling and even blockages in tanks or pipelines, which is detrimental to production. Furthermore, slurry deposition can cause stratification within the same batch, resulting in uneven elemental distribution between layers. This affects the particle size and elemental distribution of the powder obtained from subsequent spray drying, leading to an imbalance in the proportions of elements in the prepared cathode material, thus impacting the quality and electrochemical performance of the cathode material. Summary of the Invention
[0004] To address the shortcomings of existing technologies, the present invention aims to provide a colloidal mixed slurry for preparing Na4Fe3(PO4)2P2O7 / C composite cathode materials and a method for preparing composite cathode materials using the slurry. This invention aims to solve the technical problems of existing technologies in preparing sodium manganese iron pyrophosphate polyanionic cathode materials, such as the easy occurrence of solid particle sedimentation and scaling in pipelines, leading to a decline in finished product quality and thus affecting the electrochemical performance of the cathode material.
[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:
[0006] In a first aspect, the present invention provides a colloidal mixed slurry for preparing Na4Fe3(PO4)2P2O7 / C composite cathode materials, the preparation method of which includes the following steps:
[0007] (1) The iron source, carbon source and solvent are mixed and dispersed to obtain a premixed slurry; the carbon source contains citric acid and the iron source contains ferric iron;
[0008] (2) The premixed slurry described in step (1) is milled until the slurry particle size D50 is less than the first particle size. Then, a sodium source or a sodium source and a phosphorus source are added to the system. Milling is continued until the mixed system is clear and transparent, which is the reaction endpoint. A colloidal mixed slurry for preparing Na4Fe3(PO4)2P2O7 / C composite cathode material is obtained. The first particle size is 0.6 μm.
[0009] Preferably, the iron source in step (1) is selected from at least one of iron powder, iron(II,III) oxide, iron(III) oxide, iron(II,III) oxalate, iron(III) phosphate, and iron(III) pyrophosphate; the sodium source is at least one of sodium carbonate, sodium hydroxide, sodium formate, sodium acetate, sodium citrate, sodium oxalate, sodium nitrate, sodium sulfate, sodium pyrosulfate, sodium phosphate, sodium monohydrogen phosphate, sodium dihydrogen phosphate, pyrophosphate, sodium pyrophosphate, and sodium hydrogen pyrophosphate; the phosphorus source is one or more of phosphoric acid, ammonium monohydrogen phosphate, ammonium dihydrogen phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, and sodium phosphate; the solvent is water and / or an alcohol solvent; wherein the water is one or more of ultrapure water, double-distilled water, deionized water, pure water, and distilled water.
[0010] More preferably, the iron source is iron phosphate, wherein the iron-to-phosphorus ratio in the iron phosphate is between 0.97 and 0.975.
[0011] More preferably, the specific surface area of the iron source is 10-11 m². 2 / g.
[0012] Preferably, the mixing and dispersion temperature in step (1) is 40-60℃, and the mixing time is 5-140 min.
[0013] Preferably, the molar ratio of iron in the carbon source to the iron source in step (1) is greater than or equal to 3.5:3. More preferably, the molar ratio of iron in the carbon source to the iron source is (3.5-4.5):3.
[0014] Preferably, the sodium source, iron source and phosphorus source are fed according to the stoichiometric ratio of Na, Fe and P in the chemical formula of the cathode material Na4Fe3(PO4)2P2O7; the total mass ratio of the carbon source, iron source, phosphorus source and sodium source to the solvent is (5-40):(60-95).
[0015] Preferably, in step (2), the premixed slurry described in step (1) is milled until the slurry particle size D50 reaches the first particle size, and then a sodium source, or a sodium source and a phosphorus source, are added to the system; the first particle size is 0.2-0.6 μm.
[0016] Preferably, the system temperature is controlled at 20-50℃ during the sand milling process in step (2).
[0017] Preferably, the pH of the mixed slurry at the reaction endpoint is 2-3.
[0018] In the preferred embodiment, step (2) involves adding a sodium source, or a sodium source and a phosphorus source, to the system, and then continuing to mill for 1-5 hours until the mixture is clear and transparent.
[0019] Secondly, the present invention provides a method for preparing Na4Fe3(PO4)2P2O7 / C composite cathode material based on the aforementioned colloidal mixed slurry, comprising the following steps:
[0020] S1: Spray dry the colloidal mixture to obtain powder;
[0021] S2: The powder obtained by spray drying is sintered under inert gas protection to obtain the composite cathode material.
[0022] Preferably, the spray dryer in step S1 has an inlet air temperature of 200-300℃ and an outlet air temperature of 80-120℃.
[0023] Preferably, the negative pressure of the spray drying main tower in step S1 is controlled at -500 to 0 Pa.
[0024] Preferably, the particle size D50 of the powder in step S1 is 20-40 μm.
[0025] Preferably, the sintering temperature in step S2 is 300-700℃, and the holding time is 3-20h.
[0026] More preferably, the method further includes step S3: crushing the sintered material to a D50 of 1-20 μm to obtain the composite cathode material.
[0027] Thirdly, the present invention provides a Na4Fe3(PO4)2P2O7 / C composite cathode material prepared by the method described above.
[0028] Fourthly, the present invention provides a sodium-ion battery comprising the aforementioned Na4Fe3(PO4)2P2O7 / C composite cathode material.
[0029] In summary, compared with the prior art, the above-described technical solutions conceived by this invention mainly possess the following technical advantages:
[0030] (1) The carbon source used in the preparation of sodium iron pyrophosphate cathode material (Na4Fe3(PO4)2P2O7 / C composite cathode material) of this invention contains citric acid. This carbon source is premixed with an iron source containing ferric iron. Utilizing the reducing properties of citric acid, the premixing and milling processes promote the contact between the carbon and iron sources, the reduction reaction of ferric iron, and the chelation reaction, thus promoting the conversion of ferric iron to ferrous iron. After premixing and milling to a specific particle size range, a sodium source is added and milled again to obtain a colloidal mixed slurry. By controlling the process steps and conditions, this invention can obtain a colloidal mixed slurry that is clear and transparent, and can produce the Tyndall effect, thereby solving the problems of deposition and stratification caused by existing suspension mixed slurries, which affect the quality and electrochemical performance of the cathode material.
[0031] (2) The citric acid used in the preparation of the sodium iron phosphate pyrophosphate cathode material (Na4Fe3(PO4)2P2O7 / C composite cathode material) of this invention not only serves as a carbon source but also acts as a reducing agent and chelating agent in the preparation of the colloidal mixed slurry. It is speculated that citric acid, as a carbon source and chelating agent, can reduce Fe2+ in the sand milling stage. 3+ All reduced to Fe 2+ Ions, and because citric acid makes the solution acidic overall, it can cause Fe... 2+ The ions can exist stably in the solution because they do not generate Fe(OH)3 or Fe(OH)2, which ensures that no other magnetic substances are generated during the sintering process, thus ensuring that the content of magnetic substances in the finished cathode material prepared by this invention meets the standards.
[0032] (3) The raw materials used in the preparation of sodium iron phosphate pyrophosphate cathode material (Na4Fe3(PO4)2P2O7 / C composite cathode material) of the present invention are inexpensive and widely available, and the preparation method is simple and easy to scale up.
[0033] (4) By controlling the types of raw materials, adjusting the mixing sequence and controlling the process, this invention provides a solution to the problem of slurry instability (easily deposited, structural, stratified, etc.), and makes the slurry into a colloid, thereby improving the stability of the slurry and thus greatly improving the production quality.
[0034] (5) This invention provides a method for preparing Na4Fe3(PO4)2P2O7 / C composite cathode material by a high carbon method, and can effectively control the magnetic materials such as iron phosphide and iron tetroxide generated by side reactions during the production process, thereby greatly improving the safety performance of the battery. Attached Figure Description
[0035] Figure 1 This is a flowchart illustrating the preparation method of the colloidal mixed slurry for preparing Na4Fe3(PO4)2P2O7 / C composite cathode material according to the present invention.
[0036] Figure 2 The images show the mixture during the sand milling process after adding the sodium source in Example 1, and the clear, transparent colloidal solution obtained after sand milling.
[0037] Figure 3 The image shows the coin cell diagram of the Na4Fe3(PO4)2P2O7 / C composite cathode material prepared in Example 1.
[0038] Figure 4 The image shows the XRD pattern of the Na4Fe3(PO4)2P2O7 / C composite cathode material prepared in Example 1.
[0039] Figure 5 The image shows a SEM image of the Na4Fe3(PO4)2P2O7 / C composite cathode material prepared in Example 1.
[0040] Figure 6 The image shows a scanning image of magnetic metal particles in the Na4Fe3(PO4)2P2O7 / C composite cathode material prepared in Example 1.
[0041] Figure 7 Scanning image of magnetic metal particles in the Na4Fe3(PO4)2P2O7 / C composite cathode material prepared for Comparative Example 1.
[0042] Figure 8 Scanning image of magnetic metal particles in the Na4Fe3(PO4)2P2O7 / C composite cathode material prepared for Comparative Example 2. Detailed Implementation
[0043] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.
[0044] To address the technical problems of existing technologies for preparing Na4Fe3(PO4)2P2O7 / C composite cathode materials, which typically involve directly mixing and milling iron, carbon, sodium, and phosphorus sources to prepare a slurry, this invention aims to improve the mixing sequence. First, a carbon source containing citric acid is thoroughly premixed and milled with an iron source containing trivalent iron. This process leverages the chelating and reducing properties of citric acid, and because citric acid makes the slurry acidic, it can reduce the amount of Fe3O4 and other magnetic impurities, leading to uneven particle size and elemental distribution in the sprayed material, resulting in an imbalance of elements in the finished product and a decline in product quality. Furthermore, the sintering process can easily generate magnetic impurities such as Fe3O4, reducing the safety performance of the finished product and impacting its quality. 2+It exists stably, so under conditions of sufficient citric acid, the Fe in the slurry can be reduced. 3+ All reduced to Fe 2+ Ultimately, this process transforms the slurry into a clear, transparent colloidal state, thus resolving the deposition problem caused by insoluble iron phosphate in the slurry, and also addressing the issue of Fe... 3+ The hydrolysis reaction causes the formation of magnetic substances in the finished product.
[0045] Specifically, this invention first provides a colloidal slurry for preparing Na4Fe3(PO4)2P2O7 / C composite cathode materials, the preparation method of which includes the following steps:
[0046] (1) Mix and disperse an iron source, a carbon source and a solvent, wherein the carbon source contains citric acid and the iron source contains ferric iron; during the mixing and dispersion process, the iron source and the carbon source are in full contact, and the ferric iron in the iron source is partially or completely reduced to ferrous iron to obtain a premixed slurry;
[0047] (2) The premixed slurry described in step (1) is milled until the particle size D50 of the slurry is less than the first particle size. Then, a sodium source or a sodium source and a phosphorus source are added to the system. Milling is continued until the mixture is clear and transparent, which is the reaction endpoint. A colloidal mixed slurry for preparing sodium iron phosphate pyrophosphate cathode material (i.e., Na4Fe3(PO4)2P2O7 / C composite cathode material) is obtained. The first particle size is 0.6 μm. Controlling the particle size within this range is beneficial for further reaction with the sodium source to generate sodium iron phosphate pyrophosphate.
[0048] In some embodiments, the carbon source in step (1) also contains a mixture of at least one of multi-walled carbon nanotubes and graphene oxide. In addition to citric acid, adding these two carbon sources can increase the conductivity of the cathode material.
[0049] In some embodiments, the iron source in step (1) is selected from at least one of iron powder, iron(II,III) oxide, iron(III) oxide, iron(II,III) oxalate, iron(III) phosphate, and iron(III) pyrophosphate; the sodium source is at least one of sodium carbonate, sodium hydroxide, sodium formate, sodium acetate, sodium citrate, sodium oxalate, sodium nitrate, sodium sulfate, sodium pyrosulfate, sodium phosphate, sodium monohydrogen phosphate, sodium dihydrogen phosphate, pyrophosphate, sodium pyrophosphate, and sodium hydrogen pyrophosphate; the phosphorus source is one or more of phosphoric acid, ammonium monohydrogen phosphate, ammonium dihydrogen phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, and sodium phosphate; the solvent is water and / or an alcohol solvent; wherein the water is one or more of ultrapure water, double-distilled water, deionized water, pure water, and distilled water.
[0050] In some embodiments, the particle size of the iron source is in the range of nanometers to micrometers, and more preferably in the range of nanometer-sized particles.
[0051] In a preferred embodiment, the iron source is ferric phosphate, and the iron-to-phosphorus ratio in the ferric phosphate is between 0.97 and 0.975; the specific surface area of the iron source is between 10⁻¹¹ m². 2 / g.
[0052] In some embodiments, the mixing in step (1) is mechanical mixing or ultrasonic dispersion; wherein the mechanical mixing is mechanical mixing performed using a stirred tank, an impingement mixer, a homogenizing pump, a jet mixer, a static mixer, or a dynamic mixer.
[0053] In some embodiments, step (1) involves mixing and dispersing the iron source, carbon source, and solvent under heating conditions to promote dispersion and reaction; preferably, the heating temperature is 40-60°C and the mixing time is 5-140 min.
[0054] The sodium source, iron source, and phosphorus source are fed according to the stoichiometric ratio of Na, Fe, and P in the chemical formula of the cathode material Na4Fe3(PO4)2P2O7. It can be understood that when iron phosphate is selected as the iron source, iron phosphate serves as both the iron source and the phosphorus source.
[0055] In some embodiments, the molar ratio of the carbon source to the iron source is greater than or equal to 3.5:3, and can further be (3.5-4.5):3; the carbon source in this range can fully utilize the reducing and / or chelating effect of citric acid to form a colloidal slurry solution, avoiding problems such as sedimentation, stratification, and scaling that occur in suspended dispersed slurries; it can also avoid the fact that excessive carbon content will affect the battery's processing performance, such as easy peeling when used as a positive electrode material for coating and preparing electrodes, as well as the reduction in volumetric energy density caused by excessive carbon content.
[0056] The amount of solvent used in step (1) can be determined as follows: the total mass ratio of the carbon source, iron source, phosphorus source and sodium source to the solvent is (5-40):(60-95), that is, the mass ratio of solute to solvent is (5-40):(60-95), so as to achieve the control of the concentration and viscosity of the mixed slurry.
[0057] In some embodiments, the system temperature is controlled at 20-50°C during the sand milling process in step (2), specifically 20-45°C, 25-45°C, 25-40°C, 30-35°C, etc. This temperature range is conducive to the reaction forming sodium iron pyrophosphate and promotes the formation of a colloid during sand milling.
[0058] In a preferred embodiment, step (2) involves milling the premixed slurry from step (1) until the slurry particle size D50 reaches the first particle size, and then adding a sodium source, or a sodium source and a phosphorus source, to the system; the first particle size is 0.2-0.6 μm.
[0059] In some embodiments, in step (2), a sodium source, or a sodium source and a phosphorus source, are added to the system, and then the mixture is milled for 1-5 hours until the mixture is clear and transparent, which is the reaction endpoint.
[0060] In some embodiments, the pH of the mixed slurry is 2-3 at the endpoint of the reaction.
[0061] The present invention also provides a method for preparing Na4Fe3(PO4)2P2O7 / C composite cathode material based on the colloidal mixed slurry, which further includes the following steps:
[0062] S1: Spray dry the colloidal mixture to obtain powder;
[0063] S2: The powder obtained by spray drying is sintered under inert gas protection to obtain Na4Fe3(PO4)2P2O7 / C composite cathode material.
[0064] In some embodiments, the inlet air temperature of the spray dryer in step S1 is 200-300℃ and the outlet air temperature is 80-120℃; the negative pressure of the main tower of the spray dryer is controlled at -500-0Pa; and the particle size D50 of the powder obtained by spray drying is 20-40μm according to the above spray drying conditions.
[0065] In some embodiments, the sintering temperature in step S2 is 300-700℃, and further, the sintering temperature can be 500-700℃, with a holding time of 3-20 hours. In a preferred embodiment, a three-stage sintering process is adopted: first, the temperature is raised from room temperature to 200-300℃ for sintering and held for 1-5 hours; then, the temperature is raised to 350-450℃ for a second-stage sintering and held for 1-5 hours; finally, the temperature is raised to 500-700℃ and held for 8-20 hours, with a heating rate of 1-10℃ / min; during the sintering process, the furnace pressure is controlled at 20-100 Pa, and the oxygen content in the furnace is controlled below 1 ppm.
[0066] In some embodiments, the sintered material is crushed to a D50 of 1-20 μm to obtain Na4Fe3(PO4)2P2O7 / C composite cathode material.
[0067] The Na4Fe3(PO4)2P2O7 / C composite cathode material prepared in this embodiment of the invention is a high-carbon sodium iron phosphate pyrophosphate cathode material, which appears as micro-nano spherical particles with a carbon content of 6-15 wt%. The carbon mainly exists in the form of a coating layer, but can also be partially doped. It is understood that the coating layer can be partially or completely coated.
[0068] The present invention also provides a sodium-ion battery comprising the Na4Fe3(PO4)2P2O7 / C composite cathode material prepared in this invention.
[0069] [Measurement Method]
[0070] 1. Slurry D50 test
[0071] The particle size D50 was obtained by using a Malvern 3000 laser particle size analyzer.
[0072] 2. Detection of carbon content
[0073] The carbon content of the material was directly measured using a carbon-sulfur analyzer, which is an instrument based on the combustion-infrared absorption method. For specific operation instructions, refer to the carbon content detection method in GB / T 30835-2014, "Carbon Composite Lithium Iron Phosphate Cathode Materials for Lithium-ion Batteries".
[0074] 3. Electrical performance testing of assembled battery samples:
[0075] Sodium-ion secondary battery construction:
[0076] The prepared sodium-ion battery positive electrode material was mixed with conductive carbon black and a binder to form a slurry, which was then uniformly coated onto aluminum foil and dried to form the electrode. Metallic sodium was used as the negative electrode material, a PP membrane was selected as the separator, and a mixed solution of 1 mol / L NaPF6 and ethylene carbonate (EC): dimethyl carbonate (DEC) = 1:1 (v / v) was used as the electrolyte. 5 wt% fluoroethylene carbonate (FEC) was used as an additive to fabricate a coin cell. Testing conditions: For the first charge-discharge test, the battery was charged to 4.3V at 0.1C (nominal capacity 129 mA / g) and then discharged to 1.7V to obtain the first discharge capacity and the first charge capacity. Cyclic performance testing: A constant current charge-discharge test was conducted at 0.1C, with a charge-discharge voltage range of 1.7V-4.3V, under constant temperature conditions of 25℃, for 100 cycles. The capacity retention rate after 100 cycles was also measured.
[0077] Examples and comparative examples of this disclosure are described below. However, these examples are not to be construed in any way as limiting the scope of the invention.
[0078] The following is an example:
[0079] Example 1
[0080] Preparation of a Na4Fe3(PO4)2P2O7 / C composite cathode material, such as Figure 1 As shown, it includes the following steps:
[0081] Step 1: First, add a certain amount of deionized water to the premixing tank, then add 4 mol of citric acid monohydrate and mix. After mixing for 5 minutes, add 3 mol of FePO4 precursor (iron-to-phosphorus ratio of 0.97-0.975, specific surface area of 10-11 m²) to the premixing tank.2 The mixture was carried out with / g) and the slurry temperature was controlled at 50℃. The homogenizing pump was turned on during the premixing process and the premixing reaction time was controlled at 2h.
[0082] Step 2: Transfer the premixed slurry to a grinding tank, turn on the sand mill, and control the main speed of the sand mill at 1200 rpm. After grinding in both tanks for 2 hours, stop grinding. At this time, the particle size D50 of the slurry is measured to be 0.4 μm. Add 1.09 mol of sodium orthophosphate and 0.365 mol of sodium carbonate to the slurry tank, continue stirring for 20 minutes, and then continue sand milling. After sand milling for 5 hours, the slurry becomes transparent, resulting in a colloidal solution. The colloidal solution exhibits the Tyndall effect. The amount of deionized water used is based on the following ratio: the total mass of carbon source (citric acid), iron source + phosphorus source (ferric phosphate), and sodium source (sodium orthophosphate and sodium carbonate) to solvent (deionized water) is 40:60. The pH of the colloidal slurry is 2.
[0083] Step 3: Spray dry the sand-ground colloidal solution to obtain powder. The spray inlet air temperature is controlled at 250℃, the outlet air temperature is controlled at 95℃, the main tower negative pressure is controlled at -400Pa, and the atomizing disc is a special atomizing disc with 6 holes and a hole diameter of 2.5mm.
[0084] Step 4: Sinter the dried spray material under nitrogen protection. Starting from room temperature, heat the material to 300°C at a rate of 2°C / min and hold for 2 hours. Then, heat the material to 400°C at the same rate and hold for 1 hour. Finally, heat the material to 520°C at the same rate and hold for 8 hours. Cool the material to room temperature and remove it to obtain the sintered material.
[0085] Step 5: Crush the sintered material using an air jet mill, and control the particle size at the end of the crushing process to 2-3 μm to obtain Na4Fe3(PO4)2P2O7 / C composite cathode material.
[0086] Example 2
[0087] The other steps are the same as in Example 1, except that the amount of citric acid monohydrate added in step 1 is changed from 4 mol to 3.5 mol. In step 2, the suspension can also be milled to a clear colloid.
[0088] Example 3
[0089] The other steps are the same as in Example 1, except that the amount of citric acid monohydrate added in step 1 is changed from 4 mol to 4.5 mol. In step 2, the suspension can also be milled to a clear colloid.
[0090] Compared to Example 1, the carbon content in the Na4Fe3(PO4)2P2O7 / C composite cathode material obtained in Example 2 is slightly lower than that in Example 1, and the carbon content in the Na4Fe3(PO4)2P2O7 / C composite cathode material obtained in Example 3 is slightly higher than that in Example 1, but both meet the performance requirements of sodium-ion batteries, and the content of magnetic materials in the cathode materials is low.
[0091] Example 4
[0092] The other steps are the same as in Example 1, except that in step 2 the slurry particle size is controlled to 0.25 μm; 1.09 mol of sodium orthophosphate and 0.365 mol of sodium carbonate are added to the slurry tank, and then grinding is continued for 3 hours to obtain a transparent colloidal solution.
[0093] Example 5
[0094] The other steps are the same as in Example 1, except that in step 2 the slurry particle size is controlled to 0.58 μm; 1.09 mol of sodium orthophosphate and 0.365 mol of sodium carbonate are added to the slurry tank, and then grinding is continued for 5 hours to obtain a transparent colloidal solution.
[0095] Example 6
[0096] Preparation of a Na4Fe3(PO4)2P2O7 / C composite cathode material, such as Figure 1 As shown, it includes the following steps:
[0097] Step 1: First, add a certain amount of deionized water to the premixing tank, then add 4 mol of citric acid monohydrate and mix. After mixing for 5 minutes, add 3 mol of FePO4 precursor to the premixing tank for mixing reaction. Control the slurry temperature at 50℃. Turn on the homogenizing pump during the premixing process and control the premixing reaction time to 5 minutes.
[0098] Step 2: Transfer the premixed slurry to a grinding tank, turn on the sand mill, and control the main speed of the sand mill at 1200 rpm. After grinding in both tanks for 4 hours, stop grinding. At this time, the particle size D50 of the slurry is measured to be 0.4 μm. Add 1.09 mol of sodium orthophosphate and 0.365 mol of sodium carbonate to the slurry tank, continue stirring for 20 minutes, and then continue sand milling. After sand milling for 5 hours, the slurry becomes transparent, resulting in a colloidal solution. The colloidal solution exhibits the Tyndall effect. The amount of deionized water used is based on the following ratio: the total mass of carbon source (citric acid), iron source + phosphorus source (ferric phosphate), and sodium source (sodium orthophosphate and sodium carbonate) to solvent (deionized water) is 40:60. The pH of the colloidal slurry is 2.
[0099] The other steps are the same as in Example 1.
[0100] Comparative Example 1
[0101] The other steps in this comparative example are the same as in Example 1, except that the amount of citric acid monohydrate added in step 1 is changed from 4 mol to 2 mol; after adding the carbon source in step 2, the mixture is still a suspension dispersion and does not become transparent and clear. The reaction endpoint is set at a particle size D50 of 0.25 μm, and the milling is stopped. Finally, the composite material of Na4Fe3(PO4)2P2O7 / C is obtained.
[0102] Comparative Example 2
[0103] This comparative example is identical to Example 1 under the same conditions, except that the 4 mol of citric acid monohydrate added in step 1 is replaced with 3 mol of glucose. During the sand milling process, the mixture remains a suspension dispersion after 10 hours of milling and has not become transparent and clear. The sand milling reaction is stopped when the slurry particle size D50 is 0.25 μm, and the final product is the Na4Fe3(PO4)2P2O7 / C composite material.
[0104] Comparative Example 3
[0105] The other steps are the same as in Example 1, except that in steps 1 and 2, deionized water, citric acid monohydrate, FePO4 precursor, sodium orthophosphate and sodium carbonate are directly mixed and milled. After milling for 12 hours, the mixture is still a suspension and dispersion and has not become transparent and clear. The milling reaction is stopped when the particle size D50 is 0.25 μm, and the Na4Fe3(PO4)2P2O7 / C composite material is finally obtained.
[0106] Figure 2 Content a is a photograph of the mixture during the sand milling process in Example 1, which is in a turbid state; while content b is a photograph of the clear colloidal mixed slurry obtained after adding 1.09 mol of sodium orthophosphate and 0.365 mol of sodium carbonate, stirring for 20 min, and then sand milling for 5 h.
[0107] Figure 3 The coin cell diagram of the Na4Fe3(PO4)2P2O7 / C composite material prepared in Example 1 shows that the plateau and capacity are both good, with an initial discharge capacity of 103 mAh / g and an initial charge capacity of 118 mAh / g.
[0108] Figure 4 The image shows the XRD pattern of the Na4Fe3(PO4)2P2O7 / C composite material prepared in Example 1. It can be seen that the Na4Fe3(PO4)2P2O7 cathode material was synthesized in this example.
[0109] Figure 5The image shows the SEM image of the Na4Fe3(PO4)2P2O77 / C composite material prepared in Example 1. It can be seen that the cathode material prepared in Example 1 consists of micro- and nano-spherical particles.
[0110] Figure 6 , Figure 7 and Figure 8 The images show the magnetic metal particles in the Na4Fe3(PO4)2P2O7 / C composite materials prepared in Example 1, Comparative Example 1, and Comparative Example 2, respectively.
[0111] The performance parameters of the Na4Fe3(PO4)2P2O7 / C composite materials prepared in the examples and comparative examples are shown in Table 1.
[0112] Table 1
[0113]
[0114] As shown in Table 1, the Na4Fe3(PO4)2P2O7 / C composite material prepared in Example 1 has a very low magnetic content, less than 0.2 ppm, while the magnetic content of the composite materials prepared in Comparative Examples 1, 2, and 3 is 11 ppm, 18 ppm, and 8 ppm, respectively, which is several tens of times higher. Correspondingly, the electrochemical performance of the composite material prepared in Example 1 is significantly better than that of the composite materials in Comparative Examples 1, 2, and 3. This indicates that by preparing the mixed slurry into a clear and transparent colloidal state, the magnetic content in the prepared composite cathode material is significantly reduced, and the electrochemical performance of the cathode material is also significantly improved.
[0115] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.
Claims
1. A method for preparing a colloidal mixed slurry for preparing a Na4Fe3(PO4)2P2O7 / C composite cathode material, characterized by, Includes the following steps: (1) The iron source, carbon source and solvent are mixed and dispersed to obtain a premixed slurry; the carbon source is citric acid, and the iron source contains ferric iron; the molar ratio of the carbon source to the iron element in the iron source is (3.5-4.5):3; the iron source is ferric phosphate; and the solvent is water; (2) The premixed slurry described in step (1) is milled until the slurry particle size D50 is less than the first particle size. Then, sodium source and phosphorus source are added to the system, and milling is continued until the mixed system is clear and transparent, which is the reaction endpoint. A colloidal mixed slurry for preparing Na4Fe3(PO4)2P2O7 / C composite cathode material is obtained. The first particle size is 0.2-0.6 μm. The sodium source is at least one of sodium carbonate, sodium hydroxide, sodium formate, sodium acetate, sodium citrate, sodium oxalate, sodium nitrate, sodium sulfate, sodium pyrosulfate, sodium phosphate, sodium monohydrogen phosphate, sodium dihydrogen phosphate, and sodium pyrophosphate. The phosphorus source is one or more of phosphoric acid, ammonium monohydrogen phosphate, ammonium dihydrogen phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, and sodium phosphate. The sodium source, iron source, and phosphorus source are added according to the stoichiometric ratio of Na, Fe, and P in the chemical formula of cathode material Na4Fe3(PO4)2P2O7.
2. The production method according to claim 1, wherein The water mentioned in step (1) is one or more of deionized water, pure water, and distilled water.
3. The production method according to claim 1, wherein The iron-to-phosphorus ratio in the ferric phosphate is between 0.97 and 0.975; and / or, The specific surface area of the iron source is between 10 and 11 m 2 / g.
4. The production method according to claim 1, wherein The mixing and dispersion temperature in step (1) is 40-60℃, and the mixing time is 5-140 min.
5. The preparation method according to claim 1, characterized in that, The total mass ratio of the carbon source, iron source, phosphorus source and sodium source to the solvent is (5-40):(60-95).
6. The production method according to claim 1, wherein Step (2) During the sand milling process, the system temperature is controlled at 20-50℃; and / or, At the endpoint of the reaction, the pH of the mixed slurry is 2-3; and / or, Step (2) Add sodium source and phosphorus source to the system, and then continue to grind for 1-5 hours to allow the mixture to react until it becomes clear and transparent.
7. The method for preparing Na4Fe3(PO4)2P2O7 / C composite cathode material by applying the preparation method of the colloidal mixed slurry according to any one of claims 1 to 6, characterized in that, Includes the following steps: S1: Spray dry the colloidal mixture to obtain powder; S2: The powder obtained by spray drying is sintered under inert gas protection to obtain the composite cathode material.
8. The method of claim 7, wherein, The spray dryer described in step S1 has an inlet air temperature of 200-300℃ and an outlet air temperature of 80-120℃; and / or, In step S1, the negative pressure of the spray drying main tower is controlled at -500 to 0 Pa; and / or, The particle size D50 of the powder in step S1 is 20-40 μm; and / or, The sintering temperature in step S2 is 300-700℃, and the holding time is 3-20h; and / or, It also includes step S3: crushing the sintered material to a D50 of 1-20μm to obtain the composite cathode material.