CN107204464A - A kind of preparation method of nano-carbon coated manganese fluorophosphate sodium and solvent-thermal method - Google Patents

Abstract

The invention relates to a preparation method of nano-carbon-coated sodium manganese fluorophosphate and a solvothermal method; in the nano-carbon-coated sodium manganese phosphate, the weight percentage of carbon is 8-13%, the particle shape is spherical, and the particle size is 20-100nm. Uniformly dispersed Na ₂ MnPO ₄ F/C particles were prepared by solvothermal method with ascorbic acid as reducing agent and glucose as carbon source. The Na ₂ MnPO ₄ F/C prepared by this method is a nano-particle with small size and uniform distribution. Glucose is used as a carbon source to coat the surface of sodium manganese fluorophosphate particles, which not only improves the dispersion of the particles, but also makes the particles Evenly dispersed, glucose is cracked into carbon under high temperature conditions to coat the particle surface to prevent the oxidation of Mn ²⁺ , and at the same time improve the conductivity between particles, reduce polarization, and improve the electrochemical performance of the material.

Description

A kind of preparation method of nano-carbon-coated sodium manganese fluorophosphate and solvothermal method

technical field

The invention relates to a preparation method of nanometer carbon-coated sodium manganese fluorophosphate and a solvothermal method, and belongs to the technical field of battery material preparation.

Background technique

With the rapid development of science and technology, people's demand for large-scale energy storage systems and environmentally friendly vehicles is increasing, and the consumption of lithium resources is quite significant. Lithium reserves are small and the safety of lithium batteries is unstable, so the development of lithium battery substitutes has become a research hotspot, among which sodium-ion batteries are the most popular and the most feasible alternative batteries. Sodium and lithium belong to the same main group, have similar physical and chemical properties, and are rich in sodium resources, accounting for about 2.64% of the earth's crustal reserves. They are evenly distributed and cheap. The half-cell potential of sodium is about 0.3V higher than that of lithium, so it can be decomposed with low potential The electrolyte system is safer than lithium-ion batteries.

The similarity in the physical and chemical properties of sodium and lithium allows researchers to start the research on sodium-ion batteries on the lithium-ion battery system. At present, layered transition metal oxides, polyanion compounds and other sodium-ion battery cathode materials have been developed. In order to pursue the high energy density of sodium-ion batteries, researchers have turned their attention to transition metal fluorophosphate sodium salt Na ₂ MPO ₄ F (M=Fe, Co, Ni, Mn) cathode materials, due to the introduction of a chlorine Ions, in order to achieve charge balance, this type of material structure contains two metal ions, so it is possible to achieve two electron exchanges per transition metal ion, and the corresponding theoretical capacity is about twice that of the corresponding phosphate. This type of material contains open channels for Na ⁺ to pass through, Na ⁺ deintercalation/intercalation stability is good, and due to the strong covalent bond of oxygen atoms in the polyanion polyhedron, it has good thermal stability. Fluorophosphoric acid system transition metal materials have a lattice structure different from that of phosphoric acid systems, providing a two-dimensional channel for ion conduction, which is conducive to the improvement of discharge stability and capacity. At the same time, due to the strong electronegativity of fluorine ions, the ionicity of MF is stronger than that of MO, which can improve the working voltage platform of the material. Therefore, fluorophosphate materials are promising cathode materials for sodium-ion batteries with high energy density. Among them, Na ₂ MnPO ₄ F has higher voltage and higher theoretical specific capacity, coupled with abundant manganese resources, etc., Na ₂ MnPO ₄ F is a new type of sodium battery material with high energy density and relatively promising development potential. Fluorophosphate theoretically contains two sodium atoms, so it is expected to have about twice the theoretical capacity of existing lithium metal phosphate salts (250mAh g ^-1 when both Na ⁺ are desorbed). Due to the strong inductive effect of PO ₄ ^- and the strong electronegativity of F ^- , Na ₂ MnPO ₄ F has a high working potential (3.66V, 4.67V VS.Na/Na ⁺ ) and good thermal stability, is A very promising cathode material for sodium-ion batteries. However, due to the low electrochemical activity of Na ₂ MnPO ₄ F, there are few early reports on this polyanionic electrode material. Until Wu et al. (J. Mater. Chem., 2011, 21, 18630) reported the synthesis of Na ₂ MnPO ₄ F materials by sol-gel method. It is found that the electrochemical performance can be significantly improved by reducing the particle size, carbon coating and increasing the test temperature. The first discharge specific capacity measured at 60℃ is close to 100mAh·g ^-1 . The electrical performance is still not ideal and needs to be further improved. At present, Na ₂ MnPO ₄ F/C materials can be synthesized by a variety of different preparation methods, mainly solid-phase method, sol-gel method, hydrothermal method and other methods. Jin Siqin et al. (Patent No. CN103137969A) used ammonium dihydrogen phosphate, sodium carbonate, manganese acetate and manganese fluoride as raw materials to prepare Na ₂ MnPO ₄ F/C by hydrothermal method. After centrifugal washing and heat treatment at 400°C for 6 hours, the The prepared Na ₂ MnPO ₄ F and LiMnPO ₄ were mixed at a molar mass ratio of 1:1 as cathode mixed powder. Jin Dongjian et al. (Patent No. CN102810669A) prepared Na ₂ MnPO ₄ F/C materials by using sodium nitrate, sodium fluoride, manganese nitrate, and ammonium dihydrogen phosphate as raw materials by a high-temperature solid-phase method. The solvothermal method is based on the hydrothermal method, using organic matter instead of water as the reaction solvent. Therefore, compared with the hydrothermal method, the solvothermal synthesis method can realize the mixing of components at the atomic level, the chemical uniformity is better, the particle size of the synthesized powder is small and the distribution is narrow, which has the advantages of operability and controllability. The physical and chemical properties of materials prepared by solvothermal method are also specific and excellent. At present, there is no relevant patent on the synthesis of Na ₂ MnPO ₄ F/C powder by solvent method.

Contents of the invention

The present invention adopts solvothermal method, uses sodium compound, fluorine compound, manganese compound and phosphorus compound as raw materials, uses deionized water, ethylene glycol and oleic acid as reaction solvent, and obtains nanometer carbon coated Sodium manganese fluoride-coated phosphate cathode material. The carbon-coated sodium manganese fluorophosphate powder prepared by the method has uniform particle shape, uniform particle size distribution and ideal crystal structure, and can be used as a positive electrode material for a sodium ion battery.

The carbon-coated sodium manganese fluoride phosphate of the present invention comprises 8-13% of carbon by weight in the carbon-coated sodium manganese fluoride phosphate, the shape of the particles is spherical, and the particle diameter is 20-100 nm.

The preparation method of carbon-coated sodium manganese fluorophosphate solvothermal method of the present invention, the steps are as follows:

(1) Using sodium compounds, fluorine compounds, manganese compounds and phosphorus compounds as raw materials, the molar ratio of the four elements is 2:1:1:1; the additive is an antioxidant, wherein the antioxidant accounts for the theoretical synthesis of fluorophosphoric acid 1% to 8% of the mass of sodium manganese; make a solution of sodium compounds, phosphorus compounds and ethylene glycol, and continue to stir until the two are fully dissolved to obtain solution A; dissolve fluorine compounds and manganese salts in a solution containing antioxidants In the aqueous solution, the uniformly mixed solution B is obtained by stirring;

(2) Mix the two solutions obtained in step (1) to obtain a white suspension, add an appropriate amount of oleic acid to the solution and stir until the solution is evenly mixed, the ratio of oleic acid to all solvents is 1:12-1:3, The solvent is the sum of water, ethylene glycol and oleic acid; add the mixed solution into the reaction kettle, put the reaction kettle into an oven and heat it up to 120°C-180°C, keep it warm for 6-24h, cool to room temperature after the reaction and take it out Reaction kettle; after the precipitate is centrifuged with detergent, it is vacuum-dried at 60°C to 80°C for 6h to 10h to obtain sodium manganese fluorophosphate;

(3) Add glucose to the sodium manganese fluorophosphate prepared in step 2) according to 5% to 15% of the mass of the final product in carbon, fully grind it and put it into a quartz crucible. Calcining at ℃ and holding for 3-5 hours to obtain carbon-coated sodium manganese fluorophosphate powder with a size of 20nm-100nm.

Described antioxidant is ascorbic acid.

The sodium compound is NaOH or CH ₃ COONa.

The fluorine compound is NH ₄ F or NaF.

The manganese salt is Mn(CH ₃ COO) ₂ or Mn(SO ₄ ) ₂ .

The phosphorus compounds are H ₃ PO ₄ , NH ₄ H ₂ PO ₄ , (NH ₄ ) ₂ HPO ₄ .

The detergent is deionized water or ethanol.

The invention has the advantage of using ascorbic acid as a reducing agent and glucose as a carbon source to prepare evenly dispersed _Na2MnPO4F /C particles by a solvothermal method _. The Na ₂ MnPO ₄ F/C prepared by this method is in the shape of spherical particles, and the particle size is between 20nm and 100nm. Glucose is used as carbon source to coat the surface of sodium manganese fluorophosphate particles, which not only improves the dispersion of the particles, but also makes the particles uniformly dispersed. Glucose is cracked into carbon at high temperature and coated on the surface of the particles to prevent the oxidation of Mn2 ⁺ , and at the same time improve The conductivity between the particles is improved, the polarization is reduced, and the electrochemical performance of the material can be improved.

Description of drawings

FIG. 1 is an X-ray diffraction pattern of Na ₂ MnPO ₄ F/C synthesized in Example 1.

FIG. 2 is a scanning electron micrograph of Na ₂ MnPO ₄ F/C synthesized in Example 1. FIG.

FIG. 3 is the initial charge-discharge curve of Na ₂ MnPO ₄ F/C synthesized in Example 1. FIG.

Fig. 4 is the X-ray diffraction pattern of Na ₂ MnPO ₄ F/C synthesized in Example 3.

detailed description

Example 1:

Using manganese sulfate, ammonium fluoride, sodium hydroxide, and phosphoric acid as raw materials, weigh the corresponding substances according to the molar ratio of the substances, so that the molar ratio of Na:Mn:P:F is 2:1:1:1, and weigh 0.8535g of sulfuric acid Dissolve manganese and 20ml of ethylene glycol in a beaker, add 0.028g of antioxidant ascorbic acid and stir evenly, then add 0.4242g of ammonium fluoride into the beaker and stir until completely dissolved. Then add 30ml of deionized water into another beaker, weigh 1.459g of sodium hydroxide and 0.576g of phosphoric acid (mass percentage is 85%) respectively into the beaker, stir until completely dissolved. Mix the above two solutions to obtain a white suspension, add 10ml of oleic acid and stir until the solution is evenly mixed. Add the mixed solution into a 100ml stainless steel reaction kettle and react at 120°C for 6 hours. The precipitate is centrifuged three times with deionized water detergent, and then centrifuged three times with ethanol detergent, then vacuum-dried at 60°C for 6 hours to obtain sodium manganese fluorophosphate powder . The above sodium manganese fluorophosphate powder was mixed and ground with 0.26 g of glucose, and heat-treated at 500°C for 3 hours under the protection of N ₂ gas to obtain carbon-coated sodium manganese fluorophosphate powder, whose X-ray diffraction is shown in Figure 1. The characteristic peaks of XRD in the figure correspond to the diffraction peaks of the XRD pattern of standard Na ₂ MnPO ₄ F/C powder. The morphology of the synthesized Na ₂ MnPO ₄ F/C is shown in Figure 2, and the particle size is between 20 and 50 nm. Its first charge-discharge curve is shown in Figure 3. At room temperature and at a charge-discharge current of 0.1C, the discharge specific capacity of Na ₂ MnPO ₄ F/C is 97.5mAh g ^-1 .

Example 2

Using manganese acetate, sodium fluoride, sodium acetate, and ammonium dihydrogen phosphate as raw materials, weigh the corresponding substances according to the molar ratio of the substances, so that the molar ratio of Na:Mn:P:F is 2:1:1:1, and weigh 1.79 Add 30ml of manganese acetate and 30ml of deionized water to dissolve in a beaker, add 0.10g of antioxidant ascorbic acid and stir evenly, then add 0.428g of sodium fluoride into the beaker and stir until completely dissolved. Then add 20ml of deionized water into another beaker, weigh 1.78g of sodium acetate and 1.19g of ammonium dihydrogen phosphate into the beaker, and stir until completely dissolved. Mix the above two solutions to obtain a white suspension, add 10ml of oleic acid and stir until the solution is evenly mixed. Add the mixed solution into a 100ml stainless steel reaction kettle, and react at 120°C for 24 hours. The precipitate is centrifuged three times with deionized water detergent, and then centrifuged three times with ethanol detergent, and vacuum dried at 70°C for 8 hours to obtain sodium manganese fluorophosphate powder. . The above sodium manganese fluorophosphate powder was mixed and ground with 0.275 g of glucose, and heat-treated at 500°C for 5 hours under the protection of N ₂ gas to obtain carbon-coated sodium manganese fluorophosphate powder, whose X-ray diffraction is shown in Figure 4. The characteristic peaks of XRD in the figure correspond to the diffraction peaks of the XRD pattern of standard Na ₂ MnPO ₄ F powder. The morphology of the synthesized Na ₂ MnPO ₄ F/C is a spherical particle, and the particle size is between 30nm and 60nm.

Example 3

Using manganese acetate, sodium fluoride, sodium acetate, and diammonium hydrogen phosphate as raw materials, weigh the corresponding substances according to the molar ratio of the substances, so that the molar ratio of Na:Mn:P:F is 2:1:1:1, and weigh 1.79 Add 30ml of manganese acetate and 30ml of deionized water to dissolve in a beaker, add 0.0150g of antioxidant ascorbic acid and stir well, then add 0.428g of sodium fluoride into the beaker and stir until completely dissolved. Then add 25ml of deionized water into another beaker, weigh 1.78g of sodium acetate and 1.38g of diammonium hydrogen phosphate into the beaker, and stir until completely dissolved. Mix the above two solutions to obtain a white suspension, add 5ml of oleic acid and stir until the solution is evenly mixed. Add the mixed solution into a 100ml stainless steel reaction kettle and react at 180°C for 6 hours. The precipitate is centrifuged three times with deionized water detergent, and then centrifuged three times with acetone lotion, then vacuum-dried at 80°C for 6 hours to obtain sodium manganese fluorophosphate powder . The above-mentioned sodium manganese fluorophosphate powder was mixed and ground with 0.216g glucose, and heat-treated at 600°C for 4 hours under the protection of N ₂ gas to obtain carbon-coated sodium manganese fluorophosphate powder. The morphology of the synthesized Na ₂ MnPO ₄ F/C was short Columnar, the particle size is about 30nm ~ 50nm.

Example 4

Using manganese sulfate, ammonium fluoride, sodium hydroxide, and diammonium hydrogen phosphate as raw materials, weigh the corresponding substances according to the molar ratio of the substances, so that the molar ratio of Na:Mn:P:F is 2:1:1:1, and weigh Dissolve 0.854g of manganese sulfate heptahydrate and 25ml of ethylene glycol in a beaker, add 0.028g of antioxidant ascorbic acid and stir evenly, then add 0.382g of ammonium fluoride into the beaker and stir until completely dissolved. Then add 30ml of deionized water into another beaker, weigh 0.8334g of sodium hydroxide and 1.38g of diammonium hydrogen phosphate into the beaker, and stir until completely dissolved. Mix the above two solutions to obtain a white suspension, add 5ml of oleic acid and stir until the solution is evenly mixed. Add the mixed solution into a 100ml stainless steel reaction kettle and react at 180°C for 6 hours. The precipitate is centrifuged three times with deionized water detergent, and then centrifuged three times with ethanol detergent, then vacuum-dried at 60°C for 10 hours to obtain sodium manganese fluorophosphate powder . Mix and grind the above-mentioned sodium manganese fluorophosphate powder with 0.108g glucose, and heat-treat at 600°C for 5 hours under the protection of Ar ₂ gas to obtain carbon-coated sodium manganese fluorophosphate powder. The shape of the synthesized Na ₂ MnPO ₄ F/C is rod-like , The particle size is between 50nm and 80nm.

Example 5

Using manganese acetate, ammonium fluoride, sodium acetate, and ammonium dihydrogen phosphate as raw materials, weigh the corresponding substances according to the molar ratio of the substances, so that the molar ratio of Na:Mn:P:F is 2:1:1:1, and weigh 1.79 Add 20ml of ethylene glycol to manganese acetate and dissolve in a beaker, add 0.12g of antioxidant ascorbic acid and stir well, then add 0.382g of ammonium fluoride into the beaker and stir until completely dissolved. Then add 20ml of deionized water into another beaker, weigh 3.56g of sodium acetate and 1.19g of ammonium dihydrogen phosphate into the beaker, and stir until completely dissolved. Mix the above two solutions to obtain a white suspension, add 20ml of oleic acid and stir until the solution is evenly mixed. Add the mixed solution into a 100ml stainless steel reaction kettle, and react at 160°C for 5 hours. The precipitate is centrifuged three times with deionized water detergent, and then centrifuged three times with acetone lotion, and vacuum dried at 80°C for 6 hours to obtain sodium manganese fluorophosphate powder. . Mix and grind the above-mentioned sodium manganese fluorophosphate powder with 0.324g glucose and heat-treat at 700°C for 3 hours under the protection of N ₂ gas to obtain carbon-coated sodium manganese fluorophosphate powder. The morphology of the synthesized Na ₂ MnPO ₄ F/C is short columnar , The particle size is between 60nm and 100nm.

The present invention discloses and proposes a preparation method of nano-carbon-coated sodium manganese fluorophosphate and solvothermal method. Those skilled in the art can realize it by referring to the content of this article and appropriately changing the conditions and routes. Although the method and preparation technology of the present invention The preferred implementation examples have been described, and those skilled in the art can obviously modify or recombine the methods and technical routes described herein without departing from the content, spirit and scope of the present invention to realize the final preparation technology. In particular, it should be pointed out that all similar substitutions and modifications will be obvious to those skilled in the art, and they are all considered to be included in the spirit, scope and content of the present invention.

Claims (8)

1. A nano-carbon-coated sodium manganese fluorophosphate, characterized in that carbon-coated sodium manganese fluorophosphate nanoparticles, the weight percentage of carbon is 8-13%, the particle shape is spherical particles, and the particle size is 20-100nm . 2. the preparation method of the solvothermal method of the nanometer carbon coating sodium manganese fluorophosphate of claim 1, it is characterized in that the steps are as follows: (1) Using sodium compounds, fluorine compounds, manganese salts and phosphorus compounds as raw materials, the molar ratio of the four elements is 2:1:1:1; the additive is an antioxidant, of which antioxidants account for the theoretical synthesis of manganese fluorophosphate 1%-8% of sodium mass; make a solution of sodium compound, phosphorus compound and ethylene glycol, and keep stirring until the two are fully dissolved to obtain solution A; dissolve fluorine compound and manganese salt in the In the aqueous solution, a uniformly mixed solution B is obtained by stirring; (2) Mix the two solutions obtained in step (1) to obtain a white suspension, add oleic acid to the solution and stir until the solution is evenly mixed, and the ratio of oleic acid to all solvents is 1:12-1:3, wherein The solvent is the sum of water, ethylene glycol and oleic acid; add the mixed solution into the reaction kettle, put the reaction kettle into an oven and heat up to 120℃～180℃, keep it warm for 6～24h, after the reaction is completed, cool to room temperature and take out the reaction Kettle; after the precipitate is centrifuged with detergent, it is vacuum-dried at 60°C to 80°C for 6h to 10h to obtain sodium manganese fluorophosphate powder; (3) Add glucose to the sodium manganese fluorophosphate powder obtained in step 2) according to 5%-15% of the final product mass accounted for by carbon, fully grind it and put it into a quartz crucible, and place it under the protection of nitrogen or argon at 500 ~ Calcined at 700°C and kept for 3-5 hours to obtain carbon-coated sodium manganese fluorophosphate powder with a size of 20nm-100nm. 3. The method of claim 2, wherein the antioxidant is ascorbic acid. 4. The method of claim 2, wherein the sodium compound is _NaOH or CH3COONa. 5. The method of claim 2, wherein the fluorine compound is NH4F or _NaF . 6. The method of claim ₂ , wherein the manganese salt is MnSO4 or Mn(CH3COO _{)2 .} 7. The method according to claim 2, characterized in that the phosphorus compound is H ₃ PO ₄ , NH ₄ H ₂ PO ₄ , (NH ₄ ) ₂ HPO ₄ . 8. The method according to claim 2, characterized in that the detergent is deionized water or ethanol.