Large-particle-size carbon-coated sodium vanadium phosphate as well as preparation method and application thereof

Abstract

The invention provides large-particle-size carbon-coated sodium vanadium phosphate and a preparation method and application thereof.The preparation method of the large-particle-size carbon-coated sodium vanadium phosphate comprises the following steps that a sodium source, a vanadium source and pure water are placed in a container, and the reaction temperature is controlled to range from 70 DEG C to 100 DEG C in a water bath; after a uniform solution is formed through the reaction, the container is placed in a water bath at the temperature of 40-60 DEG C for cooling crystallization, the crystallization time is 2-6 h, and a sodium metavanadate solid is obtained; the sodium metavanadate solid is placed in a reducing atmosphere to be roasted, and NaVO2 is prepared; the preparation method comprises the following steps: mixing NaVO2, a sodium source, a phosphorus source and a carbon source, and carrying out sanding and spray drying to obtain a sodium vanadium phosphate precursor; and placing the sodium vanadium phosphate precursor in an inert atmosphere for two-stage roasting to obtain the large-particle-size carbon-coated sodium vanadium phosphate. The prepared large-particle-size carbon-coated sodium vanadium phosphate is large and controllable in size, and when the large-particle-size carbon-coated sodium vanadium phosphate is used as a sodium-ion battery positive electrode material, the energy density of unit mass can be improved, so that the electrochemical performance of a battery is improved.

Description

Technical Field

[0001] The invention relates to battery material technology, and in particular to large-particle carbon-coated sodium vanadium phosphate, and a preparation method and use thereof. Background Art

[0002] As a new generation of power batteries, sodium ion batteries have the advantages of high energy density, long cycle life, no memory effect, low self-discharge, no pollution, good safety performance, and low price. Among the many sodium ion battery positive electrode materials, the NASICON structure positive electrode material has attracted much attention due to its stable three-dimensional skeleton structure and high ion conductivity. Among them, the most representative sodium ion battery NASICON type positive electrode material is sodium vanadium phosphate (chemical formula Na3V2(PO4)3, referred to as NVP). NVP is a rhombus structure, belonging to the R-3C space group, and is composed of oxygen atoms on the common vertices of (VO)6 octahedron and (PO)4 tetrahedron connected to each other to form a [V2(PO4)3] "lantern"-shaped basic unit, and sodium ions occupy six-coordinate and eight-coordinate positions. During the charge and discharge process, the sodium ions occupying the eight-coordinate can be reversibly deintercalated and deintercalated, forming a voltage platform near 3.4V, corresponding to a theoretical capacity of 117.6mAh / g (energy density up to 400Wh / Kg).

[0003] However, the particle size of traditional sodium vanadium phosphate is relatively small, about 0.2-1 micron, which leads to its compaction density being too low, and thus the energy density per unit mass being too low. At present, hydrothermal reaction can be used to increase the pressure and time of the reaction, thereby increasing the crystallinity of the material and thus the compaction density. However, the hydrothermal reaction equipment is a high-pressure special equipment with a low safety factor and is difficult to achieve industrial production. In addition, the reaction temperature can be increased, usually to 1000-1200°C, so that small particles can be melted together and combined into large particles. However, this method has a high reaction temperature, consumes a lot of energy, and the reaction is difficult to control, which can easily lead to particles that are too large, affecting battery performance.

[0004] Therefore, a simple and feasible preparation method for increasing the particle size of sodium vanadium phosphate is urgently needed. Summary of the invention

[0005] The purpose of the present invention is to propose a preparation method of large-particle carbon-coated sodium vanadium phosphate to address the problem that the compaction density of traditional sodium vanadium phosphate is too low, resulting in too low energy density per unit mass. The steps of the method are scientific and reasonable. The prepared large-particle carbon-coated sodium vanadium phosphate has a large size and is controllable. When used as a positive electrode material for a sodium ion battery, the energy density per unit mass can be increased, thereby improving the electrochemical performance of the battery.

[0006] It should be noted that, in the present invention, unless otherwise specified, the specific meaning of "including" in relation to composition limitations and descriptions includes both open-ended "including", "comprising", etc. and similar meanings, as well as closed-ended "composed of", "composed of", etc. and similar meanings.

[0007] To achieve the above object, the technical solution adopted by the present invention is: a method for preparing large-particle carbon-coated sodium vanadium phosphate, comprising the following steps:

[0008] Step 1, according to the molar ratio of Na:V:H2O = 1.01-1.05:1:4-5, put the sodium source, vanadium source and pure water into a container at once, and place it in a water bath, control the reaction temperature to 70-100°C, and react for 1-4 hours;

[0009] Step 2, placing the container in a 40-60° C. water bath for cooling and crystallization, the crystallization time is 2-6 hours, and filtering to obtain sodium metavanadate solid; the cooling and crystallization in a 40-60° C. water bath of the present invention is conducive to controlling the growth size of the grains, and the size of the grains is larger than the grains precipitated at room temperature;

[0010] Step 3, calcining solid sodium metavanadate in a reducing atmosphere to prepare NaVO2, the calcination temperature is 600-800°C, and the calcination time is 3-8h;

[0011] Step 4, according to the molar ratio of Na:V:P:C = 3:2:3:0.5-2, NaVO2, a sodium source, a phosphorus source, and a carbon source are mixed, sand milled, and spray-dried to obtain a sodium vanadium phosphate precursor;

[0012] Step 5: Place the sodium vanadium phosphate precursor in an inert atmosphere and perform two-stage calcination to prepare large-particle carbon-coated sodium vanadium phosphate.

[0013] Furthermore, the sodium source in step 1 is one or more of sodium carbonate, sodium oxalate, sodium citrate, sodium phosphate, sodium dihydrogen phosphate, sodium lactate, sodium bicarbonate, sodium chloride, sodium sulfate, sodium lactate, sodium nitrate and sodium hydroxide.

[0014] Furthermore, the vanadium source in step 1 is one or more of ammonium metavanadate, vanadium pentoxide and ammonium polyvanadate.

[0015] Furthermore, the reaction temperature in step 1 is 75-90°C.

[0016] Furthermore, in step 2, the water bath temperature is 40-50° C., and the crystallization time is 2-4 h.

[0017] Furthermore, the reducing atmosphere in step 3 is one or more of ammonia, hydrogen, methane and carbon monoxide.

[0018] Furthermore, the calcination temperature in step 3 is 600-700° C., and the calcination time is 3-6 hours.

[0019] Furthermore, the phosphorus source in step 4 is one or more of diammonium phosphate, phosphoric acid, sodium dihydrogen phosphate, diammonium hydrogen phosphate and monoammonium phosphate.

[0020] Furthermore, the carbon source in step 4 is one or more of citric acid, oxalic acid, glucose, stearic acid, ascorbic acid, ammonium citrate and sodium citrate.

[0021] Furthermore, in step 4, the sand milling and spray drying are performed at a sand milling speed of 1200-1500 rpm and a spray drying temperature of 200-240°C.

[0022] Furthermore, the inert atmosphere in step 5 is one or more of ammonia, argon and helium.

[0023] Furthermore, the two-stage calcination in step 5 is as follows: pre-calcination temperature is 300-500° C., pre-calcination time is 3-8 hours, and re-calcination temperature is 700-900° C., and calcination time is 5-10 hours.

[0024] Furthermore, the two-stage calcination in step 5 is as follows: pre-calcination temperature 350-450°C, pre-calcination time 3-6h, re-calcination temperature 750-850°C, calcination time 5-8h.

[0025] The reaction equation of the method for preparing large-particle carbon-coated sodium vanadium phosphate of the present invention is as follows:

[0026] 3NaVO3+2NH3=3NaVO2+N2+3H2O

[0027] 2NaVO2+3H3PO4+NaOH=Na3V2(PO4)3+5H2O

[0028] Another object of the present invention is to disclose a large-particle carbon-coated sodium vanadium phosphate prepared by the above method.

[0029] Furthermore, the particle size of the large-particle carbon-coated sodium vanadium phosphate is 1-5 microns, preferably 2-4 microns.

[0030] Furthermore, the large-particle carbon-coated sodium vanadium phosphate is in the shape of a sugar cube.

[0031] Furthermore, the compaction density of the large-particle carbon-coated sodium vanadium phosphate is 2.2-2.5 g / cm 3 .

[0032] Furthermore, the purity of the large-particle carbon-coated sodium vanadium phosphate is greater than or equal to 99.5%. Unless otherwise specified, % in the present invention refers to mass percentage.

[0033] Another object of the present invention is to disclose a use of large-particle carbon-coated sodium vanadium phosphate in the field of positive electrode materials for sodium ion batteries.

[0034] The large-particle sodium vanadium phosphate, preparation method and use thereof of the present invention have the following advantages compared with the prior art:

[0035] 1) The present invention controls the molar ratio of vanadium to water to obtain a vanadium solution of a specific concentration, which is a step that is crucial for achieving precise size control of sodium metavanadate. Furthermore, this size control strategy effectively guides the particle size of the carbon-coated sodium vanadium phosphate, ensuring the large particle size characteristics of the final product. This preparation method is not only innovative, but also easy to implement in actual operation, making large-scale production possible.

[0036] 2) The present invention adopts two-stage calcination of sodium vanadium phosphate precursor to ensure sufficient carbonization of the carbon source while also making the product more crystalline; this lays the foundation for its high performance in electrochemical applications.

[0037] 3) The large-particle carbon-coated sodium vanadium phosphate of the present invention has a large particle size. When used as a positive electrode material for sodium ion batteries, the amount of liquid absorbed by the solvent is greatly reduced (experimental data show that its liquid absorption is 0.5-0.7 times that of ordinary sodium vanadium phosphate). This feature not only reduces the amount of solvent used, reduces the cost of homogenization, but also increases the solid content of the material. The increase in solid content directly enhances the electrochemical properties of the material, making the battery perform well in terms of energy density and cycle life.

[0038] 4) The present invention uses sodium metavanadate to prepare NaVO2, and then uses NaVO2 as a vanadium source to prepare carbon-coated sodium vanadium phosphate, because the first prepared NaVO2 and the subsequent raw materials will not react to destroy the particle size when mixed, thereby the basic particle size skeleton is grown, thereby improving the particle size of the material. The particle size of the carbon-coated sodium vanadium phosphate prepared by the present invention is 1-5 microns, preferably 2-4 microns. The traditional use of sodium metavanadate as a vanadium source will react with the phosphorus source during mixing without the existence of particles, and the particle size of the subsequent sodium vanadium phosphate cannot be controlled.

[0039] In summary, the large-particle sodium vanadium phosphate and its preparation method of the present invention show significant advantages in preparation process, particle size control, crystallinity improvement and electrochemical performance optimization, providing new ideas and solutions for the development of positive electrode materials for sodium ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 The XRD diffraction pattern of NaVO2 prepared in Example 1;

[0041] Figure 2This is a SEM scanning electron microscope image of the large-particle carbon-coated sodium vanadium phosphate prepared in Example 1. DETAILED DESCRIPTION

[0042] The present invention is further described below with reference to the examples. The description of the technical features described below is based on representative embodiments and specific examples of the present invention, but the present invention is not limited to these embodiments and specific examples. It should be noted that:

[0043] Unless otherwise stated, the units used in this specification are all international standard units, and the numerical values ​​and numerical ranges appearing in the present invention should be understood to include the inevitable systematic errors in industrial production.

[0044] In this specification, the numerical range expressed using "a numerical value A to a numerical value B" means a range including the endpoints numerical values ​​A and B.

[0045] In this specification, the numerical range expressed using "above" or "below" means a numerical range including the number.

[0046] In this specification, the word "may" includes both performing a certain process and not performing a certain process.

[0047] In this specification, the use of "optional" or "optional" indicates that certain substances, components, execution steps, application conditions and other factors are used or not used.

[0048] In this specification, when "normal temperature" or "room temperature" is used, the temperature may be 15-25°C.

[0049] In this manual, the reagents or instruments used without indicating the manufacturer are all conventional products that can be obtained through commercial purchase.

[0050] Example 1

[0051] This embodiment discloses a large-particle carbon-coated sodium vanadium phosphate, and the preparation method thereof is as follows:

[0052] 1. According to the molar ratio of Na:V:H2O = 1.01:1:5, sodium hydroxide, vanadium pentoxide and pure water are put into a container at once, and placed in a water bath. The reaction temperature is controlled at 90°C and the reaction is carried out for 2 hours;

[0053] 2. After the reaction forms a uniform solution, place the container in a 50°C water bath for cooling and crystallization. The crystallization time is 3 hours to obtain sodium metavanadate solid;

[0054] 3. The sodium metavanadate solid was calcined in an ammonia atmosphere at 800°C for 2 hours. The product NaVO2 was analyzed by XRD. Figure 1 ;

[0055] 4. According to the molar ratio of Na:V:P:C=3:2:3:2, the NaVO2 obtained in 3 was mixed with sodium hydroxide, phosphoric acid and glucose, and the mixture was sand-milled at 1200 rpm for 4 h and spray-dried at 220°C to obtain a sodium vanadium phosphate precursor;

[0056] 5. The sodium vanadium phosphate precursor was placed in an argon atmosphere and calcined in two stages. The first stage was calcined at 400°C for 4 hours, and the second stage was calcined at 850°C for 6 hours. The product was tested by SEM. Figure 2 .

[0057] The characterization of the large-particle carbon-coated sodium vanadium phosphate prepared in this example is as follows Figure 1 and Figure 2 As shown, the XRD peak of the material is very high and sharp, proving that the material has high crystallinity. SEM shows that the material particle size is in the shape of sugar cubes, with a uniform particle size of 2-3 microns. The compacted density is 2.40g / cm 3 .

[0058] Example 2

[0059] This embodiment discloses a large-particle carbon-coated sodium vanadium phosphate, and the preparation method thereof is as follows:

[0060] 1. According to the molar ratio of Na:V:H2O = 1.02:1:4.5, sodium hydroxide, vanadium pentoxide and pure water are put into a container at once, and placed in a water bath. The reaction temperature is controlled at 85°C and the reaction is carried out for 3 hours;

[0061] 2. Place the container in a 55°C water bath for cooling and crystallization for 4 hours to obtain sodium metavanadate solid;

[0062] 3. The sodium metavanadate solid was calcined in a hydrogen atmosphere at a temperature of 850°C for 3 hours to obtain NaVO2;

[0063] 4. According to the molar ratio of Na:V:P:C=3:2:3:1.5, the NaVO2 obtained in 3 is mixed with sodium hydroxide, phosphoric acid and glucose, and the mixture is sand-milled and spray-dried to obtain a sodium vanadium phosphate precursor;

[0064] 5. The sodium vanadium phosphate precursor is placed in a nitrogen atmosphere and calcined in two stages. The first stage calcination temperature is 450°C and the calcination time is 3 hours. The second stage calcination temperature is 800°C and the calcination time is 7 hours.

[0065] The XRD peak of the large-particle carbon-coated sodium vanadium phosphate in this embodiment is very high and sharp, which proves that the material has high crystallinity. SEM shows that the material particle size is in the shape of sugar cubes, with a uniform particle size of 3-4 microns. The compacted density is 2.30 g / cm3 .

[0066] Example 3

[0067] This embodiment discloses a large-particle carbon-coated sodium vanadium phosphate, and the preparation method thereof is as follows:

[0068] 1. According to the molar ratio of Na:V:H2O = 1.03:1:5, sodium hydroxide, vanadium pentoxide and pure water are put into a container at once, and placed in a water bath. The reaction temperature is controlled at 85°C and the reaction is carried out for 3 hours;

[0069] 2. Place the container in a 50°C water bath for cooling and crystallization for 4 hours to obtain sodium metavanadate solid;

[0070] 3. The sodium metavanadate solid was calcined in an ammonia atmosphere at a temperature of 850°C for 2 hours to prepare NaVO2;

[0071] 4. According to the molar ratio of Na:V:P:C=3:2:3:1.8, the NaVO2 obtained in 3 is mixed with sodium hydroxide, phosphoric acid and glucose, and the mixture is sand-milled and spray-dried to obtain a sodium vanadium phosphate precursor;

[0072] 5. The sodium vanadium phosphate precursor is placed in a helium atmosphere and calcined in two stages. The first stage is calcined at 400°C for 3 hours, and the second stage is calcined at 800°C for 8 hours.

[0073] The XRD peak of the large-particle carbon-coated sodium vanadium phosphate in this embodiment is very high and sharp, which proves that the material has high crystallinity. SEM shows that the material particle size is in the shape of sugar cubes, with a uniform particle size of 2-3 microns. The compacted density is 2.33 g / cm 3 .

[0074] Example 4

[0075] This embodiment discloses a large-particle carbon-coated sodium vanadium phosphate, and the preparation method thereof is as follows:

[0076] 1. According to the molar ratio of Na:V:H2O = 1.03:1:5, sodium carbonate, ammonium metavanadate and pure water are put into a container at once, and placed in a water bath. The reaction temperature is controlled at 90°C and the reaction is carried out for 3 hours;

[0077] 2. Place the container in a 55°C water bath for cooling and crystallization for 3 hours to obtain sodium metavanadate solid;

[0078] 3. The sodium metavanadate solid was calcined in an ammonia atmosphere at a temperature of 850°C for 2 hours to prepare NaVO2;

[0079] 4. According to the molar ratio of Na:V:P:C=3:2:3:1.7, the product obtained in 3 is mixed with sodium carbonate, ammonium dihydrogen phosphate and citric acid, and the mixture is sand-milled and spray-dried to obtain a sodium vanadium phosphate precursor;

[0080] 5. The sodium vanadium phosphate precursor is placed in a helium atmosphere and calcined in two stages. The first stage calcination temperature is 450°C and the calcination time is 4 hours. The second stage calcination temperature is 800°C and the calcination time is 6 hours.

[0081] The XRD peak of the large-particle carbon-coated sodium vanadium phosphate in this embodiment is very high and sharp, which proves that the material has high crystallinity. SEM shows that the material particle size is in the shape of sugar cubes, with uniform particle size of 2-3 microns. The compacted density is 2.35g / cm 3 .

[0082] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing large-particle carbon-coated sodium vanadium phosphate, characterized in that: The following steps are involved: Step 1, according to the molar ratio of Na:V:H2O = 1.01-1.05:1:4-5, put the sodium source, vanadium source and pure water into a container at once, and place it in a water bath, control the reaction temperature to 70-100°C, and react for 1-4 hours; Step 2, placing the container in a 40-60°C water bath for cooling and crystallization for 2-6 hours, and filtering to obtain sodium metavanadate solid; Step 3, calcining solid sodium metavanadate in a reducing atmosphere to prepare NaVO2, the calcination temperature is 600-800°C, and the calcination time is 3-8h; Step 4, according to the molar ratio of Na:V:P:C = 3:2:3:0.5-2, NaVO2, a sodium source, a phosphorus source, and a carbon source are mixed, sand milled, and spray dried to obtain a sodium vanadium phosphate precursor; Step 5: Place the sodium vanadium phosphate precursor in an inert atmosphere and perform two-stage calcination to prepare large-particle carbon-coated sodium vanadium phosphate.

2. The method for preparing large-particle carbon-coated sodium vanadium phosphate according to claim 1, characterized in that: The sodium source in step 1 is one or more of sodium carbonate, sodium oxalate, sodium citrate, sodium phosphate, sodium dihydrogen phosphate, sodium lactate, sodium bicarbonate, sodium chloride, sodium sulfate, sodium lactate, sodium nitrate and sodium hydroxide.

3. The method for preparing large-particle carbon-coated sodium vanadium phosphate according to claim 1, characterized in that: The vanadium source in step 1 is one or more of ammonium metavanadate, vanadium pentoxide and ammonium polyvanadate.

4. The method for preparing large-particle carbon-coated sodium vanadium phosphate according to claim 1, characterized in that: The reducing atmosphere in step 3 is one or more of ammonia, hydrogen, methane and carbon monoxide.

5. The method for preparing large-particle carbon-coated sodium vanadium phosphate according to claim 1, characterized in that: The phosphorus source in step 4 is one or more of diammonium phosphate, phosphoric acid, sodium dihydrogen phosphate, diammonium hydrogen phosphate and monoammonium phosphate.

6. The method for preparing large-particle carbon-coated sodium vanadium phosphate according to claim 1, characterized in that: The carbon source in step 4 is one or more of citric acid, oxalic acid, glucose, stearic acid, ascorbic acid, ammonium citrate and sodium citrate.

7. The method for preparing large-particle carbon-coated sodium vanadium phosphate according to claim 1, characterized in that: The two-stage calcination in step 5 is as follows: pre-calcination temperature of 300-500°C, pre-calcination time of 3-8h, re-calcination temperature of 700-900°C, calcination time of 5-10h.

8. A large-particle carbon-coated sodium vanadium phosphate, characterized in that: The method is prepared by any one of claims 1 to 7.

9. The large-particle carbon-coated sodium vanadium phosphate according to claim 8, characterized in that: The particle size of the large-particle carbon-coated sodium vanadium phosphate is 1-5 microns.

10. Use of the large-particle carbon-coated sodium vanadium phosphate according to claim 8 or 9 in the field of positive electrode materials for sodium ion batteries.

Images