CN107195886B - A kind of pyrophosphoric acid vanadium sodium@carbon composite anode material, preparation and application - Google Patents

Abstract

The invention discloses a method for preparing a sodium vanadium pyrophosphate cathode material for a sodium ion battery. The sodium vanadium pyrophosphate with a carbon-coated microsphere structure is prepared. Vanadium source and carbon source are hydrothermally and pre-sintered to prepare vanadium oxide pre-coated with carbon layer, then ball milled with sodium source and phosphorus source, and then spray granulated to obtain a microspherical precursor, which is calcined, washed and dried Sodium vanadium pyrophosphate with carbon-coated microsphere structure is obtained. In addition, the invention also discloses the positive electrode material of the sodium ion battery prepared by the preparation method. The prepared material is a secondary microsphere formed by primary nanoparticles. The material is used in a sodium ion battery, exhibits excellent electrochemical performance, and has industrial application prospects.

Description

A kind of sodium vanadium pyrophosphate@carbon composite positive electrode material, preparation and application

technical field

The invention belongs to the field of sodium ion batteries, and in particular relates to a positive electrode material of a sodium ion battery and a preparation method thereof.

Background technique

At present, fossil fuels such as coal and oil are still the main power supply resources. However, with the unreasonable and unrestrained exploitation and utilization of human beings, coupled with the unsystematic, unreasonable and unscientific recycling, fossil energy is becoming increasingly tense. To solve this problem, large-scale power storage technology has become an important research field. Among them, secondary batteries have become the preferred choice for large-scale power storage due to their high energy density and conversion efficiency, and lithium-ion batteries with long cycle life and high energy density are considered to be the most promising secondary batteries. Since the successful advent of lithium-ion batteries in the 1990s, they have been widely used in electric vehicles and portable electronic devices. However, with the continuous progress and development of lithium-ion batteries and people's needs and requirements for secondary batteries With the improvement of battery technology, a series of hidden dangers and problems are gradually exposed to people's vision, so it is imminent to develop a low-cost and sustainable battery system.

Sodium and lithium belong to the same main group, have similar physical and chemical properties, and sodium resources are abundant and can be continuously extracted from seawater. Although compared with lithium, sodium ion has a larger radius and a lower standard electrochemical potential, resulting in relatively lower energy density and power density of sodium ion batteries, but in the future, with the increase in market demand and the optimization of battery size, Sodium-ion batteries with low cost and high safety have a very broad prospect and are bound to become one of the most important development directions in the post-lithium era.

At present, based on the consideration of material development costs and application prospects, the cathode material of sodium-ion batteries is the most researched and most concerned by researchers in sodium-ion batteries. The currently reported sodium storage cathode materials mainly include polyanionic compounds, Prussian blue sodium salts, and transition metal oxides. Transition metal oxides include sodium cobaltate and sodium manganate, which are characterized by good electronic conductivity and high capacity, but their cycle performance is poor, and their overcharge resistance and thermal stability are poor. Prussian blue sodium salt Na _x M _y [Fe(CN) ₆ ] (M=Fe, Co, Ni, Cu, etc.) is a kind of complexes containing variable valence transition metals. This type of compound has a complete cubic crystal form and has The three-dimensional space structure has a large number of coordination gaps, which is conducive to the reversible extraction and intercalation of sodium ions, but the capacity fading mechanism of these compounds is still unclear. Polyanionic compounds mainly include transition metal (pyro) phosphate, fluorophosphate and so on. Phosphate compounds often exist stably as fast sodium ion conductors or olivine structures, containing large ion channels and three-dimensional open structural frameworks. The framework structure of transition metal phosphate is relatively stable, and it has good cycle stability and high safety performance in the process of charging and discharging when used in the positive electrode. The strong binding force of the salt skeleton leads to slow diffusion of sodium ions, low volumetric energy density, and large capacity decay during high-rate discharge. Moreover, the synthesis of such materials mainly adopts a high-temperature solid-phase method, which is costly, and the preparation process is complicated, which easily causes environmental pollution. In this series of cathode materials, polyanionic compounds have attracted much attention due to their high voltage, long cycle and excellent safety.

Contents of the invention

The first purpose of the present invention is to provide a sodium vanadium pyrophosphate@carbon composite positive electrode material.

The second purpose of the present invention is to provide a preparation method of sodium vanadium pyrophosphate@carbon composite positive electrode material, aiming to provide a preparation method with simple process, good repeatability, low cost and environmental friendliness.

The third purpose of the present invention is to provide the application of the positive electrode composite material in the field of sodium ion batteries, aiming to improve the electrochemical performance of the sodium ion battery through the positive electrode material.

A sodium vanadium pyrophosphate@carbon composite positive electrode material is characterized in that it is a microspherical particle assembled from sodium vanadium pyrophosphate nanoparticles coated with carbon.

The carbon-coated sodium vanadium pyrophosphate nanoparticles have a particle diameter of 100-200nm; a specific surface area of 20-400m ² /g; and a carbon-coated layer thickness of 5-40nm.

The particle size of the microspherical particles of the composite positive electrode material is 5-30 μm.

The microspherical particles of the composite cathode material are secondary particles assembled from primary particles; the primary particles have a particle size of 100-200 nm, and the secondary particles are microspheres with a particle size of 5-30 μm.

The present invention also provides a method for preparing the sodium vanadium pyrophosphate@carbon composite positive electrode material, which involves performing a hydrothermal reaction on a solution containing a carbon source and a vanadium source, and performing primary sintering on the hydrothermal reaction product to obtain a composite Vanadium oxycarbide; wet-ball-milling the prepared carbon-coated vanadium oxide, sodium source, and phosphorus source to obtain a precursor; performing secondary sintering on the precursor to obtain the composite positive electrode material.

In the method of the present invention, the vanadium source and the carbon source are subjected to hydrothermal and primary sintering treatment firstly, so that the surface of the vanadium oxide is coated with a carbon material layer in situ, and the carbon-coated vanadium oxide is obtained, and then The carbon-coated vanadium oxide is mixed with a sodium source and a phosphorus source, and sintered to obtain the composite positive electrode material. Compared with preparation methods such as one-pot hydrothermal or direct ball milling and mixing, the performance of the prepared composite positive electrode material is better; in addition, the method of the present invention has simple process, good repeatability, low cost and environmental friendliness.

The key to the preparation method of the present invention lies in the preparation route of the present invention, that is, the vanadium source and the carbon source are hydrothermally-primarily sintered to obtain carbon-coated vanadium oxide; then ball milling, spraying, secondary sintering, and assembly Obtain the secondary particles. In addition, with the control of the hydrothermal reaction conditions, the molar ratio of Na, V, P elements, and the temperature of the sintering process, the electrical properties of the prepared composite cathode material can be further improved.

In the present invention, the vanadium source and the carbon source are dissolved and/or dispersed in a solvent to obtain the solution, and then the hydrothermal reaction is carried out. The solvent can be water, or a solvent miscible with water in an infinite ratio, for example, C1-4 alcohol or acetone; the C1-4 alcohol is, for example, methanol, ethanol, isopropanol, etc.

Preferably, the solvent medium for the hydrothermal reaction is water and/or ethanol.

A preferred preparation method of the present invention, the carbon source and the vanadium source are dissolved in the ethanol medium, and the vanadium oxide pre-coated with carbon is obtained through hydrothermal and sintering; then ball milled with the sodium source and the phosphorus source, spray granulated, and calcined Sodium vanadium pyrophosphate with carbon-coated nano-microsphere structure is obtained. The positive electrode material with a spherical structure prepared in the present invention is a secondary microsphere of 5-30 μm formed by nanoparticles with a particle size of 100-200nm, and the surface of the primary nanoparticles is coated with a uniform carbon layer, and the carbon-coated carbon layer is realized while the material is nano-sized. Covering, a good solution to the shortcomings of sodium vanadium pyrophosphate poor electronic conductivity. The prepared material can be used as the positive electrode of sodium ion battery, which can show good rate performance and long-term cycle stability. In addition, the method of the invention has the advantages of simple process, good repeatability, low cost and environmental friendliness, and can realize industrial mass production.

Preferably, the carbon source is a reducing compound.

Further preferably, the carbon source is at least one of glucose, citric acid, oxalic acid, lactose, and galactose.

More preferably, the carbon source is at least one of glucose, citric acid, and oxalic acid.

The vanadium source is at least one compound of trivalent, tetravalent and pentavalent vanadium. The vanadium source can be a water-soluble compound at normal temperature, or a vanadium oxide that is difficult to dissolve in water; for example, it is an oxide of vanadium or its organic or inorganic salt.

Preferably, the vanadium source is at least one of vanadium trioxide, vanadium pentoxide, ammonium metavanadate, vanadyl acetylacetonate and vanadium acetylacetonate.

Further preferably, the vanadium source is at least one of vanadium trioxide, vanadium pentoxide and ammonium metavanadate.

Preferably, during the hydrothermal reaction, the molar ratio of the carbon source to the vanadium source is 0.1-10. The vanadium in the vanadium oxide obtained within the preferred ratio range is V ³⁺ , and the thickness of the carbon-coated layer is moderate and relatively uniform. If the ratio is too high, the carbon layer is too thick, and if the ratio is too low, V ^{4 +} and V ⁵⁺ will appear.

Further preferably, the molar ratio of the carbon source to the vanadium source is 1-10.

More preferably, the molar ratio of the carbon source to the vanadium source is 1-5; most preferably 1-2.

Preferably, before the hydrothermal reaction, the initial concentration of the carbon source is 0.01-10 g/mL. The hydrothermal products prepared in this preferred concentration range have better dispersibility and more uniform particle size. If the concentration is too high, the particle agglomeration phenomenon will be serious; if the concentration is too low, the yield will be too low.

Further preferably, the initial concentration of the carbon source is 0.01-1 g/mL; even more preferably 0.01-0.1 g/mL.

Preferably, the hydrothermal reaction temperature is 120-200°C; more preferably 150-200°C

At the preferred hydrothermal temperature, the preferred reaction time is 10-25 hours; more preferably 10-20 hours.

The primary sintering process is carried out under a protective atmosphere. The protective atmosphere is preferably at least one of nitrogen, argon and hydrogen-argon mixed gas (5% hydrogen).

Preferably, the primary sintering temperature is 450-850°C. Sintered at this temperature, the resulting carbon coating is more uniform and has better conductivity.

More preferably, the primary sintering temperature is 500-700°C; still more preferably 500-650°C; most preferably 550-650°C.

The heating rate of the primary sintering process is 1-10°C/min, and the cooling rate is 1-10°C/min. The preferred heating and cooling rates are more conducive to ensuring the regularity of the material's morphology and structure.

Further preferably, the heating rate of the primary sintering process is 4-8°C/min, and the cooling rate is 2-6°C/min.

In the present invention, the carbon-coated vanadium oxide obtained by hydrothermal treatment is ball-milled with a sodium source and a phosphorus source, and sprayed and granulated to obtain carbon-coated sodium vanadium pyrophosphate microspheres. The inventors found that better control of the particle size, thickness and uniformity of the carbon-coated layer are all helpful to further improve the electrochemical performance of the material. The invention regulates particle size, carbon layer thickness and uniformity by selecting and proportioning raw materials, as well as spray drying and sintering systems.

The sodium source is preferably a compound that can be dissolved in an aqueous solution and can be ionized to release Na ⁺ .

Preferably, the sodium source is at least one of sodium carbonate, sodium acetate, sodium oxalate, sodium pyrophosphate, sodium monohydrogen phosphate, and sodium dihydrogen phosphate.

More preferably, the sodium source is at least one of sodium carbonate, sodium acetate, sodium oxalate, sodium monohydrogen phosphate, and sodium dihydrogen phosphate.

The phosphorus source is preferably a compound that can be dissolved in an aqueous solution and can be ionized to release PO ₄ ^3- .

Preferably, the phosphorus source is at least one of sodium pyrophosphate, phosphoric acid, ammonium monohydrogen phosphate, ammonium dihydrogen phosphate, sodium monohydrogen phosphate, and sodium dihydrogen phosphate.

More preferably, the phosphorus source is at least one of phosphoric acid, sodium monohydrogen phosphate, and sodium dihydrogen phosphate.

Through extensive research, the present inventors also found that controlling the molar ratios of Na, V, and P elements of the sodium source, vanadium source, and phosphorus source within an appropriate range helps to improve the electrical properties of the composite positive electrode material.

Preferably, the Na, V and P elements of the sodium source, vanadium source and phosphorus source are mixed in a molar ratio of 0.5-10:1:0.1-10. The ratio of Na in the sodium source, V in the vanadium source, and P in the phosphorus source is within the preferred range, which helps to reduce the impurities in the prepared sodium vanadium pyrophosphate and is relatively pure. Each ratio is not controlled within the preferred range, and impurities such as sodium vanadium phosphate, sodium pyrophosphate, and sodium phosphate are easily produced.

More preferably, the molar ratio of Na, V and P in the sodium source, vanadium source and phosphorus source is 0.5-7:1:0.1-5.

More preferably, the molar ratio of Na, V and P in the sodium source, vanadium source and phosphorus source is 1-5:1:0.1-2.

Most preferably, the molar ratio of Na, V and P in the sodium source, vanadium source and phosphorus source is 3.5-5:1:1.3-1.8. Under the synergy of optimized parameters, the obtained sodium vanadium pyrophosphate has fewer impurities and better electrochemical performance.

Preferably, the ball milling medium is at least one of water, ethanol and acetone. During ball milling, the mass ratio of material to ball milling beads is 0.05-0.1, and the mass ratio of ball milling beads to medium is 2-4.

Preferably, the ball milling speed is 150-550 rpm, and the ball milling time is 5-25h. Under the ball milling system, the raw materials are mixed evenly, and the pre-coated carbon layer will not fall off, which is more conducive to the preparation of microspheres with good shape uniformity and a thin and uniform coated carbon layer.

Further preferably, the rotational speed of the ball mill is 150-250 rpm.

Under the preferred ball milling speed, the preferred ball milling time is 5-25h; more preferably 10-15h; the ball milling time is 5-25h; more preferably 5-10h.

In the method of the present invention, a spherical precursor is obtained after the ball milling and spray granulation, and carbon-coated sodium vanadium pyrophosphate nanometer microspheres are obtained from the precursor.

The spray drying process can adopt existing conventional and mature methods; the inlet temperature of the preferred spray drying of the present invention is 180-220°C, and the outlet temperature is 200-250°C; the feed rate is 45-55g/min, and the working pressure is 4-10MPa , the rotational speed of the atomizer is 15000-20000rad/min.

Preferably, the secondary sintering is performed under a protective atmosphere, and the protective atmosphere is preferably at least one of nitrogen and argon.

Preferably, the secondary sintering temperature is 450-850°C. Under the synergy of the aforementioned ball milling conditions, raw material selection and proportioning, and in conjunction with the calcination temperature, the positive electrode material with a spherical structure is a secondary 5-30 μm nanoparticle with a particle size of 100-200 nm (assembled). Microspheres, and the surface of primary nanoparticles is coated with a uniform carbon layer, which realizes carbon coating while nano-materials, showing good rate performance and long-term cycle stability.

More preferably, the secondary sintering temperature is 500-700°C. Within the preferred temperature range, secondary microspheres of 5-30 μm formed by nanoparticles with a particle size of 100-200 nm can be obtained, which improves the rate performance and cycle performance.

More preferably, the secondary sintering temperature is 500-650°C; most preferably 550-650°C.

The heating rate of the secondary sintering process is 1-10°C/min, and the cooling rate is 1-10°C/min. The preferred heating and cooling rates are more conducive to ensuring the regularity of the material's morphology and structure.

Further preferably, the heating rate of the secondary sintering process is 4-8°C/min, and the cooling rate is 2-6°C/min.

Under the above-mentioned secondary sintering temperature and heating and cooling rates, the preferred holding time is 10-40 h; more preferably 10-15 h.

The product after secondary sintering is washed and dried to obtain the positive electrode material.

The preparation method of a kind of preferred sodium vanadium pyrophosphate positive electrode material of sodium ion battery of the present invention specifically comprises the following steps:

Step (a): dissolving the vanadium source and the carbon source in deionized water and hydroheating at 120-200°C for 10-20h; the hydrothermal product is calcined in a protective atmosphere at 550-650°C for 10-15h, and the product is washed and dried to obtain Vanadium oxide pre-coated with carbon; the carbon source is at least one of glucose, citric acid, oxalic acid, lactose, and galactose; the molar ratio of the carbon source to the vanadium source is 0.1-10;

Step (b): According to the molar ratio of Na, V, P elements of 3.5-5:1:1.3-1.8, the sodium source, phosphorus source and pre-coated vanadium oxycarbide are ball milled at 150-250 rpm for 5-10 hours, Then spray drying to obtain a spherical precursor;

Step (c): Calcining the precursor prepared in step (b), the calcination temperature is 550-650°C, the calcination time is 10-15h, and the heating rate is 4-8°C/min; the calcined product is washed and dried to obtain Carbon-coated sodium vanadium pyrophosphate nanospheres.

The present invention also includes a sodium vanadium pyrophosphate@carbon composite positive electrode material prepared by the preparation method, which is a microspherical particle assembled from sodium vanadium pyrophosphate nanoparticles coated with carbon.

That is to say, the present invention consists of agglomerated microspherical particles (secondary microspheres) of several carbon-coated sodium vanadium pyrophosphate nanoparticles (primary microspheres).

The particle size of the carbon-coated sodium vanadium pyrophosphate nanoparticles is 100-200 nm; the particle size of the microspherical particles of the composite positive electrode material is 5-30 μm.

The positive electrode material with a spherical structure prepared in the present invention is a secondary microsphere of 5-30 μm formed by nanoparticles with a particle size of 100-200nm, and the surface of the primary nanoparticles is coated with a uniform carbon layer, and the carbon-coated carbon layer is realized while the material is nano-sized. Covering, a good solution to the shortcomings of sodium vanadium pyrophosphate poor electronic conductivity. The prepared material can be used as the positive electrode of sodium ion battery, which can show good rate performance and long-term cycle stability.

The present invention also provides an application of the sodium vanadium pyrophosphate/carbon composite positive electrode material, and the positive electrode composite material is used as a sodium ion positive electrode material.

Preferably, in the application, it is applied to the preparation of the positive electrode of the sodium ion battery.

The coating of the carbon layer not only improves the electronic conductivity of the material, but also inhibits the growth of particles to a certain extent in the subsequent sintering process of forming sodium vanadium pyrophosphate, which is conducive to the realization of nanomaterials, and combined with spray granulation to obtain The microsphere precursor is used to obtain nano-scale primary particles during the sintering process. By controlling a certain sintering temperature and sintering time, secondary particles of 5-30 μm are obtained. The material is a secondary microsphere composed of carbon-coated nano-scale primary particles, which shortens the migration path of electrons and particles, has good electronic conductivity and particle conductivity, and solves the problem of poor rate performance of pyrophosphate , but also has good cycle stability.

The beneficial effects brought by the technical solution of the present invention:

1) The present invention adopts the method for solid-liquid phase coordination to prepare carbon-coated sodium vanadium pyrophosphate nano-microspheres. The positive electrode material is a secondary microsphere composed of nano-scale primary particles, and the material is used as a sodium-ion battery. The positive electrode can solve the shortcomings of poor rate performance and poor cycle stability of the pyrophosphate system, and has excellent electrochemical performance.

2) In the preparation method of the present invention, through the selection of the reducing carbon source, the weight ratio of the carbon source and the vanadium source, the ball milling and calcination mechanism, etc., the particle size of the particles and the coating carbon layer can be uniform The properties are well regulated, thereby significantly improving the electrochemical performance of the obtained cathode material.

3) The voltage platform of sodium vanadium pyrophosphate, anode material for sodium ion batteries prepared by the present invention can reach more than 4V, which can realize high energy density of sodium ion batteries.

4) The preparation method of the present invention is simple and reliable in operation, good in repeatability, strong in operability, environmentally friendly, suitable for mass production, and the cost of raw materials used is low, and has broad industrial application prospects.

Description of drawings

[Fig. 1] is the scanning electron micrograph of the sodium ion battery cathode material that embodiment 1 makes;

[Fig. 2] is the discharge cycle diagram of the sodium-ion battery cathode material prepared in Example 1.

Detailed ways

The following examples are intended to further describe the content of the present invention in detail; and the protection scope of the claims of the present invention is not limited by the examples.

The following examples and comparative examples, the spray drying parameters described, unless otherwise stated, the inlet temperature is 180-220 ℃, the outlet temperature is 200-250 ℃; the feed rate is 45-55g/min, the working The pressure is 4-10MPa, and the speed of the atomizer is 15000-20000rad/min.

Example 1

First take by weighing 2g vanadium pentoxide (0.01mol) and 5g citric acid (0.026mol), be dissolved in 100ml deionized water, stir to form a homogeneous solution, the aqueous solution is poured in the polytetrafluoroethylene reactor, and then The polytetrafluoroethylene reaction kettle was put into a stainless steel hydrothermal kettle and sealed, and finally the stainless steel hydrothermal kettle was placed in a homogeneous reactor, and hydrothermal reaction was carried out at 180° C. for 10 hours. The hydrothermal product was dried in an oven at 70 °C for 12 h. Then, under the protective atmosphere of nitrogen or argon, sinter at 600°C for 12 hours in a tube furnace, wash the product three times with deionized water, wash twice with alcohol, and dry at 70°C for 2 hours to obtain pre-coated vanadium oxycarbide .

The pre-coated vanadium oxycarbide, 3.5 g (0.03 mol) of sodium dihydrogen phosphate, and 3 g (0.028 mol) of sodium carbonate prepared above were ball milled in an alcohol medium for 7 hours at a speed of 200 rpm; the spherical precursor was obtained by spray drying . The precursor was heated to 600°C in a tube furnace at a rate of 4°C/min under a nitrogen atmosphere, and calcined for 15 hours to obtain a black powder; finally, the black powder was washed three times with deionized water, washed twice with alcohol, and dried to obtain the final product ( Na ₇ V ₃ (P ₂ O ₇ ) ₄ ). The scanning electron microscope picture of the product that makes is shown in Fig. 1; Known from Fig. 1, the composite anode material that present embodiment makes has the microsphere that the nanoparticle (primary particle) of sodium vanadium pyrophosphate is agglomerated into;, its primary The particle diameter is 150nm, the specific surface area of the particle is 250-300m ² /g, the thickness of the coated carbon layer is 10nm, and the secondary microsphere particle diameter is 30μm.

Using the sodium vanadium pyrophosphate material prepared in this example as the working electrode, sodium as the counter electrode, assembled into a button battery, and tested the cycle performance at a current density of 160mA/g (2C). Fig. 2 is the discharge specific capacity and cycle efficiency data of the positive electrode material prepared in this embodiment at a current density of 160mA/g (2C).

From the test results in Figure 2, it can be seen that the sodium cathode prepared in this example has good electrochemical performance; at a current density of 160mA/g (2C), the first-cycle capacity is 68mAh/g, and after 50 cycles, it can still maintain 62mAh /g specific capacity.

Example 2

First weigh 3g of ammonium metavanadate (0.025mol) and 7.5g of glucose (0.04mol) and dissolve them in 100ml deionized water, stir to form a uniform solution, pour the aqueous solution into a polytetrafluoroethylene reactor, and then pour the The polytetrafluoroethylene reaction kettle was put into a stainless steel hydrothermal kettle and sealed, and finally the stainless steel hydrothermal kettle was placed in a homogeneous reactor, and hydrothermal reaction was carried out at 180° C. for 10 hours. The hydrothermal product was dried in an oven at 70 °C for 12 h. Then, under the protective atmosphere of nitrogen or argon, sinter at 600°C for 12 hours in a tube furnace, wash the product three times with deionized water, wash twice with alcohol, and dry at 70°C for 2 hours to obtain pre-coated vanadium oxycarbide .

The pre-coated vanadium oxycarbide, 5 g (0.04 mol) of sodium dihydrogen phosphate, and 4.5 g (0.042 mol) of sodium carbonate prepared above were ball-milled for 7 hours at a rotation speed of 200 rpm; the spherical precursor was obtained by spray drying. The precursor was heated to 600°C in a tube furnace at a rate of 4°C/min under a nitrogen atmosphere, and calcined for 15 hours to obtain a black powder; finally, the black powder was washed three times with deionized water, washed twice with alcohol, and dried to obtain the final product coke Sodium vanadium phosphate (Na ₇ V ₃ (P ₂ O ₇ ) ₄ ).

The composite anode material obtained in this embodiment has microspheres formed by the agglomeration of carbon-coated ^sodium vanadium pyrophosphate nanoparticles (primary particles); The thickness of the carbon layer is 10 nm, and the particle size of the secondary microspheres is 20-30 μm.

Using the sodium vanadium pyrophosphate material prepared in this example as the working electrode, sodium as the counter electrode, assembled into a button battery, and tested the cycle performance at a current density of 160mA/g (2C). Under the current density of 160mA/g (2C), the specific capacity of the first cycle is 67mAh/g, and after 50 cycles, the specific capacity of 60mAh/g can be maintained. It can be seen that when the reducing carbon source is changed from citric acid to glucose, the rate performance and cycle performance are slightly decreased.

Example 3

First weigh 2g of vanadium pentoxide (0.01mol) and 5g of citric acid (0.026mol) and dissolve them in 100ml deionized water, stir to form a uniform solution, pour the aqueous solution into a polytetrafluoroethylene reactor, and then put the The polytetrafluoroethylene reaction kettle was put into a stainless steel hydrothermal kettle and sealed, and finally the stainless steel hydrothermal kettle was placed in a homogeneous reactor, and hydrothermal reaction was carried out at 150° C. for 10 hours. The hydrothermal product was dried in an oven at 70 °C for 12 h. Then, under a protective atmosphere of nitrogen, sinter at 600°C for 12 hours in a tube furnace, wash the product three times with deionized water, wash twice with alcohol, and dry at 70°C for 2 hours to obtain pre-coated vanadium oxycarbide.

The pre-coated vanadium oxycarbide, 3.5 g (0.03 mol) of sodium dihydrogen phosphate, and 3 g (0.028 mol) of sodium carbonate prepared above were ball milled for 7 hours at a rotation speed of 200 rpm; and the spherical precursor was obtained by spray drying. The precursor was heated to 600°C in a tube furnace at a rate of 4°C/min under a nitrogen atmosphere, and calcined for 15 hours to obtain a black powder; finally, the black powder was washed three times with deionized water, washed twice with alcohol, and dried to obtain the final product ( Na ₇ V ₃ (P ₂ O ₇ ) ₄ ).

The composite positive electrode material prepared in this example has microspheres formed by the agglomeration of carbon-coated sodium vanadium pyrophosphate nanoparticles (primary particles); the primary particle diameter is 120nm, and the particle specific surface area is 180-250m ² /g. The thickness of the carbon coating layer is 8nm, and the particle size of the secondary microspheres is 25-30μm.

Using the sodium vanadium pyrophosphate material prepared in this example as the working electrode, sodium as the counter electrode, assembled into a button battery, and tested the cycle performance at a current density of 160mA/g (2C). Under the current density of 160mA/g (2C), the capacity of the first cycle is 68mAh/g, and after 50 cycles, the specific capacity of 63mAh/g can be maintained. It can be seen that the properties of the material remain basically unchanged when the hydrothermal temperature is lowered to 150 °C.

Example 4

First take by weighing 2g vanadium pentoxide (0.022mol V) and 5g citric acid (0.026mol) and be dissolved in 100ml deionized water, stir to form a homogeneous solution, the aqueous solution is poured in the polytetrafluoroethylene reactor, and then The polytetrafluoroethylene reaction kettle was put into a stainless steel hydrothermal kettle and sealed, and finally the stainless steel hydrothermal kettle was placed in a homogeneous reactor, and hydrothermal reaction was carried out at 180° C. for 10 hours. The hydrothermal product was dried in an oven at 70 °C for 12 h. Then, under a protective atmosphere of nitrogen, sinter at 650°C for 15 hours in a tube furnace, wash the product three times with deionized water, wash twice with alcohol, and dry at 70°C for 2 hours to obtain pre-coated vanadium oxycarbide.

The pre-coated vanadium oxycarbide, 3.5 g (0.03 mol) of sodium dihydrogen phosphate, and 3 g (0.056 mol Na) of sodium carbonate prepared above were ball-milled for 7 hours at a rotation speed of 200 rpm; the spherical precursor was obtained by spray drying. The precursor was heated to 550°C in a tube furnace at a rate of 4°C/min under a nitrogen atmosphere, and calcined for 15 hours to obtain a black powder; finally, the black powder was washed three times with deionized water, washed twice with alcohol, and dried to obtain the final product coke Sodium vanadium phosphate (Na ₇ V ₃ (P ₂ O ₇ ) ₄ ).

The composite positive electrode material prepared in this embodiment has microspheres formed by the agglomeration of carbon-coated sodium vanadium pyrophosphate nanoparticles (primary particles); the primary particle diameter is 150 nm, and the particle specific surface area is 200-250 m ² /g. The thickness of the carbon coating layer is 15nm, and the particle size of the secondary microspheres is 20-25μm.

Using the sodium vanadium pyrophosphate material prepared in this example as the working electrode, sodium as the counter electrode, assembled into a button battery, and tested the cycle performance at a current density of 160mA/g (2C). At a current density of 160mA/g (2C), the first-cycle capacity is 67mAh/g, and after 50 cycles, the specific capacity of 56mAh/g can be maintained.

Example 5

First weigh 2g of ammonium metavanadate (0.017mol) and 5g of citric acid (0.026mol) and dissolve them in 100ml deionized water, stir to form a uniform solution, pour the aqueous solution into a polytetrafluoroethylene reactor, and then pour the The polytetrafluoroethylene reaction kettle was put into a stainless steel hydrothermal kettle and sealed, and finally the stainless steel hydrothermal kettle was placed in a homogeneous reactor, and hydrothermal reaction was carried out at 180° C. for 10 hours. The hydrothermal product was dried in an oven at 70 °C for 12 h. Then, under a protective atmosphere of nitrogen, sinter at 650°C for 12 hours in a tube furnace, wash the product three times with deionized water, wash twice with alcohol, and dry at 70°C for 2 hours to obtain pre-coated vanadium oxycarbide.

The above-prepared pre-coated vanadium oxycarbide, 3.5 g (0.03 mol) of sodium dihydrogen phosphate, and 3 g (0.028 mol) of sodium carbonate were ball-milled for 7 hours at a rotation speed of 200 rpm; the spherical precursor was obtained by spray drying. The precursor was heated to 650°C in a tube furnace at a rate of 4°C/min under a nitrogen atmosphere, and calcined for 15 hours to obtain a black powder; finally, the black powder was washed three times with deionized water, washed twice with alcohol, and dried to obtain the final product coke Sodium vanadium phosphate (Na ₇ V ₃ (P ₂ O ₇ ) ₄ ).

The composite positive electrode material prepared in this embodiment has microspheres formed by the agglomeration of carbon-coated sodium vanadium pyrophosphate nanoparticles (primary particles); the primary particle diameter is 120nm, and the particle specific surface area is 250-300m ² /g. The thickness of the carbon coating layer is 10nm, and the particle size of the secondary microspheres is 25-30μm.

Using the sodium vanadium pyrophosphate material prepared in this example as the working electrode, sodium as the counter electrode, assembled into a button battery, and tested the cycle performance at a current density of 160mA/g (2C). Under the current density of 160mA/g (2C), the capacity of the first cycle is 72mAh/g, and after 50 cycles, the specific capacity of 63mAh/g can be maintained.

Example 6

First weigh 2g of ammonium metavanadate (0.017mol) and 5g of citric acid (0.026mol) and dissolve them in 100ml deionized water, stir to form a uniform solution, pour the aqueous solution into a polytetrafluoroethylene reactor, and then pour the The polytetrafluoroethylene reaction kettle was put into a stainless steel hydrothermal kettle and sealed, and finally the stainless steel hydrothermal kettle was placed in a homogeneous reactor, and hydrothermal reaction was carried out at 180° C. for 10 hours. The hydrothermal product was dried in an oven at 70 °C for 12 h. Then, under a protective atmosphere of nitrogen, sinter at 650°C for 12 hours in a tube furnace, wash the product three times with deionized water, wash twice with alcohol, and dry at 70°C for 2 hours to obtain pre-coated vanadium oxycarbide.

The prepared pre-coated vanadium oxycarbide, 3.5 g (0.03 mol) of sodium dihydrogen phosphate, and 3 g (0.028 mol) of sodium carbonate were ball-milled for 7 hours at a rotation speed of 200 rpm; the spherical precursor was obtained by spray drying. The precursor was heated to 550°C in a tube furnace at a rate of 4°C/min under a nitrogen atmosphere, and calcined for 15 hours to obtain a black powder; finally, the black powder was washed three times with deionized water, washed twice with alcohol, and dried to obtain the final product coke Sodium vanadium phosphate (Na ₇ V ₃ (P ₂ O ₇ ) ₄ ).

The composite positive electrode material prepared in this embodiment has microspheres formed by the agglomeration of carbon-coated sodium vanadium pyrophosphate nanoparticles (primary particles); the primary particle diameter is 150 nm, and the particle specific surface area is 250-300 m ² /g. The thickness of the carbon coating layer is 12nm, and the particle size of the secondary microspheres is 25-30 μm.

Using the sodium vanadium pyrophosphate material prepared in this example as the working electrode, sodium as the counter electrode, assembled into a button battery, and tested the cycle performance at a current density of 160mA/g (2C). Under the current density of 160mA/g (2C), the capacity of the first cycle is 70mAh/g, and after 50 cycles, the specific capacity of 62mAh/g can be maintained.

Example 7

First weigh 2g of ammonium metavanadate (0.017mol) and 5g of citric acid (0.026mol) and dissolve them in 100ml deionized water, stir to form a uniform solution, pour the aqueous solution into a polytetrafluoroethylene reactor, and then pour the The polytetrafluoroethylene reaction kettle was put into a stainless steel hydrothermal kettle and sealed, and finally the stainless steel hydrothermal kettle was placed in a homogeneous reactor, and hydrothermal reaction was carried out at 180° C. for 15 hours. The hydrothermal product was dried in an oven at 70 °C for 12 h. Then, under a protective atmosphere of nitrogen, sinter at 650°C for 12 hours in a tube furnace, wash the product three times with deionized water, wash twice with alcohol, and dry at 70°C for 2 hours to obtain pre-coated vanadium oxycarbide.

The prepared pre-coated vanadium oxycarbide, 3.5 g (0.03 mol) of sodium dihydrogen phosphate, and 3 g (0.028 mol) of sodium carbonate were ball-milled for 7 hours at a rotation speed of 200 rpm; the spherical precursor was obtained by spray drying. The precursor was heated to 650°C in a tube furnace at a rate of 4°C/min under a nitrogen atmosphere, and calcined for 15 hours to obtain a black powder; finally, the black powder was washed three times with deionized water, washed twice with alcohol, and dried to obtain the final product coke Sodium vanadium phosphate (Na ₇ V ₃ (P ₂ O ₇ ) ₄ ).

The composite positive electrode material prepared in this example has microspheres formed by the agglomeration of carbon-coated sodium vanadium pyrophosphate nanoparticles (primary particles); the primary particle diameter is 120nm, and the particle specific surface area is 180-250m ² /g. The thickness of the carbon coating layer is 15nm, and the particle size of the secondary microspheres is 25-30μm.

Using the sodium vanadium pyrophosphate material prepared in this example as the working electrode, sodium as the counter electrode, assembled into a button battery, and tested the cycle performance at a current density of 160mA/g (2C). Under the current density of 160mA/g (2C), the capacity of the first cycle is 70mAh/g, and after 50 cycles, the specific capacity of 64mAh/g can be maintained.

Example 8

First weigh 2g of vanadium pentoxide (0.011mol) and 5g of citric acid (0.026mol) and dissolve them in 100ml deionized water, stir to form a uniform solution, pour the aqueous solution into a polytetrafluoroethylene reactor, and then put the The polytetrafluoroethylene reaction kettle was put into a stainless steel hydrothermal kettle and sealed, and finally the stainless steel hydrothermal kettle was placed in a homogeneous reactor, and hydrothermal reaction was carried out at 180° C. for 10 hours. The hydrothermal product was dried in an oven at 70 °C for 12 h. Then, under a protective atmosphere of nitrogen, sinter at 600°C for 12 hours in a tube furnace, wash the product three times with deionized water, wash twice with alcohol, and dry at 70°C for 2 hours to obtain pre-coated vanadium oxycarbide.

The prepared pre-coated vanadium oxycarbide, 3.45 g (0.03 mol) of ammonium dihydrogen phosphate, and 2.3 g (0.028 mol) of sodium acetate were ball milled for 7 hours at a speed of 200 rpm. The precursor was heated to 600°C in a tube furnace at a rate of 4°C/min under a nitrogen atmosphere, and calcined for 15 hours to obtain a black powder; finally, the black powder was washed three times with deionized water, washed twice with alcohol, and dried to obtain the final product ( Na7V3(P2O7)4).

The composite positive electrode material prepared in this example has microspheres formed by the agglomeration of carbon-coated sodium vanadium pyrophosphate nanoparticles (primary particles); the primary particle diameter is 120nm, and the particle specific surface area is 180-250m ² /g. The thickness of the carbon coating layer is 8nm, and the particle size of the secondary microspheres is 25-30μm.

The sodium vanadium pyrophosphate material prepared by this embodiment is used as the working electrode, and the sodium is used as the counter electrode, and is assembled into a button cell. Under the current density of 160mA/g (2C), the cycle performance is tested; the test results show that the The electrochemical performance of the sodium electrode is poor; at a current density of 160mA/g (2C), the specific capacity of the first cycle discharge is 71mA/g, and the specific capacity of 64mAh/g is maintained after 50 cycles.

Comparative example 1

First weigh 2g of vanadium pentoxide (0.011mol) and 5g of citric acid (0.026mol) and dissolve them in 100ml deionized water, stir to form a uniform solution, pour the aqueous solution into a polytetrafluoroethylene reactor, and then put the The polytetrafluoroethylene reaction kettle was put into a stainless steel hydrothermal kettle and sealed, and finally the stainless steel hydrothermal kettle was placed in a homogeneous reactor, and hydrothermal reaction was carried out at 180° C. for 10 hours. The hydrothermal product was dried in an oven at 70 °C for 12 h. Then, under a protective atmosphere of nitrogen, sinter at 600°C for 12 hours in a tube furnace, wash the product three times with deionized water, wash twice with alcohol, and dry at 70°C for 2 hours to obtain pre-coated vanadium oxycarbide.

The prepared pre-coated vanadium oxycarbide, 3.5 g (0.03 mol) of sodium dihydrogen phosphate, and 3 g (0.028 mol) of sodium carbonate were ball milled for 7 hours at a speed of 200 rpm. The precursor was heated to 600°C in a tube furnace at a rate of 4°C/min under a nitrogen atmosphere, and calcined for 15 hours to obtain a black powder; finally, the black powder was washed three times with deionized water, washed twice with alcohol, and dried to obtain the final product ( Na ₇ V ₃ (P ₂ O ₇ ) ₄ ).

The composite anode material obtained in this embodiment has microspheres formed by the agglomeration of carbon-coated ^sodium vanadium pyrophosphate nanoparticles (primary particles); The thickness of the carbon layer is 20nm, and the particle size of the secondary microsphere is 70-80μm.

The sodium vanadium pyrophosphate material prepared by this embodiment is used as the working electrode, and the sodium is used as the counter electrode, and is assembled into a button cell. Under the current density of 160mA/g (2C), the cycle performance is tested; the test results show that the The electrochemical performance of the sodium electrode is poor; at a current density of 160mA/g (2C), the specific capacity of the first discharge is only 45mA/g, and the specific capacity of 22mAh/g is maintained after 50 cycles. Without spray drying, the primary particles of the material are larger, and the secondary particles formed are larger, which increases the particle transmission path, and deteriorates the rate performance and cycle stability.

Comparative example 2

First take by weighing 2g of vanadium pentoxide (0.011mol), 5g of citric acid (0.026mol), 3.5g of sodium dihydrogen phosphate (0.03mol) and 3g of sodium carbonate (0.028mol), add in the ball mill jar of cleaning, then Add 150g of agate beads and 40mL of ethanol, and perform ball milling for 12h, with the ball milling speed at 500 rpm. The ball-milled product was dried in an oven at 70°C for 12 hours. The dried product was spray-dried to obtain a spherical precursor. The precursor was heated to 600°C in a tube furnace at a rate of 4°C/min under a nitrogen atmosphere, and calcined for 15 hours to obtain a black powder; finally, the black powder was washed three times with deionized water, washed twice with alcohol, and dried to obtain the final product ( Na ₇ V ₃ (P ₂ O ₇ ) ₄ ).

The composite positive electrode material prepared in this embodiment has microspheres formed by the agglomeration of carbon-coated sodium vanadium pyrophosphate nanoparticles (primary particles); the primary particle diameter is 600nm, and the particle specific surface area is 80-120m ² /g. The thickness of the carbon coating layer is 40nm, and the particle size of the secondary microspheres is 70-80μm.

The sodium vanadium pyrophosphate material prepared by the present embodiment is the working electrode, and the sodium is the counter electrode, which is assembled into a button cell. Under the current density of 160mA/g (2C), the cycle performance is tested; at 160mA/g (2C) Under the current density, the capacity of the first cycle is 48mA/g, and after 50 cycles, the specific capacity of 38mAh/g can be maintained. The results show that the rate performance of the material obtained by direct ball milling and calcination without hydrothermal preparation of carbon-coated vanadium oxide is relatively poor. The crystal growth is not restricted, and the carbon coating layer of the calcined product is not uniform enough.

Comparative example 3

First weigh 2g of vanadium pentoxide (0.011mol), 5g of citric acid (0.026mol), 3.5g of sodium dihydrogen phosphate (0.03mol) and 3g of sodium carbonate (0.028mol), add it to 100mL of deionized water, stir to form a uniform solution, pour the aqueous solution into a polytetrafluoroethylene reactor, then put the polytetrafluoroethylene reactor into a stainless steel hydrothermal kettle and seal it, and finally place the stainless steel hydrothermal kettle in a homogeneous reactor , hydrothermal reaction was carried out at 180°C for 10 hours. The hydrothermal product was dried in an oven at 70 °C for 12 h. The dried product was spray-dried to obtain a spherical precursor. The precursor was heated to 600°C in a tube furnace at a rate of 4°C/min under a nitrogen atmosphere, and calcined for 15 hours to obtain a black powder; finally, the black powder was washed three times with deionized water, washed twice with alcohol, and dried to obtain the final product ( Na ₇ V ₃ (P ₂ O ₇ ) ₄ ).

The composite positive electrode material prepared in this embodiment has microspheres formed by the agglomeration of carbon-coated sodium vanadium pyrophosphate nanoparticles (primary particles); the primary particle diameter is 400nm, and the particle specific surface area is 80-100m ² /g. The thickness of the carbon coating layer is 25nm, and the particle size of the secondary microspheres is 50-60 μm.

The sodium vanadium pyrophosphate material prepared by the present embodiment is the working electrode, and the sodium is the counter electrode, which is assembled into a button cell. Under the current density of 160mA/g (2C), the cycle performance is tested; at 160mA/g (2C) Under the current density, the capacity of the first cycle is 54mA/g, and after 50 cycles, the specific capacity of 38mAh/g can be maintained. The results show that the rate performance of the material obtained by one-step hydrothermal heating and calcination without pre-coating carbon is relatively poor. It may be that there is no pre-coated carbon layer, and the growth of sodium vanadium pyrophosphate crystals in the precursor is not affected by the subsequent sintering process. Limitation, resulting in larger particle size and lower rate performance.

Comparative example 4

First weigh 2g of vanadium pentoxide (0.011mol) and 5g of citric acid (0.026mol) and dissolve them in 100ml deionized water, stir to form a uniform solution, pour the aqueous solution into a polytetrafluoroethylene reactor, and then put the The polytetrafluoroethylene reaction kettle was put into a stainless steel hydrothermal kettle and sealed, and finally the stainless steel hydrothermal kettle was placed in a homogeneous reactor, and hydrothermal reaction was carried out at 230° C. for 10 hours. The hydrothermal product was dried in an oven at 70 °C for 12 h. Then, under a protective atmosphere of nitrogen, sinter at 600°C for 12 hours in a tube furnace, wash the product three times with deionized water, wash twice with alcohol, and dry at 70°C for 2 hours to obtain pre-coated vanadium oxycarbide.

The prepared pre-coated vanadium oxycarbide, 3.5 g (0.03 mol) of sodium dihydrogen phosphate, and 3 g (0.028 mol) of sodium carbonate were ball milled for 7 hours at a speed of 200 rpm. The precursor was heated to 600°C in a tube furnace at a rate of 4°C/min under a nitrogen atmosphere, and calcined for 15 hours to obtain a black powder; finally, the black powder was washed three times with deionized water, washed twice with alcohol, and dried to obtain the final product ( Na7V3(P2O7)4).

The composite positive electrode material prepared in this embodiment has microspheres formed by the agglomeration of carbon-coated sodium vanadium pyrophosphate nanoparticles (primary particles); the primary particle diameter is 400nm, and the particle specific surface area is 50-80m ² /g. The thickness of the carbon coating layer is 35nm, and the particle size of the secondary microsphere is 60-80μm.

The sodium vanadium pyrophosphate material prepared by this embodiment is used as the working electrode, and the sodium is used as the counter electrode, and is assembled into a button cell. Under the current density of 160mA/g (2C), the cycle performance is tested; the test results show that the The electrochemical performance of the sodium electrode is poor; at a current density of 160mA/g (2C), the specific capacity of the first discharge is only 45mA/g, and the specific capacity of 34mAh/g is maintained after 50 cycles. Increasing the hydrothermal temperature to 230 °C is beyond the optimal range. Under the condition that other conditions remain unchanged, the rate performance and cycle stability decrease more. It can be seen that the control of hydrothermal conditions has a great influence on the primary morphology regulation of materials.

Comparative example 5

First weigh 2g of vanadium pentoxide (0.011mol) and 5g of citric acid (0.026mol) and dissolve them in 100ml deionized water, stir to form a uniform solution, pour the aqueous solution into a polytetrafluoroethylene reactor, and then put the The polytetrafluoroethylene reaction kettle was put into a stainless steel hydrothermal kettle and sealed, and finally the stainless steel hydrothermal kettle was placed in a homogeneous reactor, and hydrothermal reaction was carried out at 100° C. for 10 hours. The hydrothermal product was dried in an oven at 70 °C for 12 h. Then, under a protective atmosphere of nitrogen, sinter at 600°C for 12 hours in a tube furnace, wash the product three times with deionized water, wash twice with alcohol, and dry at 70°C for 2 hours to obtain pre-coated vanadium oxycarbide.

The prepared pre-coated vanadium oxycarbide, 3.5 g (0.03 mol) of sodium dihydrogen phosphate, and 3 g (0.028 mol) of sodium carbonate were ball milled for 7 hours at a speed of 200 rpm. The precursor was heated to 600°C in a tube furnace at a rate of 4°C/min under a nitrogen atmosphere, and calcined for 15 hours to obtain a black powder; finally, the black powder was washed three times with deionized water, washed twice with alcohol, and dried to obtain the final product ( Na7V3(P2O7)4).

The composite positive electrode material prepared in this embodiment has carbon-coated sodium vanadium pyrophosphate nanoparticles (primary particles) agglomerated into microspheres; the primary particle diameter is 400-700nm, and the particle specific surface area is 80-100m ² /g , the thickness of the coated carbon layer is 30-50nm, and the particle size of the secondary microspheres is 60-85μm.

The sodium vanadium pyrophosphate material prepared by this embodiment is used as the working electrode, and the sodium is used as the counter electrode, and is assembled into a button cell. Under the current density of 160mA/g (2C), the cycle performance is tested; the test results show that the The electrochemical performance of the sodium electrode is poor; at a current density of 160mA/g (2C), the specific capacity of the first discharge is only 45mA/g, and the specific capacity of 34mAh/g is maintained after 50 cycles. When the hydrothermal temperature is lowered to 100 °C, and other conditions remain unchanged, the rate performance of the material drops more, which may be due to the lower hydrothermal temperature and the larger and uneven product particles.

Comparative example 6

First take by weighing 2g vanadium pentoxide (0.011mol) and 5g citric acid (0.026mol) and dissolve in 100ml deionized water, stir to form a uniform solution, pour the aqueous solution into a polytetrafluoroethylene reactor, and then put the The polytetrafluoroethylene reaction kettle was put into a stainless steel hydrothermal kettle and sealed, and finally the stainless steel hydrothermal kettle was placed in a homogeneous reactor, and hydrothermal reaction was carried out at 180° C. for 30 hours. The hydrothermal product was dried in an oven at 70 °C for 12 h. Then, under a protective atmosphere of nitrogen, sinter at 600°C for 12 hours in a tube furnace, wash the product three times with deionized water, wash twice with alcohol, and dry at 70°C for 2 hours to obtain pre-coated vanadium oxycarbide.

The prepared pre-coated vanadium oxycarbide, 3.5 g (0.03 mol) of sodium dihydrogen phosphate, and 3 g (0.028 mol) of sodium carbonate were ball milled for 7 hours at a speed of 200 rpm. The precursor was heated to 600°C in a tube furnace at a rate of 4°C/min under a nitrogen atmosphere, and calcined for 15 hours to obtain a black powder; finally, the black powder was washed three times with deionized water, washed twice with alcohol, and dried to obtain the final product ( Na7V3(P2O7)4).

The composite positive electrode material prepared in this embodiment has carbon-coated sodium vanadium pyrophosphate nanoparticles (primary particles) agglomerated into microspheres; the primary particle size is 600-700nm, and the particle specific surface area is 80-100m ² /g , the thickness of the coated carbon layer is 20-40nm, and the particle size of the secondary microspheres is 60-80μm.

The sodium vanadium pyrophosphate material prepared by this embodiment is used as the working electrode, and the sodium is used as the counter electrode, and is assembled into a button cell. Under the current density of 160mA/g (2C), the cycle performance is tested; the test results show that the The electrochemical performance of the sodium electrode is poor; at a current density of 160mA/g (2C), the specific capacity of the first discharge is only 44mA/g, and the specific capacity of 32mAh/g is maintained after 50 cycles. When the hydrothermal time is increased to 30h, and other conditions remain unchanged, the rate performance and cycle stability decrease more. It can be seen that the control of hydrothermal conditions has a great influence on the regulation of the primary morphology of the material.

Comparative example 7

First weigh 2g of vanadium pentoxide (0.011mol) and 5g of citric acid (0.026mol) and dissolve them in 100ml deionized water, stir to form a uniform solution, pour the aqueous solution into a polytetrafluoroethylene reactor, and then put the The polytetrafluoroethylene reaction kettle was put into a stainless steel hydrothermal kettle and sealed, and finally the stainless steel hydrothermal kettle was placed in a homogeneous reactor, and hydrothermal reaction was carried out at 180° C. for 10 hours. The hydrothermal product was dried in an oven at 70 °C for 12 h. Then, under a protective atmosphere of nitrogen, sinter at 600°C for 12 hours in a tube furnace, wash the product three times with deionized water, wash twice with alcohol, and dry at 70°C for 2 hours to obtain pre-coated vanadium oxycarbide.

The prepared pre-coated vanadium oxycarbide, 3.5 g (0.03 mol) of sodium dihydrogen phosphate, and 3 g (0.028 mol) of sodium carbonate were ball milled for 7 hours at a speed of 200 rpm. The precursor was heated to 600°C in a tube furnace at a rate of 4°C/min under a nitrogen atmosphere, and calcined for 45 hours to obtain a black powder; finally, the black powder was washed three times with deionized water, washed twice with alcohol, and dried to obtain the final product ( Na7V3(P2O7)4).

The composite positive electrode material prepared in this embodiment has microspheres formed by the agglomeration of carbon-coated sodium vanadium pyrophosphate nanoparticles (primary particles); the primary particle diameter is 700nm, and the particle specific surface area is 80-100m ² /g. The thickness of the carbon coating layer is 35nm, and the particle size of the secondary microspheres is 78-80μm.

The sodium vanadium pyrophosphate material prepared by this embodiment is used as the working electrode, and the sodium is used as the counter electrode, and is assembled into a button cell. Under the current density of 160mA/g (2C), the cycle performance is tested; the test results show that the The electrochemical performance of the sodium electrode is poor; at a current density of 160mA/g (2C), the specific capacity of the first discharge is only 45mA/g, and the specific capacity of 34mAh/g is maintained after 50 cycles. Increasing the secondary calcination time from 15h to 45h is beyond the optimal range, while other conditions remain unchanged, the electrochemical performance of the material is severely reduced, which may be due to the increase of the calcination time leading to the increase of the particle size and the deterioration of the material performance.

Claims (9)

1. a kind of preparation method of pyrophosphoric acid vanadium sodium@carbon composite anode material, which is characterized in that will be molten comprising carbon source and vanadium source Liquid carries out hydro-thermal reaction, and hydro-thermal reaction product is carried out level-one sintering, packet oxidation of coal vanadium is made；By packet oxidation of coal vanadium obtained, It is spray-dried after sodium source, phosphorus source wet ball grinding, obtains presoma；Presoma carries out second level and is sintered to obtain the composite positive pole；

The carbon source is at least one of glucose, citric acid, oxalic acid, lactose, galactolipin；

The hydrothermal temperature is 120-200 DEG C；Reaction time is 10-25h；

The temperature of level-one sintering and double sintering is 450 alone^oC-850℃ ；Time is 10-40h alone；

The composite positive pole is the micro-spherical particle assembled by the pyrophosphoric acid vanadium sodium nano particle for being coated with carbon.

2. the preparation method of pyrophosphoric acid vanadium sodium@carbon composite anode material as described in claim 1, which is characterized in that be coated with The partial size of the pyrophosphoric acid vanadium sodium nano particle of carbon is 100-200nm；The partial size of the micro-spherical particle of the composite positive pole is 5-30μm；Specific surface area is 20-400 ㎡/g；Cladding carbon layers having thicknesses are 5-40nm.

3. the preparation method of pyrophosphoric acid vanadium sodium@carbon composite anode material as described in claim 1, which is characterized in that described Vanadium source is at least one of vanadium trioxide, vanadic anhydride, ammonium metavanadate, vanadyl acetylacetonate, vanadium acetylacetonate；

Carbon source and the molar ratio in vanadium source are 0.1-10.

4. the preparation method of pyrophosphoric acid vanadium sodium@carbon composite anode material as described in claim 1, which is characterized in that hydro-thermal is anti- Answering temperature is 150-200 DEG C；Reaction time is 10-20h.

5. the preparation method of pyrophosphoric acid vanadium sodium@carbon composite anode material as described in claim 1, which is characterized in that sodium source is Sodium carbonate, sodium acetate, sodium oxalate, sodium pyrophosphate, phosphoric acid, monoammonium phosphate, ammonium dihydrogen phosphate, disodium-hydrogen, biphosphate At least one of sodium；

Phosphorus source is sodium pyrophosphate, phosphoric acid, monoammonium phosphate, ammonium dihydrogen phosphate, disodium-hydrogen, at least one in sodium dihydrogen phosphate Kind.

6. the preparation method of pyrophosphoric acid vanadium sodium@carbon composite anode material as described in claim 1, which is characterized in that sodium source, vanadium The ratio mixing of Na, V of source and phosphorus source, P element molar ratio 0.5-10:1:0.1-10.

7. the preparation method of pyrophosphoric acid vanadium sodium@carbon composite anode material as described in claim 1, which is characterized in that wet process ball The medium of honed journey is for water or with water infinitely than miscible at least one of solvent；Rotational speed of ball-mill is 150-550 revs/min； Ball-milling Time is 5-25h.

8. the preparation method of pyrophosphoric acid vanadium sodium@carbon composite anode material as described in claim 1, which is characterized in that level-one is burnt The temperature of knot and double sintering is 500-700 DEG C alone；Time is 10-15h alone.

9. the pyrophosphoric acid vanadium sodium@carbon composite anode material answers made from a kind of any one of claim 1 ~ 8 preparation method With, which is characterized in that it is used as sodium-ion battery positive material.