CN107814564B - A method for batch preparation of low-cost carbon-coated titanium phosphate compounds - Google Patents

Abstract

The invention relates to a method for batch preparation of a low-cost carbon-coated titanium phosphate compound, wherein the chemical formula of the titanium phosphate compound is M _x Ti ₂ (PO ₄ ) ₃ , wherein M is selected from at least one of alkali metals, x = 1 to 1.05, the method includes: step 1) using alkali metal source, phosphorus source, titanium source and carbon source in stoichiometric ratio as raw materials, wet ball milling to prepare slurry; step 2) using the slurry with The carbon-coated titanium phosphate compound precursor mixed powder is obtained by a centrifugal spray drying method; step 3) the precursor mixed powder is sintered by a solid-phase synthesis method to obtain a carbon-coated titanium phosphate compound powder. The invention has simple process and low cost, and can be widely used in large-scale production of titanium phosphate compounds.

Description

A method for batch preparation of low-cost carbon-coated titanium phosphate compounds

technical field

The invention relates to a method suitable for batch preparation of carbon-coated titanium phosphate compound ceramic powders, in particular to a method for ball-milling mixing, spray-drying and granulating by using carbon-containing precursors and precursors of various phase components, The carbon-coated titanium phosphate compound powder is prepared by a high-temperature solid-phase synthesis reaction method, and belongs to the field of ion conductive ceramic materials.

Background technique

Titanium phosphate compound is a typical NASICON structure, and its large tunnel size allows free migration of alkali metal ions. It is a fast ionic conductor with high ionic conductivity and small electronic conduction, excellent thermal stability, and is an important electrode material for alkali metal ion batteries. Taking NaTi ₂ (PO ₄ ) ₃ as an example, in 1mol/L Na ₂ SO ₄ solution, NaTi ₂ (PO ₄ ) ₃ has a pair of very symmetrical redox peaks at -0.82V (vs. Ag/AgCl), indicating that Na ions can undergo reversible intercalation and deintercalation reactions at -0.82V. This reaction potential range is slightly higher than the hydrogen evolution potential of water. This relatively negative anode potential not only makes full use of the hydrogen evolution potential window of water, which is beneficial to improve the working voltage of the battery, but also ensures that during the normal intercalation and de-sodium reaction process Hydrogen evolution side reaction does not occur. The charge-discharge curve shows that NaTi ₂ (PO ₄ ) ₃ has a stable charge-discharge plateau at -0.82V, and the reversible capacity is 120mAh/g, which is equivalent to the de-intercalation capacity of two sodium ions. Benefiting from the fast ionic conductor structure of NaTi ₂ (PO ₄ ) ₃ material, it can still release 70% of the reversible specific capacity when charged and discharged at a high rate of 100C, so it can be used as a high-power anode material. After carbon coating treatment of M _x Ti ₂ (PO ₄ ) ₃ , not only the electronic conductivity of the material is improved, but also the utilization rate of active material is also significantly improved. Since the direct contact between the electrolyte and the material surface is avoided, it can be It can effectively prevent the occurrence of side reactions, thereby greatly improving its cycle stability.

At present, the methods for preparing carbon-coated titanium phosphate compounds mainly include microwave heating synthesis method, hydrothermal method, sol-gel method, etc. [J.Mater.Chem.A,2015,3,12089-12096]. Usually, compared with the traditional solid-phase synthesis method, the powder prepared by these methods has higher purity and excellent performance, but the production process is complex and the equipment is more, which makes it difficult to achieve large-scale production, especially when carbon coating requires multiple heat treatments And grinding, the cost is high, can not meet the requirements of reducing battery cost. The traditional solid-phase synthesis method also has its own defects, such as many side reactions caused by uneven mixing of powders and impure products.

SUMMARY OF THE INVENTION

In view of the above problems, the purpose of the present invention is to provide a method capable of preparing high-purity carbon-coated titanium phosphate compound with simple process, low cost and large-scale production.

The present invention provides a method for preparing a carbon-coated titanium phosphate compound, wherein the chemical formula of the titanium phosphate compound is M _x Ti ₂ (PO ₄ ) ₃ , wherein M is selected from at least one of alkali metals, and x=1-1.05 , the method includes:

Step 1) using alkali metal source, phosphorus source, titanium source and carbon source (preferably inorganic carbon source) in stoichiometric ratio as raw materials, wet ball milling to prepare slurry;

Step 2) obtaining carbon-coated titanium phosphate compound precursor mixed powder by centrifugal spray drying of the slurry;

Step 3) Sintering the precursor mixed powder by a solid-phase synthesis method to obtain a carbon-coated titanium phosphate compound powder.

Different from the traditional solid phase synthesis method, the present invention adopts the method of making slurry by ball milling and spray drying and granulation, so that the obtained powder particles are spherical, so that the precursor of the titanium phosphate compound is mixed evenly and the titanium phosphate compound is easily coated with carbon. The obtained powder is then subjected to a high-temperature solid-phase reaction to prepare carbon-coated titanium phosphate compounds in batches, especially to avoid the uneven high-temperature reaction components caused by uneven mixing in the traditional solid-phase reaction, and other occurrences in powder sintering. crystal phase impurities. The product obtained by the invention has high purity, can well improve the electrical conductivity of the material, greatly improves the electrochemical performance of the material, has simple process and low cost, and can be widely used in large-scale production of titanium phosphate compounds.

Preferably, in step 1), the solvent of wet ball milling is water or a mixed solvent of water and ethanol, and the content of ethanol in the mixed solvent is 0-10 wt.%. The present invention selects cheap, easily available, environmentally friendly water (preferably deionized water) as the main solvent, which can reduce costs and is environmentally friendly.

Preferably, in step 1), the content of the carbon source is 0-20 wt.%. Preferably, the carbon source is pretreated with an organic solvent containing hydroxyl functional groups to enhance wettability prior to addition to the ball mill. According to the present invention, the titanium phosphate compound precursor can be mixed more uniformly and the titanium phosphate compound can be more easily coated with carbon.

Preferably, step 1) includes: mixing the alkali metal source, the titanium source and the phosphorus source according to the molar ratio of (1-1.05):2:3, pouring the mixed raw materials into the ball mill barrel, and according to the solid content of 10-50wt % Add deionized water, and ball mill at 50-300 r/min for 1-5 hours to obtain the first slurry; and add carbon source to the obtained first slurry, and mix at 50-300 r/min Ball mill for 1 to 5 hours.

In the present invention, the slurry with a certain viscosity and particle size can be obtained by the step-by-step ball milling method. Compared with the one-step ball milling, the material can be mixed more uniformly, and because the initial particle size of each powder is different, the step-by-step ball milling can make the final product The particle size distribution of the slurry powder is controllable.

Preferably, in step 1), a defoaming agent and/or a dispersing agent are also added. Preferably, the defoaming agent is a higher alcohol, the addition amount of the higher alcohol is 0.5-5 wt.% of the powder, and the addition amount of the dispersant is 0.5-5 wt.% of the powder. Preferably, the dispersing agent is selected from any one or more of polyacrylic acid, sodium hexametaphosphate, polyethylene glycol, fish oil and castor oil.

Preferably, in step 1), the alkali metal source is any one of alkali metal carbonate, hydroxide, oxalate, acetate, dihydrogen phosphate and nitrate;

The titanium source is any one of titanium dioxide, metatitanic acid, titanic acid and titanium tetrachloride;

The phosphorus source is any one of lithium dihydrogen phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate and ammonium phosphate;

The carbon source is any one or more of graphite, activated carbon, acetylene black, graphene and the like.

Preferably, in step 1), the solid content of the obtained slurry is 20-60 wt.%.

Preferably, in step 2), centrifugal spray drying equipment is used to control the inlet air temperature to be 100-240°C, preferably 200-240°C, the outlet air temperature to be 80-110°C, preferably 100-110°C, and the centrifugal speed to be 10000-20000°C. RPM, preferably 12000-15000 RPM. By controlling the process parameters of the centrifugal spray drying equipment as described above, spherical particles with more uniform size distribution can be obtained.

Preferably, in step 3), the sintering is carried out under a protective atmosphere of nitrogen or argon at 600-1000° C. for 1-24 hours. According to the present invention, a carbon-coated titanium phosphate compound ceramic powder with high crystal phase purity can be obtained.

Preferably, in step 3), before heating up to the sintering temperature, the deamination reaction is carried out at a constant temperature of 200-400°C (eg, 200-350°C or 250-400°C) for 1-3 hours.

The present invention adopts the method of ball milling mixing and spray drying, and obtains carbon-coated titanium phosphate compound ceramic powder through high-temperature solid-phase reaction. Compared with the prior art, the present invention has the following advantages and beneficial effects:

1. Through spray drying, carbon coating of graphite and other active materials can be achieved, the electrical conductivity of the material can be improved, and the electrochemical performance of the material can be greatly improved;

2. Through spray drying, particles with uniform size distribution can be obtained, which is beneficial to improve the sintering performance of powder materials;

3. The carbon-coated alkali metal ion electrode material with NASICON structure synthesized by solid-phase method has good electrochemical performance, simple synthesis process, easy control and low price, and can be used in energy storage equipment, backup power supply, storage power supply, etc.;

4. The invention has the advantages of short synthesis period, cheap raw materials, simple process and easy control, and has significant practical value and good application prospect.

Description of drawings

1 is a flow chart of mass production of titanium phosphate compounds according to an embodiment of the present invention;

2 is a SEM image of the powder after sintering according to an embodiment of the present invention;

3 is a particle size distribution diagram of powder after sintering according to an embodiment of the present invention;

FIG. 4 is an XRD pattern of the powder after sintering according to an embodiment of the present invention.

Detailed ways

The present invention will be further described below with reference to the accompanying drawings and the following embodiments. It should be understood that the accompanying drawings and the following embodiments are only used to illustrate the present invention, but not to limit the present invention.

The present invention provides a low-cost batch preparation method of carbon-coated titanium phosphate compound M _x Ti ₂ (PO ₄ ) ₃ (M=Na, Li, K, etc., wherein x=1-1.05). By ball milling dispersion, centrifugal spray drying and granulation, the prepared powder is spherical, so that the precursor of titanium phosphate compound is evenly mixed and easily coated with carbon. The obtained powder is then subjected to high temperature solid-phase reaction method to prepare carbon coating Coated titanium phosphate compound. FIG. 1 shows a flow chart of mass production of titanium phosphate compounds according to an embodiment of the present invention. Hereinafter, referring to FIG. 1 , a method for producing a titanium phosphate compound will be specifically described.

First, ball mill compounding is performed. In the present invention, the raw material may contain an alkali metal source, a phosphorus source, a titanium source and a carbon source. Powder can be used for each raw material. The present invention does not have too high requirements on the purity of the raw material powder, and industrial-grade raw materials can be used. Each raw material can be synthesized by existing methods or purchased commercially.

As an alkali metal source, including but not limited to lithium carbonate (sodium, potassium), lithium hydroxide (sodium, potassium), lithium oxalate (sodium, potassium), lithium acetate (sodium, potassium), lithium dihydrogen phosphate (sodium, potassium) ) or any one or more of lithium nitrate (sodium, potassium).

The phosphorus source includes, but is not limited to, any one or more of lithium dihydrogen phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate or ammonium phosphate.

The titanium source includes but is not limited to any one or more of titanium dioxide, metatitanic acid, titanic acid, and titanium tetrachloride. Wherein the titanium dioxide can be any one or several of the three types of rutile, anatase and brookite.

The carbon source is preferably an inorganic carbon source, including but not limited to any one or more of graphite, activated carbon, acetylene black, and graphene.

Alkali metal source, phosphorus source and titanium source are proportioned according to the stoichiometric formula of titanium phosphate compound M _x Ti ₂ (PO ₄ ) ₃ (M=Na, Li, K, etc., wherein x=1-1.05).

The content of the carbon source may be 0-50 wt.%, preferably 10-20 wt.%. In addition, the carbon source can be pretreated with ethanol or other organic solvent containing hydroxyl functional groups to enhance wettability before adding to the ball mill.

Deionized water, which is cheap, easy to obtain and environmentally friendly, can be used as the main solvent during ball milling. A mixed solvent of water and ethanol can also be used. The ethanol content is preferably 0-20 wt.%.

During ball milling, a small amount of higher alcohol (preferably C7-C9 alcohol) can also be added as a defoaming agent. In addition, a small amount of dispersant can also be added, and the added amount of the dispersant can be 0.5wt.% to 5wt.% of the powder. As a dispersing agent, it includes but is not limited to one or more of polyacrylic acid, sodium hexametaphosphate, polyethylene glycol, fish oil, and castor oil.

In the present invention, the ball-milling mixture can adopt a step-by-step ball milling method. In one example, it includes: a first ball milling step of mixing an alkali metal source, a phosphorus source, and a titanium source with a solvent and then ball milling; and a second ball milling step of adding a carbon source for further ball milling. In the first ball milling step, the mass ratio of the total mass of the powder to the solvent and the grinding ball may be (10-50):(50-90):(10-30). The rotation speed can be 50-300 rpm, and the ball milling time can be 1-5 hours. In the second ball milling step, the rotational speed may be 50-300 rpm, and the ball-milling time may be 1-5 hours.

The solid content of the slurry obtained by ball milling is controlled at 0-60 wt.%, preferably, at 20-30 wt.%. The particle size of the slurry is 1 to 10 μm.

Next, the obtained slurry was granulated with a centrifugal spray dryer to obtain a carbon-coated titanium phosphate compound precursor mixed powder. Centrifugal spray drying equipment can be used to control the inlet air temperature 100-240°C, preferably 200-240°C, the outlet air temperature 80-110°C, preferably 100-110°C, and the centrifugal speed 10000-20000 rpm, preferably 10000-15000 rev/min.

The granulated powder is further sintered by a traditional solid-phase synthesis method and sintered at a high temperature in an atmosphere furnace to obtain a carbon-coated titanium phosphate compound powder. The deamination reaction can be carried out at medium and low temperature (for example, 250-400° C.), and then sintered at a constant temperature of 650-1000° C. (preferably 650-950° C.) for 1-24 hours (for example, 10 hours). During sintering, an inert gas can be used as the protective gas in the sintering furnace, for example, the atmosphere can be one or more of argon and nitrogen.

The invention uses several specific raw materials to obtain slurry with a certain viscosity and particle size through a step-by-step ball milling method. Through further spray drying treatment of the slurry, the precursor powder with uniform mixing and good dispersion is obtained, and the carbon-coated titanium phosphate compound powder is synthesized by solid-phase reaction under specific sintering conditions. The invention has the advantages of simple process, low cost, uniform ball milling and good powder dispersion. The powder particles obtained by the centrifugal spray drying method are spherical, so that the titanium phosphate compound is easily coated with carbon, which can especially avoid the uneven high-temperature reaction components caused by uneven mixing in the traditional solid-phase reaction. Other crystalline phase impurities appear. This invention is suitable for mass production of carbon-coated titanium phosphate compounds. The key point of the present invention is that, different from the traditional solid-phase synthesis method, the method of making slurry by ball milling and spray drying granulation is adopted, and the obtained powder particles are spherical, so that the titanium phosphate compound is easily coated with carbon, and carbon is successfully prepared. The coated titanium phosphate compound powder adopts a high-temperature solid-phase synthesis method and uses an atmosphere furnace to perform deamination reaction at a medium and low temperature, and maintain it at a certain temperature for a period of time to obtain a carbon-coated titanium phosphate compound ceramic with high crystal phase purity. powder.

2 and 3 show the SEM image and particle size distribution diagram of the carbon-coated titanium phosphate compound powder prepared by an embodiment of the present invention, it can be seen that the particle size is about 1-10 μm, and the prepared powder is uniformly dispersed. Good carbon coating. FIG. 4 shows the XRD pattern of the carbon-coated titanium phosphate compound powder prepared by an embodiment of the present invention. The results show that the sintered ceramic powder has a relatively high crystal purity and no impurity peaks. Combined with atomic absorption spectrometry, carbon is measured by atomic absorption spectrometry. The content of the coated titanium phosphate compound is 95-99.9%, preferably 99.9%.

The following further examples are given to illustrate the present invention in detail. It should also be understood that the following examples are only used to further illustrate the present invention, and should not be construed as limiting the protection scope of the present invention. Some non-essential improvements and adjustments made by those skilled in the art according to the above content of the present invention belong to the present invention. scope of protection. The specific process parameters and the like in the following examples are only an example of a suitable range, that is, those skilled in the art can make selections within the suitable range through the description herein, and are not intended to be limited to the specific numerical values exemplified below.

Example 1

Sodium carbonate, ammonium dihydrogen phosphate, and titanium dioxide powder are used as raw materials. The mass ratio of the mixture with water is 30:70. Polyacrylic acid was selected as the dispersant, and the addition amount of the dispersant was 1 wt. % of the powder, and a uniform slurry was obtained by ball milling at a high speed of 200 rpm in a coarse mill for 2 hours. Continue to add the active material graphite pretreated by ethanol 20wt.%), further ball mill at 200 r/min for 2 h, and then pour out the slurry. The obtained slurry was spray-dried, and the inlet air temperature was set at 220° C., the outlet air temperature was 110° C., and the centrifugal speed was 12,000 rpm, and the obtained spherical powder precursor was collected. The precursor is put into an inert gas filled sintering furnace, and carbon-coated titanium phosphate ceramic powder can be obtained after sintering in a nitrogen atmosphere at 750°C for 10 hours. The SEM image, particle size distribution image and XRD image can be seen in Figures 2-4, respectively.

Example 2

Lithium carbonate, ammonium dihydrogen phosphate, and titanium dioxide powder are used as raw materials, and the content of lithium, titanium, and phosphorus is added to a mixture of ethanol and water (1:10) in a molar ratio of 1:2:3, and the raw material powder is mixed with ethanol. The mass ratio of the mixture with water is 30:70. Sodium hexametaphosphate was selected as the dispersant, and the addition amount of the dispersant was 1 wt.% of the powder, and a uniform slurry was obtained by ball milling at a high speed of 200 rpm in a coarse mill for 2 hours. Continue to add the active material graphite pretreated by ethanol 20wt.%), further ball mill at 200 r/min for 2 h, and then pour out the slurry. The obtained slurry is spray-dried, the inlet air temperature is set to 220°C, the outlet air temperature is 110°C, and the centrifugal rotation speed is 15,000 rpm, and the obtained spherical powder precursor is collected. The precursor is put into an inert gas filled sintering furnace, and carbon-coated titanium phosphate ceramic powder can be obtained after sintering in a nitrogen atmosphere at 750°C for 10 hours.

Example 3

Sodium carbonate, ammonium dihydrogen phosphate, and titanium dioxide powder are used as raw materials, and the contents of potassium, titanium and phosphorus are added to the mixture of ethanol and water (1:10) in a molar ratio of 1:2:3, and the raw material powder is mixed with ethanol. The mass ratio of the mixture with water is 20:80. Castor oil was selected as the dispersant, and the addition amount of the dispersant was 1 wt.% of the powder, and a uniform slurry was obtained by ball milling at a high speed of 200 rpm in a coarse mill for 2 hours. Continue to add the active material graphite pretreated by ethanol 20wt.%), further ball mill at 200 r/min for 2 h, and then pour out the slurry. The obtained slurry was spray-dried, and the inlet air temperature was set at 220° C., the outlet air temperature was 110° C., and the centrifugal speed was 17,000 rpm, and the obtained spherical powder precursor was collected. The precursor is put into an inert gas filled sintering furnace, and carbon-coated titanium phosphate ceramic powder can be obtained after sintering in a nitrogen atmosphere at 750°C for 10 hours.

Industrial applicability: The method of the present invention reduces the production cost of carbon-coated titanium phosphate compound ceramic powder, improves the purity and performance of the produced powder, and lays a foundation for the commercial production of aqueous sodium ion electrodes.

Claims (8)

1. A method for preparing a carbon-coated titanium phosphate compound, wherein the chemical formula of the titanium phosphate compound is M _x Ti ₂ (PO ₄ ) ₃ , wherein M is selected from at least one of alkali metals, and x= 1 to 1.05, the method includes: Step 1) Using stoichiometric ratio of alkali metal source, phosphorus source, titanium source and carbon source as raw materials, wet ball milling to prepare slurry; the alkali metal source is alkali metal carbonate, hydroxide, oxalic acid at least one of salt, acetate, dihydrogen phosphate and nitrate; the titanium source is any one of titanium dioxide, metatitanic acid, titanic acid, and titanium tetrachloride; the phosphorus source is dihydrogen phosphate Any one of lithium, ammonium dihydrogen phosphate, diammonium hydrogen phosphate and ammonium phosphate; the carbon source is any one or more of graphite, activated carbon, hard carbon, graphene, and carbon black; the content of the carbon source %, the carbon source is pretreated with an organic solvent containing a hydroxyl functional group to enhance wettability before being added to the ball mill; the solvent for wet ball milling is water, or a mixed solvent of water and ethanol, in the mixed solvent ethanol The content is 0～10 wt.%; Step 2) obtaining spherical carbon-coated titanium phosphate compound precursor mixed powder by centrifugal spray drying of the slurry; Step 3) Sintering the precursor mixed powder by a solid-phase synthesis method to obtain a carbon-coated titanium phosphate compound powder; the sintering is performed under a protective atmosphere at a constant temperature of 600-1000° C. for 1-24 hours. 2. The method according to claim 1, wherein step 1) comprises: Mix the alkali metal source, titanium source and phosphorus source according to the molar ratio of (1～1.05):2:3, pour the mixed raw materials into the ball mill barrel, add deionized water according to the solid content of 10～50wt. The first slurry is obtained by ball milling at a speed of ~300 r/min for 1 to 5 hours; and a carbon source is added to the obtained first slurry, and the ball is mixed and ball-milled at a rotation speed of 50 to 300 r/min for 1 to 5 hours. 3. The method according to claim 1, characterized in that, in step 1), a defoaming agent and/or a dispersing agent are also added, and the addition amount of the defoaming agent is 0.5-5 wt.% of the powder, so The added amount of the dispersant is 0.5wt.% to 5wt.% of the powder, the defoamer is a higher alcohol, and the dispersant is selected from polyacrylic acid, sodium hexametaphosphate, polyethylene glycol, fish oil and castor at least one of sesame oil. 4. The method according to claim 1, wherein in step 1), the solid content of the obtained slurry is 0-60 wt.%. The method according to claim 4, characterized in that, in step 1), the solid content of the obtained slurry is 20-30 wt.%. 6. The method according to claim 1, characterized in that, in step 2), centrifugal spray drying equipment is used to control the inlet air temperature of 100-240°C, the outlet air temperature of 80-110°C, and the centrifugal speed of 10,000-20,000 rpm /Minute. 7. The method according to claim 6, characterized in that, in step 2), centrifugal spray drying equipment is used to control the inlet air temperature of 200-240°C, the outlet air temperature of 100-110°C, and the centrifugal speed of 12000-15000 rpm /Minute. 8 . The method according to claim 1 , wherein in step 3), before raising the temperature to the sintering temperature, the deamination reaction is performed at a constant temperature of 200-350° C. for 1-5 hours. 9 .