Green preparation method and application of carbon-coated sodium titanium phosphate composite material

Abstract

The invention belongs to the technical field of energy storage batteries and electrochemistry, and discloses a green preparation method and application of a carbon-coated sodium titanium phosphate composite material, titanyl sulfate and sodium dihydrogen phosphate are only used as raw materials, a simple coprecipitation method is used for preparing a precursor, the precursor and sodium dihydrogen phosphate are mixed and roasted, and sodium titanium phosphate can be obtained. Hydrothermal treatment is not needed, and harsh preparation conditions of high temperature and high pressure are avoided; meanwhile, ammonia-containing substances and acid do not need to be used, so that the ammonia-containing substances and the acid are prevented from being transported, stored, used, discharged and treated; the used raw materials are all solid materials and are not easy to volatilize or leak, so that the safety risk and loss in the transportation process are reduced. The titanyl sulfate used in the invention belongs to an intermediate for preparing titanium dioxide, is rich in source and low in price, and is suitable for industrial preparation. The carbon-coated sodium titanium phosphate prepared by the invention is used as a negative electrode of a sodium-ion battery, and has the material characteristic of high phase purity and the electrochemical characteristics of excellent specific capacity, rate, long cycle and the like.

Description

Technical Field

[0001] The present invention belongs to the fields of nanomaterials and sodium-ion energy storage batteries, and particularly relates to a green preparation method and application of a carbon-coated sodium titanium phosphate composite material. Background Art

[0002] With multiple countries committing to the "carbon neutrality" goal, the energy system is transitioning from fossil fuels to renewable energy sources such as wind and solar energy. Wind power and photovoltaic power generation are intermittent and unpredictable, and an energy storage system is needed to suppress fluctuations. Although lithium-ion batteries have good performance in various energy storage fields, due to the uneven distribution and limited nature of lithium resources. As a sodium element in the same group as lithium, although it has a large atomic radius, its abundance is high. The idea of using sodium-ion batteries to partially replace lithium-ion batteries has led to the rapid development of sodium-ion batteries; the use of organic electrolytes also increases the risk of application of organic sodium-ion batteries in large-scale energy storage scenarios. The water-based electrolyte used in aqueous sodium-ion batteries is more environmentally friendly than organic solvent electrolytes, which helps to reduce the dependence on harmful chemicals and thus meets the requirements of sustainable development and becomes one of the choices in the energy storage field.

[0003] Sodium titanium phosphate (NaTi2(PO4)3) is a high-performance anode material for sodium-ion batteries. Currently, most synthesis methods use a one-step synthesis method, which requires that other elements in the titanium source can be removed during high-temperature roasting. Generally, titanium dioxide, metatitanic acid, organic titanium, etc. are selected as raw materials, and these raw materials are relatively expensive. China is rich in titanium mineral resources, and 98% of the titanium ore exists in the form of ilmenite. During the process of preparing titanium dioxide from ilmenite by the sulfuric acid method, an intermediate product of titanyl sulfate will be produced. Therefore, if titanyl sulfate can be used as a raw material to prepare sodium titanium phosphate, not only can a technical process with more extensive resources be developed, but also the preparation cost can be greatly reduced. For the phosphorus source, currently, one or more of ammonium phosphate, ammonium dihydrogen phosphate, or phosphoric acid are used in the synthesis method. The first two will produce ammonia gas, and phosphoric acid is a liquid acid with certain corrosiveness, which is not convenient for transportation and storage.

[0004] Although the raw materials of Patent CN 119160868 A also use titanyl sulfate and sodium dihydrogen phosphate, since the sodium titanium phosphate obtained by the coprecipitation reaction requires a large excess ratio of sodium dihydrogen phosphate, the raw material cost will be increased; and titanyl sulfate and sodium dihydrogen phosphate will also coprecipitate to produce titanium phosphate, which is a competitive reaction with the coprecipitation to produce sodium titanium phosphate. In the actual reaction process, titanium phosphate substances will inevitably be obtained, resulting in impurity. Although Patent CN 113697788B avoids the use of ammonia-containing substances, it uses liquid phosphoric acid, which is not conducive to storage and transportation, and the highly acidic liquid acid has high requirements for equipment. Summary of the Invention

[0005] The object of the present invention is to provide a new synthesis scheme for sodium titanium phosphate in view of the problem that the preparation of existing sodium titanium phosphate must use an acid-containing liquid and an ammonia-producing substance. The present invention can avoid the use and transportation of the acid-containing liquid, and no ammonia gas is generated during the whole process, which has the characteristics of low cost and environmental friendliness.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A green preparation method of a carbon-coated sodium titanium phosphate composite material, comprising the following steps:

[0008] (1) Prepare a solution of sodium dihydrogen phosphate at 100-400 g / L, and prepare a solution of titanium oxysulfate at 40-120 g / L. Only sodium dihydrogen phosphate is used as the phosphorus source;

[0009] (2) According to the molar ratio of sodium dihydrogen phosphate to titanium oxysulfate of 1:1, simultaneously drop the solutions prepared in step (1) into a co-precipitation reaction kettle, and continuously stir sufficiently during the dropping process. After the solution is added, continue to stir for a period of time, and then carry out aging. Among them, the reaction temperature is 25-40 °C, the aging temperature is 25-40 °C, the reaction time is 0.5-1 h, the continuous stirring time is 1-3 h, and the aging time is 3-6 h;

[0010] (3) Carry out solid-liquid separation on the aged slurry to obtain a filter cake, and wash the filter cake repeatedly until the filtrate is neutral, and at this time, obtain a sodium titanium phosphate precursor;

[0011] (4) Prepare a slurry by mixing the sodium titanium phosphate precursor, sodium dihydrogen phosphate and a carbon source, and then carry out sand grinding. Among them, the molar amount of sodium dihydrogen phosphate added is in a ratio of 1:1 to the molar amount of the sodium titanium phosphate precursor;

[0012] (5) Spray-dry the sand-ground slurry;

[0013] (6) Sinter the spray-dried solid powder under the protection of an inert atmosphere;

[0014] (7) Carry out air flow crushing on the sintered material to obtain the final product of carbon-coated sodium titanium phosphate.

[0015] Preferably, in step (3), the solid-liquid separation and washing methods are one or more of suction filtration, centrifugation, and plate-and-frame pressure filtration.

[0016] Preferably, in step (4), the carbon source is an organic carbon source and / or an inorganic carbon source. The organic carbon source includes one or more of starch, glucose, sucrose, citric acid, ascorbic acid, polyethylene glycol, and polyvinyl alcohol. The inorganic carbon source includes one or more of acetylene black, activated carbon, graphite, graphene, carbon nanotubes, and hard carbon.

[0017] Preferably, in step (4), the solid content of the slurry is 20% - 40%, the sanding time is 1 - 5 h, and the sanding particle size is controlled such that D50 is 100 - 300 nm.

[0018] Preferably, in step (5), during spray drying, the inlet air temperature is 180 - 250 °C, the outlet air temperature is 100 - 120 °C, and the water content of the discharged material is 0.1% - 1%.

[0019] Preferably, in step (6), the sintering heating rate is 2 - 5 °C / min, the temperature is 600 - 750 °C, the sintering time is 7 - 15 h, and the inert atmosphere is nitrogen or argon.

[0020] Preferably, in step (7), the particle size control of airflow crushing is such that D50 is 2 - 5 μm.

[0021] The sodium titanate phosphate coated with carbon prepared by any of the above methods can also be used as a negative electrode material in aqueous sodium ion batteries and / or lithium ion batteries.

[0022] The beneficial effects of the present invention are as follows:

[0023] (1) Using the low-cost titanium source titanyl sulfate can reduce costs in terms of raw materials. At the same time, the easy availability of titanyl sulfate makes this method suitable for large-scale preparation;

[0024] (2) Avoid the use of ammonium-containing substances and liquid acids, and cause little pollution to the air and water bodies during the production process;

[0025] (3) All raw materials used are solids, which are not easy to volatilize or leak, reducing safety risks and losses during transportation. Description of the Drawings

[0026] Figure 1 It is the XRD pattern of the sodium titanate phosphate coated with carbon synthesized in Example 1 and Comparative Example 1;

[0027] Figure 2 It is the charge-discharge curve of the sodium titanate phosphate coated with carbon synthesized in Example 1 and Comparative Example 1. Detailed Embodiments

[0028] The following further illustrates the specific implementation of the present invention in conjunction with examples and drawings, but the specific implementation manners of the present invention are not limited thereto.

[0029] Example 1:

[0030] Prepare 1.4 L of a 200 g / L sodium dihydrogen phosphate solution and 4.6 L of an 80 g / L titanyl sulfate solution respectively. Add the prepared solutions to the co-precipitation reactor simultaneously. The reaction temperature is 25 °C, the aging temperature is 25 °C, the reaction time is 1 h, the continuous stirring time is 2 h, and the aging time is 6 h.

[0031] The aged slurry is subjected to solid-liquid separation by plate-and-frame filtration, and is washed repeatedly until the filtrate is neutral, thus obtaining a titanium phosphate filter cake.

[0032] The titanium phosphate filter cake, 280 g of sodium dihydrogen phosphate, and glucose are formulated into a slurry and subjected to sand milling. The solid content of the slurry is 20%, sand milling is carried out for 3 h, and the sand milling particle size is controlled such that D50 is 100 nm.

[0033] The sand-milled slurry is subjected to spray drying, wherein the inlet air temperature is 250 °C, the outlet air temperature is 120 °C, and the water content of the discharged material is 0.45%.

[0034] The spray-dried material is sintered in a nitrogen atmosphere. The sintering heating rate is 3 °C / min, the maximum temperature is 750 °C, and the holding time is 10 h.

[0035] The sintered material is subjected to air jet milling to obtain the final product, carbon-coated sodium titanium phosphate. The particle size of the air jet milling is controlled such that D50 is 1 μm.

[0036] Comparative Example 1:

[0037] A titanium oxysulfate and phosphoric acid aqueous solution is prepared. The homogeneous aqueous solution of titanium oxysulfate and the phosphoric acid aqueous solution are mixed and reacted, and then left to age, followed by vacuum filtration to obtain a filter cake.

[0038] After washing the filter cake, it is put into a hydrothermal reaction kettle together with water and sodium dihydrogen phosphate for reaction. After the reaction, it is cooled, filtered, and washed to obtain pure-phase sodium titanium phosphate.

[0039] The sodium titanium phosphate and the carbon source are added to a reaction kettle and stirred for reaction to obtain a slurry; after subjecting the obtained slurry to spray drying, it is sintered in an inert atmosphere, and after cooling, it is crushed to obtain a carbon-coated sodium titanium phosphate composite material.

[0040] Comparative Example 2:

[0041] 1.4 L of 500 g / L sodium dihydrogen phosphate and 5.5 L of 150 g / L titanium oxysulfate are respectively prepared. The prepared solutions are simultaneously added dropwise to a reaction vessel using a peristaltic pump. The reaction temperature is 25 °C, the aging temperature is 25 °C, the reaction time is 1 h, the continuous stirring time is 2 h, and the aging time is 6 h.

[0042] The aged slurry is washed repeatedly by centrifugation until the filtrate is neutral, and at the same time, solid powder particles, namely sodium titanium phosphate, are obtained.

[0043] The solid powder particles and glucose are formulated into a slurry and subjected to sand milling. The solid content of the slurry is 20%, sand milling is carried out for 3 h, and the sand milling particle size is controlled such that D50 is 100 nm.

[0044] The sanded slurry is spray-dried, with an inlet air temperature of 250 °C, an outlet air temperature of 120 °C, and a water content of the discharged material of 0.45%.

[0045] The spray-dried material is sintered under nitrogen. The sintering heating rate is 3 °C / min, the maximum temperature is 750 °C, and the holding time is 10 h.

[0046] The sintered material is subjected to air jet milling to obtain the final product sodium titanium phosphate coated with carbon. The particle size of the air jet milling is controlled such that D50 is 1 μm.

[0047] Figure 1 is the XRD pattern of sodium titanium phosphate coated with carbon. It can be found that the sodium titanium phosphate coated with carbon samples synthesized in Example 1 and Comparative Example 1 are both highly pure, free of impurities, and have good crystallinity.

[0048] Figure 2 is the charge-discharge curve of sodium titanium phosphate coated with carbon. It can be seen that the discharge capacities of the sodium titanium phosphate coated with carbon samples synthesized in Example 1 and Comparative Example 1 are 123.8 mAh / g and 115.9 mAh / g respectively, indicating that the samples synthesized in the ammonium-free and acid-free system even have better electrochemical performance.

[0049] The discharge capacity of the sodium titanium phosphate coated with carbon sample synthesized in Comparative Example 2 is 118.8 mAh / g, indicating that adding a large amount of sodium dihydrogen phosphate to the raw materials in the hope of directly preparing sodium titanium phosphate in one step not only does not save costs, but also the electrochemical performance of the synthesized sample is inferior to that of Example 1.

Claims

1. A green preparation method of a carbon-coated sodium titanium phosphate composite material, characterized in that: The following steps are involved: (1) sodium dihydrogen phosphate is prepared into a solution of 100 to 400 g / L, titanyl sulfate is prepared into a solution of 40 to 120 g / L, and only sodium dihydrogen phosphate is used as the phosphorus source; (2) according to the molar ratio of sodium dihydrogen phosphate and titanyl sulfate being 1:1, the solution prepared in step (1) is simultaneously added dropwise to the coprecipitation reactor, and the mixture is continuously stirred during the addition process. After the solution is added, stirring is continued for a period of time, and then aging is performed, wherein the reaction temperature is 25 to 40° C., the aging temperature is 25 to 40° C., the reaction time is 0.5 to 1 h, the continuous stirring time is 1 to 3 h, and the aging time is 3 to 6 h; (3) performing solid-liquid separation on the aged slurry to obtain a filter cake, and washing the filter cake multiple times until the filtrate is neutral, thereby obtaining a titanium phosphate precursor; (4) preparing a titanium phosphate precursor, sodium dihydrogen phosphate and a carbon source into a slurry, and then sand milling, wherein the molar ratio of the added sodium dihydrogen phosphate to the molar ratio of the titanium phosphate precursor is 1:1; (5) spray drying the sand-milled slurry; (6) sintering the spray-dried solid powder under the protection of an inert atmosphere; (7) The sintered material is subjected to air flow crushing to obtain the final product, carbon-coated sodium titanium phosphate.

2. The method according to claim 1, characterized in that: In step (3), the solid-liquid separation and washing method is one or more of suction filtration, centrifugation, and plate and frame filter press.

3. The method according to claim 1, characterized in that In step (4), the carbon source is an organic carbon source and / or an inorganic carbon source, the organic carbon source includes one or more of starch, glucose, sucrose, citric acid, ascorbic acid, polyethylene glycol, and polyvinyl alcohol, and the inorganic carbon source includes one or more of acetylene black, activated carbon, graphite, graphene, carbon nanotubes, and hard carbon.

4. The method according to claim 1, characterized in that: In step (4), the solid content of the slurry is 20% to 40%, the sand grinding time is 1 to 5 hours, and the sand grinding particle size is controlled to be D50 between 100 and 300 nm.

5. The method according to claim 1, characterized in that In step (5), during spray drying, the inlet air temperature is 180-250° C., the outlet air temperature is 100-120° C., and the water content of the output material is 0.1%-1%.

6. The method according to claim 1, characterized in that In step (6), the sintering heating rate is 2-5°C / min, the temperature is 600-750°C, the sintering time is 7-15h, and the inert atmosphere is nitrogen or argon.

7. The method according to claim 1, characterized in that: In step (7), the particle size of the air flow crushing is controlled to be D50 between 2 and 5 μm.

8. Use of the carbon-coated sodium titanium phosphate prepared by the method according to any one of claims 1 to 7 as a negative electrode material in aqueous sodium ion batteries and / or lithium ion batteries.

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