Harmless preparation method and application of carbon-coated sodium titanium phosphate

Abstract

The invention belongs to the technical field of energy storage batteries and electrochemistry, and particularly discloses a harmless preparation method and application of carbon-coated sodium titanium phosphate. According to the method, preparation can be achieved through simple wet coprecipitation, hydrothermal treatment is not needed, and harsh preparation conditions of high temperature and high pressure are avoided; meanwhile, ammonium-containing substances and acid do not need to be used, and transportation, storage, use, discharge and treatment of the ammonium-containing substances and the acid are avoided. The carbon-coated sodium titanium phosphate prepared by the method is used as a battery negative electrode, and has the characteristics of high purity, pure phase, high cycle retention rate and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of energy storage batteries and electrochemical technology, and specifically relates to a harmless preparation method and application of carbon-coated sodium titanium phosphate. Background Art

[0002] With the rapid development of renewable energy sources such as solar and wind power, energy storage technology has become crucial to balance the volatility of energy supply. Although traditional lithium-ion batteries have performed well in the field of energy storage, the limited resources of lithium and the environmental impact of the mining process have gradually become prominent. Against this background, sodium-ion batteries have developed rapidly; the use of organic electrolytes has also increased the risk of organic sodium-ion batteries in large-scale energy storage scenarios. The water-based electrolytes used in aqueous sodium-ion batteries are more environmentally friendly than organic solvent electrolytes, which helps reduce dependence on harmful chemicals, thereby meeting the requirements of sustainable development and becoming one of the options in the field of energy storage.

[0003] The three-dimensional structure of sodium titanium phosphate (NaTi 2 (PO 4 ) 3 ) has high sodium ion conductivity and chemical stability, and can be used as the negative electrode of aqueous sodium ion batteries. A phosphorus source must be present to synthesize sodium titanium phosphate, and in order not to introduce impurities, except for phosphorus and oxygen elements, the remaining elements must be easily removable elements. At present, almost all methods use one or more of diammonium phosphate, diammonium hydrogen phosphate, phosphoric acid, etc. Only these phosphorus sources do not introduce new impurity elements, and both ammonium ions and protons can be sintered and removed or reacted and neutralized. Phosphorus sources other than these will result in the introduction of new impurities, and these impurities are not easy to remove. At the same time, a titanium source is also required in the synthesis process. At present, most of the titanium sources used are titanium dioxide and titanium sulfate with higher purity. Titanium dioxide and titanium sulfate are both insoluble in water. During the reaction process, the reaction particle size needs to be controlled by grinding, and the kinetic process of solid-liquid reaction is worse than that of liquid-liquid reaction. At the same time, the preparation cost of titanium sulfate is high, and it is not suitable for use as a production raw material.

[0004] For example, although Chinese patent CN107814564B mentions that lithium dihydrogen phosphate can be used as a phosphorus source, the introduction of lithium will inevitably result in impure substances; and claim 8 in the patent also mentions the ammonia discharge process, indicating that the use of ammonium-containing substances is inevitable. Although Chinese patent CN113697788B avoids the use of ammonium-containing substances, and the patent also mentions that "phosphoric acid is very acidic and is a very viscous liquid", it still inevitably uses phosphoric acid. Chinese patents CN115611257B, CN107732167B, CN115626623B, etc. also use acids or ammonium-containing substances. The use of acid poses challenges to transportation and storage, requires the corrosion resistance of equipment, and poses a threat to the safety of operators; the use of ammonium-containing compounds needs to consider the emission and treatment of ammonia, and the ammonia capture device will increase costs and require technical and equipment support. If the treatment is not complete, it may also cause air pollution, acid rain, land acidification and other environmental pollution problems. Summary of the invention

[0005] The purpose of the present invention is to address the problem that the existing preparation method of sodium titanium phosphate must use acid and / or ammonium-containing substances, and to propose a harmless preparation method and application of carbon-coated sodium titanium phosphate. The present invention can completely avoid the use of acid and / or ammonium-containing substances to prepare carbon-coated sodium titanium phosphate, and has the advantages of low cost and environmental friendliness.

[0006] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions:

[0007] A harmless preparation method of carbon-coated sodium titanium phosphate comprises the following steps:

[0008] (1) preparing a sodium dihydrogen phosphate solution and a titanyl sulfate solution, wherein only sodium dihydrogen phosphate is used as the phosphorus source, and no ammonium or acid-containing phosphorus source is used;

[0009] (2) adding the prepared solution dropwise into the reaction vessel using a peristaltic pump for reaction and aging;

[0010] (3) separating the aged slurry into solid and liquid to obtain powder, and washing the slurry several times until the filtrate is neutral. The solid powder obtained is sodium titanium phosphate;

[0011] (4) preparing sodium titanium phosphate and a carbon source into a slurry and sand-grinding;

[0012] (5) spray drying the sand-milled slurry;

[0013] (6) sintering the spray-dried material under the protection of an inert atmosphere;

[0014] (7) The sintered material is subjected to air flow crushing to obtain the final product, carbon-coated sodium titanium phosphate.

[0015] Preferably, in step (1), sodium dihydrogen phosphate is configured to 20-800 g / L, and titanyl sulfate is configured to 20-200 g / L. The reaction is carried out according to a molar ratio of phosphorus to titanium of 3:2, wherein the sodium dihydrogen phosphate is in excess of 0%-500%.

[0016] Preferably, in step (2), the reaction temperature is 20-95°C, the aging temperature is 20-95°C, and the aging time is 0.5-24h.

[0017] Preferably, in step (3), the solid-liquid separation is one or more of suction filtration, centrifugation, and plate and frame filter press.

[0018] 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, and the inorganic carbon source includes one or more of acetylene black, activated carbon, graphite, graphene, carbon nanotubes, and hard carbon.

[0019] Preferably, in step (4), the solid content of the slurry is 15%-55%, the sand grinding time is 0.5-12h, and the sand grinding particle size is controlled to D50 at 70-500nm.

[0020] Preferably, in step (5), during spray drying, the air inlet temperature is 160-300°C, the air outlet temperature is 90-140°C, and the water content of the output material is 0.01%-2%.

[0021] Preferably, in step (6), the sintering heating rate is 1-20°C / min, the maximum temperature is 300-800°C, and the sintering time is 5-20h.

[0022] Preferably, in step (7), the particle size of the air flow crushing is controlled to be D50 between 0.5 and 10 microns.

[0023] The carbon-coated sodium titanium phosphate 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.

[0024] The beneficial effects of the present invention are:

[0025] (1) This method synthesizes sodium titanium phosphate by a wet process, saving energy consumption. The synthesized carbon-coated sodium titanium phosphate has the advantages of high specific capacity, cycle stability, and good rate performance.

[0026] (2) This method reduces the use of ammonium-containing substances and acids, reduces the risk of air and water pollution, and is environmentally friendly.

[0027] (3) This method avoids the problems encountered in the transportation, storage, use, discharge and treatment of raw materials such as ammonium substances and acids, simplifies the production process of carbon-coated sodium titanium phosphate, and reduces costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The XRD diagram of carbon-coated sodium titanium phosphate synthesized in the examples and comparative examples;

[0029] Figure 2 The charge and discharge curves of the carbon-coated sodium titanium phosphate synthesized in the example and the comparative example. DETAILED DESCRIPTION

[0030] The technical scheme of the present invention is further described below by specific implementation methods. The embodiments described herein are only to help understand the present invention and should not be regarded as specific limitations of the present invention. The described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Unless otherwise defined, the professional terms used below are consistent with the meanings understood by professionals and technicians in the field; unless otherwise specified, the raw materials and reagents involved in this article can be purchased from the market or prepared by publicly known methods.

[0031] Example: Synthesis of carbon-coated sodium titanium phosphate using sodium dihydrogen phosphate and titanyl sulfate as raw materials

[0032] Prepare 1.4 L of 500 g / L sodium dihydrogen phosphate and 5.5 L of 150 g / L titanium oxysulfate respectively, and add the prepared solutions dropwise into the reaction container using a peristaltic pump. The reaction temperature is 65° C., the aging temperature is 65° C., and the aging time is 12 h.

[0033] The aged slurry is washed multiple times by centrifugation until the filtrate is neutral, and solid powder particles, namely sodium titanium phosphate, are obtained.

[0034] The solid powder particles and sucrose are mixed together to form a slurry for sand grinding. The slurry has a solid content of 30%, and the slurry is sand ground for 2 hours. The sand grinding particle size is controlled to be D50 at 200 nm.

[0035] The sand-milled slurry was spray-dried, wherein the air inlet temperature was 200° C., the air outlet temperature was 110° C., and the water content of the outlet was 0.35%.

[0036] The spray-dried material was sintered under nitrogen with a sintering heating rate of 2°C / min, a maximum temperature of 800°C, and a heat preservation period of 10 hours.

[0037] The sintered material is subjected to air flow crushing to obtain the final product, carbon-coated sodium titanium phosphate, and the particle size of the air flow crushing is controlled to be D50 at 0.87 microns.

[0038] Comparative Example: Synthesis of carbon-coated sodium titanium phosphate using diammonium phosphate and titanium dioxide as raw materials

[0039] Sodium dihydrogen phosphate, ammonium dihydrogen phosphate and titanium dioxide are mixed according to a molar ratio and mixed with sucrose to form a slurry for sand grinding. The slurry has a solid content of 30%, and is sand ground for 2 hours. The sand grinding particle size D50 is controlled to be about 200 nm.

[0040] The sand-milled slurry was spray-dried, wherein the air inlet temperature was 200° C., the air outlet temperature was 110° C., and the water content of the outlet was 0.35%.

[0041] The spray-dried material was sintered under nitrogen with a sintering heating rate of 2°C / min, a maximum temperature of 800°C, and a heat preservation period of 10 hours.

[0042] The sintered material is subjected to air flow crushing to obtain the final product, carbon-coated sodium titanium phosphate, and the particle size of the air flow crushing is controlled to be D50 at 0.87 microns.

[0043] Figure 1 : This is the XRD diagram of carbon-coated sodium titanium phosphate. It can be found that the carbon-coated sodium titanium phosphate samples synthesized in the embodiment and the comparative example are high in purity, free of impurities, and have good crystallinity.

[0044] Figure 2 : is the charge and discharge curve diagram of carbon-coated sodium titanium phosphate. It can be seen that the discharge capacities of the carbon-coated sodium titanium phosphate samples synthesized in the embodiment and the comparative example are 120 mAh / g and 113 mAh / g, respectively, indicating that the samples synthesized in the ammonium-free and acid-free system have the same or better electrochemical performance.

Claims

1. A harmless preparation method of carbon-coated sodium titanium phosphate, characterized in that: The following steps are involved: (1) preparing a sodium dihydrogen phosphate solution and a titanyl sulfate solution, wherein only sodium dihydrogen phosphate is used as the phosphorus source, and no ammonium or acid-containing phosphorus source is used; (2) adding the prepared solution dropwise into the reaction vessel using a peristaltic pump for reaction and aging; (3) separating the aged slurry into solid and liquid to obtain powder, and washing the slurry several times until the filtrate is neutral. The solid powder obtained is sodium titanium phosphate; (4) preparing sodium titanium phosphate and a carbon source into a slurry and sand-grinding; (5) spray drying the sand-milled slurry; (6) sintering the spray-dried material 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 (1), sodium dihydrogen phosphate is configured to 20-800 g / L, and titanyl sulfate is configured to 20-200 g / L. The reaction is carried out according to a molar ratio of phosphorus to titanium of 3:2, wherein the sodium dihydrogen phosphate is in excess of 0%-500%.

3. The method according to claim 1, characterized in that In step (2), the reaction temperature is 20-95°C, the aging temperature is 20-95°C, and the aging time is 0.5-24h.

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

5. 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.

6. The method according to claim 1, characterized in that In step (4), the solid content of the slurry is 15%-55%, the sand grinding time is 0.5-12h, and the sand grinding particle size is controlled to be D50 at 70-500nm.

7. The method according to claim 1, characterized in that In step (5), during spray drying, the air inlet temperature is 160-300°C, the air outlet temperature is 90-140°C, and the water content of the output material is 0.01%-2%.

8. The method according to claim 1, characterized in that: In step (6), the sintering heating rate is 1-20°C / min, the maximum temperature is 300-800°C, and the sintering time is 5-20h.

9. 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 in the range of 0.5-10 microns.

10. Use of the carbon-coated sodium titanium phosphate prepared by the method according to any one of claims 1 to 9 as a negative electrode material in aqueous sodium ion batteries and / or lithium ion batteries.

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