JP2021520601A - Microwave-assisted sol-gel process for preparing in-situ carbon-coated electrode materials and their products - Google Patents

Abstract

In the present invention, the general formulas [A3M2 (PO4) 3] and [A3M2 (PO4) 2F3] (“A” is an alkali ion selected from Li, Na and K, “M” is Fe, Ni, Co, V, Mn, A microwave-assisted sol-gel process for preparing in-situ carbon-coated electrode materials selected from alkaline ion transition metal phosphates and alkaline ion transition metal fluorophosphates with transition metals selected from Ti and Cr). Regarding. The steps involved in this synthesis begin with the preparation of a homogeneous aqueous solution containing sodium, vanadium and phosphorus precursors using deionized water as the solvent. Fluorine precursors are used in the case of fluorophosphate preparation. After exposing a homogeneous aqueous solution to microwaves in an open container for gelation under ambient pressure at a temperature of 80-170 ° C. under atmospheric pressure, the gel is dried in air at 100-120 ° C. and the formed gel is crushed. A two-step heat treatment is performed to obtain phase pure phosphoric acid / sodium fluorophosphate vanadium. [Selection diagram] None

Description

The present invention relates to methods and products thereof for preparing electrode materials for alkaline ion transition metal phosphates, in particular vanadium phosphate and sodium phosphate carbon coated in-situ (in the field) by a microwave assisted sol-gel process. It relates to sodium vanadium fluorophosphate and methods for preparing derivatives thereof. Due to their high specific capacity and high specific capacitance dual properties, they can be used as electrode materials for "supercabattery". They can also be used as electrode materials for sodium ion batteries and sodium ion capacitors.

In terms of specific energy and output density, batteries are the most preferred choice as an energy storage device. Lithium-ion batteries (LIBs) have the highest specific energy of all other commercially available battery systems. LIB was successfully commercialized by Sony in 1990 for a variety of applications such as portable electronics and electric / hybrid electric vehicles [MS Whittingham, "Lithium Batteries and Cathode Materials", Chem. Rev. (2004) 104, 4271-4302].

However, lithium resources are rapidly depleting and are expected to remain for about a few more years. Moreover, the cost of lithium makes LIB unsuitable for large grid storage applications. Due to the low cost of sodium, the same level of specific energy and abundance (one of the major elements in seawater), sodium ion batteries (SIBs) have become suitable alternatives to LIBs. In addition, LIB-like principles of action, such as the reversible shuttling of sodium ions between electrode materials via electrolytes, add to their qualities [JY Hwang, ST Myung, YK Sun, “Sodium-ion batteries: present and future”. , Chem. Soc. Rev. (2017) 46, 3529-3614; C. Delmas, “Sodium and Sodium-Ion Batteries: 50 Years of research”, Adv. Energy Mater. (2018) 1703137].

Sodium-containing electrode materials are more stable than their lithium-compatible products, and therefore sodium-containing electrode materials are suitable for a variety of applications. Intercalation chemistry, which is the same for both lithium and sodium, allows similar types of compounds to be used in SIBs. The difference between these two systems would be that sodium ions are larger than lithium ions and affect phase stability, transport properties and solid electrolyte phase-to-phase (SEI) formation [B. Dunn, H. Kamath, JM Tarascon, “Electrical Energy Storage for the Grid: A battery of choices”, Science (2011) 334, 928-935].

Various cathode materials such as layered sodium transition metal oxide Na _x MO ₂ (M = Co, Mn, Fe and Ni, etc.) (0.44 <x ≦ 1), Olivin Nampo ₄ (M = Fe, Mn, Ni and Co), spinel Namn ₂ O ₄ and NASICON type (Na superion conductor) Na ₃ V ₂ (PO ₄ ) ₃ have been studied and are currently used as electrode materials for SIB. Oxide materials tend to release oxygen evolution during charging in a highly charged state (System), resulting in a serious capacity loss. In addition, the inadequate thermal stability of oxide materials hinders their use at high temperatures [N. Yabuuchi, K. Kubota, M. Dahbi, S. Komaba, “Research Development on Sodium-Ion Batteries”, Chem. . Rev. (2014) 114, 11636-11682].

Phosphate-based materials are known to be structurally and thermally stable and can be used as potential electrode materials for SIBs. In particular, NASICON-type structures having an open 3D ion transport channel and promoting fast ion transport have been extensively studied as electrode materials. The NASICON-type structure of Na ₃ V ₂ (PO ₄ ) ₃ is an example of a promising cathode material showing a flat voltage plateau of about 3.4 V vs. Na / Na + and a high reversible capacitance of 118 mAh / g. However, the associated inadequate electron conductivity results in reduced capacitance.

Furthermore, if the phosphate skeleton in sodium vanadium phosphate is doped with fluorine _{to give a chemical composition of Na 3} V ₂ (PO ₄ ) _3-x F _3x (0 <x ≦ 1). Increases in voltage and specific volume are observed. The resulting compound exhibits a high voltage of about 3.7 V vs. Na / Na + and a specific volume of about 128 mAh / g when x = 1.

First, researchers focused on various methods or combinations of methods, such as conductive coatings on particle surfaces and elemental doping to increase the conductivity of materials. The various synthetic routes developed to prepare these materials were solid phase reactions, sol-gel, electrospinning, hydrothermal and solvent thermal synthesis. However, these synthetic routes have a secondary phase (solid phase route), are costly in low yields (hydrothermal, electrospinning and lyophilization), or are heterogeneous gelling over long reaction times (conventional). It was accompanied by the formation of a material that produced the sol-gel).

Related Prior Art:
There are numerous prior patents / applications for methods of preparing electrode materials for alkaline ion transition metal phosphates, especially sodium vanadium phosphate and sodium fluorophosphate vanadium, and their products. Some of them related to the present invention are described below, explaining how the present invention differs from their prior art disclosures, and how much the invention is superior to the prior art disclosures. Will be explained. Microwave radiation has been widely used as a heat source during material synthesis. There are various reports in the literature regarding the use of microwave radiation during solid-phase and solution-based synthesis. In 2004, Barker et al. Reported the synthesis of transition metal-based compounds as cathode active materials using electromagnetic waves, such as microwave, infrared and radio-assisted solid-phase routes (US Patent Application Publication No. 200406632). No. specification (A1)). Similarly, a microwave-assisted solid-phase synthetic route has been adopted to prepare a composite of phosphodiesterase sodium vanadium oxide / alkenyl and graphite, as reported elsewhere (Chinese Patent No. 104078766 (B)). , China Patent Application Publication No. 104078766 (A)), adopted to prepare compounds containing different metals for lithium, sodium and potassium ion batteries (Korean Patent Application Publication No. 20150080652 (A)). .. Microwave-assisted solid-phase synthesis was adopted to prepare large amounts of these electrode active materials, but the phase purity was higher than that of solution-based synthetic routes such as hydrothermal synthesis, solvent thermal synthesis and sol-gel synthesis. It can result in electrode materials that are low, heterogeneous in composition and non-chemically quantitative. Poor, inhomogeneous, non-stoichiometric compositions can result in inadequate electrochemical performance when used as electrode materials for various battery chemistries. In addition, different solution-based synthetic routes have been adopted to prepare different electrode materials to address these issues. In 2017, Ikejeri et al. Proposed the synthesis of composites as electrodes for sodium ion batteries by various chemical routes, such as sol-gel, mechanochemical and chemical vapor deposition (US Patent Application Publication No. 2017000005337). No. (A1)). These methods involve heterogeneity (for sol-gel routes and mechanochemical routes), defects in the material (for mechanochemical routes), and low yields (for chemical vapor deposition). In another report, the conventional sol-gel method was used to prepare sodium phosphate vanadium cathode materials for sodium ion battery and sodium hybrid capacitor applications (Chinese Patent Application Publication No. 106328911 (A). , Korean Patent No. 1017843435 (B1)). Disadvantages of conventional sol-gel methods include long gelation times (24-36 hours) and non-uniform gelation due to non-uniform mixing of precursors. Microwave-assisted high-pressure hydrothermal reaction was adopted as another effective route for synthesizing electrode materials such as sodium / lithium transition metal phosphates (US Pat. No. 9,809,456 (B2), Japanese Patent). 5623821 (B2), US Pat. No. 20090117020 (A1)). However, the synthesis of large-scale electrode materials poses safety problems and high costs.

In the present invention, microwave-assisted sol-gel synthesis of alkaline ion transition metal phosphates and their derivatives is disclosed.

Solution-based microwave-assisted sol-gel synthesis has various advantages over other synthetic routes, such as a)-d) below.
a) Volumetric heating: In general, the solvent and solute components of a solution absorb microwaves rather than transmit or reflect them, as in the case of gases or solids, respectively. This results in uniform and rapid heating of the solution components, resulting in a faster reaction rate.
b) Uniform gelation: Especially in solution mode, microwaves create rapid charging fields, such as dipoles, in a solvent that are continuously aligned in the direction of the field to generate heat. .. This heat is evenly distributed to obtain local overheating, reducing defects / impurities by increasing the purity of the material. This local overheating results in chemical uniformity, resulting in uniform gelation, which further affects the properties of the final product compared to that of conventional sol-gel products. .. Moreover, unlike conventional sol-gel roots, in-situ carbon coating with uniform thickness can be achieved.
c) Ambient pressure synthesis: The use of microwave-assisted sol-gel synthesis based on an open vessel allows for the easy escape of evaporated chemicals and what is a microwave-irradiated high-pressure hydrothermal reaction? Unlike, it reduces the risk of high pressure.
d) Very economical: For large-scale synthesis of electrode materials, processing time is much more important than other parameters, as processing time can affect the productivity of the industry. Therefore, the process results in the formation of uniform gelation in minutes rather than hours as in conventional sol-gels, making microwave-assisted sol-gels a very effective process for synthesizing electrode active materials. To.

These advantages associated with the microwave-assisted sol-gel route result in the synthesis of effective electrode materials with superior storage performance compared to electrode materials synthesized by other synthetic routes.

U.S. Patent Application Publication No. 2004/0016632 (A1) Chinese Patent Application Publication No. 1055523228 (A) Chinese Patent No. 104078766 (B) Chinese Patent Application Publication No. 107425190 (A) Chinese Patent Application Publication No. 107492635 (A) Korean Patent No. 1017843435 (B1) Chinese Patent Application Publication No. 105140468 (A) U.S. Patent Application Publication No. 2017005337 (A1) Chinese Patent Application Publication No. 105098179 (A) Chinese Patent Application Publication No. 106558202 (A) Chinese Patent Application Publication No. 106410193 (A) Chinese Patent Application Publication No. 106328911 (A) Chinese Patent Application Publication No. 1078781865 (A)

M.S. Whittingham, “Lithium Batteries and Cathode Materials”, Chem. Rev. (2004) 104, 4271-4302. J.Y. Hwang, S.T. Myung, Y.K. Sun, “Sodium-ion batteries: present and future”, Chem. Soc. Rev. (2017) 46, 3529-3614. C. Delmas, “Sodium and Sodium-Ion Batteries: 50 Years of research”, Adv. Energy Mater. (2018) 8, 1703137. B. Dunn, H. Kamath, J. M. Tarascon, “Electrical Energy Storage for the Grid: A battery of choices”, Science (2011) 334, 928-935. N. Yabuuchi, K. Kubota, M. Dahbi, S. Komaba, “Research Development on Sodium-Ion Batteries”, Chem. Rev. (2014) 114, 11636-11682. Y.J. Zhu, F. Chen, “Microwave Assissted Preparation of Inorganic Nanostructures in Liquid Phase”, Chem. Rev. (2014) 114, 6462-6555.

An object of the present invention is to provide a rapid synthetic route for the preparation of in-situ carbon-coated alkaline ion transition metal phosphates and their derivatives as potential electrode materials.

A main object of the present invention is therefore to prepare in-situ carbon-coated sodium vanadium phosphate / vanadium fluorophosphate with high storage performance by microwave-assisted sol-gel root.

Another object of the present invention is to provide a uniform carbon-coated sodium vanadium phosphate / vanadium fluorophosphate having a controlled particle size.

Yet another object of the present invention is to provide large-scale synthesis of uniform carbon-coated sodium vanadium phosphate / vanadium fluorophosphate with a controlled particle size.

Yet another object of the present invention is to provide the use of the prepared electrode active material in sodium ion batteries, sodium ion capacitors and sodium ion superca batteries.

Therefore, the present invention relates to a method for preparing an in-situ carbon-coated electrode material by a microwave-assisted sol-gel process and a product thereof. This electrode material is selected from the general formulas [A ₃ M ₂ (PO ₄ ) ₃ ] and [A ₃ M ₂ (PO ₄ ) ₂ F ₃ ] (in the formula, "A" is selected from Li, Na and K. It is an alkali ion, and "M" is a transition metal selected from Fe, Ni, Co, V, Mn, Ti and Cr).) Alkaline ion transition metal phosphate and alkali ion transition metal fluoro. Selected from phosphates. This synthesis process consists of the following steps:
a) A step of mixing by adding an alkali ion precursor, a transition metal precursor, a phosphorus precursor and a gelling / chelating agent in a ratio of 3: 2: 3: 2;
b) At the same time, the amount of transition metal precursors was considered in deionized water or in a non-aqueous solvent selected from ethylene glycol, polyethylene glycol, tetraethylene glycol and a solvent having a low to moderate boiling point in the vessel. Step of incorporating alkali ion precursor, phosphorus precursor and chelating agent based on the corresponding molar ratio;
c) The step of stirring the mixture in a container for a period of time to obtain a homogeneous mixture;
d) A step of irradiating microwaves in an open container with constant stirring at a constant temperature in the temperature range of 80 to 170 ° C. under atmospheric pressure to bring about homogeneous gelation;
e) A step of drying the obtained gel in the air in a temperature range of 100 to 120 ° C .;
f) Step of crushing the dried gel; and g) The dried gel is calcined in an inert atmosphere in a temperature range of 600 to 800 ° C. for 8 to 10 hours, and an intermediate firing temperature of 300 to 500 ° C. is calcined for 3 to 5 hours. The process of forming an in-situ carbon coating layer on the electrode material as well as forming a mesoporous carbon network;
including.

Here, the alkaline ion transition metal phosphate is sodium vanadium phosphate [Na ₃ V ₂ (PO ₄ ) ₃ ], and the component added in the mixing of step a) is sodium dihydrogen phosphate (NaH ₂ PO _4). ), Sodium acetate dihydrate (CH ₃ COONa ・ 2H ₂ O), Sodium hydroxide monohydrate (NaOH ・ H ₂ O), Sodium hydroxide (NaOH), Sodium carbonate (Na ₂ CO ₃ ), Phosphoric acid sodium acid _(Na 3 _PO 4), is selected from the group consisting of sodium phosphate twelve dihydrate _{(Na 3 PO 4 · 12H 2} O), sodium oxalate _{(Na 2} C _{2 O 4)} and mixtures thereof Sodium precursors; vanadium oxide (V) (V ₂ O ₅ ), ammonium metavanadate (NH ₄ VO ₃ ), vanadium oxide (III) (V ₂ O ₃ ), vanadyl acetylacetonate [VO (C ₅ H ₇ O) ₂ ) ₂ ], a vanadium precursor selected from the group consisting of trihydroxy (oxo) vanadium (H ₃ VO ₄ ) and mixtures thereof; ammonium phosphate [(NH ₄ ) ₃ PO ₄ ], diammonium phosphate [ (NH ₄ ) ₂ HPO ₄ ], ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ ), phosphoric acid (H ₃ PO ₄ ), sodium dihydrogen phosphate (NaH ₂ PO ₄ ) and a mixture thereof. Phosphoric acid precursors selected from; as well as gelling / chelating precursors used as a source of in-situ carbon coatings, the mesoporous carbon network consists of the group consisting of citric acid, ascorbic acid, oxalic acid and gluconic acid. Be selected.

One aspect of the present invention also includes drying the gel formed during microwave synthesis at a constant temperature in an ambient atmosphere and further subjecting it to a two-step heat treatment under an inert atmosphere.

Another aspect of the invention is a dramatic reduction in reaction time for gel formation.

Another aspect of the present invention comprises the formation of an in-situ carbon coating on the sodium vanadium phosphate and sodium fluorophosphate vanadium electrode materials obtained by the microwave assisted sol-gel method.

Another aspect of the invention is the synthesis of uniform and controlled particle sizes by microwave assisted sol-gel routes.

Another aspect of the invention focuses on the scalability of this process. This route facilitates large-scale synthesis of the desired electrode material.

Another aspect of the present invention is the application of the synthesized electrode material to sodium ion batteries, sodium ion symmetric cells and hybrid supercapacitors due to the long-term cycling stability and high specific energy of the synthesized electrode material.

Another aspect of the present invention is the application of the synthesized electrode material to a "supercapacitor" due to the high output density of the synthesized electrode material at higher specific energies compared to conventional supercapacitors. be.

Compared to conventional sol-gel synthetic routes, microwave sol-gels are an effective method for preparing homogeneous gels within a very short reaction time. Therefore, the long time for gelation is unacceptable to keep costs down. Furthermore, sodium vanadium phosphate and sodium fluorophosphate vanadium having a uniform and controlled particle size distribution can be easily obtained.

This carbon-coated electrode material has a wide range of industrial applications. This carbon-coated electrode material is used in the production of sodium ion cells / batteries, superca batteries and sodium ion capacitors.

FIG. 1a is an X-ray diffraction (XRD) pattern of carbon-coated sodium vanadium phosphate. FIG. 1b is an X-ray diffraction (XRD) pattern of carbon-coated sodium vanadium fluorophosphate (Examples 1 and 2) prepared according to an embodiment of the present invention. FIG. 2a is a photographic image of a carbon-coated sodium vanadium phosphate scanning electron microscope (SEM). FIG. 2b is a scanning electron microscope (SEM) photographic image of carbon-coated sodium fluorophosphate vanadium prepared according to an embodiment of the present invention. FIG. 3 is a photographic image of a transmission electron microscope (TEM) of carbon-coated sodium vanadium phosphate (Example 1) prepared according to an embodiment of the present invention. FIG. 4 shows a cyclic voltammogram (CV) of carbon-coated sodium vanadium phosphate at a constant scanning speed (100 μV / s) in a 2.3-3.9 V vs. Na / Na + voltage window. FIG. 5 is a comparison of constant current charge / discharge cycling plots at 0.1 C rate (1C = 118 mA / g) for Na / Na + at various potential windows for carbon-coated sodium vanadium phosphate. FIG. 6 is a comparison of specific volume vs. cycle count plots at 0.1 C rate at various voltage windows for carbon-coated sodium vanadium phosphate. FIG. 7 shows a constant current charge / discharge cycling plot at 0.1 to 1.0 A / g over a 0 to 3 V voltage window for a carbon-coated sodium vanadium phosphate symmetric cell. FIG. 8 shows a specific volume vs. cycle count plot at 0.1 A / g up to 100 cycles and 1 A / g up to 1400 cycles over a 0-3 V voltage window for a carbon-coated sodium vanadium phosphate symmetric cell. show. FIG. 9a shows constant current charge / discharge cycling plots for carbon-coated sodium vanadium phosphate supercapacitors at various current densities in a 0-3 V potential window. FIG. 9b shows the specific volume vs. current density of a carbon-coated sodium vanadium phosphate supercapacitor. FIG. 10 shows a cyclic voltammogram (CV) of carbon-coated sodium vanadium fluorophosphate at a constant scanning speed (100 μV / s) in a 2.5-4.5 V vs. Na / Na + voltage window. FIG. 11 shows a constant current charge / discharge cycling plot for carbon-coated sodium fluorophosphate vanadium at a 1C rate (1C = 128mA / g) in a 2.5-4.5V vs Na / Na + potential window. FIG. 12 shows a specific volume vs. cycle number plot at a 1 C rate in a 2.5-4.5 V potential window for carbon-coated sodium fluorophosphate vanadium.

The present invention presents in-situ carbon-coated alkaline ion transition metal phosphate electrode active materials and derivatives thereof, such as the general formulas [A ₃ M ₂ (PO ₄ ) ₃ ] and [A ₃ M ₂ (PO _{4), respectively. 2} F ₃ ] (In the formula, "A" is an alkaline ion selected from Li, Na and K, and "M" is a transition selected from Fe, Ni, Co, V, Mn, Ti and Cr. The focus will be on a novel microwave-assisted sol-gel process for the preparation of alkali ion transition metal phosphates and alkali ion transition metal fluorophosphates represented by (Metal). This method involves solid phase reactions, hydrothermal, conventional sol-gels, other synthetic routes such as electrospinning and lyophilization, safety issues, long reaction times, formation and cost of phase pure materials. Address the issue of degradation.

In one embodiment that achieves the above-mentioned aspect of preparing a gel, the synthetic route is to add (a) an alkali ion precursor, a transition metal precursor, a phosphorus precursor, and a gelling / chelating agent to an aqueous / non-aqueous solvent. Further a stirring step is carried out to obtain a homogeneous solution of the precursors to which (b) alkaline ion precursors, transition metal precursors, phosphorus precursors and gelling agents have been added. You may. (C) To prepare the gel under ambient pressure, the mixture solution can be placed in an open container and exposed to microwave irradiation. (D) The container used can be an open container. Unlike hydrothermal synthesis, supercritical hydrothermal synthesis or solvent thermal synthesis, where a pressure vessel is essential for successful reaction, no special pressure conditions are required.

In another embodiment, the reaction solvent, for example or those of an aqueous, such as deionized H _{2 O,} or, for example, ethylene glycol, polyethylene glycol, a non-like solvents having a tetraethylene glycol and low to medium boiling point It can be water-based.

In one embodiment of the present invention, gelation can be performed in a temperature range of 80 to 170 ° C. under atmospheric pressure.

In another embodiment of the invention, the resulting gel can be dried in the air in a temperature range of 100 ° C to 120 ° C. The dried gel is then ground and subjected to a two-step heat treatment.

In another embodiment, the heat treatment is not particularly limited, and the gel is calcined in a temperature range of 600 to 800 ° C. for 8 to 10 hours in an inert atmosphere with an intermediate firing temperature of 300 to 500 ° C. for 3 to 5 hours. May be done by. The inert atmosphere can be, but is not limited to, _{argon and N 2.} During the heat treatment, an in-situ carbon coating layer can be formed on the alkali ion transition metal phosphate, along with the formation of mesoporous carbon networks.

In one embodiment of the invention, the alkali ion transition metal phosphate [A ₃ M ₂ (PO ₄ ) ₃ ] (in the formula, the alkali ion "A" can be Li, Na and K, and the transition metal "A""M" can be Fe, Ni, Co, V, Mn, Ti, Cr, or the like.)

In one embodiment that achieves one aspect of the invention, a microwave assisted sol-gel process was used _{to synthesize sodium vanadium phosphate [Na 3} V ₂ (PO ₄ ) ₃ ] cathode active material.

The sodium precursors added in this way are sodium dihydrogen phosphate (NaH ₂ PO ₄ ), sodium acetate dihydrate (CH ₃ COONa ・ 2H ₂ O), and sodium hydroxide monohydrate (NaOH ・ H _2). O), sodium hydroxide (NaOH), sodium carbonate _(Na 2 _CO 3), sodium phosphate _(Na 3 _PO 4), sodium phosphate, dodecahydrate _{(Na 3 PO 4 · 12H 2} O), oxalic acid It can be at least one selected from the group consisting of sodium (Na ₂ C ₂ O _{4) and mixtures thereof.}

The vanadium precursors added are vanadium oxide (V) (V ₂ O ₅ ), ammonium metavanadate (NH ₄ VO ₃ ), vanadium oxide (III) (V ₂ O ₃ ), vanadyl acetylacetonate [VO (C _5). It can be at least one selected from the group consisting of H ₇ O ₂ ) ₂ ], trihydroxy (oxo) vanadium (H ₃ VO _{4) and mixtures thereof.}

The phosphorus precursors to be added are ammonium phosphate [(NH ₄ ) ₃ PO ₄ ], diammonium phosphate [(NH ₄ ) ₂ HPO ₄ ], ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ ), and phosphoric acid. It can be at least one selected from the group consisting of (H ₃ PO ₄ ), sodium dihydrogen phosphate (NaH ₂ PO _{4) and mixtures thereof.}

Gelation / chelation precursors are used as a source of in-situ carbon coatings and mesoporous carbon networks. The gelling / chelating precursor can be at least one selected from the group consisting of citric acid, ascorbic acid, oxalic acid, gluconic acid and the like.

In addition to gelling / chelating agents, there are several organic precursors that can be used for in-situ carbon coating. These organic precursors are not particularly limited and must be at least one selected from the group consisting of glucose, sucrose, galactose, fructose, lactose, starch, mannose, ribose, aldohexose, ketohexose and combinations thereof. Can be done.

The mixing ratio of the sodium precursor, vanadium precursor, phosphorus precursor and chelating agent during solution preparation is maintained at 3: 2: 3: 2. Sodium precursors, phosphorus precursors and chelating agents can be added in corresponding molar ratios taking into account the amount of vanadium precursors.

In one embodiment of the present invention, gelation in the case of sodium vanadium phosphate can be carried out at a temperature of 80 ° C. The obtained gel can be dried at 120 ° C. in the ambient atmosphere.

In another embodiment for obtaining sodium vanadium phosphate of the present invention, the intermediate firing at 400 ° C. is for 4 hours, and the final firing can be performed at a temperature of 800 ° C. for 10 hours in an argon atmosphere.

In another embodiment of the invention, sodium fluorophosphate vanadium [Na ₃ V ₂ (PO ₄ ) ₂ F ₃ ] as the cathode active material can be synthesized using a microwave assisted sol-gel process. The fluorine precursor added can be at least one selected from the group consisting of _{NaF, NH 4} F and NH ₄ HF _{2, and mixtures thereof.}

In one embodiment, the above process step is of the general formula A ₃ M _2-x C _x (PO ₄ ) ₃ (0 <x <2, where C is Mg, Al, Ti, Ca, Sc, etc. It can be extended to the preparation of cation-doped alkaline ion transition metal phosphates represented by (which can be any one).

In another embodiment, the above process steps are carried out in the general formula A ₃ M ₂ (PO ₄ ) _3-y N _3y (0 <y ≦ 1) and A ₃ M _2-x C _x (PO ₄ ) _3-y. It can be extended to the preparation of anion-doped alkali ion transition metal phosphates represented by N _{3y (0 <x <2, 0 <y ≦ 1).} Here, N can be any one of Cl, Br, I, and the like.

In another embodiment of the present invention, the microwave-assisted sol-gel synthesis process uses the general formula Na ₄ M ₃ (PO ₄ ) ₂ P ₂ O ₇ (M = Fe, Mn, Co and Ni, etc.) as the electrode active material. ), And the _{layered sodium transition represented by the general formula Na x} MO ₂ (0.44 <x ≦ 1, M = Fe, Mn, Co, Ni, Ti, etc.). It can be extended to the preparation of metal oxides.

The phosphoric acid / sodium fluorophosphate vanadium particles prepared by the above series of steps are of the NASICON (Na superion conductor) type, as confirmed by the X-ray diffraction patterns (FIGS. 1A and 1B). May have a rhombohedral / tetragonal crystal structure.

The particle size and its distribution can be controlled by varying the content of the gelling / chelating agent or by adjusting process parameters such as reaction temperature and reaction time.

The sodium vanadium phosphate and sodium fluorophosphate vanadium prepared by the above method can have particle sizes in the range of 300 to 500 nm and 30 to 50 nm, respectively, as shown in FIG.

The thickness of the carbon coating formed on the surfaces of sodium vanadium phosphate and sodium fluorophosphate vanadium is not limited and can be 10 nm or less, as shown in FIG.

Fabrication of Sodium Ion Battery In the present invention, the electrode material is a composite material containing a cathode active material, a conductive material and a binder in an appropriate ratio.

The conductive material is any material with good electron conductivity, such as graphite in the form of natural graphite and synthetic graphite; amorphous carbon in the form of carbon black, acetylene black, kechen black; carbon fiber, carbon nanotubes and graphene. Can be included. The conductive material can be added in an amount of 1 to 15% by mass based on the total amount of the mixture containing the cathode active material.

The binder can be any component that imparts mechanical rigidity and helps to bind the active material particles to each other and also to bind the active material particles to the current collector. As the binder, polyvinylidene fluoride, polyvinyl alcohol, etc. can be used. , Carboxymethyl cellulose, polyvinylpyrrolidone, tetrafluoroethylene and the like.

The binder can be added in an amount of 1 to 15% by mass based on the total amount of the mixture containing the cathode active material.

Electrode for sodium ion batteries, for example, a cathode active material, a conductive material and a binder, a solvent, for example, non-aqueous NMP (N-methyl-2-pyrrolidone) / aqueous (H 2 _O) slurry is dissolved in a solvent It can be prepared and prepared by coating the slurry onto a current collector and then drying and solvent.

The current collector can be any material with good electrical conductivity, and the current collector can be stainless steel, aluminum, copper, nickel, carbon film, or a surface-treated material, such as carbon. Examples thereof include aluminum or stainless steel surface-treated by the above.

In another embodiment of the invention, the manufacture of a sodium ion battery may incorporate a non-aqueous electrolyte containing a cathode, an anode (which can be, but is not limited to, Na metal), a separator, and a sodium salt. can.

Non-aqueous organic solvents for electrolytes include aprotic organic solvents such as propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate and derivatives thereof.

Sodium salt materials that are preferably soluble in non-aqueous electrolytes include NaClO ₄ , NaBF ₄ , NaPF ₆ , NaCF ₃ SO ₃ , NaCF ₃ CO ₂ , CF ₃ SO ₃ Na, and (CF ₃ SO ₂ ) ₂ NNa. And so on.

In addition, aqueous electrolytes may be used in the manufacture of sodium ion batteries.

In one embodiment of the invention, the prepared sodium ion battery containing vanadium phosphate as the cathode active material exhibits high specific volume and cycle stability (FIGS. 4, 5 and 6).

In one embodiment of the invention, the prepared sodium ion capacitors containing vanadium phosphate as cathodes and anodes exhibit high specific capacitance, specific capacitance and cycle stability (FIGS. 7, 8 and 9).

In one embodiment of the invention, the prepared sodium ion battery containing sodium fluorophosphate vanadium as the cathode active material exhibits high specific volume and cycle stability (FIGS. 10, 11 and 12).

The active material developed by the microwave assisted sol-gel method has applications as an electrode active material for alkaline ion batteries, alkaline ion capacitors and superca battery devices.

Experimental Example 1
_{Sodium vanadium phosphate Na 3} V ₂ (PO ₄ ) ₃ was synthesized by the microwave assisted sol-gel method. Stoichiometric amounts of each precursor were used to prepare Na ₃ V ₂ (PO ₄ ) _3. Precursor _{used, NaH 2 PO 4 · 2H 2} O [99%, Sigma Aldrich], NH 4 VO 3 [98%, Loba Chemie] and citric acid _{(C 6 H 8 O 7)} [99.5%, Sigma Aldrich]. NaH ₂ PO ₄ · 2H ₂ O was added to deionized _{water, NaH 2 PO 4 · 2H 2} O was sonicated for 5 minutes to form a clear solution was completely dissolved. _{NH 4} VO ₃ and citric acid were added to the above solution, and the solution was continuously stirred at 80 ° C. until a dark orange transparent solution was formed. The solution was then transferred to a microwave synthesizer and kept at 80 ° C. for 10 minutes to give a dark blue gel. The gel was then washed and dried in the ambient atmosphere at 120 ° C. The dried gel was ground and then preheated at 400 ° C. for 4 hours in an argon atmosphere. Finally, the preheated sample was calcined at 800 ° C. for 10 hours under an argon atmosphere to obtain _{single-phase Na 3} V ₂ (PO ₄ ) _3.

Experimental Example 2
Using NaF [Merck 99%], NH ₄ H ₂ PO ₄ [Sigma Aldrich 98.5%], NH ₄ VO ₃ [Loba Chemie 98%] and citrate [Merck 99.5%] as precursors, _{Na 3 V 2 (PO 4)} 3 where similarly to microwave assisted sol - gel method, sodium fluorophosphate vanadium _Na 3 _V 2 a _{(PO 4)} 2 _{F 3} was prepared. Stoichiometric amounts of the precursor were mixed in deionized water, transferred to an open vessel and subjected to a microwave reaction at a constant temperature (80 ° C.) and stirring rate until a gel was formed. Next, the gel was washed and dried in a hot air oven at 120 ° C. under ambient air. _{The dried gel is crushed, pulverized, and then phase-pure Na 3} V ₂ (PO) over two-step heat treatment in an argon atmosphere, i) 350 ° C. for 4 hours, and ii) 650 ° C. for 6 hours. ₄ ) ₂ F ₃ was obtained.

After synthesizing both Na ₃ V ₂ (PO ₄ ) ₃ / Na ₃ V ₂ (PO ₄ ) ₂ F ₃ , X-ray diffractometer (Rigaku Smartlab X-ray diffractometer using _{Cu-K α ray), scanning type} Various structural and morphological investigations were carried out using an electron microscope (FE-SEM; Zeiss merlin Compact) and a transmission electron microscope (TEM; Technai G20).

Novel features of the invention have been clarified by describing some of the preferred embodiments of the invention so that those skilled in the art can understand and imagine the invention. It should also be understood that the present invention is not limited to the details described above or shown in the drawings in its use. The present invention has been described in considerable detail with reference to its particular preferred embodiments, without departing from the spirit and scope of the invention as described in this disclosure and as defined in the claims below. , Various changes can be made.

Claims (15)

A microwave-assisted sol-gel process for preparing an in-situ carbon-coated electrode material, wherein the electrode material is of the general formula [A ₃ M ₂ (PO ₄ ) ₃ ] and [A ₃ M ₂ (PO _4). ) ₂ F ₃ ] (In the formula, "A" is an alkaline ion selected from Li, Na and K, and "M" is selected from Fe, Ni, Co, V, Mn, Ti and Cr. It is selected from an alkali ion transition metal phosphate and an alkali ion transition metal fluorophosphate represented by), and the following steps:
a) A step of mixing by adding an alkali ion precursor, a transition metal precursor, a phosphorus precursor and a gelling / chelating agent in an appropriate molar ratio;
b) At the same time, consider the amount of transition metal precursors in deionized water or in a non-aqueous solvent selected from ethylene glycol, polyethylene glycol, tetraethylene glycol and a solvent having a low to moderate boiling point in the vessel. The step of incorporating the alkali ion precursor, the phosphorus precursor and the chelating agent based on the corresponding molar ratios;
c) The step of stirring the mixture in the container for a period of time to obtain a homogeneous mixture;
d) A step of irradiating microwaves in an open container with constant stirring at a constant temperature in the temperature range of 80 to 170 ° C. under atmospheric pressure to bring about homogeneous gelation;
e) A step of drying the obtained gel in the air in a temperature range of 100 to 120 ° C .;
f) Step of crushing the dried gel; and g) The dried gel is calcined in an inert atmosphere in a temperature range of 600 to 800 ° C. for 8 to 10 hours, and an intermediate calcining temperature of 300 to 500 ° C. is 3 to 5 The process of forming an in-situ carbon coating layer on the electrode material along with the formation of a mesoporous carbon network over time;
A microwave-assisted sol-gel process for preparing in-situ carbon-coated electrode materials, including. The in-situ carbon-coated electrode material according to claim 1, wherein the alkali ion precursor, the transition metal precursor, the phosphorus precursor and the gelling / chelating agent are mixed in a ratio of 3: 2: 3: 2. Microwave assisted sol-gel process for preparation. The alkaline ion transition metal phosphate is sodium vanadium phosphate [Na ₃ V ₂ (PO ₄ ) ₃ ], and the components added in the mixture of step a) are sodium dihydrogen phosphate and sodium dihydrate acetate (sodium dihydrogen phosphate). CH ₃ COONa ・ 2H ₂ O), sodium hydroxide monohydrate (NaOH ・ H ₂ O), sodium hydroxide (NaOH), sodium carbonate (Na ₂ CO ₃ ), sodium phosphate (Na ₃ PO ₄ ), sodium precursor is selected from the group consisting of sodium phosphate twelve dihydrate _{(Na 3 PO 4 · 12H 2} O), sodium oxalate _{(Na 2} C _{2 O 4)} and mixtures thereof; vanadium (V) oxide (V ₂ O ₅ ), ammonium metavanadate (NH ₄ VO ₃ ), vanadium oxide (III) (V ₂ O ₃ ), vanadyl acetylacetonate [VO (C ₅ H ₇ O ₂ ) ₂ ], trihydroxy (oxo) ) Vanadium precursors selected from the group consisting of vanadium (H ₃ VO ₄ ) and mixtures thereof; ammonium phosphate [(NH ₄ ) ₃ PO ₄ ], diammonium phosphate [(NH ₄ ) ₂ HPO ₄ ], A phosphorus precursor selected from the group consisting of ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ ), phosphoric acid (H ₃ PO ₄ ), sodium dihydrogen phosphate (NaH ₂ PO _{4) and mixtures thereof; and} The gelling / chelating precursor used as a source of in-situ carbon coating, wherein the mesoporous carbon network is selected from the group consisting of citric acid, ascorbic acid, oxalic acid and gluconic acid, according to claim 1. Microwave-assisted sol-gel process for preparing in-situ carbon-coated electrode materials. As an additional reagent for in-situ carbon coating, an organic precursor selected from the group consisting of glucose, sucrose, galactose, fructose, lactose, starch, mannose, ribose, aldohexose, ketohexose and combinations thereof is used in step a. ), A microwave-assisted sol-gel process for preparing the in-situ carbon-coated electrode material according to claim 1. In step g), the microwave-assisted sol-gel for preparing the in-situ carbon-coated electrode material according to claim 1, wherein the dried gel is calcined under an inert gas selected from argon or nitrogen. process. The alkali ion transition metal fluorophosphate is [Na ₃ V ₂ (PO ₄ ) ₂ F ₃ ], the precursor of alkali ion consisting of NaF and fluorine is added in step a), and the other steps are the same. , A microwave-assisted sol-gel process for preparing the in-situ carbon-coated electrode material according to claim 1. The in-situ carbon-coated electrode material according to claim 1, wherein the particle size and its distribution are controlled by varying the content of the gelling / chelating agent or by adjusting the process parameters based on the requirements. Microwave assisted sol-gel process for preparing. By the general formula A ₃ M _2-x C _x (PO ₄ ) ₃ (in the formula, 0 <x <2, C is any one of Mg, Al, Ti, Ca and Sc). The microwave assist for preparing the in-situ carbon-coated electrode material according to claim 1, wherein the cation-doped alkaline ion transition metal phosphate represented is further added in step a) and the other steps are the same. Sol-gel process. General formula A ₃ M ₂ (PO ₄ ) _3-y N _3y (in the formula, 0 <y ≦ 1) and A ₃ M _2-x C _x (PO ₄ ) _3-y N _3y (in the formula, 0 <y ≦ 1) The anion-doped alkaline ion transition metal phosphate represented by 0 <x <2, 0 <y ≦ 1) (where N is any one of Cl, Br and I) is the step a. ), And the other steps are the same, the microwave assisted sol-gel process for preparing the in-situ carbon-coated electrode material according to claim 1. By selecting the appropriate precursor in step a) at the required molar ratio, the general formula Na ₄ M ₃ (PO ₄ ) ₂ P ₂ O ₇ (in the formula, M = Fe, Mn, Co and Ni. ), And the _{layered sodium transition represented by the general formula Na x} MO ₂ (in the formula, 0.44 <x <1, M = Fe, Mn, Co, Ni and Ti). A microwave-assisted sol-gel process for preparing an in-situ carbon-coated electrode material according to claim 1, wherein a metal oxide can also be prepared. An in-situ carbon-coated electrode material prepared by the microwave-assisted sol-gel process according to claims 1-10. The in-situ carbon-coated electrode material according to claims 3 and 6, each having a NASICON (Na superionic conductor) type rhombohedral crystal and a tetragonal crystal structure. The in-situ carbon-coated electrode material according to claim 6, wherein the prepared sodium vanadium phosphate and sodium fluorophosphate vanadium have particle sizes in the range of 300 to 500 nm and 30 to 50 nm, respectively. The in-situ carbon-coated electrode material according to claims 3 and 6, wherein the thickness of the carbon coating formed on the surface of the carbon-coated electrode material is 10 nm or less. A sodium ion cell / battery, a superca battery and a sodium ion capacitor having an in-situ carbon-coated electrode material prepared by the microwave-assisted sol-gel process according to claim 1.

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