RU2713401C1 - METHOD OF PRODUCING TiS3 BASED ELECTRODES FOR ELECTROCHEMICAL ENERGY STORAGES WITH INORGANIC AQUEOUS Mg-ION ELECTROLYTE - Google Patents

Abstract

FIELD: electrical engineering.

SUBSTANCE: invention relates to electrical engineering and specifically to a method of producing electrode material for use in Mg-ion batteries meeting environmental requirements, which is an urgent problem of power engineering. To obtain an electrode, initial elementary sulfur, titanium powder (150–300 mcm, 80 mesh) or ground titanium sheet pieces are used as initial reagents, which are fired in a sealed pyrex ampoule for 12 hours at 400 °C with isothermal holding, after which, based on the obtained powdered product, a paste is prepared, which contains 75 % of the obtained powdered product, 5 % fluoroplastic and 20 % of soot, which are mixed and grinded in mortar for 15–20 minutes, then poured into an Eppendorf tube and a solvent is added, the amount of which is selected depending on the weight of the dry substance and the desired consistency of the solution, then the solution is mixed and deposited on the steel mesh, which is dried in vacuum furnace for 2 hours at 60 °C. Electrode material obtained during solid-phase synthesis has high Mg²⁺-ionic and electronic electrical conductivity at room temperature, and also has high specific capacitance (709.3 F/g), charge/discharge rate and stability.

EFFECT: technical result of invention is increase of homogeneity of composite electrode material, having low resistance.

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Description

The invention relates to methods for producing electrodes for new efficient energy sources, compact, energy-intensive, satisfying environmental requirements, which is an urgent problem of energy technology.

Electrochemical energy storage devices (batteries, supercapacitors) are an electrochemical cell that converts the electrochemical energy of the reduction and oxidation reactions into electrical energy. For the operation of such devices, it is necessary to have electrodes on which oxidation / reduction reactions occur (anode, cathode) and an electrolyte through which electroactive ions are transported. In this case, electrons pass through an external circuit, creating useful energy of electric current. In this case, as the electrolyte can be both aqueous solutions of salts, and also organic solutions, as well as solid electrolytes. Li ^{+ is} used as electroactive ions, however, recently Na ⁺ , K ⁺ , Mg ²⁺ and Ca ^{2+ have} attracted attention. Interest in the latter is due to the fact that these cations have a significantly lower cost than Li ⁺ , which allows the use of such batteries in mass devices, to create large batteries, as well as significantly reduce the cost of electric vehicles. Inorganic aqueous electrolytes are also fireproof and more environmentally friendly than organic ones (propylene carbonate / ethylene carbonate).

Graphite is widely used as anode material, cathode - some oxide compounds with a layered structure (Ni-enriched NMC, HENMC, HV-spinel, NCA), polyanionic (LiFePO ₄ ) and spinel. In all these materials, Li ⁺ , which has high mobility, is used as electroactive ions.

The advantages of electrochemical energy storage devices are the possibility of their use in portable devices, wireless solutions, the ability to provide vehicles with high efficiency, and the fundamental absence of harmful emissions into the atmosphere.

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) позволит существенно снизить стоимость батареи. Органический электролит, используемый в настоящее время горюч и не экологичен, в отличие от неорганического водного. Также Со, используемый в материале катода дорог и токсичен, в отличие от Ti, например.However, despite the fact that Li ⁺ has high mobility, the use of Li ⁺ and Co significantly increases the cost of the battery, making, for example, electric cars very expensive. The use of Mg ²⁺ with a close ionic radius (0.72

vs 0.76

) will significantly reduce the cost of the battery. The organic electrolyte currently in use is flammable and environmentally friendly, unlike inorganic water. Also, Co used in the cathode material is expensive and toxic, unlike Ti, for example.

TiS ₃ could act as an alternative cathode material in aqueous Mg-ion batteries, which would ensure the absence of the above disadvantages. The current tendency to increase research in the field of sulfur-containing anodes as opposed to oxygen-containing ones makes it possible to provide higher mobility of Mg ²⁺ , bringing it closer to values suitable for mass use in industry and the national economy.

Several patents for cathodes for Mg-ion batteries are known in the art, for example, US 20160111720 "Metastable vanadium oxide cathode materials for rechargeable magnesium battery", US 8932760 "High capacity cathode material for a magnesium battery", US 9240612 "Layered materials with improved magnesium intercalation for rechargeable magnesium ion cells ".

The cathode material described in the invention according to the patent US 20160111720 "Metastable vanadium oxide cathode materials for rechargeable magnesium battery" has the composition [V ₂ O ₅ ] _c [M _a O _b ] _d , where M is an element from the series P, B, Si , Ge and Mo, a is an integer from 1 to 2, b is an integer from 1-5, s is an integer of 35-80 mol. %, d - from 20 to 65 mol. % The active material represented in the above formula is a metastable structural and morphological phase between the amorphous phase and the crystalline phase. Amorphization of V ₂ O ₅ can be carried out using methods of hardening and grinding into balls, which are usually known. The addition of glass-forming agents containing at least P ₂ O ₅ , B ₂ O ₃ , SiO ₂ , GeO ₂ or MoO ₃ ) to V ₂ O ₅ during preparation and by carefully monitoring the formation conditions gives a substantially amorphous material, which means that the material, analyzed by XRD, does not have crystalline peaks. The invention allows to create a cathode active material based on V ₂ O ₅ having a high specific stored energy.

, а молярное отношение стабилизирующего иона или молекулы к Mn составляет от 0,1 до 0,125. В предпочтительных вариантах осуществления изобретения стабилизирующий ион или молекула выбирается из группы, состоящей из K⁺, Au⁺, Am⁺, НО⁺. Nd²⁺, Ва²⁺ и H₂O.US 8932760 B2 "High capacity cathode material for a magnesium battery" discloses the relationship of the ion radius of the ion with the characteristic as a stabilizing ion for α-MnO ₂ or the molar ratio of the stabilizing ion to manganese as factors affecting the cathode characteristic. A cathode material is proposed for use as a magnesium battery with a high capacity and a service life for use in industry and the national economy with a magnesium-ion cell including an anode containing magnesium; electrolyte; and a cathode containing α-MnO, where α - MnO contains a stabilizing ion or molecule with a radius of 1.35 to 1.55

and the molar ratio of the stabilizing ion or molecule to Mn is from 0.1 to 0.125. In preferred embodiments, the stabilizing ion or molecule is selected from the group consisting of K ⁺ , Au ⁺ , Am ⁺ , HO ⁺ . Nd ²⁺ , Ba ²⁺ and H ₂ O.

US 9240612, "Layered materials with improved magnesium intercalation for rechargeable magnesium ion cells", establishes the fact that diffusion of multivalent ions in layered cathode materials is a limiting factor in rechargeable multivalent electrochemical cells and there is a need for materials capable of combining high capacity and mobility Mg ²⁺ . The essence of the invention of the authors is the use of organic clusters for the separation of layers of various types in layered materials. As a cathode, a material with the formula Mg _a M _b X _y is proposed, where M is a cation or a mixture of metal cations, X is an anion or a mixture of anions, and in the range 0-2, b = 1-2, and y = 9. As the anode, alloys AZ31, AZ61, AZ63, AZ80, AZ81, AZ91, AM50, AM60, Elektron 675, ZK51, ZK60, ZK61, ZC63, M1A, ZC71, Elektron 21, Elektron 675, Elektron, Magnox, and Mg, containing at least Al, Ca, Bi, Sb, Sn, Ag, Cu or Si.

However, the materials proposed in the described inventions are not stable enough (metastable), either difficult to manufacture, or do not provide sufficient mobility of Mg ²⁺ . Nanocrystalline materials are difficult to pack into the cathode, which means that the thickness of the cathode based on them should be much larger than that of traditional materials of a few microns. Thus, the energy density per unit volume for the cell based on these materials will be lower. In addition, nanocrystalline materials will contribute to the decomposition of the electrolyte due to the extremely high surface area characteristic of them. In hydrated forms of V ₂ O _{5, a} large amount of water acts as a ligand in the structure. During magnesium intercalation / deintercalation in a typical non-aqueous medium, water is an undesirable molecule, since a non-conductive resistive blocking layer forms on the anode due to the release of water. The redox potentials predicted by the ab-initio method for VOPO and V ₂ O ₅ are 2.3-2.6 V, which is lower than other known materials, where the potential is more than 3 V. As a result, a lower voltage reduces the density of the stored battery power.

The objective of the invention is to create a composite electrode of an electrochemical magnesium battery by using the method of solid-phase synthesis of graphite-like titanium trisulfide powder from simple substances in a sealed ampoule, followed by applying the resulting powder to a current collector (stainless steel mesh) with improved electrophysical properties.

The choice of this composition and structure of the material is due to the need to ensure high mobility of Mg ²⁺ in the structure. Namely: the graphite-like material structure is observed in the vast majority of commercially successful cathode and anode materials of Li-batteries. In the TiS ₃ composition material, overlap of the electron shells near S and Ti is close in energy levels, which allows one to achieve the high electronic conductivity necessary to create a strong screening effect for Mg ²⁺ cations moving in the TiS ₃ structure. The screening effect has proved to be the most effective method and the main reason for the high mobility in a material such as, for example, the Chevrell phase. The main reason for the presence of this effect in the material is that Mg ²⁺ cations moving in the TiS ₃ structure electrostatically strongly interact with the cations of the crystal lattice due to the double charge of Mg ²⁺ compared, for example, with Li ⁺ . It is shielding that allows you to significantly counteract this electrostatic interaction, and to achieve high mobility of Mg ²⁺ in the structure while ensuring high specific characteristics (energy density per unit mass and volume).

To obtain titanium sulfide-based nanopowders, the so-called “traditional” chemistry methods are often used. In this way, it is easiest to get chlorine-free products. To do this, use either crushed pieces of sheet titanium or powdered titanium (although it usually does not differ in such a high metal content). When synthesizing composite ceramic compositions by this method, it is necessary to take into account the chemical properties of each of the reagents that participate in the synthesis. In this regard, the technology for obtaining TiS ₃ was developed individually. In addition, according to the complex phase diagram of the Ti-S system, it was necessary to avoid the decomposition of TiS ₃ into TiS ₂ and S at temperatures above 500 ° C. The TiS ₃ compound crystallizes in a narrow temperature range of 500-632 ° C and the ratios between S and Ti. All these factors had to be taken into account to obtain a quality product.

The essence of the claimed technical solution is expressed in the following set of essential features, sufficient to solve the technical problem indicated by the applicant and to obtain the technical result provided by the invention.

According to the invention, the method for producing TiS ₃ -based electrodes for electrochemical energy storage with an inorganic aqueous Mg-ionic electrolyte is characterized in that crystalline elemental sulfur, titanium powder (150-300 μm, 80 mesh) or ground pieces of titanium sheet are used as starting reagents, which are fired in a sealed pyrex ampoule for 12 h at 400 ° C with isothermal exposure, after which a paste is prepared on the basis of the obtained powdery product, which contains 75% of the obtained pore co-product, 5% fluoroplastic and 20% carbon black, which are mixed and ground in a mortar for 15-20 minutes, then poured into an Eppendorf tube and a solvent is added, the amount of which is selected depending on the dry matter mass and the desired consistency of the solution, then the solution is mixed and applied to a steel mesh, which is dried in a vacuum oven for 2 hours at 60 ° C.

In addition, the claimed technical solution is characterized by the presence of a number of additional optional features, namely.

- mixing the solution is carried out using an ultrasonic bath with a frequency of up to 22 kHz;

- mixing the solution is carried out using a rotor with a holder rotation speed of 99 rpm for 10-15 minutes;

- I carry out preliminary preparation of a steel mesh, which is washed with hot water with a detergent, then rinsed with distilled water and treated with ethyl alcohol or acetone, after which the steel mesh is dried in an oven for 30 minutes at a temperature of 60 ° C.

The claimed combination of essential features ensures the achievement of a technical result, which is as follows. The use of simple substances in solid-phase synthesis is more appropriate than substances of complex composition, different dispersion or origin, as this allows you to get a better precipitation product, the most homogeneous and crystallized. The solid-phase synthesis method in a sealed pyrex ampoule provides isolation of the initial reaction products from the atmosphere, while reducing the cost of the technology and obtaining a product with the above properties. Thorough mixing of all components of the paste for application to the electrode ensures the achievement of low internal resistance and high electrochemical properties by increasing the electrical contact and connectivity of all components of the composite.

The invention is illustrated by drawings, where in FIG. 1 is a flow chart of an electrode based on a material of composition TiS ₃ . The appearance of the starting reagents and the obtained powder is shown in FIG. 2. It is seen that the obtained TiS ₃ is a finely divided black powder. An X-ray powder pattern of a TiS ₃ material is shown in FIG. 3. X-ray phase analysis was carried out on a D8-Advance "Bruker" X-ray diffractometer (monochromatic CuK _α radiation, operating voltage 40 kV at a current of 40 mA in the range of angles 2θ = 5-90 °). the analysis results were processed using the program "WINFIT 1.2.1.", using the Fourier transform of the profile of the reflex. To estimate the size of coherent scattering regions (CSRs), we used the Selyakov-Scherer equation: DOКP = 0.9 λ / (β⋅cosθ), where λ is the CuKα wavelength, β is the half-height diffraction reflection width. To decode the diffraction patterns, the ICDD-2006 international database was used. The Δ notation is the peak corresponding to the crystalline phase of TiS ₃ . The results show the presence of a well crystallized product, a monophasic TiS ₃ sample. Monoclinic P2 ₁ / m (11)) is observed, a crystalline structure with parameters a = 4.958, b = 3.401 and c = 8.778 and a CSR size of ~ 81 nm.

The claimed method is as follows.

Crystalline elemental sulfur, titanium powder (150-300 microns, 80 mesh) or crushed pieces of titanium sheet, which are characterized by a higher titanium content, which are placed in a perix ampoule and sealed with a gas burner, are selected as initial reagents. When carrying out this process, it was found that when these starting materials are placed in an ampoule, slight ignition is observed during sealing, which is presumably associated with the combustion and oxidation of finely divided metal powder. The addition of oxidized metal to the composition of the starting reagents is capable of ultimately introducing impurities into the final product, the formation of oxysulfide. To avoid this, carefully wipe the sealed ends of the tube from the perix. The use of simple substances in solid-phase synthesis is more appropriate than substances of complex composition, different dispersion or origin, as this allows you to get a better precipitation product, the most homogeneous and crystallized.

When synthesizing a powder of an active substance of TiS ₃ composition, it is necessary to strictly observe the ratio of components, temperature, synthesis conditions and avoid ingress of impurities. It is also necessary to take into account the chemical properties of each of the reagents that participate in the synthesis. According to the phase diagram of the Ti-S system, the TiS ₃ compound crystallizes in a narrow temperature range of 500-632 ° C and the ratios between S and Ti. Thus, it is also necessary to avoid decomposition of TiS ₃ into TiS ₂ and S at temperatures above 500 ° C. All these factors must be considered to obtain a quality product.

The sealed pyrex ampoule is fired for 12 hours at 400 ° C in an Nabertherm tube furnace with isothermal exposure and then cooled.

Then, based on the obtained powdery product, a paste is made: the weight of the initial starting components is calculated and weighed on a balance based on the ratio: 75% of the active substance (powder), 5% of fluoroplastic, 20% of carbon black (Super P brand) are mixed and ground in an agate mortar for 15-20 minutes. Then pour into an Eppendorf tube and add up to 9 drops of solvent. The amount of solvent is selected depending on the mass of dry matter and the desired consistency of the solution. For homogeneity, the solution is mixed using special installations: in an ultrasonic bath (dispersant UZDN-2T) with a frequency of up to 22 kHz or a rotor from ELMI (model RM-1L, holder rotation speed: 99 rpm, mixing time: 10-15 minutes). In the first case, mixing was carried out by an indirect method. The nozzle of the installation was placed not in a solution, but in a container with water, where a test tube with paste was previously placed. The second case was used for a pasty consistency.

Directly for the manufacture of electrodes, a stainless steel mesh is used, as a substrate and previously prepared paste. To ensure low internal resistance and connectivity of all components of the composite, careful preparation of the substrate occurs. Wash steel mesh with hot water and detergent. Then rinse with distilled water and treat with ethyl alcohol or acetone. The steel mesh is dried in an oven for 30 minutes at a temperature of 60 ° C. Then the paste is applied with a brush to a steel mesh and dried in a vacuum oven for 2 hours at 60 ° C.

To obtain information on the degree of electrode coverage and the kinetics of electrode reactions, cyclic voltammetry was used. In cyclic voltammetry, triangular potential pulses are applied to the electrode and the resulting current is recorded. As a result, cyclic voltammograms of the electrode are obtained at different scan rates. When analyzing the response, it is necessary to separate the capacitance created by the reversible redox reactions (the desired result), the irreversible redox reactions and the capacitance created by the double electric layer, therefore, the scan is carried out for several cycles (more than 10) and at different scan rates, observing the changes .

The results obtained by cyclic voltammetry are presented in FIG. 4 (sweep speed 50 mV / s). Stable peaks are fixed on the cyclic voltammogram at ~ 200, 850, and -350 mV, which clearly indicates the presence of intercalation of Mg ²⁺ in the TiS ₃ crystal lattice and the associated reversible redox reactions.

In the same way, a number of other experimental samples were obtained, which are presented in Table. 1-3, however, the sharpest peaks are observed in the sample described above.

The resulting nanocomposite electrode in its electrochemical properties (specific capacity, charge / discharge rate, stability) and environmental friendliness and availability of starting materials for manufacturing is promising as an electrode and an electrolyte with Mg ²⁺ as an electroactive ion and can be recommended for use in Mg-ion batteries.

When creating new materials for modern energy, the key issue is the development of technologies for producing high-quality composites with desired physicochemical, electrical, and mechanical properties. As a result of the studies conducted in this work, a solid-phase synthesis technology of the active material of the TiS ₃ composition is proposed to create a composite electrode based on it for use as part of Mg-ion batteries. The ratio of the starting materials and the optimal conditions for obtaining a crystalline powder of a material of TiS ₃ composition were selected and the conditions for its formation were revealed. It was established that the crystallite size of monoclinic TiS _{3 is} not 81 nm at a temperature of 400 ° C. The resulting electrode materials have high Mg ²⁺ -ionic and electronic conductivity at room temperature, as well as high specific capacitance (709.3 F / g), charge / discharge rate and stability.

Thus, the obtained results testify to the prospects of using the proposed technology for the synthesis of powder of an active material of the composition TiS ₃ and a composite electrode based on it for use in Mg-ion batteries.

Claims (4)

1. The method of producing electrodes based on TiS ₃ for electrochemical energy storage with an inorganic aqueous Mg-ionic electrolyte, characterized in that the initial reagents use crystalline elemental sulfur, titanium powder (150-300 μm, 80 mesh) or crushed pieces of sheet titanium which are fired in a sealed pyrex ampoule for 12 hours at 400 ° C with isothermal exposure, after which a paste is prepared based on the obtained powder product, which contains 75% of the obtained powder product a, 5% fluoroplastic and 20% carbon black, which are mixed and ground in a mortar for 15-20 minutes, then poured into an Eppendorf tube and a solvent is added, the amount of which is selected depending on the dry matter mass and the desired solution consistency, then the solution is mixed and applied to a steel mesh, which is dried in a vacuum oven for 2 hours at 60 ° C. 2. The method according to p. 1, characterized in that the stirring of the solution is carried out using an ultrasonic bath with a frequency of up to 22 kHz. 3. The method according to p. 1, characterized in that the stirring of the solution is carried out using a rotor with a holder rotation speed of 99 rpm for 10-15 minutes. 4. The method according to p. 1, characterized in that the preliminary preparation of the steel mesh is carried out, which is washed with hot water using detergent, then rinsed with distilled water and treated with ethanol or acetone, after which the steel mesh is dried in an oven for 30 minutes at a temperature of 60 ° C.

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