RU2518150C2 - Nanocomposite electrochemical capacitor and its manufacturing method - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: invention relates to electrical engineering, particularly to manufacturing of electrochemical capacitors. A nanocomposite electrochemical capacitor consists of two or more electrodes, electrolytes, separators and current collectors placed in the temperature-controlled space; at that each pair of electrode and electrolyte is represented as nanocomposite made of nanocarbon material and solid ionic organic or inorganic compound of eutectic composition, at that electrodes are made of nanocarbon material with specific area more than 1300 m²/g in the form plates or sheets with thickness of 0.1-10 mm and density of 0.8-1.2 g/cm³. The method of capacitor manufacturing includes dispersion of the prepared electrode mixture with binding agent; moulding of plates or sheets out of dispersed electrode mixture with binding agent, annealing of moulded plates or sheets in oxidising and/or deoxidising atmosphere or under vacuum and impregnation of compacted electrodes in fused bath or electrolyte solution at high temperature and under vacuum with further cooling.

EFFECT: improved specific energy capacity of the claimed capacitor is the technical result of this invention.

20 cl, 6 dwg

Description

The invention relates to electrical engineering, in particular to the production of electrochemical capacitors with a combined charge storage mechanism and other similar rechargeable energy storage devices.

Known capacitors that store energy due to the capacitance of a double electric layer at the electrode-electrolyte interface (V.P. Kuznetsov et al. "Ways and prospects for the development and use of capacitors with a double electric layer (ionistors)") / 1 /. In particular, in / 1 / describes a two-layer capacitor FA OH 105Z manufactured by NEC, Japan. The assembly consists of 8 series-connected capacitors, the positive and negative electrodes are made of activated carbon and are separated by a separator. The electrolyte is a 38% solution of sulfuric acid in water. The disadvantages of this capacitor are low specific energy, low operating voltage and low maximum operating temperature. These disadvantages are due to the presence of a solvent (water) having a relatively low decomposition voltage and a low temperature limit of the liquid state, even when mixed with sulfuric acid of the indicated concentration.

The invention of the authors Oh Dzae-Seung, Lee Bioung-Bae, Park Dzae-Duk, Park Ji-Won “An electrolyte containing a eutectic mixture and an electrochemical device using it” (WO 2007/021151 20070222), in which the authors claim The problems of evaporation, exhaustion and flammability of electrolytes due to the use of an ordinary aqueous or organic solvent as an electrolyte can be solved and thereby improve safety as a result of the use of a cost-effective eutectic in electrolyte for electrochemical devices mixtures characterized by thermal and chemical resistance, excellent conductivity and a wide electrochemical window / 2 /. In accordance with / 2 / an electrolyte is proposed containing a eutectic mixture formed from: (a) a compound containing an amide group; and (b) an ionizable lithium-free salt. An electrochemical device, preferably an electrochromic device containing the aforementioned electrolyte, is also provided. The disadvantage of this invention is the use as an electrolyte of cyanide compounds having high toxicity. In addition, this invention does not indicate methods of connecting the electrolyte with the electrode, which is a key problem in creating electrochemical capacitors. The invention does not address the issue of using the proposed electrolyte in the design of an electrochemical capacitor.

Known technical solution of the authors Popov A.V., Gitelson A.V., Kuzmina G.Ya. "Double-layer capacitor with molten electrolyte" (1997) / 3 /, which is the closest analogue of the present invention, representing the design of an electrochemical capacitor, consisting of at least a housing, a positive and a negative electrode, and at least one of them is a polarizable electrode with a developed surface made of activated carbon material, highly dispersed carbon (soot) or an electrochemically inert highly dispersed metal; and electrolyte. The electrodes are in contact with the electrolyte and are isolated from each other by an ion-conductive pad. A porous dielectric moistened with an electrolyte, an ion-exchange membrane or a solid electrolyte membrane can be used as an ion-conducting pad. As an electrolyte, a practically solvent-free melt is used.

The disadvantages of the known technical solutions are the difficulty in impregnating the activated carbon or highly dispersed carbon (soot) used in the / 3 / design of the electrochemical capacitor with molten salts; relatively low specific area of recommended carbon materials. As a result, the relatively low specific capacity of the double layer formed on the surface of the carbon material; relatively low electrical conductivity of the recommended carbon materials and large ohmic losses at the points of contact of the electrode material with current leads; low chemical and electrochemical resistance of the recommended carbon materials in contact with molten electrolyte, leading to a reduction in the electrochemical window. All these shortcomings are caused by relatively low energy and power characteristics of the electrochemical capacitor described in / 3 /, - specific energy consumption at the level of 5 W · h / kg, specific power at the level of 3 kW / kg.

The aim of the present invention is to increase the specific energy consumption of the electrochemical capacitor, as well as the specific power. The problem to which the claimed invention is directed, is to create an electrode-electrolyte composition for use in an electrochemical capacitor, devoid of the disadvantages of the closest analogue that implements practical specific characteristics that ensure the technical and economic feasibility of its use. The technical result common for the method and device is to increase the specific characteristics of an electrochemical energy storage device, to ensure the stability of specific characteristics and to increase the resource.

The technical result is achieved due to the fact that in a nanocomposite electrochemical capacitor, consisting of at least two electrodes made of nanocarbon material, at least one electrolyte, separators and current collectors placed in a thermostatically controlled volume, each pair is an electrode and an electrolyte It is a nanocomposite made of nanocarbon material and a solid ionic organic or inorganic compound of eutectic composition.

The electrodes are made of nanocarbon material, which is graphene layers with a specific surface above 1300 m ² / g, with or without the addition of carbon materials and / or materials with electronic conductivity. The electrodes are made in the form of compacted plates or sheets with a thickness of 0.1 ... 10 mm and a density of 0.8 ... 1.2 g / cm ³ with a specific surface area that differs by two or more times, and have a mass that differs by two or more times .

The electrolyte is a solid ionic organic or inorganic compound of eutectic composition having a melting point in the operating temperature range of the nanocomposite capacitor. At temperatures below the operating temperature range, the electrolyte is a solid compound. At operating temperatures, the electrolyte is a melt. As the electrolyte, a eutectic mixture of inorganic salts, organic salts or a mixture of inorganic and organic salts can be used. The electrolyte may be a mixture of alkali and alkaline earth metal chlorides. The electrolyte may be a mixture of alkali and alkaline earth metal borofluorides with an ionic liquid based on imidazole derivatives borofluoride.

The separator may be a track membrane with a pore density of 10 ⁷ -10 ⁹ pores / cm ² and the pores have a cylindrical or conical shape. The separator may be a solid electrolyte, for example, based on a sulfcationite ion exchange membrane.

The technical result is also achieved due to the fact that the method of manufacturing a composite electrochemical capacitor includes: 1) preparation of electrode mixtures for the anode and cathode, consisting of nanocarbon materials; 2) dispersing the prepared electrode mixture with a binder; 3) pressing plates or sheets of electrode mixture dispersed with a binder; 4) annealing pressed plates or sheets of electrode mixture dispersed with a binder in an oxidizing and / or reducing atmosphere or under vacuum; 5) impregnation of compacted electrodes in a melt or electrolyte solution at high temperature and under vacuum; 6) cooling the compacted electrodes impregnated with electrolyte under vacuum to solidify the electrolyte; 7) connection of compacted electrodes impregnated with electrolyte with a separator and current collectors.

To prepare the electrode mixture can be used nanocarbon material made by pyrolysis of a mixture of liquid and / or gaseous hydrocarbon and hydrogen, having a specific surface area of more than 1300 m ² / g, conductivity of 10 S / cm or more.

During the pyrolysis of a mixture of gaseous hydrocarbon and hydrogen, the temperature can be maintained in the range of 850-900 ° C, pressure in the range of 0.1-1.0 MPa, compounds based on cobalt and molybdenum are used as catalyst, natural gas can be used as gaseous hydrocarbon or propane or butane or ethylene.

After the production of nanocarbon material, it can be treated with an acid or alkaline solution in order to form surface functional groups: hydroxyl, carboxyl, phenolic, hydroquinone, sulfonic, etc., which increase the wettability and sorption of electrolyte ions on the surface.

The electrode mixture can be pressed into plates or sheets at pressures of 5-10 MPa and at a temperature of 150-350 ° C with or without the addition of a binder.

Plates or sheets of compacted nanocarbon material can be annealed in an oxidizing and / or reducing atmosphere or under vacuum at a temperature of 350 ... 500 ° C for 1 ... 5 hours.

Annealed plates or sheets of compacted nanocarbon material can be impregnated in a melt or electrolyte solution at a temperature 50 ° C higher than the melting temperature of this electrolyte under vacuum for 1 ... 5 hours.

The electrolyte in the form of an anhydrous salt or a mixture of salts can be introduced into the electrode mixture before pressing by mixing in a predetermined proportion, grinding, heating to the melting temperature of the electrolyte. To exclude contact with air and atmospheric moisture, operations can be performed in an inert gas atmosphere. To improve the filling of the pores of the nanocarbon material, evacuation can be performed to remove gas before and / or during mixing. Also, the electrolyte can be introduced into the electrode mixture before pressing by impregnation of the electrode mixture in a saturated aqueous solution of electrolyte salts, followed by drying and dehydration of the electrode mixture under vacuum at a temperature of 150-250 ° C for 1 ... 5 hours.

To increase the wettability of the surface of the nanocarbon material, which contributes to a more complete filling of the pores and a more complete use of the adsorption surface and thereby increase the electrode capacity, a surfactant, for example sodium dodecyl sulfate, can be introduced into the electrode mixture.

A compacted electrode containing a solid state electrolyte can be mechanically connected to a separator and current collectors in an inert atmosphere. After connecting a compacted electrode containing a solid electrolyte, connected to a separator and current collectors, this design can be heated in an inert atmosphere to the melting temperature of the electrolyte under the influence of a static or variable mechanical load in order to compact nanocarbon material.

After the electrolyte is melted inside a compacted electrode connected to a separator and current collectors, this electrochemical system can be polarized by small currents at voltages not exceeding 10% of the electrolyte decomposition voltage in this electrochemical system.

The invention is illustrated by drawings.

Figure 1 shows a schematic representation of a nanocomposite electrochemical capacitor;

figure 2 shows a schematic illustration of the design of a nanocomposite electrode;

figure 3 shows micrographs taken using a scanning electron microscope (SEM) and transmission electron microscope (TEM);

figure 4 shows a schematic representation of the technological process of manufacturing a nanocomposite electrochemical capacitor;

figure 5 shows an example of a cyclic voltammogram of a nanocomposite electrochemical capacitor manufactured by the claimed method;

6 shows an example of a charge-discharge cycle of a nanocomposite electrochemical capacitor.

Description of the design and operation of the nanocomposite electrochemical capacitor.

A nanocomposite electrochemical capacitor, consisting of at least two electrodes 1, in a multiple of two, is made of 6 electrodes 1 sequentially placed in the housing, embedded in monopolar 4 and bipolar 3 collector washers made of electrically conductive carbon-graphite material. The electrodes 1 are separated by an ion-conducting, but non-conducting, electron separator 2 made of a polymeric material, for example a polyethylene terephthalate track membrane. The membrane has a porosity of at least 12%, providing ionic conductivity at a level of at least 10 ³ S / cm. The separator 2 has a size slightly larger than the transverse size of the electrode 1, in order to exclude direct electrical contact of adjacent electrodes. Subsequent pairs of electrodes 1 are separated from each other by a sealed electrolyte and gas-tight bipolar conductive washer 3, which ensures the transmission of electric potential and current to adjacent pairs of electrodes. The outermost electrodes are separated from the battery case by monopolar conductive washers 4, to the external surfaces of which are connected electric current-carrying terminals 5. Capacitor cells formed by a pair of adjacent electrodes 1, separated by a separator 2, and supported by bipolar conductive washers 3, are hermetically isolated from each other along the plane of the conductive a washer 3, around the perimeter - an insulating sleeve 7 made of a high-temperature gas-tight polymer or composite material, for example, h polyaramide fibers with a high temperature epoxy compound. The housing 6, made of a metal, or polymeric, or composite material, for example, aluminum, provides mechanical strength to the capacitor structure and seals it from the external atmosphere.

The principle of operation of the capacitor is as follows. In the initial uncharged state, the capacitor can be at ambient temperature, for example, in the range + 50 ... -50 ° C. The operating temperature at which the nanocomposite capacitor is charged and discharged is selected above the melting temperature of the eutectic composition electrolyte, for example, above + 100 ° C. At temperatures below the temperature of the eutectic point of the molten electrolyte, the latter is in a crystallized solid state. For charging, the capacitor is transferred to the range of operating states by heating an external heat source to the electrolyte melt temperature, for example, T = 120 ° C for the electrolyte of the eutectic composition LiNO ₃ -KNO ₃ -NaNO ₃ . In this case, the mobility of electrolyte ions increases, the resistance to ion current drops to values below 10-3 Ohm · cm, ensuring the flow of charge / discharge currents. The capacitor is charged when voltage is applied from an external source to the terminals of current terminals 5. In this case, a double electric layer is formed at the boundary of the contact surface of the molten electrolyte 9 and nanocarbon particle 8, providing charge accumulation. The charge energy of the capacitor is used when discharging to an external loading device while maintaining the temperature of the electrolyte melt. To preserve the charge stored during charging of the capacitor for a long time, in order to reduce self-discharge currents, the capacitor temperature can be reduced and maintained during storage time below the crystallization temperature of the electrolyte. If it is necessary to discharge a charged capacitor with electrolyte crystallized during storage, the temperature rises above the melting point of the electrolyte. In this case, the capacitor switches to the state of discharge / charge readiness.

In contrast to the prototype, the inventive electrochemical capacitor implements improved specific characteristics (specific energy consumption, energy density, current density, specific power, specific charge, voltage) compared to electrochemical capacitors described in / 1, 3 /, or chemical current sources operating on reversible redox chemical reactions at close cost of materials. Thus, the task is solved to create an electrochemical capacitor that implements specific characteristics acceptable for practice, ensuring the technical and economic feasibility of its use.

Examples confirming the possibility of implementing the claimed design of a nanocomposite electrochemical capacitor.

Example 1

Capacitor cell made of nanocarbon material obtained by pyrolysis of methane on an MgO catalyst at T = 900 ° C, with a specific surface area measured by the BET method S _beats . - 1500 m ² / g. The electrodes are formed in the form of a flat tablet with a diameter of 50 mm, a thickness of 2 mm by pressing a mixture of the specified NUM and a mixture of inorganic salts KNO ₃ -NaNO _{3 of} eutectic composition (50% -50%, mol.), Melted at T _pl. = 220 ° C with a pressure of 200 kg / cm ² . The electrodes were placed in frames in the form of two flat cylindrical washers with recesses made of an electrically conductive composite carbon material serving as current collectors. The electrodes were brought into contact with a separator of 0.5 mm thick chrysolite asbestos, made in the form of a disk with a diameter of 60 mm. The assembly was compressed by a force of 100 kg / cm ² , heated to T = 230 ° C, and a cyclic current – voltage characteristic was recorded. At a scanning speed of 10 mV / s, the specific capacitance (by weight of nanocarbon material) capacitance C _{beats was} obtained _. = 3.3 f / g (Figure 5).

Example 2

Capacitor cell made of nanocarbon material obtained by pyrolysis of benzene on a Fe catalyst (ferrocene) at T = 850 ° C, with a specific surface area measured by the BET method equal to S _beats. = 67 m ² / g. Nanocarbon material was mixed with inorganic salts LiNO ₃ -KNO ₃ -NaNO _{3 of} eutectic composition (30% -53% -17%, mol.), Melted at T _pl. = 120 ° С, the capacitor cell was formed in the form of a disk with a diameter of 40 mm by pressing a three-layer electrode-separator-electrode structure. The separator was a track membrane made of PET with a thickness of 23 μm and a porosity of 12%. The current collectors are made of carbon foil Graflex GF-D with a thickness of 2 mm. The assembly was compressed by a force of 100 kg / cm ² , heated to T = 130 ° C, and a cyclic current – voltage characteristic was recorded. At a scanning speed of 5 mV / s, the values of specific (by mass of nanocarbon material) capacitance C _beats were obtained _. = 6.8 f / g (Fig.6).

Claims (20)

1. Nanocomposite electrochemical capacitor, comprising at least two electrodes, an electrolyte, separators and current collectors placed in a thermostatically controlled volume, in which each electrode and electrolyte pair is a nanocomposite made of a nanocarbon material and a solid ionic organic or inorganic eutectic compound composition, wherein the electrodes are made of the nanocarbon material with a specific surface area above 1300 m ² / g in the form of plates or sheets of a thickness of 0.1 ... 10 mm and a density of 0.8 ... 1.2 g / ^m3. 2. The capacitor according to claim 1, characterized in that the electrolyte in working condition is a melt of an inorganic or organic salt or a mixture of inorganic and organic salts. 3. The capacitor according to claim 1, characterized in that the electrolyte in working condition is a eutectic melt of inorganic salts, organic salts or a mixture of inorganic and organic salts. 4. The capacitor according to claim 1, characterized in that the electrolyte in working condition is a mixture of alkali and alkaline earth metal chlorides. 5. The capacitor according to claim 1, characterized in that the electrolyte in working condition is a mixture of alkali and alkaline earth metal borofluorides with an ionic liquid based on imidazole derivatives borofluoride. 6. The capacitor according to claim 1, characterized in that the separator is a track membrane with a pore density of 10 ⁷ -10 ⁹ pores / cm ² and the pores are cylindrical or conical in shape. 7. The capacitor according to claim 1, characterized in that the separator is a solid electrolyte. 8. A method of manufacturing a nanocomposite electrochemical capacitor according to paragraph 1, comprising preparing electrode mixtures for the anode and cathode, consisting of nanocarbon materials; dispersing the prepared electrode mixture with a binder; pressing plates or sheets of electrode mixture dispersed with a binder; annealing pressed plates or sheets of electrode mixture dispersed with a binder in an oxidizing and / or reducing atmosphere or under vacuum; impregnation of compacted electrodes in a melt or electrolyte solution at high temperature and under vacuum; cooling electrolyte-impregnated compacted electrodes under vacuum to solidify the electrolyte; connection of compacted electrodes impregnated with electrolyte with a separator and current collectors. 9. The method according to claim 8, characterized in that for the preparation of the electrode mixture using nanocarbon material made by pyrolysis of a mixture of liquid and / or gaseous hydrocarbon and hydrogen, having a specific surface area of more than 1300 m ² / g, conductivity 10 S / cm and more. 10. The method according to claim 9, characterized in that during the pyrolysis of a mixture of gaseous hydrocarbon and hydrogen, the temperature is maintained in the range of 850-900 ° C, the pressure in the range of 0.1-1.0 MPa, cobalt-based compounds are used as catalyst and molybdenum, natural gas or propane or butane or ethylene is used as the gaseous hydrocarbon. 11. The method according to claim 9, characterized in that after the manufacture of nanocarbon material it is subjected to treatment with an acid or alkaline solution. 12. The method according to claim 8, characterized in that the electrode mixture is pressed into plates at pressures of 5-10 MPa and at a temperature of 150-350 ° C with or without the addition of a binder. 13. The method according to claim 8, characterized in that the plates of compacted nanocarbon material are annealed in an oxidizing and / or reducing atmosphere or under vacuum at a temperature of 350 ... 500 ° C for 1 ... 5 hours. 14. The method according to claim 8, characterized in that the annealed plates of compacted nanocarbon material are impregnated in the electrolyte melt at a temperature of 50 ° C above the melting temperature of this electrolyte under vacuum for 1 ... 5 hours. 15. The method according to claim 8, characterized in that the electrolyte in the form of an anhydrous salt or a mixture of salts is introduced into the electrode mixture before pressing by mixing in a predetermined proportion, grinding, heating to the melting temperature of the electrolyte, the operation being carried out in an inert gas atmosphere, and to fill the pores of the nanocarbon material, evacuation is carried out. 16. The method according to claim 8, characterized in that the electrolyte is introduced into the electrode mixture before pressing by impregnation of the electrode mixture in a saturated aqueous solution of electrolyte salts, followed by drying and dehydration of the electrode mixture under vacuum at a temperature of 150-250 ° C for 1 ... 5 hours. 17. The method according to claim 8, characterized in that a surfactant, for example sodium dodecyl sulfate, is introduced into the electrode mixture. 18. The method according to claim 8, characterized in that the compacted electrode, containing in its composition an electrolyte in the solid state, is connected mechanically with a separator and current collectors in an inert atmosphere. 19. The method according to claim 8, characterized in that after connecting a compacted electrode containing a solid electrolyte connected to a separator and current collectors, this structure is heated in an inert atmosphere to the melting temperature of the electrolyte under the influence of a static or variable mechanical load. 20. The method according to claim 8, characterized in that after the electrolyte is melted inside a compacted electrode connected to a separator and current collectors, this electrochemical system is polarized with small currents at voltages not exceeding 10% of the electrolyte decomposition voltage in this electrochemical system.

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