RU2528010C2 - Solid-state multi-component oxide-based supercapacitor - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: present invention relates to electrical engineering and specifically to solid-state multi-component oxide-based supercapacitors. The technical result of the invention is higher capacitance and density of stored energy and reduced leakage current of the capacitor. The supercapacitor has two electrodes and a dielectric layer in between, wherein the lower electrode is made of material with a larger specific surface area, the dielectric layer is conformally and uniformly placed on the lower electrode, the upper electrode is conformally and uniformly placed on the dielectric layer and is made of zinc oxide doped with aluminium, wherein the dielectric layer is made of a multi-component oxide containing a mixture of at least two oxides selected from TiO₂, HfO₃, ZrO₂, Al₂O₃, Ta₂O₅, Nb₂O₅, Y₂O₃ and lanthanide oxides, and is such that the relative permittivity of the active dielectric layer is in the range of 10-30.

EFFECT: disclosed solid-state capacitor can be used in electric cars where they can be mounted on the internal surface of the car body and can be an ideal power source in emergency situations.

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Description

The invention relates to the field of solid-state micro- and nanoelectronics based on promising materials, namely to solid-state two-layer supercapacitors, and can be used as devices for storing energy and power supply for a variety of high-power consumers, which are subject to stringent requirements for environmental cleanliness, cyclic resource and readiness for work, for example in electric vehicles, solar panels, satellites.

At present, supercapacitors, or, as they are commonly called, ionistors, which store hundreds of times more energy than traditional capacitive elements, open up great prospects in the field of energy conservation, and do this for a long time without charge leakage.

Supercapacitors are electric capacitors that are characterized by large capacitance with respect to dimensions, extremely low level of series resistance and ultra-low leakage current, which makes them very promising for use in power networks, electric vehicles and electronic equipment.

Supercapacitors belong to devices in which the accumulation of electrical energy occurs due to the charge of the double electric layer. This layer is formed by the surface of the conductor and the layer of electrolyte ions adjacent to it. Due to the fact that the distance between the charged surface of the capacitor plate and the ion layer is very small (measured by angstroms), and the specific surface area of the plate reaches values from 1000 to 2000 m ² / g, the capacity of such a capacitor weighing 1 g can theoretically be from 100 to 500 F. .

However, the values of specific capacity obtained in practice are units and tens of f / g. The reasons for the decrease in capacity compared with theoretically predicted values are that the ions of organic electrolytes, which are widely used in the production of supercapacitors, hardly penetrate the pores of carbon. Currently commercially available supercapacitors made using porous carbon materials have an energy density in the range of 4 to 5 W · h / kg and a power density in the range of 1 to 2 kW / kg [1].

The discovery of carbon nanotubes in 1991 gave a new impetus to the development of supercapacitors, with which it became possible to obtain electrodes with a huge specific surface area. In addition, carbon nanotubes are highly conductive and have a sufficient distance between individual nanotubes (tens of nm) for the penetration of organic electrolyte ions. Therefore, despite the relatively smaller specific surface area of carbon nanotubes (about 1315 m ² / g [2] and about 400 m ² / g [3] for single-walled and multi-walled carbon nanotubes, respectively), their actual specific surface area exceeds the specific surface area of the porous carbon.

The high capacitance of carbon nanotube-based capacitors has been used to improve the power densities and energy of supercapacitors. Thus, the well-known supercapacitor based on electrodes of single-walled carbon nanotubes and KOH electrolyte showed a power density of approximately 20 kW / kg and a maximum energy density of about 10 Wh / kg, and a supercapacitor based on electrodes of multi-walled carbon nanotubes, respectively, a power density of more than 8 kW / kg and the maximum energy density of the order of 1 W · h / kg [3].

Recently, vertical carbon nanotubes have been investigated for applications in supercapacitors. It was shown that such carbon nanotubes have a number of advantages compared to non-oriented carbon nanotubes [4]. In particular, vertically oriented carbon nanotubes have the largest effective surface area, due to the fact that the distance between separate nanotubes in the electrode is of the order of several tens of nm, which means that electrolyte ions have free access to the electrode surface [5].

Thus, carbon nanotubes along with conventional porous carbon materials can be used to improve the properties of capacitive elements.

Along with the obvious advantages of supercapacitors, such as high energy ability and the ability to store a charge for a long time, there are a number of no less obvious disadvantages.

One of them is the fact that energy can be released in these devices only at strictly limited discharge speeds, that is, at low frequencies. Thus, the operating frequency of commercially available supercapacitors is from 1 to 10 Hz, which corresponds to a charge / discharge time in the range from 0.1 to 1 s and, in rare cases, approaches 100 Hz [2]. Such a narrow window of the operating frequencies of supercapacitors limits the scope of application of devices based on them.

The second obvious drawback of supercapacitors is the presence of an electrolyte in their structure. The presence of liquid electrolyte limits the range of possible application of supercapacitors. In this regard, classical solid-state capacitive devices (traditional electric capacitors) are still widely used, despite the much lower density of the stored energy compared to ionistors. And finally, the third drawback of supercapacitors is the limited operating voltage of these devices. Commercially available supercapacitors operate at a voltage in the range from 2.3 to 2.7 V. This is due to the fact that at high values of the operating voltage, electrolysis of the electrolyte occurs on the electrodes of the device, and, therefore, irreversible degradation of the device.

The closest device adopted for the prototype is a solid-state supercapacitor, in which Al ₂ O ₃ was used as a dielectric layer in a wide range of thicknesses [6]. In [6], the idea was proposed of creating a solid-state supercapacitor capable of eliminating the shortcomings of the above-described supercapacitors, while preserving the advantages of commercially available supercapacitors. The use of materials with a high specific surface density, namely, carbon nanotubes and porous carbon, as an electrode of this device allows one to obtain stored energy densities that are many times higher than traditional solid-state capacitive elements (from 1 to 10 Wh / kg), and the rejection of electrolyte in favor of the solid-state dielectric layer, it extends the operating frequency range by several orders of magnitude and increases the operating voltage of the device. In addition, a device based on solid materials exhibits stability in a wide range of environmental conditions, increasing the versatility of its application.

This device consists of two electrodes separated by a thin (about 10 nm) dielectric layer obtained by atomic layer deposition, and materials with a very developed surface, such as porous carbon and carbon nanotubes, are used as the lower electrode.

The dielectric layer has a number of requirements to ensure the operability of the device. In particular, the linear dependence of the capacitance, and hence the density of the energy stored by the device, on the dielectric constant of the coating makes it necessary to use a dielectric with a high dielectric constant (high-k dielectric). In addition, to ensure long-term storage of the charge, it is necessary to create a dielectric layer with low leakage currents (less than 1 · 10 ^-3 A / cm ² ).

The main disadvantage of the developed device is the relatively low density of stored energy (from 0.05 to 0.5 W · h / kg), which is associated with insufficient dielectric constant of Al ₂ O ₃ (about 9). In this work, it was also proposed to use a number of metal oxides, namely HfO ₂ and TiO _2, as the dielectric layer. In this case, the theoretically predicted density of stored energy is from 7 to 10 W · h / kg and from 11 to 15 W · h / kg for HfO ₂ and TiO _2, respectively, due to the higher dielectric constant of these oxides compared to Al ₂ O ₃ . Despite the fact that the predicted characteristics are satisfactory for this class of devices, TiO _{2 is} characterized by fairly high leakage currents (of the order of 0.07 A / cm ² ), which may limit its implementation.

According to the applicant, to eliminate the above disadvantages of the prototype in the form of a low density of stored energy and high leakage currents, it is possible if the supercapacitor uses dielectric materials with a high dielectric constant from the class of multicomponent oxides containing a mixture of at least two oxides from the TiO ₂ series as a material of the dielectric layer , HfO ₂ , ZrO ₂ , Al ₂ O ₃ , Ta ₂ O ₅ , Nb ₂ O ₅ , Y ₂ O ₃ , and oxides of elements from the lanthanide group. These multicomponent oxides can be obtained by atomic layer deposition, and the ability to vary the deposition parameters, as well as the mass ratio of the components of multicomponent oxides, allows you to flexibly control their dielectric constant, and, as a result, increase the capacity and density of the stored energy and reduce the leakage currents of solid-state supercapacitor compared with those shown in [6].

The objective of the invention is to increase the capacitance and density of the stored energy of a solid-state supercapacitor and reduce leakage currents, which, in turn, will provide a wider range of operating frequencies and voltages compared to traditional supercapacitors.

The solution of the technical problem is achieved by the fact that in a solid-state supercapacitor containing two electrodes and a dielectric layer placed between them, in which the lower electrode is made of material with a large specific surface area, the dielectric layer is conformally and uniformly located on the lower electrode, the upper electrode is conformally and uniformly located on the dielectric layer and made of zinc oxide doped with aluminum, the material of the dielectric layer is a multicomponent oxide containing mixture of at least two oxides from the series TiO ₂ , HfO ₂ , ZrO ₂ , Al ₂ O ₃ , Ta ₂ O ₅ , Nb ₂ O ₅ , Y ₂ O ₃ , (lantanoid) ₂ O ₃ , the material of the dielectric layer having dielectric constant of the layer in the range of 10-30. In a solid-state supercapacitor, the lower electrode may be made of a material in the form of carbon nanotubes or of a material in the form of porous carbon.

The invention is illustrated by drawings, where figure 1 presents a diagram of a solid-state supercapacitor based on multicomponent oxides;

figure 2 presents a comparative table of the parameters of the prototype and the proposed solid-state supercapacitor;

figure 3 presents a comparative table of experimental data.

The solid-state supercapacitor (figure 1) consists of two conductive electrodes - the lower 2 and the upper 3, and the dielectric layer 1 placed between them. The electrodes 2 and 3 are connected to the corresponding ohmic contacts 4 and 5. The voltage source 6 is connected to the ohmic contacts 5 and 4 . In addition, a current meter and capacitance meter 7 are connected to the circuit.

The lower conductive electrode 2 is a material with a large specific surface area, which may include single-walled and multi-walled carbon nanotubes or porous carbon.

The dielectric layer 1 is conformally and uniformly located on the lower conductive electrode 2. A conformal and uniform arrangement means that the disposable material precisely follows the surface shape of the object on which it is applied. This property is necessary to increase the effective surface area of the solid-state supercapacitor on which charge accumulation occurs, and also to reduce the likelihood of defects that can lead to increased leakage currents and breakdown of the dielectric layer.

The upper conductive electrode 3 conformally and uniformly located on the dielectric layer 1 and is a zinc oxide doped with aluminum. The use of the upper conductive electrode of just such a composition is due to the possibility of its conformal deposition on a surface with a developed relief.

A conformal and uniform arrangement of the dielectric layer 1 on the lower electrode 2, as well as a conformal and uniform arrangement of the upper electrode 3 on the dielectric layer 1, is achieved using the atomic layer deposition method.

The device operates as follows.

When a solid-state supercapacitor is connected to the power circuit under the influence of electric current, electrodes 2 and 3 accumulate charge. This charge has a certain value and depends on the surface area of the electrodes, as well as the thickness and permittivity of the dielectric layer 1. Due to the fact that carbon nanotubes or porous carbon having a high specific surface area are used as one of the electrodes in a solid-state supercapacitor, dielectric layer 1 is a material with high dielectric constant based on multicomponent oxides, and the thickness of the dielectric layer 1 obtained by atomic o-layer deposition, is only a few tens of nanometers, a large charge is accumulated. When the power source is disconnected and the load is connected, the charge is redistributed or the solid-state supercapacitor is discharged.

Solid state supercapacitor implementation examples.

Example 1. To implement a solid-state supercapacitor, we used a series consisting of three samples, which are substrates of 1 cm × 1 cm multi-walled carbon nanotubes, obtained by the method of [7] on aluminum foil. Carbon nanotubes underwent preliminary surface modification in an N ₂ O discharge plasma at a temperature of 40 ° C and a discharge power of 100 W to form active deposition centers, without which further synthesis of the dielectric coating by atomic layer deposition would not have been possible.

Then, a dielectric layer was deposited onto the obtained sample by atomic layer deposition. In this case, titanium dioxide TiO ₂ with a thickness of 20 nm was deposited on the first three samples. The film was deposited at a temperature of the reaction chamber of 300 ° C using pulses of Ti (OC ₂ H ₅ ) ₄ -H ₂ O. The total number of cycles was 500. The next three samples were coated with multicomponent Al _0.85 Ti _0.15 O _x oxide of the same thickness. An Al _0.85 Ti _0.15 O _x film was deposited at a reaction chamber temperature of 300 ° C with alternating reaction cycles: 2 Al (CH ₃ ) ₃ -H ₂ O cycles and 1 Ti (OC ₂ H ₅ ) ₄ -H ₂ O cycle. Total cycles amounted to 270. Next, the next three samples were applied alumina Al ₂ O ₃ the same thickness. The film was deposited at a temperature of the reaction chamber of 300 ° C using Al (CH ₃ ) ₃ -H ₂ O pulses. The total number of cycles was 200.

Further, by the method of atomic layer deposition in the same reaction chamber, a ZnO film doped with Al particles 20 nm thick was deposited on each sample. The ZnO-Al film was deposited at a temperature of the reaction chamber of 180 ° C with alternating reaction cycles: 1 cycle of Al (CH ₃ ) ₃ -H ₂ O and 24 cycles of Zn (C ₂ H ₅ ) ₂ -H ₂ O. The total number of cycles was 100 .

In order for the upper and lower electrodes to be electrically isolated from each other, the edges of each sample were treated with a solution of 1 M HCl. Next, each prototype was prepared for electrophysical measurements. To do this, an indium gallium eutectic was deposited on the lower electrode (Al), and the upper ohmic contact was formed by electron beam evaporation of Al.

The upper and lower electrodes were connected to a measuring device consisting of an EPS 1000 probe station and an Agilent E 49080 A LCR meter. Measurement of current-voltage current-voltage-voltage characteristics in the voltage range [-6 V ... 6 V], as well as removing the frequency dependence device capacities in the frequency range 10 Hz - 100 kHz was carried out using the standard control program of the device.

For a solid-state capacitor using the first sample with a dielectric layer of TiO ₂ , despite the theoretically high value of the dielectric constant (about 40), unsatisfactory characteristics were obtained, namely high leakage currents (about 4 · 10 ^-2 A / cm ² ) and a breakdown voltage of less than 1 V. In this regard, a capacitance value close to zero was observed, which means that the deliberately underestimated values of the dielectric constant and the density of stored energy were observed. Since the obtained results do not satisfy the declared value, the operating frequency range of the device was not evaluated.

For a solid-state capacitor using a sample with multicomponent Al _0.85 Ti _0.15 O _x oxide as the dielectric layer, the following characteristics were obtained: relative permittivity of about 13, leakage current below the maximum measurable value (less than 3 · 10 ^-6 A / cm ² ), the breakdown voltage of the dielectric layer is more than 6 V, the specific capacitance is about 1.8 F / g at an operating frequency from 10 Hz to 100 G, and with a further increase in the operating frequency from 100 Hz to 100 kHz, the sample capacitance did not fall below 25% of the initial value and I. The density of the stored energy was 9.1 W · h / kg.

For a solid-state supercapacitor using a sample with a single-component oxide Al ₂ O ₃ , a small value of the dielectric constant was shown (about 8), and the value of the stored energy density is about 1.5 Wh / kg, i.e. below the required value. Since the obtained results do not satisfy the declared value, the operating frequency range of the device was not evaluated

These results indicate that the use of multicomponent Al _0.85 Ti _0.15 O _x oxide as the dielectric layer of a solid-state supercapacitor allows one to obtain large values of the stored energy and also provides energy storage in a wide range of frequencies and voltages. At the same time, the use of single-component oxides Al ₂ O ₃ and TiO ₂ does not meet the stated requirements for the device.

Example 2. The second example of the implementation of a solid-state supercapacitor is technically similar to the first. The difference is that single-component oxides Ta ₂ O ₅ and a multicomponent oxide Ta _0.75 Ti _0.25 O _x 20 nm thick were used as the dielectric layer of the solid-state capacitor.

For the first solid-state capacitor using a sample with a dielectric layer of Ta ₂ O ₅ , despite the theoretically high value of the dielectric constant (about 25), unsatisfactory characteristics were obtained, namely high leakage currents (9 · 10 ^-3 A / cm ² ), which are not allow the device to accumulate a charge, as well as a low level of breakdown voltage of the order of 2.5 V. In this regard, a capacitance value close to zero was observed, which means that the deliberately underestimated values of the dielectric constant and density of the stored energy are observed. Since the obtained results do not satisfy the declared values, the operating frequency range of the device was not evaluated.

For a solid-state capacitor using a sample with multicomponent oxide Ta _0.75 Ti _0.25 O _x as the dielectric layer, the following characteristics were obtained: relative permittivity of about 28, leakage current below the maximum measurable value (less than 3 · 10 ^-6 A / cm ² ), the breakdown voltage of the dielectric layer is more than 6 V, the specific capacitance is about 4 F / g at an operating frequency of 10 Hz to 100 G, and with a further increase in the operating frequency from 100 Hz to 100 kHz, the sample capacitance did not fall below 23% of the initial significant i. The density of stored energy was 22 W · h / kg.

These results suggest that the use of multicomponent oxide Ta _0.75 Ti _0.25 O _x with a dielectric constant lying in the claimed range as the dielectric layer of a solid-state supercapacitor allows to obtain high values of stored energy, and also provides energy storage in a wide frequency range and stress. At the same time, the use of one-component oxide Ta ₂ O ₃ does not meet the stated requirements for the device.

Example 3. The third example of the implementation of a solid-state supercapacitor is technically similar to the first. The difference is that the single-component HfO ₂ oxide and the multicomponent Hf _0.85 Al _0.15 O _x oxide 20 nm thick were used as the dielectric layer.

For the first solid-state capacitor using a sample with an HfO ₂ dielectric layer, despite the high dielectric constant (about 16), unsatisfactory characteristics were obtained, namely high leakage currents (of the order of 2 · 10 ^-2 A / cm ^-2 ), which do not allow the device to accumulate a charge, as well as a low level of breakdown voltage of about 4 V. In this regard, a capacitance value close to zero was observed, which means deliberately underestimated values of the dielectric constant and density of stored energy. Since the obtained results do not satisfy the declared value, the operating frequency range of the device was not evaluated.

For a solid-state capacitor using a sample with multicomponent oxide Hf _0.85 Al _0.15 O _x as the dielectric layer, the following characteristics were obtained: relative permittivity of about 14, leakage current below the maximum measurable value, dielectric breakdown voltage of more than 6 V, specific capacitance is of the order of 2.2 F / g at an operating frequency from 10 Hz to 80 Hz, and with a further increase in the operating frequency from 80 Hz to 100 kHz, the sample capacitance did not fall below 27% of the initial value. The density of stored energy was 11 W · h / kg.

These results suggest that the use of multicomponent Hf oxide of _0.85 Al _0.15 O _x with a dielectric constant lying in the claimed range as the dielectric layer of a solid-state supercapacitor allows to obtain high values of the stored energy, and also provides energy storage in a wide frequency range and stress. At the same time, the use of one-component oxide HfO ₂ does not meet the stated requirements for the device.

Example 4. The fourth implementation example of a solid-state supercapacitor is technically similar to the first. The difference is that a single-component oxide was used as a dielectric layer, as well as a multicomponent oxide Hf _0.85 Al _0.15 O _x with a thickness of 20 nm.

For a solid-state capacitor using a sample with multicomponent oxide Hf _0.85 Al _0.15 O _x as the dielectric layer, the following characteristics were obtained: relative permittivity of about 25, leakage current below the maximum measurable value, dielectric breakdown voltage of more than 6 V, specific capacitance of the order of 3.2 F / g at an operating frequency from 10 Hz to 100 Hz, and with a further increase in the operating frequency from 100 Hz to 100 kHz, the sample capacitance did not fall below 25% of the initial value. The density of stored energy was 20 W · h / kg.

These results suggest that the use of multicomponent oxide Hf _0.85 Al _0.15 O _x with a permittivity lying in the claimed range from 10 to 30 as the dielectric layer of a solid-state supercapacitor allows to obtain high values of the stored energy and also provides storage energy in a wide range of frequencies and voltages.

Example 5. The fifth example of the implementation of a solid-state supercapacitor is technically similar to the third. The difference is that porous carbon is used as the bottom electrode, not carbon nanotubes.

For a solid-state capacitor using a sample with multicomponent oxide Hf _0.85 Al _0.15 O _x as the dielectric layer, the following characteristics were obtained: relative permittivity of about 25, leakage current below the maximum measurable value, dielectric breakdown voltage of more than 6 V, specific capacitance of the order of 2.7 F / g at an operating frequency from 10 Hz to 100 Hz, and with a further increase in the operating frequency from 100 Hz to 100 kHz, the sample capacitance did not fall below 25% of the initial value. The density of the stored energy was 18 W · h / kg.

These results suggest that for the implementation of a solid-state supercapacitor, it is possible to use both carbon nanotubes and porous carbon as the lower electrode.

Thus, it was shown that a combination of the known features of a solid-state supercapacitor and distinctive features in the form of using materials based on multicomponent oxides as a material of the dielectric layer, providing a high dielectric constant of the dielectric layer, allows to obtain a new technical result, namely, a significant increase in the capacitance and density of the stored energy compared to the prototype, ensuring low leakage currents and the operation of the supercapacitor in the shea rock working voltage range.

Sources

[1] Burke, A. & Arulepp, M. (2001). Recent Developments in Carbon-based Electrochemcial Capacitors: Status of the Technology and Future Prospects, Electrochemical Society Proceedings, 2001-21, pp. 576.

[2] Niu, C .; Sichel, E.K .; Hoch, R .; Moy, D. & Tennent, H. (1997). High power electrochemical capacitors based on carbon nanotube electrodes. Appl. Phys. Lett., 70 (11), 1480-1482.

[3] An, K.H .; Kim, W.S., Park, Y.S .; Moon, J.-M; Bae, D.J .; Lim, S.C .; Lee, Y.S. & Lee, Y.H. (2001). Electrochemical Properties of High-Power Supercapacitors Using Single-Walled Carbon Nanotube Electrodes. Adv. Funct. Mater., 11 (5). 387-392.

[4] Dai, L .; Patil, A .; Gong, X .; Guo, Z .; Liu, L .; Liu, Y. & Zhu, D. (2003). Aligned Nanotubes. ChemPhysChem, 4 (11), 1150-1169.

[5] Zilli, D .; Bonelli, P.R. & Cukierman, A.L. (2006). Effect of alignment on adsorption characteristics of self-oriented multi-walled carbon nanotube arrays.

Nanotechnology, 17 (20), 5136-5141.

[6] Cary L. Pint et al. (2011). Three dimensional solid-state supercapacitors from aligned single-walled carbon nanotube array templates. Carbon 49.4890-4897.

[7] Dorfler S .; Meier A .; Althues H .; Dani I .; Kaskel S. (2009). Vertical aligned carbon nanotube deposition on metallic substrates by CVD. ECS Transactions, 25 (8), 1047-1051

Claims (2)

1. A solid state supercapacitor containing two electrodes and a dielectric layer placed between them, the lower electrode being made of a material with a large specific surface area, the dielectric layer is conformally and uniformly located on the lower electrode, the upper electrode is conformally and uniformly located on the dielectric layer and made of Zinc oxide doped with aluminum, characterized in that the material of the dielectric layer is a multicomponent oxide containing a mixture of at least two oxides from a number and TiO ₂ , HfO ₂ , ZrO ₂ , Al ₂ O ₃ , Ta ₂ O ₅ , Nb ₂ O ₅ , Y ₂ O ₃ , (lantanoid) ₂ O ₃ , and the material of the dielectric layer has a dielectric constant of the layer in the range of 10-30 . 2. The solid-state supercapacitor according to claim 1, characterized in that the lower electrode is made of a material in the form of carbon nanotubes or of a material in the form of porous carbon.

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