DE19948742C1 - Electrochemical capacitor used e.g. in telecommunications consists of single cell(s) with electrodes formed of an electrically conducting or semiconducting nano-structured film - Google Patents

Abstract

Electrochemical capacitor consists of a single cell or a stack of single cells. Each cell comprises an electrode (8), a counter electrode (9) and an electrolyte (6) that moistens the electrodes. The electrodes are formed of an electrically conducting or semiconducting nano-structured film. Nano-structured discrete needle-like elements are anchored to one surface.

Description

The invention relates to an electrochemical capacitor according to the preamble of claim 1.

Electrochemical capacitors, also known in the literature as double-layer capacitors called gates or supercapacitors are electrochemical energy stores, which are compared to batteries due to a significantly higher power density conventional capacitors through an order of magnitude higher energy mark density. They are based on the potential-controlled training of Helmholtz double layers and / or electrochemical redox reactions higher Charge capacity and reversibility on electrically conductive electrode surfaces in suitable electrolytes. Priority potential areas of application with special For example, economic importance lies in the areas of electrical traction (Motor vehicles) and telecommunications. This can be done by intercepting Peak power reduces the nominal power of the primary energy source, which is life Duration and range extended and thus the profitability of the overall system be significantly improved.

For the production of the supercapacitor electrodes, they have to be activated carbon material-based material concepts, which in combination with organic electrolytes currently the largest in terms of performance data and costs Market potential is attributed. The first products in small series exist stadium, the energy densities of about 3 Wh / kg reach z. B. WO 98/15962 A1. Of there are also a number of concepts for the production of these activated carbons fabric supercapacitors or their electrodes, e.g. B. EP 0 712 143 A2, DE 197 24 712 A1. Typically, a maximum of 50 to 100 farads can be used here Achieve capacity per gram of active electrode material. With a super  capacitor itself currently accounts for approx. 25 percent by mass of the actual Electrodes and approx. 75 percent by mass on housing components, current collectors and Electrolyte. For use as a peak load storage is however with these elements the ratio of useful energy and storage weight is often still too small to be in to use real applications economically sensible. The optimization of the performance data can thus both via the stack design (several electrically in Series connected single cells stacked on top of each other) as well as over the actual ones Capacitor electrodes (surface structures and materials) are made.

Activated carbon materials have an extremely high porous surface, but that Distribution of pore sizes is very wide and extends down to the Range ≈ 1 nm. Since typical Helmholtz layer thicknesses are up to 5 nm, the Helmholtz storage layer cannot completely with this electrode material be formed on the surface actually present.

The typically rather sponge-like geometry of activated carbon materials works also adversely affect the frequency behavior of the capacitance. Because for the electrolyte it is synonymous with relatively long and narrow paths and therefore inevitably linked to a relatively high ohmic internal resistance. Due to the high capacities connected in series, this leads to a Lowering the cut-off frequency of the entire component, d. H. already at moderate Frequencies (typically around 1 Hz) are only fractions of those with direct voltage available electrode capacity. This limits the practical Use of supercapacitors with such electrodes continues.

It is also known from activated carbon electrodes that due to high transition resistance to metals such as aluminum a low-resistance contact of the active Electrode material difficult and with increased effort (in terms of mass or Volume, and thus also costs). In addition, the i. d. R existing granular internal structure of the electrode material - also through Contact resistance - for an increased internal resistance of the active electrode self.  

In addition to the negative impact on frequency behavior already described The relatively high ohmic resistance also causes dissipative losses caused by the accompanying thermal stress on the component and its possible uses restrict even further or with appropriate design measures (Cooling plates etc.) the usable mass and volume-related energy storage drastically reduce density.

The present invention is therefore based on the object of a supercon capacitor with improved performance data compared to the known capacitors to create its electrode geometry and electrode material at the same time allow significantly improved stack design.

This object is achieved with the subject matter of claim 1. Beneficial Embodiments of the invention are the subject of dependent claims.

According to the invention, the electrodes are made of an electrically conductive or semi-lead tendency, nanostructured film formed in the nanostructured discrete, needle shaped elements are anchored electrically conductive on a surface.

Nanostructured element in the sense of the present invention denotes a material structure with dimensions of at least one structural dimension in Nanometer range (<1 µm).

The electrodes according to the invention produce a large effective surface for forming the Helmholtz storage layer. Their size on a flat metallic surface is typically about 40 μF / cm ² in the aqueous electrolyte. The areal density of the nanostructured elements is preferably in the range of 1-500 per µm ² , the diameter of which is preferably in the range of 15-500 nm. B. the necessary material stability is guaranteed for metallic structures. In advantageous embodiments, the aspect ratio (ratio between height and average diameter) of the nanostructured needle-shaped elements is greater than 20.

In contrast to the known sponge-like electrode structures, the Discrete - preferably regular - arrangement of the nanostructure according to the invention elements also made training faster and more complete of the Helmholtz layers on the existing surface and thus a clear one Improvement in performance characteristics.

Furthermore, the electrode structure according to the invention in shape laterally arranged nanostructured elements the thermal losses in charging and Discharge processes are reduced and thus the area of application of the supercapacitors also extended for higher frequency applications (<1 Hz). A good electrically conductive (e.g. metallic) carrier foil and thereon a good electrically conductive contact (e.g. metallic) nanostructured elements, in particular made of the same material, minimize the material and contact resistance significantly. This will go beyond that supported by the use of single-crystalline nanostructured elements, as in suitable growth processes (e.g. electrochemical deposition) can be.

With knowledge of the geometry parameters of the nanostructured elements (diam water, aspect ratio and areal density) can be the effective surface of a single electrode directly. It has been shown that in the manufacture of the Electrode by electrochemical growth using a suitable choice of Concentration also elements with additional inner spongy porosity as well as hollow cylindrical elements (tubes) can be formed. Thereby can further increase the effective surface area by at least one A factor of two and thus an increase in the Helmholtz capacity can be achieved.

Some metal oxides (e.g. RuO ₂ ) or conductive polymers allow energy storage in suitable electrolytes through redox reactions that occur on the surface. The reloading of such redox systems on the electrode surface leads to the formation of the Helmholtz double layer and an additional electrode capacity (pseudo capacity). This property can be achieved in the electrodes of the present invention either by a thin (<10 nm) coating with a corresponding redox system (for example RuO ₂ ) or by direct formation of the nano-structured elements from precisely this material.

Another advantage of the supercapacitor according to the invention is that nanostructured electrode film using suitable manufacturing processes from belie other semiconducting or conductive materials such as metals, precious metals, Galvanometals (electrodepositable metals), especially nickel or conductive polymers can be generated.

The production of the carrier film and then the growth of the nanostructured Elements can be used in one step when using electrochemical deposition respectively. The thickness of the carrier film is advantageously between 1 and 20 μm put. This is the electrical conductivity, contactability and also mechanical stability for the construction of a supercapacitor single cell or stack guaranteed.

The invention is based on exemplary embodiments with reference to Drawings explained in more detail. Show it:

FIG. 1 shows an inventive super capacitor electrode;

Fig. 2: SEM image of a super-capacitor electrode according to the invention;

Fig. 3: consisting a super capacitor cell according to the invention from a single;

FIG. 4 is a supercapacitor according to the invention, consisting of a stack of several individual cells;

FIG. 5 shows frequency response of the specific capacities of a Helmholtz-fiction, modern super-capacitor electrode of Figure 2 in 1 molar KOH..

Fig. 1 shows an inventive super capacitor electrode made of a self-supporting film 2 and then anchored nanostructured discrete elements 1, which are needle-shaped. Discrete in the sense of the present invention means that there are separate elements with their own structure, that is, not elements that are connected to one another, as is the case, for example, with B. is the case with a sponge-like structure.

Fig. 2 shows the SEM image of a supercapacitor electrode according to the invention made of a self-supporting nickel foil 4 and anchored thereon nanostructured elements 3 made of nickel. The nanostructured needle-shaped elements 3 are oriented essentially perpendicular to the surface of the film 4 in this embodiment and are evenly distributed over the surface of the film 4 .

Fig. 3 shows a supercapacitor according to the invention. In this embodiment, it consists of a single cell, which comprises the electrodes 8 , 9 , a spacer 5 , and a liquid electrolyte 6 , which wets the electrodes and the spacer. According to the invention, the electrodes are designed in the form of nanostructured thin-film electrodes. The spacer 5 prevents mechanical contact between the electrodes 8 , 9 and is permeable to the electrolyte. He is z. B. porous. Reference number 7 designates the external contacting of the supercapacitor. If a solid electrolyte is used instead of a liquid electrolyte, the spacer 5 is omitted.

To construct the cell, two electrodes 8 , 9 according to the invention are pressed onto the porous spacer 5 , the nanostructured sides of the two electrodes 8 , 9 facing each other. The electrodes are contacted on their unstructured side, the entire system is filled with the electrolyte 6 and enclosed in a suitable housing and sealed.

Fig. 4 shows a supercapacitor according to the invention, which in this embodiment consists of a plurality of n individual cells which are arranged next to one another or one above the other in the manner of a stack.

To build up the stack, the individual cells are stacked on top of one another and attached presses. A series connection is thus created over the conductive electrode films individual capacitor elements without additional contacting steps. The contact  stacking, filling with electrolyte and packaging in a housing analogous to the single cell.

Fig. 5 is a diagram for frequency response of the Helmholtz shows specific capacity (broken line: by mass; solid line: by volume) according to the invention a supercapacitor electrode. KOH was used as the electrolyte.

As can be seen from this, the capacity decreases with frequency Impact compared to the DC voltage value (0 Hz) only slowly and remains at higher frequencies, e.g. B. 100 Hz largely preserved.

In general, the electrodes according to the invention advantageously have a DC voltage value of the specific Helmholtz capacitance of more than 10 F / g or more than 10 F / cm ³ , particularly advantageously more than 50 F / g or more than 50 F / cm ³ .

At a frequency of 100 Hz, the electrodes according to the invention advantageously have a value of the specific Helmholtz capacitance of more than 1 F / g or more than 1 F / cm ³ , particularly advantageously more than 5 F / g or more than 5 F / cm ³ .

The following example shows the manufacture of an electrode according to the invention described on a laboratory scale. In principle, on an industrial scale similar methods are used.

example

The anodic oxidation of an aluminum substrate creates a nanoporous oxide film with parallel, continuously cylindrical pores oriented perpendicular to the substrate surface. The pore diameter can be set in the range of 15-500 nm, the surface density of the pores from approx. 1 to 500 per µm ² , and the pore length up to 100 µm. The oxide film is detached from the aluminum substrate, so that a ceramic nanoporous filter membrane is created. This membrane is vapor-coated on one side with a metallic film as a contact electrode. The film thickness is selected so that the oxide pores are closed. To produce nanostructured nickel elements on a nickel film, the vapor-deposited membrane is contacted and placed in a galvanic nickel bath. In the case of galvanic deposition, on the one hand the oxide pores are filled with the desired nanostructured elements from the vapor-deposited base electrode, and on the other hand the base electrode is thickened to a metallic film in the micrometer range. The oxide ceramic can then be selectively pickled using wet chemistry, so that the desired electrode film with conductively bonded nanostructured nickel elements is produced.

Claims (18)

1. Electrochemical capacitor from a single cell or a stack of single cells, each individual cell comprising an electrode ( 8 ), a counter electrode ( 9 ) and an electrolyte ( 6 ) wetting the electrodes ( 8 , 9 ), characterized in that the electrodes ( 8 , 9 ) are formed from an electrically conductive or semiconducting, nanostructured film, in which nano-structured discrete, needle-shaped elements ( 1 , 3 ) are anchored electrically conductive on a surface. 2. Electrochemical capacitor according to claim 1, characterized in that the areal density of the nanostructured elements is between 1 and 500 per µm ² . 3. Electrochemical capacitor according to one of the preceding claims, characterized in that the nanostructured elements ( 1 , 3 ) and the surface on which the nanostructured elements ( 1 , 3 ) are anchored consist of the same material. 4. Electrochemical capacitor according to claim 1, 2 or 3, characterized in that the surface on which the nanostructured elements are anchored is the surface of a self-supporting film ( 2 , 4 ). 5. Electrochemical capacitor claim 4, characterized in that the film ( 2 , 4 ) has a thickness between 1 and 20 microns. 6. Electrochemical capacitor according to one of the preceding claims, characterized in that the nanostructured elements ( 1 , 3 ) have an aspect ratio greater than 20. 7. Electrochemical capacitor according to one of the preceding claims, characterized in that the nanostructured elements ( 1 , 3 ) have a diameter between 15 and 500 nm. 8. Electrochemical capacitor according to one of the preceding claims, characterized in that the nanostructured elements ( 1 , 3 ) are mono-crystalline. 9. Electrochemical capacitor according to one of the preceding claims, characterized in that the nanostructured elements ( 1 , 3 ) have a hollow cylindrical structure. 10. Electrochemical capacitor according to one of the preceding claims, characterized in that the nanostructured elements ( 1 , 3 ) have an internal porosity. 11. Electrochemical capacitor according to one of the preceding claims, characterized in that the nanostructured elements ( 1 , 3 ) are coated with a redox material or consist entirely of this material. 12. Electrochemical capacitor according to one of the preceding claims, characterized in that the nanostructured elements ( 1 , 3 ) and / or the surface on which the nanostructured elements are anchored, made of a metal, a galvanometal z. B. nickel, a noble metal or a conductive polymer. 13. Electrochemical capacitor according to one of the preceding claims, characterized in that the electrodes ( 8 , 9 ) at 0 Hz have a specific Helmholtz capacitance of more than 10 F / g, in particular more than 50 F / g. 14. Electrochemical capacitor according to one of the preceding claims, characterized in that the electrodes ( 8 , 9 ) have a specific Helmholtz capacitance of more than 10 F / cm ³ , in particular more than 50 F / cm ³ , at 0 Hz. 15. Electrochemical capacitor according to one of the preceding claims, characterized in that the electrodes ( 8 , 9 ) at 100 Hz have a specific Helmholtz capacitance of more than 1 F / g, in particular more than 5 F / g. 16. Electrochemical capacitor according to one of the preceding claims, characterized in that the electrodes ( 8 , 9 ) at 100 Hz have a specific Helmholtz capacitance of more than 1 F / cm ³ , in particular more than 5 F / cm ³ . 17. Electrochemical capacitor according to one of the preceding claims, characterized in that the nanostructured elements ( 1 , 3 ) are oriented substantially perpendicular to the surface. 18. Electrochemical capacitor according to one of the preceding claims, characterized in that the electrolyte ( 6 ) is a liquid electrolyte or a solid electrolyte.