U.S. patent application number 10/435081 was filed with the patent office on 2003-11-20 for capacitors having a high energy density.
Invention is credited to Kuhling, Klaus, Sterzel, Hans-Josef.
Application Number | 20030214776 10/435081 |
Document ID | / |
Family ID | 29413822 |
Filed Date | 2003-11-20 |
United States Patent
Application |
20030214776 |
Kind Code |
A1 |
Sterzel, Hans-Josef ; et
al. |
November 20, 2003 |
Capacitors having a high energy density
Abstract
Capacitors comprising an inert porous shaped body onto which a
first electrically conductive layer, a second layer of barium
titanate and a further electrically conductive layer have been
applied.
Inventors: |
Sterzel, Hans-Josef;
(Dannstadt-Schauernheim, DE) ; Kuhling, Klaus;
(Mutterstadt, DE) |
Correspondence
Address: |
Herbert B. Keil
KEIL & WEINKAUF
1350 Connecticut Ave., N.W.
Washington
DC
20036
US
|
Family ID: |
29413822 |
Appl. No.: |
10/435081 |
Filed: |
May 12, 2003 |
Current U.S.
Class: |
361/329 |
Current CPC
Class: |
H01G 4/005 20130101;
H01G 4/1227 20130101; H05K 1/162 20130101 |
Class at
Publication: |
361/329 |
International
Class: |
H01G 004/38 |
Foreign Application Data
Date |
Code |
Application Number |
May 14, 2002 |
DE |
10221498.0 |
Claims
We claim:
1. A capacitor comprising an inert porous shaped body onto which a
first electrically conductive layer, a second layer of barium
titanate and a further electrically conductive layer have been
applied.
2. A capacitor as claimed in claim 1 consisting of an inert porous
shaped body onto which a first electrically conductive layer, a
second layer of barium titanate and a further electrically
conductive layer have been applied.
3. A capacitor as claimed in claim 1 or 2, wherein the BET surface
area of the inert porous shaped body is from 0.1 to 20
m.sup.2/g.
4. A capacitor as claimed in any of claims 1, 2 and 3, wherein the
pore content of the inert, porous shaped body is from 10 to 90% by
volume.
5. A process for producing capacitors as claimed in any of claims
1, 2, 3 and 4, which comprises applying an electrically conductive
layer with contact onto an inert porous shaped body, applying a
layer of barium titanate on top of this and applying an
electrically conductive layer with contact on top of the
latter.
6. The use of the capacitors in electric energy engineering as
smoothing capacitor or energy storage capacitor or phase shift
capacitor and in information technology as coupling capacitor,
filter capacitor or miniature energy storage capacitor.
Description
[0001] The present invention relates to capacitors comprising an
inert porous shaped body onto which a first electrically conductive
layer, a second layer of barium titanate and a further electrically
conductive layer have been applied.
[0002] Capacitors perform many tasks in information technology and
electric energy engineering. There has in recent times been a
search for capacitors which have a high energy density and can
perform the task of batteries or be used for covering short-term
high load requirements.
[0003] Electrochemica Acta 45 (2000), 2483 to 2498, discloses
electrochemical or double-layer capacitors. These devices, also
known as supercapacitors or ultracapacitors, store electric energy
in two capacitors which are connected in series and each have an
electric double layer which is formed between the two electrodes
and the ions in the electrolyte. The distance in which charge
separation occurs is only a few Angstrom. As electrolytes, use is
made of highly porous carbon having internal surface areas of up to
2 500 m.sup.2/g. As indicated by the capacitor formula
C=E.sub.0.multidot.E.multidot.A/d
[0004] where C is the capacitance, E.sub.0 is the absolute
dielectric constant, E is the dielectric constant of the
dielectric, A is the area of the capacitor and d is the distance
between the electrodes, capacitances of up to 100 farad/cm.sup.3
are possible at large areas A and small spacings d.
[0005] Such double-layer capacitors (supercapacitors) at present
achieve energy densities of from 3 to 7 Wh/kg or Wh/liter, which
are far below the energy densities of conventional batteries
(lithium ion batteries achieve from 150 to 200 Wh/kg). This is due
to the maximum possible voltage loading being restricted to about
3.5 V by the electrochemical stability of the electrolyte.
[0006] On the other hand, there is a type of capacitor which
operates at high voltages, namely ceramic capacitors comprising
dielectrics based on barium titanate.
[0007] Ceramic capacitors which comprise dielectrics based on
barium titanate and operate at high working voltages because of the
high dielectric breakdown resistance of the titanates of up to 200
V/0.1 .mu.m are known from the prior art. However, ceramic
capacitors have relatively low capacitances.
[0008] It is an object of the present invention to remedy the
abovementioned disadvantages.
[0009] We have found that this object is achieved by new and
improved capacitors which comprise an inert porous shaped body onto
which a first electrically conductive layer, a second layer of
barium titanate and a further electrically conductive layer have
been applied.
[0010] The capacitors of the present invention can be produced as
follows:
[0011] An inert porous shaped body can, in a first step, be
provided with a first electrically conductive layer and this can be
provided with a contact. A second layer of barium titanate can be
applied on top of the first layer and, finally, another
electrically conductive layer can be applied on top of this
titanate layer and be provided with a contact. The capacitors
obtained in this way can be hermetically sealed, e.g. encapsulated,
except for the electric contacts.
[0012] Suitable porous shaped bodies are in general catalyst
support materials, for example those based on metal oxides such as
aluminum oxide, silicon dioxide, titanium dioxide, zirconium
dioxide, chromium oxide or mixtures thereof, preferably aluminum
oxide, silicon dioxide, titanium dioxide, zirconium dioxide or
mixtures thereof, particularly preferably aluminum oxide, zirconium
dioxide or mixtures thereof, or carbides, preferably silicon
carbide, having a BET surface area of from 0.1 to 20 m.sup.2/g,
preferably from 0.5 to 10 m.sup.2/g, particularly preferably from 1
to 5 m.sup.2/g, a pore content of from 10 to 90% by volume,
preferably from 30 to 85% by volume, particularly preferably from
50 to 80% by volume, and pore sizes of from 0.01 to 100 .mu.m,
preferably from 0.1 to 30 .mu.m, particularly preferably from 1 to
10 .mu.m.
[0013] The shaped bodies can have any shapes, for example rings,
pellets, stars, wagon wheels, honeycombs, preferably cuboids,
cylinders, rectangles or boxes of generally any size (diameter,
longest edge length). In the case of capacitors for information
technology, for example, the size is generally in the range from 1
to 10 mm. Larger dimensions are necessary in energy
engineering.
[0014] To produce the first conductive layer on the shaped body,
metals such as copper, nickel, chromium or mixtures thereof can be
applied in any layer thickness, generally from 10 nm to 1 000 nm,
preferably from 50 nm to 500 nm, particularly preferably from 100
nm to 200 nm.
[0015] The application of the electrically conductive layer to the
shaped body can be carried out using all known methods such as
vapor deposition, sputtering or electroless plating, preferably
electroless plating. In electroless plating, the shaped bodies are
infiltrated or impregnated with suitable, commercially available
plating liquids and heated to temperatures below 100.degree. C. to
deposit the metal. After metal deposition, the liquid, usually
water, can be removed at elevated temperatures and, if desired,
under reduced pressure.
[0016] It is also possible, for example in the case of iron or
nickel, to produce the first conductive layer by heating the shaped
bodies in iron carbonyl or nickel carbonyl vapors. In the case of
iron, the shaped bodies can be heated to from about 150 to
200.degree. C., and in the case of nickel to from 50 to 100.degree.
C.
[0017] In a preferred embodiment, the shaped bodies can be heated
to elevated temperatures of from 50 to 100.degree. C. in an inert
atmosphere (e.g. nitrogen or argon) to produce a homogeneous metal
layer. It may be advantageous to apply crystallization nuclei, e.g.
nuclei based on platinum metals, likewise by impregnation with
suitable liquids (see above).
[0018] Finally, the first metal layer can be provided with a
contact. This can be carried out, for example, by soldering a metal
foil onto an area of the metal-coated shaped body (production of
the first electrode).
[0019] A dielectric can then be applied on top of the initially
produced electrode. This is advantageously carried out using
dispersions of crystalline titanate particles having sizes of less
than 10 nm in alcohols. Such dispersions can be prepared by
reaction of titanium alkoxides with barium hydroxides or strontium
hydroxides in alcoholic solution as described in the German
application No.: 102 21 499.9 (O.Z. 0050/53537).
[0020] The shaped body can be infiltrated or impregnated with such
a dispersion which may contain from 5 to 60% by weight, preferably
from 10 to 40% by weight, of titanate particles, followed by
removal of the alcohol by increasing the temperature to
30-100.degree. C., preferably 50-80.degree. C., and, if desired,
reducing the ambient pressure to deposit the titanium particles on
the first electrode.
[0021] To produce a homogeneous, dense layer of the dielectric, the
shaped bodies can be heated to from 700 to 1 200.degree. C.,
preferably from 900 to 1 100.degree. C., in an inert gas atmosphere
so that the titanate particles sinter together to form a dense
film.
[0022] To increase the layer thickness, the impregnation with the
titanate dispersion and the sintering can be repeated a number of
times. The layer thickness is generally from 10 to 1 000 nm,
preferably from 20 to 500 nm, particularly preferably from 100 to
300 nm.
[0023] Finally, a second electrode layer can be applied in a manner
analogous to that employed for the first.
[0024] After the second electrode layer has been applied, this can
be provided with a contact on the side opposite the first contact,
thus producing the capacitor. The latter can be hermetically
encapsulated to protect it and for the purposes of insulation.
[0025] The capacitors of the present invention are suitable as
smoothing capacitors or energy storing capacitors or phase shift
capacitors in electric energy engineering and as coupling
capacitors, filter capacitors or miniature energy storage
capacitors in information technology.
[0026] The capacitors of the present invention may be illustrated
as follows:
[0027] A specific surface area (BET surface area) of the porous
shaped body of 2 m.sup.2/g and a barium titanate layer thickness of
0.1 .mu.m at a relative dielectric constant of 5 000 ("The Effect
of Grain Size on the Dielectric Properties of Barium Titanate
Ceramic", A. J. Bell and A. J. Moulson, in Electrical Ceramics,
British Ceramic Proceedings No. 36, October 1985, pages 57-65)
gives a capacitance calculated according to the formula on page 1,
line 29, of about 1 farad/cm.sup.3. Such a capacitor can be charged
to a voltage of 200 V, and its energy density is then 20 000
Ws/cm.sup.3 or approximately 5.5 kWh/liter.
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