U.S. patent application number 13/914803 was filed with the patent office on 2013-12-12 for electrode unit.
The applicant listed for this patent is BASF SE. Invention is credited to Anna Katharina Durr, Katrin Freitag, Gunther Huber, Wolfgang Jabczynski, Jesus Enrique Zerpa Unda.
Application Number | 20130330634 13/914803 |
Document ID | / |
Family ID | 49715540 |
Filed Date | 2013-12-12 |
United States Patent
Application |
20130330634 |
Kind Code |
A1 |
Huber; Gunther ; et
al. |
December 12, 2013 |
ELECTRODE UNIT
Abstract
The invention relates to an electrode unit for an
electrochemical device for storing electrical energy, comprising a
solid electrolyte (3) and a porous electrode (7), the solid
electrolyte (3) dividing a compartment for cathode material and a
compartment for anode material and the porous electrode (7) being
extensively connected to the solid electrolyte (3) and the cathode
material flowing along the porous electrode (7) during discharging.
On the side remote from the solid electrolyte (3), the porous
electrode (7) is covered towards the compartment for the cathode
material with a segment wall (9), the segment wall (9) comprising
inlet openings (15) in the direction of flow of the cathode
material, through which the cathode material penetrates into the
porous electrode (7), reacts chemically with the anode material in
the porous electrode (7) and emerges back out of the porous
electrode (7) through outlet openings (17) downstream in the
direction of flow.
Inventors: |
Huber; Gunther;
(Ludwigshafen, DE) ; Zerpa Unda; Jesus Enrique;
(Viernheim, DE) ; Durr; Anna Katharina;
(Ludwigshafen, DE) ; Jabczynski; Wolfgang;
(Venningen, DE) ; Freitag; Katrin; (Ludwigshafen,
DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
BASF SE |
Ludwigshafen |
|
DE |
|
|
Family ID: |
49715540 |
Appl. No.: |
13/914803 |
Filed: |
June 11, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61657915 |
Jun 11, 2012 |
|
|
|
Current U.S.
Class: |
429/320 ;
429/209; 429/213; 429/218.1; 429/231.9 |
Current CPC
Class: |
H01M 2/18 20130101; H01M
10/3945 20130101; H01M 10/3909 20130101; Y02E 60/10 20130101; H01M
2004/025 20130101; H01M 4/38 20130101; C25B 13/02 20130101; C25B
13/04 20130101; H01M 10/3954 20130101; H01M 4/58 20130101; H01M
2/0252 20130101; H01M 2/1673 20130101; H01M 4/381 20130101 |
Class at
Publication: |
429/320 ;
429/209; 429/231.9; 429/218.1; 429/213 |
International
Class: |
H01M 4/38 20060101
H01M004/38 |
Claims
1-26. (canceled)
27. An electrode unit for an electrochemical device for storing
electrical energy, comprising a solid electrolyte and a porous
electrode, the solid electrolyte dividing a compartment for cathode
material and a compartment for anode material and the porous
electrode being extensively connected to the solid electrolyte and
the cathode material flowing along the porous electrode during
discharging, wherein, on the side remote from the solid
electrolyte, the porous electrode is covered towards the
compartment for the cathode material with a segment wall, the
segment wall comprising inlet openings in the direction of flow of
the cathode material, through which the cathode material penetrates
into the porous electrode, reacts chemically with the anode
material in the porous electrode and emerges back out of the porous
electrode through outlet openings downstream in the direction of
flow.
28. The electrode unit according to claim 27, wherein the segment
wall comprises a plurality of rows of inlet openings and outlet
openings oriented transversely of the direction of flow, the inlet
openings and outlet openings alternating in the direction of flow
and flow barriers being accommodated in the porous electrode, in
each case in the direction of flow, upstream of the inlet openings
and downstream of the outlet openings.
29. The electrode unit according to claim 27, wherein a row of
outlet openings is in each case immediately followed by a row of
inlet openings.
30. The electrode unit according to claim 27, wherein the inlet
openings which follow the outlet openings in the direction of flow
of the cathode material are arranged in a staggered manner relative
to the outlet openings.
31. The electrode unit according to claim 27, wherein a cover
adjoins the segment wall, the cover being constructed such that the
cover forms flow channels along the electrode.
32. The electrode unit according to claim 31, wherein the cover is
of corrugated construction.
33. The electrode unit according to claim 27, wherein the solid
electrolyte is of cylindrical construction and the porous electrode
encloses the solid electrolyte.
34. The electrode unit according to claim 33, wherein the segment
wall is at least one sleeve which encloses the porous electrode,
the inlet openings and outlet openings being formed in the
sleeve.
35. The electrode unit according to claim 33, wherein the segment
wall comprises at least two sleeves, the inlet openings in each
case being formed at one end of the sleeve and the outlet openings
at the opposite end and the sleeves being rotated relative to one
another on the porous electrode such that the outlet openings of
one sleeve are arranged in a staggered manner relative to the inlet
openings of a downstream sleeve.
36. The electrode unit according to claim 33, wherein the cover is
a cladding tube and is configured such that the flow channels are
oriented in the axial direction along the porous electrode.
37. The electrode unit according to claim 33, wherein a displacer
is accommodated in the solid electrolyte of cylindrical
construction, the displacer not being in contact with the solid
electrolyte in the circumferential direction.
38. The electrode unit according to claim 37, wherein a channel is
formed in the displacer, through which channel the anode material
is supplied.
39. The electrode unit according to claim 37, wherein the displacer
is made from a special steel.
40. The electrode unit according to claim 37, wherein the displacer
rests resiliently against the solid electrolyte.
41. The electrode unit according to claim 37, wherein the displacer
comprises an outer contour with projections and recesses.
42. The electrode unit according to claim 39, wherein the displacer
comprises current conducting means.
43. The electrode unit according to claim 41, wherein the current
conducting means comprise a special steel tube closed at both ends
and with a core of an electrically highly conductive material and
are arranged in recesses of the displacer or wherein the current
conducting means comprise a coating of an electrically highly
conductive material on the inside of the displacer.
44. The electrode unit according to claim 41, wherein the current
conducting means comprising a special steel tube closed at both
ends and with a core of an electrically highly conductive material
are clamped in the recesses.
45. The electrode unit according to claim 27, wherein a
non-electron-conducting layer is arranged between the solid
electrolyte and the porous electrode.
46. The electrode unit according to claim 27, wherein the solid
electrolyte is made from .beta.''-alumina.
47. The electrode unit according to claim 27, wherein the porous
electrode is a graphite felt electrode.
48. The electrode unit according to claim 27, wherein the segment
wall is made from steel.
49. The electrode unit according to claim 48, wherein the segment
wall is electrically conductive and comprises additional current
conducting means.
50. The electrode unit according to claim 49, wherein the current
conducting means comprise a special steel tube closed at both ends
and with a core of an electrically highly conductive material and
are arranged with a clamp connection in troughs of the cover which
is of corrugated construction.
51. The electrode unit according to claim 27, wherein the anode
material is an alkali metal.
52. The electrode unit according to claim 27, wherein the cathode
material is sulfur or polysulfide.
53. The electrode unit according to claim 27, wherein the special
steel is molybdenum-stabilized special steel 1.4571, 1.4401,
1.4404, 1.4405 or 1.4539.
Description
[0001] The invention relates to an electrode unit for an
electrochemical device for storing electrical energy, comprising a
solid electrolyte and a porous solid electrode, the solid
electrolyte dividing a compartment for molten cathode material and
a compartment for molten anode material and the porous electrode
being connected via a non-electron-conductive interlayer to the
solid electrolyte and the molten cathode material flowing along the
electrode during charging or discharging.
[0002] Generating electrical energy by means of fossil fuel-fired
power stations is associated with the production of CO.sub.2 and
thus has a considerable impact on the greenhouse effect. Generating
energy from renewable energy sources, for example wind, sun,
geothermal energy or hydroelectric power, avoids this disadvantage.
However, these renewable energy sources are not always available at
the times they are required by load profiles. In addition, the
energy is often generated at locations which differ from the places
where the energy demand is located. If this systemic disadvantage
is to be overcome, the energy generated must be stored, buffered
and possibly even transported.
[0003] Against this background, it is not possible to base a stable
power grid solely on renewable energy sources. There is accordingly
a need to compensate and buffer such fluctuations by highly
effective systems which are inexpensive and energy-efficient.
[0004] Electrical energy is currently stored on an industrial scale
using pumped-storage power stations in which the potential energy
arising from the geodetic difference in height of the water is
utilized for conversion into electricity. However, the construction
of such pumped-storage power stations is restricted by topographic
and environmental considerations. Pressure storage power plants,
which make use of air compression for storing energy, are limited
by their comparatively low efficiency. Other forms of energy
storage, such as supercapacitors or flywheels are intended for
other target markets, in particular short-term storage. Electrical
energy may in particular be stored using batteries, various designs
of which have been implemented industrially. In particular, it is
necessary to use batteries which are rechargeable for this
purpose.
[0005] Corresponding batteries which function on the basis of a
molten alkali metal as anode and a cathodic reaction partner,
generally sulfur, are known for example from DE-A 26 35 900 or DE-A
26 10 222. The molten alkali metal and the cathodic reaction
partner are divided by a solid electrolyte which is permeable to
cations. The alkali metal reacts with the cathodic reaction partner
on the cathode. For example when using sodium as the alkali metal
and sulfur as the cathodic reaction partner, this is sodium
polysulfide. The battery is charged by splitting the sodium
polysulfide on the electrode back into sodium and sulfur by
applying electrical energy.
[0006] The storage capacity of batteries based on a molten alkali
metal and a cathodic reaction partner is increased by using
batteries in which the quantity of reactants used in increased by
additional storage vessels. The liquid sodium is supplied to the
solid electrolyte for discharging. The liquid sodium simultaneously
acts as anode and forms cations which are transported to the
cathode through the cation-conductive solid electrolyte. At the
cathode, the sulfur flowing to the cathode is reduced to
polysulfide, i.e. is reacted with the sodium ions to yield sodium
polysulfide. The corresponding sodium polysulfide may be collected
in a further vessel. It is alternatively also possible to collect
the sodium polysulfide together with the sulfur in the vessel
around the cathode compartment. Due to the difference in density,
the sulfur rises up and the sodium polysulfide settles out. This
difference in density may also be exploited to bring about flow
along the cathode. A corresponding battery design is described, for
example, in WO 2011/161072.
[0007] In batteries which operate using a redox-system based on
sodium and sulfur, electrical energy may be obtained on reacting
sodium and sulfur to yield sodium polysulfide at a high level of
efficiency of roughly 90%. The battery is charged by reversing the
procedure by introducing electricity and cleaving the sodium
polysulfide into sulfur and sodium. Since all the electrochemical
reactants are in molten form and the ideal conductivity range of
the ion-conductive ceramic membrane is not achieved until
relatively high temperatures, the operating temperature of such a
battery is conventionally approx. 300.degree. C.
[0008] The solid, sodium ion-conductive electrolyte used in the
battery is conventionally .beta.''-alumina. Mechanical failure
cannot be ruled out with such a ceramic. In such an event, an
uncontrolled reaction between sodium and sulfur may occur, which
due to its exothermic nature may lead to an undesired temperature
rise in the battery. In order to keep the temperature rise as small
as possible in such a case, it is known, for example from JP-A
10270073, to use a displacer of aluminum with which the compartment
for the sodium on the sodium side of the solid electrolyte is
restricted to a gap with a width of 0.01 to 0.2 mm. The gap is here
produced by a combination of plastic deformation and elastic
rebound during heat treatment of the displacer which was introduced
into the solid electrolyte which is conventionally of tubular
construction.
[0009] In order to keep the internal resistance of such battery
systems as low as possible, current is supplied on both the
positive and the negative sides by metallic supply lines which must
be not only corrosion-resistant in the surrounding medium but also
highly electrically conductive. The prior art therefore prefers
electrical conductors made of aluminum or aluminum alloys, since
for example copper, which is highly conductive, has inadequate
corrosion-resistance to sulfur and polysulfide.
[0010] The disadvantage of the anode and current conductor design
described here is the elevated labile reaction potential of
aluminum and sulfur and in particular of aluminum and sodium
polysulfide. In the event of mechanical failure of the ceramic
membrane, not only is an exothermic sodium-sulfur reaction to be
anticipated, but also an exothermic aluminum-sulfur reaction, the
metals reacting similarly violently with sodium polysulfide as they
do with sulfur.
[0011] Another disadvantage of the battery design described in WO
2011/161072 is, however, also that when a porous electrode is used,
sulfur enters the upper region of the electrode during discharging
and reacts to form sodium polysulfide. This remains in the
electrode. As discharge operation continues, the sodium polysulfide
is reduced further and thus takes up more sodium, so reducing the
electrochemical potential and the voltage in the electrode thus
falls. Under certain circumstances, sodium uptake may go as far as
complete conversion into sodium sulfide (Na.sub.2S) with formation
of a solid, the solid clogging the electrode or sodium and sulfur
at least being removed from the system for further charging cycles
so leading to a decline in charge/discharge life.
[0012] A further disadvantage of the batteries known from the prior
art is that the sulfur which arises during charging is electrically
insulating, which may lead to an uncontrolled increase in internal
resistance and thus in charging voltage.
[0013] The object of the present invention was accordingly to
provide an electrode unit which does not exhibit the disadvantages
of the electrodes known from the prior art.
[0014] Said object is achieved by an electrode unit for an
electrochemical device for storing electrical energy, comprising a
solid electrolyte and a porous solid electrode, the solid
electrolyte dividing a compartment for molten cathode material and
a compartment for molten anode material and the porous electrode
being extensively connected via a non-electron-conductive
interlayer to the solid electrolyte and the molten cathode material
flowing along the porous electrode during charging or discharging,
wherein, on the side remote from the solid electrolyte, the porous
electrode is covered towards the compartment for the molten cathode
material with an extensive tube or sheet metal wall, the extensive
tube or sheet metal wall comprising inlet openings in the direction
of flow of the cathode material, through which the cathode material
penetrates into the porous electrode, reacts electrochemically in
the porous electrode and emerges back out of the porous electrode
through outlet openings downstream in the direction of flow.
[0015] The device according to the invention provides uniform flow
through the porous electrode, so ensuring not only more uniform
distribution of substances but also uniform electrical power from
the battery during the discharge process. Battery power does not
decline as the discharge process progresses.
[0016] For the purposes of the present invention, an anode material
should be taken to mean a liquid reactant which is supplied to the
anode side during discharging. The anode material is preferably
electrically conductive, in particular a liquid alkali metal is
used as the anode material. Suitable anode materials are for
example lithium, sodium, potassium, in particular sodium or
potassium.
[0017] The cathode material is a liquid reactant which is
electrochemically reacted with the anode material. The cathode
material conventionally forms a salt by chemical reaction with the
anode material. Suitable cathode materials are for example sulfur
or polysulfides. The cathode material is here used in liquid
form.
[0018] Transport through the porous electrode proceeds solely by
convection and diffusion. In this way it is possible to dispense
with pumps or similar devices providing forced transport. The
disadvantage of such devices is generally that they require
electricity which is then no longer available. A further
disadvantage of forced transport devices is the wear they
undergo.
[0019] In order to achieve uniform functioning of the entire
electrode, in particular in large electrochemical devices for
storing electrical energy, hereinafter also designated "battery",
in a preferred embodiment for large devices for electrochemical
energy storage, the extensive tube or sheet metal wall has the
structure of corrugated sheet metal, such that alternate,
perpendicularly oriented lengthwise channels are formed between the
boundary of the porous electrode material and the corrugated sheet
metal-like tube or sheet metal wall, which lengthwise channels are,
however, capable of communicating with the cavities of the
electrode material. Convective flow driven by the difference in
density, for example between polysulfide and sulfide, can develop
in these lengthwise channels, said flow being directed upwards
during charging and downwards during discharging.
[0020] In a further particularly preferred embodiment, the porous
electrode material is subdivided into lengthwise segments, flow
barriers being arranged between the lengthwise segments in order to
force mass transfer of liquid cathode material between porous
electrode and lengthwise channel.
[0021] In a further embodiment, the porous electrode segments are
additionally encased by means of segment walls closed at the sides
in order to force purposeful inflow into and outflow from the
porous electrode. In this preferred embodiment, the segment wall
comprises a plurality of rows of inlet openings and outlet openings
oriented transversely of the direction of flow, the inlet openings
and outlet openings alternating in the direction of flow and flow
barriers being accommodated in the porous electrode, in each case
in the direction of flow, upstream of the inlet openings and
downstream of the outlet openings.
[0022] During discharging of the battery, i.e. when releasing
electrical energy, the cathode material enters through the inlet
openings into the porous electrode and is electrochemically reacted
with the anode material. The reaction product then emerges through
the outlet openings. The flow barriers in the porous electrode
ensure that the reaction product is forced to emerge at the outlet
openings, such that the reaction product cannot flow onwards in the
porous electrode. This allows cathode material to enter through
inlet openings downstream of the outlet openings into the porous
electrode where it can be reacted. In this way, the entire length
of the electrode may be uniformly used for electrochemical reaction
of the anode material with the cathode material.
[0023] In order to be able to utilize the entire surface area of
the porous electrode, it is furthermore preferred for a row of
outlet openings in each case immediately to be followed by a row of
inlet openings. In this case, the optionally unreacted cathode
material and the reaction product flow up to a flow barrier and
pass out from the electrode through the outlet openings, and fresh
cathode material, which is reacted with the anode material, is
supplied to the porous electrode directly below the flow
barrier.
[0024] In order to prevent reaction product which has formed in the
porous electrode and emerges through the outlet openings from
immediately entering the porous electrode again through the
downstream inlet openings, it is furthermore preferred for the
inlet openings which follow the outlet openings in the direction of
flow of the cathode material to be arranged in a staggered manner
relative to the outlet openings.
[0025] It is for example here possible to construct the inlet
openings and the outlet openings in each case with a rectangular
cross-section and to provide a web of the extensive electrode in
each case between two adjacent inlet openings or two adjacent
outlet openings in the width of the inlet openings or outlet
openings respectively. In the case of the staggered arrangement, an
inlet opening is in each case followed by the web between two
outlet openings while an outlet opening is followed by the web
between two inlet openings.
[0026] In addition to a design with rectangular inlet openings and
outlet openings, it is also possible to construct the inlet
openings and outlet openings in any desired other shape. These may
accordingly be constructed for example in a circular, semicircular,
elliptical, oval, triangular or polygonal shape with as many
vertices as desired. A circular, semicircular or rectangular shape
of the inlet openings and outlet openings is here preferred. It is
also possible to provide inlet openings and outlet openings of
different shapes, an identical shape of inlet openings and outlet
openings being preferred.
[0027] According to the invention, the segment wall is electrically
conductively connected to the porous electrode. During discharging
of the device, the electrical voltage released during the
electrochemical reaction of the anode material with the cathode
material is conducted via the porous electrode to the segment wall
and can be picked off from the segment wall. It is particularly
preferred for this purpose for the segment wall to be electrically
conductively connected to one or more bus conductors. In order to
avoid the risk, arising from the nature of the material, of an
undesired exothermic reaction of the current conductor with sulfur
or polysulfide, in a preferred embodiment the bus conductors are
made from highly conductive materials such as aluminum, copper or
sodium jacketed or encased in special steel. The bus conductor may
here also be provided in the form of a cover, which is preferably
constructed such that the cover forms flow channels along the
electrode. It is alternatively also possible to provide a cover
which is constructed such that flow channels are formed along the
electrode, to make the electrical contact through the cover and to
arrange the bus conductor outside the cover. It is preferred,
however, to construct the cover electrically conductively as a bus
conductor. It is here furthermore preferred for the cover
additionally to accommodate rod electrodes which are preferably
made from an electrically highly conductive material which differs
from the material of the cover. The rod electrodes may here for
example lie outside on the cover or are enclosed by the material of
the cover. The individual rod electrodes are here preferably
arranged equidistantly in the cover. The rod electrodes may, for
example, be arranged in each case between two flow channels.
Alternatively, however, the rod electrodes may for example also be
arranged in each case in the region of a flow channel.
[0028] In one particularly preferred embodiment, the cover is of
corrugated construction in order to form the flow channels, the
troughs in each case resting against the extensive electrode and
the flow channels being formed by the corresponding peaks. In
addition to a corrugated design, it is alternatively also possible,
for example, to make the cover flat with webs, the flow channels in
each case being formed between two webs and the webs resting
against the extensive electrode to form the flow channels.
[0029] In one particularly preferred embodiment, the solid
electrolyte is of cylindrical construction and the porous electrode
encloses the solid electrolyte. In this case, the anode material is
located in the interior of the cylindrically shaped solid
electrolyte and the cathode material flows outside along the porous
electrode. In a cylindrical design of the solid electrolyte, the
segment wall is preferably formed by at least one sleeve which
encloses the porous electrode. In this case, the inlet openings and
outlet openings are formed in the sleeve. In order to ensure
current flow from the porous electrode to the sleeve-type extensive
electrode, the external diameter of the porous electrode here
corresponds to the internal diameter of the sleeve. In this way,
the sleeve rests extensively against the porous electrode.
[0030] If the segment wall is formed by just one sleeve, it is
possible to form a plurality of rows of inlet openings and outlet
openings in the sleeve. A design with a plurality of sleeves is
preferred, however, the inlet openings and outlet openings in this
case being formed in each case at the ends of a sleeve. To this
end, it is for example possible in each case to shape the ends of
the sleeve as a rectangular profile. In this case, the opposite
rectangular profiles in a sleeve are constructed such that the
recesses are in each case opposite one another. A plurality of
sleeves are then successively placed on the electrode, the sleeves
each being rotated relative to one another such that the recesses
of one sleeve are opposite the projecting regions located
therebetween. In this way, the inlet openings and outlet openings
are formed by the recesses and the adjacent sleeve.
[0031] In the case of a cylindrically shaped solid electrolyte, the
cover likewise preferably takes the form of a sleeve and is
configured such that the channels are oriented in the axial
direction along the porous electrode. It is here possible on the
one hand to construct the cover as an annular sleeve which is
provided with webs which divide the individual flow channels or the
sleeve is of corrugated construction such that the peaks and
troughs form the channels, the peaks in each case resting against
the sleeves which form the segment walls. During discharging of the
battery, the cathode material flows through the flow channels and
in each case enters via inlet openings into the porous electrode
and, after electrochemical reaction, emerges back out of the outlet
openings as the reaction product. Due to the staggered arrangement
of inlet openings and outlet openings, the material emerging from
the outlet openings cannot immediately enter the porous electrode
again through downstream inlet openings. In this way it is ensured
that in each case sufficient unreacted cathode material reaches the
porous electrode through the inlet openings.
[0032] In addition to the above-described embodiment, in which the
inlet openings and downstream outlet openings are arranged directly
one above the other and the flow channels are formed in the axial
direction along the porous electrode, it is also possible for the
flow channels to extend spirally. In the case of a flat electrode
unit, the flow channels may extend obliquely. In this case, the
arrangement of the inlet openings and outlet openings is preferably
such that in each case in one flow channel an outlet opening
follows an inlet opening and the inlet opening immediately
downstream of the outlet opening is located in an adjacent flow
channel. In this case too, a corresponding arrangement of the inlet
openings and outlet openings ensures that the reaction product
emerging from the outlet openings does not immediately enter the
porous electrode again via downstream inlet openings.
[0033] In order to reduce the quantity of liquid anode material, it
is furthermore preferred, in particular in the case of a
cylindrical configuration of the solid electrolyte, for a displacer
to be accommodated in the solid electrolyte. A gap into which the
anode material can flow is here formed between the displacer and
the solid electrolyte. The anode material may here for example be
introduced via an annular gap at the end of the solid electrolyte
or alternatively be supplied through a flow channel in the
displacer. The anode material is preferably fed through a flow
channel in the displacer.
[0034] As is known from the prior art, the displacer may for
example be made from aluminum. It is, however, preferred to make
the displacer from special steel. Suitable special steels are in
particular molybdenum-stabilized special steels 1.4571, 1.4401,
1.4404, 1.4405 and 1.4539. If the displacer is made from special
steel, it is preferably made from special steel sheet. The
advantage of using special steel over aluminum is that while
special steel does indeed corrode at relatively high temperatures,
which may for example occur in the event of failure of the solid
electrolyte, an uncontrollably rapid reaction with sulfur and
polysulfide does not proceed, unlike with aluminum.
[0035] Since the mechanical strength of special steel is greater
than that of aluminum and thus very much less plastic deformation
occurs at the battery operating temperature, the special steel
cannot adapt to the shape of the solid electrolyte in the case of a
cylindrical design of the displacer. Thermal expansion may thus
lead to failure of the solid electrolyte if the displacer made from
special steel is pressed nonuniformly against the solid
electrolyte. Such nonuniform contact pressure by the displacer
against the solid electrolyte is the result, for example, of
manufacturing inaccuracies in the production of the ceramic solid
electrolyte. In order to equalize longitudinal expansion due to
temperature changes, it is therefore preferred to construct the
displacer in such a manner that it rests resiliently against the
internal geometry of the solid electrolyte. Loading of the solid
electrolyte is additionally minimized by using special steel sheet
with a thickness in the range from 0.05 to 0.5 mm, preferably in
the range from 0.07 to 0.15 mm, for example 0.1 mm, to make the
displacer.
[0036] In order to obtain a shape which rests resiliently against
the internal geometry, the displacer preferably comprises an outer
contour with projections and recesses. The projections and recesses
may be obtained, for example, by a corrugated or zig-zag-shaped
design of the displacer.
[0037] Since special steel is only a moderately good electrical
conductor, it is furthermore preferred for the displacer
additionally to comprise current conducting means. The current
conducting means ensure a uniform current supply both during
charging and during discharging. Suitable current conducting means
are for example preferably current collectors arranged uniformly
over the circumference of the displacer, which current collectors
are made in a preferred embodiment from a special steel tube closed
at both ends in which a core of an electrically highly conductive
material is introduced. The surface of the special steel tube here
rests continuously against the core of electrically highly
conductive material. The special steel tube protects the
electrically highly conductive core from attack by sulfur and
polysulfide in the event of failure of the solid electrolyte.
[0038] In an alternative embodiment, the current conducting means
comprise a continuous or patterned coating of an electrically
highly conductive material on the inside of the displacer.
[0039] Suitable electrically highly conductive materials for the
current collector or the coating are for example copper, aluminum,
silver or gold. If a current collector with a special steel tube is
used, the electrically highly conductive material may also be
sodium. While the sodium will indeed be liquid at a conventional
operating temperature 300.degree. C., it cannot escape due to the
special steel tube. The electrically highly conductive material is
particularly preferably copper or aluminum.
[0040] In order to ensure proper functioning of the electrode unit,
the current conducting means must be connected highly electrically
conductively to the displacer. When using current collectors, this
may for example be achieved by in each case welding the current
collectors to the displacer. It is preferred, however, to clamp the
current collectors in recesses of the displacer. The current
collectors are here preferably arranged on the outside of the
displacer.
[0041] The current collectors may be firmly connected to the
displacer for example by making the recesses omega-shaped with the
diameter of the omega matching the external diameter of the wire.
Given an appropriate design of the recesses, the wires may in each
case be clamped in the recesses with a stable connection and form a
uniform contact with the displacer over their entire length.
[0042] In the above description, the directions of flow and
transport paths of the anode material and cathode material were in
each case stated for the discharge process in which current is
generated. Transport proceeds in the opposite direction for
charging the device for storing electrical energy. In this case,
the reaction product arising during discharging is passed into the
porous electrode through the outlet openings, reacted in the porous
electrode to yield the anode material and cathode material and the
cathode material passes through the inlet openings back out of the
porous electrode and flows into a storage vessel. The cations
formed during the charging process are transported through the
solid electrolyte, take up an electron and are transported as
neutral anode material through the flow channel in the displacer or
through the annular feed device, through which the anode material
flows during charging, back into a storage vessel.
[0043] The electrode unit according to the invention is in
particular suitable for use in devices for storing electrical
energy which are operated with an alkali metal as anode material. A
suitable anode material is here for example lithium, sodium or
potassium, preferably sodium or potassium. The device for storing
electrical energy is here operated at a temperature at which the
alkali metal used is in liquid form. Corresponding temperatures may
be provided, for example, by simultaneously constructing the
displacer present in the cylindrical solid electrolyte as a heating
element, such that the latter may be used to keep the temperature
in the electrode unit within a range in which the anode material is
in liquid form. Since the anode material is a liquid metal, it is
electrically conductive and may thus directly be used as an anode.
All that is required for this purpose is to contact an electrical
conductor through which the current can flow with the liquid anode
material.
[0044] The cathode material used is a material which is capable of
reacting chemically with the anode material. Sulfur or polysulfide
is preferably used as the cathode material.
[0045] In a preferred embodiment, a ceramic is used as the solid
electrolyte. .beta.-Alumina or .beta.''-alumina is particularly
suitable as a material for the solid electrolyte. This is
preferably stabilized, for example with MgO or Li.sub.2O.
[0046] As an alternative to .beta.-alumina or .beta.''-alumina,
other ceramic materials may also be used as the solid electrolyte.
The ceramic known as NASCION.RTM., the composition of which is
stated in EP-A 0 553 400, may for example be used. The ceramic
known in everyday language as "ceramic" is also particularly
preferred. Sodium ion-conductive glasses or zeolites and feldspas
may also be used as an alternative to ceramics. In particular,
however, sodium .beta.''-alumina, sodium .beta.-alumina or sodium
.beta./.beta.''-alumina are preferred. The sodium ion-conductive
ceramics are preferably thin-walled tubes closed at one end at the
bottom and open at the top if the solid electrolyte is of
cylindrical construction. In this case, it is furthermore preferred
for the tubes to have a diameter of 20 to 50 mm and a length in the
range from 0.5 m to 2 m. The wall thickness is preferably in the
range from 0.5 mm to 3 mm, in particular in the range from 1.5 mm
to 2 mm.
[0047] The porous electrode is made from a material which is inert
towards the substances used in the electrochemical reaction.
Carbon, in particular in the form of graphite, is for example
suitable as the electrode material.
[0048] According to the invention, the electrode is porous so that
the substances participating in the electrochemical reaction can
flow through it. This is achieved, for example, in that the
material of the porous electrodes assumes the form of a felt or
nonwoven. The electrode is very particularly preferably a graphite
felt electrode.
[0049] In order to avoid the electrode coming into direct contact
with the solid electrolyte, a porous liquid electrolyte-filled
layer which is insulating in terms of electron conduction is
arranged between the porous electrode and the solid electrolyte.
For the purposes of the present invention, "insulating in terms of
electron conduction" should be taken to mean a material which
exhibits a specific resistance of at least 10.sup.8 Ohm*cm and in
particular of at least 10.sup.9 Ohm*cm. The material for the
insulating layer should here be selected such that cations which
are transported through the solid electrolyte can also pass through
the insulating layer to the porous electrode while electron
conductivity is negligibly small. Examples of a suitable
electrically insulating material which is arranged between the
solid electrolyte and the electrode are anodized or
sulfide-passivated aluminum fabric, ceramic fibers, glass fibers or
carbon fabric. Using the electrically nonconductive material
ensures that nonconductive cathode material, for example sulfur, is
not deposited on the solid electrolyte, so limiting current flow
during charging.
[0050] The segment wall, via which the porous electrode is
current-conductively connected to the bus conductor, is preferably
made from a metallic material, in particular from steel. Suitable
steels are the same as those which may also be used for the
displacer.
[0051] If the segment wall is made from a steel, it is preferred,
as with the displacer, for additional current conducting means to
be included. Since the segment wall is in contact with sulfur and
polysulfide on both sides, coating with an electrically highly
conductive material is not possible here. The current conducting
means used here are therefore preferably current collectors made
from a special steel tube closed at both ends and with an
electrically highly conductive core, as were described above in
relation to the displacer. Using the current conducting means
improves the electrical conductivity of the electrode. In a
particularly preferred embodiment, the special steel tube of the
bus conductor is additionally chromium-plated.
[0052] As likewise with the displacer, it is preferred to arrange
the electrically conductive wires with a clamp connection in
troughs of the extensive electrode which is of corrugated
construction.
[0053] The cover which forms the channels is likewise preferably
made from an electrically conductive material and, in a
particularly preferred embodiment, simultaneously serves as the bus
conductor. It is alternatively also possible to provide the bus
conductor outside the cover. The cover is preferably likewise made
from a metallic material, for example from steel. The same material
as for the segment wall is preferably used here.
[0054] Exemplary embodiments of the invention are illustrated in
the figures and explained in more detail in the following
description.
[0055] In the drawings:
[0056] FIG. 1 shows a sectional representation through an electrode
unit constructed according to the invention,
[0057] FIG. 2 shows a plan view of an electrode unit constructed
according to the invention with a segment wall,
[0058] FIG. 3 shows a three-dimensional representation of the
electrode unit according to the invention with a segment wall,
[0059] FIG. 4 shows a sectional representation of a displacer
constructed according to the invention,
[0060] FIG. 5 shows a sectional representation of an extensive
electrode configured according to the invention.
[0061] FIG. 1 shows an electrode unit according to the invention in
the form of a longitudinal section.
[0062] An electrode unit 1 comprises a solid electrolyte 3, which
in the embodiment shown here is of cylindrical construction and is
closed at one end. The solid electrolyte 3 is generally a ceramic
membrane which is permeable to specific cations. As described
above, .beta.''-alumina is for example suitable as a material for
the solid electrolyte 3.
[0063] The solid electrolyte 3 is adjoined by an interlayer 5 which
is insulating in terms of electron conduction. The interlayer 5
which is insulating in terms of electron conduction is for example
a passivated aluminum fabric, for example an anodized or
sulfide-passivated aluminum fabric, or carbon fabric or is made up
of ceramic fibers or glass fibers. It is alternatively also
possible to apply a special coating to the porous electrode as the
interlayer 5 which is insulating in terms of electron conduction.
In the present context, insulating in terms of electron conduction
means that the specific resistance of the layer is greater than
10.sup.8 Ohm*cm, preferably greater than 10.sup.9 Ohm*cm and in
particular greater than 2.times.10.sup.9 Ohm*cm.
[0064] The interlayer 5 which is insulating in terms of electron
conduction is enclosed by a porous electrode 7. The porous
electrode 7 is for example made from a graphite felt. In a
preferred embodiment, as shown in FIGS. 2 and 3, the porous
electrode 7 is enclosed by a segment wall 9. In the embodiment
shown here with a cylindrical solid electrolyte 3, the segment wall
9 takes the form of a sleeve.
[0065] The segment wall 9 is adjoined by a cover 11. In the
embodiment shown here, the cover 11 takes the form of a cladding
tube which has a corrugated cross-section. In this way, the cover
11 constructed in the form of a cladding tube rests in each case
with the troughs against the segment wall 9 and, with the peaks,
forms channels 13 along the segment wall 9. During charging or
discharging, cathode material flows through the channels 13. As has
already been described above, the cathode material is for example
sulfur or an alkali metal polysulfide.
[0066] In the embodiments shown in FIGS. 2 and 3, when the
electrode unit 1 is in operation, during discharging the cathode
material flows out of the flow channel 13 through inlet openings 15
into the porous electrode 7 where it is reduced electrochemically
to the anion. The anion reacts with the cations likewise
transported through the solid electrolyte 3 into the porous
electrode 7 to form a salt. The cations are particularly preferably
alkali metal ions, such that an alkali metal salt, in particular an
alkali metal polysulfide, very particularly preferably sodium
polysulfide, is formed in the porous electrode 7. The reaction
product formed in the porous electrode 7, for example the alkali
metal polysulfide, emerges via outlet openings 17 back out of the
porous electrode 7 into the flow channel 13.
[0067] The number of sleeves used for the segment wall 9 here
depends on the height of the sleeve and the length of the electrode
unit and may also be greater than the number shown here. It is also
possible to provide only one sleeve and to form a plurality of rows
of inlet openings 15 and outlet openings 17 in the sleeve.
[0068] In order to be able to output a constant electrical power
irrespective of the state of discharge, the porous electrode 7 is
segmented by flow barriers 19. The flow barrier 19 prevents the
reaction product which has formed in the porous electrode 7 from
continuing to flow onwards through the porous electrode 7 in the
region of the outlet openings 17. The flow barrier 19 ensures that
all the material emerges from the porous electrode 7 into the flow
channel 13 in the region of the outlet opening 17. This ensures
fresh cathode material is supplied to the porous electrode 7 in a
downstream segment, so improving the performance of the electrode
unit 1. So that material which has emerged from an outlet opening
17 does not immediately enter the next segment of the porous
electrode, the inlet openings 15 downstream from the outlet
openings 17 are arranged in a staggered manner relative to the
outlet openings 17.
[0069] The current released during discharging is picked off via a
current terminal 21. To this end, the respective segments of the
porous electrode 7 are contacted with the current terminal 21.
Contact is made, for example, via the segment wall 9 and the cover
11. Both the segment wall 9 and the cover 11 are here of
electrically conductive construction. It is alternatively also
possible in each case to connect the porous electrodes 7, which are
enclosed by the segment walls 9, to a central conductor which is
contacted with the current terminal 21. Any other possible way
known to a person skilled in the art of electrically contacting the
porous electrode 7 is also possible.
[0070] In the simplified embodiment shown in FIG. 5, the structure
comprises no segment walls. The porous electrodes 7 are in direct
contact with the corrugated cover 11, such that in this case too
vertically directed flow channels 13 are formed. The current supply
lines are in direct electrical contact with the porous electrode
7.
[0071] During discharging, the porous electrode 7 is the cathode.
The anode is formed by the anode material which is located on the
opposite side of the solid electrolyte 3 from the porous electrode
7. In the embodiment shown here with a cylindrical solid
electrolyte 3, the anode material is located in the interior of the
solid electrolyte 3. In order to be able to keep the quantity of
anode material small, a displacer 23 is located in the solid
electrolyte 3. The displacer 23 is here constructed such that a gap
25 is provided between the solid electrolyte 3 and the displacer
23. The anode material is located in the gap 25. If an alkali metal
is used as the anode material, the anode material is itself
electrically conductive and may be used directly as an electrode,
during discharging, as the anode. To this end, it is for example
possible for the displacer 23 to be electrically conductive and the
displacer 23 to form the current terminal.
[0072] A channel 27 is constructed in the displacer 23 for feeding
the anode material. The anode material flows through the channel 27
into the gap 25 and, on electrochemical reduction, forms cations
which pass through the cation-conductive solid electrolyte 3 into
the porous electrode 7 where the cations enter into a
neutralization reaction with the anions formed therein.
[0073] It is furthermore possible to heat the displacer 23 in order
to establish the temperature required for operation so that the
anode material and cathode material remain molten. Heating may be
provided electrically for example with a heating rod.
[0074] In one particular embodiment, heating is provided with
variable heating power distributed over the length of the electrode
unit, such that more heating is provided at the top and the least
at the bottom. This means that alkali metal which has cooled to
below the melting point and the surrounding cathode material melt
from above downwards in the form of a melt cone so ensuring that
destructive pressures cannot arise due to entrapped melt.
[0075] For charging, the salt, for example sodium polysulfide, is
supplied via the channels 13, enters through the outlet openings 17
into the porous electrode and is split by an applied voltage into
sodium ions and sulfur, wherein the sodium ions can flow through
the solid electrolyte 3 into the gap 25 and emerge through the
channel 27. The sulfur passes out of the porous electrode 7,
through the inlet openings 15 in the segment wall 9, into the flow
channel 13. Flow is initiated by the difference in density between
sodium polysulfide and sulfur. Since the sodium polysulfide has a
higher density than sulfur, the sodium polysulfide sinks downwards
and forms a flow, such that the electrode unit 1 may be
continuously operated provided that a supply of alkali metal and
sulfur is available.
[0076] The sulfur and alkali metal are stored in storage vessels
arranged separately from one another, wherein the storage vessel
for the sulfur may for example also enclose the cover 11 and flows
via the channels 13 formed by the cover 11 to the porous electrode
7. The resultant salt is then likewise collected in the storage
vessels for sulfur. Due to the difference in density, a biphasic
system forms, the sodium polysulfide being located below and the
sulfur on top.
[0077] FIG. 2 shows a plan view of the electrode unit 1 constructed
according to the invention. The plan view shown in FIG. 2 in
particular reveals the corrugated design of the cover 11 in the
form of a cladding tube. The corrugated cover 11 here rests with
troughs 29 against the segment wall 9 and individual channels 13
are formed by the peaks 31, which alternate with the troughs 29.
During discharging, the cathode material flows into the channels
13, which are formed by the peaks 31, and then enters through inlet
openings 15 into the porous electrode. The material which does not
pass into the porous electrode 7 flows onward through the flow
channel 13. At the outlet openings 17, the material flowing through
the channel mixes with the emerging material, such that a mixture
enters into downstream inlet openings 15 in the same flow channel
13, which mixture comprises a higher proportion of unreacted
cathode material than the material emerging from the outlet
openings.
[0078] FIG. 3 shows the electrode unit according to the invention
in three dimensions, the cover 11 having a cutaway to show the
underlying components. Said cutaway is not present in the installed
electrode unit 1. The representation in FIG. 3 reveals that the
outlet openings 17 are arranged in a staggered manner relative to
the downstream inlet openings 15. This prevents material from an
outlet opening 17 from being able to flow directly into the
downstream inlet opening 15. In the embodiment show here, the inlet
openings 15 and outlet openings 17 are in each case constructed
with a rectangular cross-section, an extension 33 of the extensive
electrode 9 constructed as a sleeve in each case being located
between two inlet openings 15 or two outlet openings 17, which
extension is respectively of the same width as the downstream inlet
opening 15 or the preceding outlet opening 17.
[0079] In the embodiment shown here, the extensive electrodes 9 are
made as separate sleeves which in each case comprise the inlet
openings 15 at one end and the outlet openings 17 at the other end.
Design as individual sleeves facilitates installation and
production. Alternatively, however, it is also possible to provide
only one sleeve in which inlet openings 15 and outlet openings 17
are formed. The design with separate sleeves, the ends of which
respectively comprise inlet openings 15 and outlet openings 17, is
preferred however. In one particularly preferred embodiment, the
inlet openings 15 and the outlet openings 17 on one sleeve are in
each case in axial alignment with one another. It is furthermore
also possible, in addition to the rectangular inlet openings 15 and
outlet openings 17 shown here, to construct the inlet openings and
outlet openings in any other desired shape. The openings may
accordingly, for example, be constructed in the form of a
semicircle or a semiellipse or even as a triangle, if the openings
are in each case at the end of the sleeve. If only one extensive
electrode is provided, in which a plurality of rows of inlet
openings 15 and outlet openings 17 are constructed, said openings
may also be constructed in any other desired shape, for example
elliptical, circular, triangular or polygonal with as many vertices
as desired.
[0080] In addition to the embodiment shown here with a cylindrical
solid electrolyte 3 and thus likewise cylindrical porous electrodes
7, it is also possible to construct the electrode unit 1 with any
other desired cross-section and also as an extensive electrode
unit. Preferably, however, the electrode unit 1 is cylindrical, as
shown here.
[0081] In order to create a longer electrode unit 1, more than the
two segment walls 9 constructed as a sleeve which are shown here
may be provided.
[0082] FIG. 4 shows a sectional representation through a displacer
constructed according to the invention.
[0083] The displacer 23 is preferably made from special steel. In
order to avoid damaging the solid electrolyte 3 by thermal
expansion of the displacer 23, the displacer 23 is preferably
configured such that it rests resiliently against the solid
electrolyte 3. Resting in a resilient manner against the solid
electrolyte may for example be achieved by a design with
projections 35 and recesses 37. This results for example in a
corrugated design of the displacer 23. It is furthermore also
possible, in particular, if additional current conductors 39 are
provided, to make the recesses 37 omega-shaped, into which current
conductors 39 with a circular cross-section are clamped.
[0084] In the embodiment shown here, the current conductors 39
comprise a jacket in the form of a tube 41 closed at both ends and
a core 43 of an electrically highly conductive material. The entire
circumference of the core 43 here rests against the tube 41. As has
already been described above, the tube is preferably made from a
special steel and the core is of aluminum, copper, silver, gold or
sodium. Using the current conductors 39 improves the electrical
conductivity of the displacer 23 made from special steel which has
comparatively poor conductivity.
[0085] The displacer is conventionally hollow on the inside. The
internal region 45 of the displacer may for example be used to
accommodate a vessel comprising sodium. The vessel is here
preferably likewise made from special steel.
[0086] FIG. 5 shows a sectional representation of the extensive
electrode in one embodiment of the invention.
[0087] The solid electrolyte 3 is enclosed by an electrically
insulating layer 5 and a porous electrode 7. The porous electrode 7
is adjoined by the cover 11 which, in the embodiment shown here, is
of corrugated construction. Flow channels 13, through which sulfur
and polysulfide flow, are formed by the corrugated design of the
cover 11.
[0088] If the cover 11 is made from steel, additional current
conductors 47 should be provided to improve electrical
characteristics. The current conductors 47 are here preferably
arranged on the side of the cover 11 which faces towards the solid
electrolyte 3. In the embodiment shown here, the current conductors
47 are accommodated in flow channels 23 of the extensive electrode.
The geometries of the flow channels 23 and current conductors 47
are here adapted to one another such that a current conductor 47 in
each case rests continuously against the wall of a flow channel 13.
In order to avoid an unwanted reaction of the current conductor
with the sulfur or polysulfide, the current conductor 47, like the
current conductor 39 arranged on the displacer side, is made with a
jacket of a special steel tube 49 closed at both ends and a core 51
of an electrically highly conductive material. The electrically
highly conductive material is preferably copper, aluminum, silver
or gold, particularly preferably copper or aluminum.
[0089] In addition to being arranged in every other flow channel
13, as shown here, any other desired uniform or nonuniform
distribution of the current conductor 39 is possible. For example,
in the case of a uniform distribution it is accordingly also
possible to provide the current conductors only in every third or
every fourth flow channel 13.
[0090] In addition to the embodiment shown here, it is furthermore
also possible to arrange current conductors on the side of the
cover 11 remote from the solid electrolyte 3. In this case, it is
preferred to contact the electrically highly conductive material
directly with the material of the cover 11, for example by a
coating or also by a clamp connection of a wire made from the
electrically highly conductive material in a trough of the cover 11
of corrugated construction that is remote from the solid
electrolyte 3. In order to prevent reaction of the electrically
highly conductive material with sulfur or polysulfide, a cover,
which is not shown here, in this case encloses the extensive
electrode and thus also the electrically highly conductive
material. The same cover material is here preferably selected as
for the cover 11.
LIST OF REFERENCE NUMERALS
[0091] 1 Electrode unit [0092] 3 Solid electrolyte [0093] 5 Layer
insulating in terms of electron conduction [0094] 7 Porous
electrode [0095] 9 Segment wall [0096] 11 Cover [0097] 13 Flow
channel [0098] 15 Inlet opening [0099] 17 Outlet opening [0100] 19
Flow barrier [0101] 21 Current terminal [0102] 23 Displacer [0103]
25 Gap [0104] 27 Channel [0105] 29 Trough [0106] 31 Peak [0107] 33
Extension [0108] 35 Projection [0109] 37 Recess [0110] 39 Current
conductor [0111] 41 Tube [0112] 43 Core [0113] 45 Internal region
of the displacer 23 [0114] 47 Current conductor [0115] 49 Special
steel tube [0116] 51 Core
* * * * *