Note: Descriptions are shown in the official language in which they were submitted.
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ELECTROCHEMICAL CELL
Technical Field
This invention relates to electrochemical cells and in particu-
lar to electrochemical cells having an air cathode.
Background Art
One conventional form of electrochemical cell for providing
electrical power utilizes a lithium anode and an air cathode.
limitation on the power developing ability of such cells, however,
adversely restricts the usefulness thereof in high power density
applications, such as present in aeronautical propulsion systems.
Another form of conventional battery utilizes a lithium anode
with hydrogen peroxide electrolyte. Such batteries provide gxeater
power output than the air cell batteries, but have a serious disad-
vantage in relatively high weight and cost. Thus, again, such per-
oxide system batteries are not adapted for use in aeronautical pro-
pulsion high power density systems.
Disclosure of Invention
The present invention comprehends an improved lithium-air cell
having means for providing supplemental oxidizer to the cathode
reaction whenever the air cathode reaction cannot provide a suffi-
ciently high rate of electrochemical reaction.
More specifically, the novel method of the present invention
comprehends contacting a first surface portion of the air cathode
with atmospheric air, and contacting a second surface portion of
?5 the air cathode with an electrolyte containing soluble oxygen for
providing oxidizer to the cathode.
In another form of the invention, there is provided a method
of providing electrical energy in such an electrochemical cell by
providing the oxidizer to the cathode in the event the air cathode
30 reaction with the contacted air is in~uE;eicient to provide the
desired rate of electrochemical reaction of the cell.
Still another form of the invention comprehends the further
step of catalyzing the decomposition of the soluble oxygen which
may be present in the form of H2O2 in the electrolyte for
35 increasing the reaction thereof with the cathode ions.
Yet another embodiment of the invention comprehends the provi-
sion of an electrochemical cell having a lithium anode and a hydro-
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phobic air cathode comprising a porous element having a first
surface portion exposed to ambient air and fluid electrolyte
comprising an aqueous solution of hydrogen peroxide contacted with
a second surface portion of the air cathode porous element.
The invention further comprehends in another embodiment, the
provision in such an electrochemical cell of means disposed inter-
mediate the anode and cathode for catalyzing the decomposition of
the hydrogen peroxide and the reaction between the hydrogen per-
oxide and the cathode ions.
In the illustrated embodiment of the invention, the air
cathode is porous.
In the illustrated embodiment, the electrolyte is flowed
through the cell.
The concentration of the soluble oxygen in the electrolyte may
be varied selectively to meet the power demand needs. Alterna-
tively, the rate of flow of the electrolyte may be con-trolled for
this purpose.
The method of providing electrical energy and the electro-
chemical cell structure utilizing the method are extremely simple
and economical, while yet providing a highly improved, lightweight
air cathode electrochemical cell power supply permitting high power
demand when desired.
Brief Description of the ~rawing.
Other features and advantages of the invention will be appar-
ent from the following description taken in connection with thedrawing wherein the figure is a transverse section illustrating an
electrochemical cell embodying the invention and illustrating the
method of providing electrical energy from an air cathode electro-
chemical cell embodying the invention.
Best Mode for Carrying Out the Invention
In the illustrative embodiment of the invention as disclosed
in the drawing, an electrochemical cell generally designated 10 is
shown to include an anode 11, an air cathode 12, and a catalytic
screen 13 interposed between the anode and cathode within an outer
housing 14.
One surface 15 of the air cathode is exposed to ambient atmos-
phere in a chamber 16 of housing 14, and the opposite surface 17 of
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the air cathode is contacted by electrolyte fluid 18 flowed through
a second chamber 19 in housing 14 as by a suitable pump 20.
In the illustrated embodiment, the electrolyte is provided
from a reservoir 21 for suitable delivery when needed.
More specifically, anode 11 comprises a lithium anode which
may comprise elemental lithium metal or lithium alloyed with alloy-
ing material, such as small amounts of aluminum.
The air cathode 12 may comprise a conventional cathode struc-
ture formed of a suitable porous hydrophobic material, such as
"Teflon"* synthetic resin coated with a suitable catalytic
material, such as a graphite-platinum matrix, for catalyzing the
cathodic reaction of atmospheric oxygen with cathode ions.
The catalytic screen 13 illustratively may comprise a woven
metal wire screen formed of suitable catalytic metal, such as pala-
dium, ruthenium, or silver plated wire.
In the illustrated embodiment, the electrolyte comprises afluid containing soluble oxygen for providing a supplemental
oxidizer to the cathode. In the illustrated embodiment, the elec-
trolyte comprises a solution of 4.2 + molar lithium hydroxide in
water with a preselected concentration of H2O2. The H2O2
provides water soluble oxygen for providing the oxidizer to the
cathode reaction whenever the air cathode reaction is insufficient
to meet the power demands of the cell.
The H2O2 may be present in a concentration of up to
approximately 1.0 molar in the aqueous solution.
Thus, the invention comprehends an improved method of provid-
ing electrical energy from an electrochemical cell having a
lithium-containing anode and an air cathode, wherein supplemental
oxidizer is provided to the cathode as required to meet intermit-
tent high power demands exceeding the ability of the cathode to pro-
vide the desired power by an air cathode reaction wlth atmospheric
air alone.
~y contacting opposite sides of an active cathode with peroxide
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1 and a-tmospheric oxygen, respectively, a novel method and structural
2 arrangement is provided, solving the vexatious problem of the prior art
3 wherein air cathode electrochemical cells have not been found capable of
4 adaptation for high power demana loads where weight is at a premium.
6 Industrial Applicabillty
7 The present invention is advantageously adapted for use in
8 aeronautical propulsion applications. Illustratively, where a hydrogen
g peroxide cell of the prior art was utilized to provide the e~ectrical
power in the power plant of a Hughes Model 269 helicopter, the hydrogen
11 peroxide weight accounted for 50 percent of the entire power train.
12 It has been found that use of an electrochemical cell in
13 accordance with this invention, providing approximately 400 ma/cm2 out
4 of a design load of lOOO ma/cm2, would reduce the peroxide weight by
40 percent or more, and thus substantially improve the power-to-weight
16 ratio of the electrochemical cell system, making it advantageously
17 adapted for such aeronautical propulsion use.
18 Obviously, other industrial applications requiring high
1~ intermittent power demand output at light weight of the electrochemical
cell structure may utilize the method and apparatus of the present
21 invention advantageously.
22 The foregoing disclosure of specific embodiments is
23 illustrative of` the broad inventive concepts comprehended by the
24 invention.
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