HIGH ENERGY ELECTROCHEMICAL POWER CELL

PILE ELECTROCHIMIQUE HAUTE ENERGIE

English Abstract

ABSTRACT OF THE DISCLOSURE
An improved high energy electrochemical power cell is
obtained by adding cupric chloride to the high surface area carbon
black cathode of a lithium-inorganic electrolyte cell.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In a high energy electrochemical power cell employing lithium as the
anode, a solution of a highly soluble lithium salt in an oxychloride solvent
as the electrolyte and a high surface area carbon black cathode, the improve-
ment of preparing the cathode by adding cupric chloride to the high surface
area carbon black so that the initial cathode composition is a mixture of
high surface area carbon black and cupric chloride and incorporating said
cathode in the lithium-oxychloride solvent system to reduce cathode polariza-
tion at high discharge rates.
2. A high energy electrochemical power cell according to claim 1 using
about 20 to 25 weight percent cupric chloride as the additive.
3. A high energy electrochemical power cell according to claim 2 wherein
the lithium salt is lithium tetrachloroaluminate.
4. A high energy electrochemical power cell according to claim 3 wherein
the oxychloride solvent is selected from the group consisting of phosphorous
oxychloride, thionyl chloride, and sulfuryl chloride.
5. A high energy electrochemical power cell according to claim 4 wherein
the oxychloride solvent is phosphorous oxychloride.
6. A high energy electrochemical power cell according to claim 4 wherein
the oxychloride solvent is thionyl chloride.
7. A high energy electrochemical power cell according to claim 4 wherein
the oxychloride solvent is sulfuryl chloride.
8. A high energy electrochemical power cell according to claims 1,2, or 5,
wherein the high surface area carbon black has a surface area of about 50 m2/gm
to 1000 m2/gm.

9. In a high energy electrochemical power cell employing lithium as the
anode, a solution of lithium tetrachloroaluminate in thionyl chloride as the
electrolyte, and a carbon black cathode having a surface area of about 60 m2/gm,
the improvement of preparing the cathode by adding about 20 to 25 weight
percent of cupric chloride to the carbon black so that the initial cathode
composition is a mixture of carbon black having a surface area of about 60 m2/gm
and about 20 to 25 percent of cupric chloride and incorporating said cathode in
the lithium-oxychloride solvent system to reduce cathode polarization at high
discharge rates.
10. A high energy electrochemical power cell according to claim 2 wherein
the oxychloride solvent is selected from the group consisting of phosphorous
oxychloride, thionyl chloride, and sulfuryl chloride.
11. A high energy electrochemical power cell according to claim 10 wherein
the oxychloride solvent is phosphorous oxychloride.
12. A high energy electrochemical power cell according to claim 10 wherein
the oxychloride solvent is thionyl chloride.
13. A high energy electrochemical power cell according to claim 10 wherein
the oxychloride so vent is sulfuryl chloride.
14. A high energy electrochemical power cell according to claim 10 wherein
the high surface area carbon black has a surface area of about 50 m2/gm to
1000 m2/gm.
15. A high energy electrochemical power cell according to claim 2 wherein
the high surface area carbon black has a surface area of about 50 m2/gm to
1000 m2/gm.

16. A high energy electrochemical power cell according to claim 15 wherein
the lithium salt is lithium tetrachloroaluminate.
17. A high energy electrochemical power cell according to claim 16 wherein
the oxychloride solvent is selected from the group consisting of phosphorous
oxychloride, thionyl chloride, and sulfuryl chloride.
18. A high energy electrochemical power cell according to claim 17 wherein
the oxychloride solvent is phosphorous oxychloride.
19. A high energy electrochemical power cell according to claim 17 wherein
the oxychloride solvent is thionyl chloride.
20. A high energy electrochemical power cell according to claim 17 wherein
the oxychloride solvent is sulfuryl chloride.

Description

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This invention relates in general to improvements in high energy
electrochemical power cells and in particular to an improved lithium-
inorganic electrolyte electrochemical cell.
Lithium-inorganic electrolyte cells are capable of providing high
energy densities at ambient temperature. These cells employ a lithium
anode, a solution of a highly soluble lithium salt such as lithium tetra-
chloroaluminate in an oxychloride solvent such as phosphorous oxychloride,
thionyl chloride or sulfuryl chloride as the electrolyte and a high surface
area carbon black cathode. A novel feature of these cells is that the oxy-
chloride serves the dual purpose of being a solvent for the lithium salt
and acting as a cathode depolarizer. One of the hest known of these lithium-
inorganic electrolyte cells is the lithium-thionyl chloride cell which has
been demonstrated to deliver energy densities of the order of 250 watt hours
per pound at ambient temperature.
A difficulty encountered, however, with the carbon black cathodes
of the lithium-thionyl chloride cells is that while they show slight polariza-
tion at low discharge rates, they suffer from excessive polarization at high
discharge rates.
It has recently been suggested in Great Britain patent application
o GB 2,003,651A, to L~Ro Giattino, published 14 March, 1979, that the lithium-
thionyl chloride cell could be benefited by adding copper to the cell. The
difficulty with copper as the additive, however, is that copper is unstable
in the electrolyte and partially goes into solution and is deposited on the
lithium anode. This deposition decreases the shelf life of the cell as well
as causing a worsening of the voltage delay.
The general object of this invention is to provide an improved
high energy electrochemical power cell. A more particular object of
the invention is to provide an improved lithium-inorganic electrolyte
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~'9~446
cell wherein cathode polarization at high discharge rates is reduced.
It has now been found that the foregoing objects can be
attained by adding cupric chloride to a high surface area carbon black
cathode of a lithium-thionyl chloride cell.
Cupric chloride is insoluble in thionyl chloride solutions
and undergoes reduction in the solid state at about 3.56 volts versus a
lithium reference. Thus, when high surface area carbon black cathodes are
prepared using about 20 to 25 weight percent of cupric chloride as additive,
cupric chloride undergoes reduction concurrently with thionyl chloride and
enables the cathode to sustain higher currents without as much polarization
as occurs with carbon cathodes made without the cupric chloride additive.
A carbon paste electrode with cupric chloride additive is
prepared by adding about 21.7 weight percent of cupric chloride to a high
surface area carbon black.
When the carbon black electrode with cupric chloride
additive is incorporated in a lithium-thionyl chloride system, experiments
with laboratory cells indicates that the carbon black paste electrode con-
taining the cupric chloride additive increases the current carrying capabilities
of carbon cathodes as compared to the carbon black paste electrode without
the cupric chloride additive. Thus, carbon cathodes containing cupric
chloride additive can deliver cell voltages above 3 volts at current densities
up to 50 mA/cm whereas carbon cathodes without the cupric chloride additive
can deliver cell voltages above 3 volts at current densities only up to
25 mA¦cm2. The improvement allows the cathode potential and cell voltages
to be maintained at high levels out to current densities which are encountered
in such applications as laser designators. Moreover, the reduction in cathode
polarization decreases release of entropic heat and thereby results in the
enhancement of cell safety.
In the high energy electrochemical power cells of the
invention, in lieu of thionyl chloride, one may use other oxychloride solvents
such as phosphorous oxychloride and sulfuryl chloride. Similarly, in lieu of
lithium tetrachloroaluminate as the solute, one may use other highly soluble
lithium salts.

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~he high surface area carbon black used should have a
surface area of about 50 m2/gm to 1000 m21gm. Preferred for use in the
invention is Shawinigan black, a carbon black having a surface area of
about 60 m /gm.
I wish it to be understood that I do not desire to be
limited to the exact details as described for obvious modifications will
occur to a person skilled in the art.
* denotes trademark
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