CA1113540A

CA1113540A - Additive to lithium anode, thionyl chloride active cathode electrochemical cell

Info

Publication number: CA1113540A
Application number: CA310,153A
Authority: CA
Inventors: Louis R. Giattino
Original assignee: Individual
Current assignee: Individual
Priority date: 1977-08-29
Filing date: 1978-08-28
Publication date: 1981-12-01
Also published as: GB2003651B; GB2083684B; FR2402307B1; IL55428A0; GB2083684A; FR2402307A1; DE2837511A1; DE2837511C2; GB2003651A

Abstract

ADDITIVE FOR LITHIUM ANODE, THIONYL CHLORIDE ACTIVE CATHODE ELECTROCHEMICAL CELL

ABSTRACT OF THE DISCLOSURE
Electrochemical power cells having a lithium anode, a carbonaceous current collector, and thionyl chloride active cathode depolarizer and electrolyte solvent are enhanced by adding copper thereto.

Description

1~13S4~;) This invention relates to high energy electro-chemical power cells. More particularly, it relates to cells having an oxidizable anode material and a liquid active cathode material and a solid current collector.
- Recently there has been a rapid growth in portable electronic products requiring electrochemical cells to supply the energy. Examples are calculators, cameras and digital watches. These products, however, have highlighted the deficiencies of the existing power ce'ls Sor demanding 1~ applications. For example, digital watches were developed using the silver oxide cell, and although these watches have become popular, it is now generally recognized that the least developed component of the digital watch system is the power cell. In particular, the energy density of the silver cells is such that thin, stylish watches with reasonable operating life are difficult to make. Additionally, these cells have poor storage characteristics, low cell voltages, and leakage problems.
In an effort to develop a cell that a~dresses one or more of the foregoing problems, substantial work has been done with cell chemistries using a lithium anode. The cathode and electrolyte material consisting of a solvent and solute vary. Indeed the literature is replete with examples of lithium anode cells with different cathodes and elec-trolytes. The ~lectrical characteristics of these cellssuch as energy per unit volume, called energy density; cell :

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voltage; and internal impedance vary greatly.
Among all of the known combinations of lithium anodes with different cathodes and electrolytes, those believed to have among the highest energy density and lowest internal impedance use certain inorganic liquids as the active cathode depolarizer. This type of cell chemistry i5 commonly referred to as "liquid cathode".
Early liquid cathode cells used liquid sulfur dioxide as the active cathode depolarizer as described in U.S. Patent No. 3,567,515 issued to Maricle, et al. on March

2, 1971. Since sulfur dioxide is not a liquid at room temperature and at atmospheric pressure, it proved to be quite a difficult chemistry with which to work. More importantly, sulfur dioxide cells are unsafe for most i5 consumer applications due to their propensity to explode under certain circumstances.
A major step forward in the development of liquid cathode cells was the discovery of a class of inorganic materials, generally called exyhalides, that are liquids at room temperature and also perform the function of being the active cathode depolarizer. Additionally~ these materials may also be used as the electrolyte solvent. Liquid cathode cells using oxyhalides are described in U.S. Patent No.

3,926,669 issued to Auborn on December 16, 1975, and in British Patent No. 1,409,307 issued to Blomgren et al. on October 18, 1975. At least one of the oxyhalides, thionyl .

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~__~,.,4~) chloride (SOC12), in addition to having the general charac-teristics described above, also provides substantial addi-tional energy density.
As described in the Auborn and Blomgren patents, the anode is lithium metal or alloys of lithium and the electrolyte solution is an ionically conductive solute dissolved in a solvent that is also an active cathode depolarizer.
The solute may be a simple or double salt which will produce an ionically conductive solution when dissolved in the solven~. Preferred solutes are complexes of inor-ganic or organic Lewis acids and inorganic ionizable salts.
The requirements for utility are that the salt, whether simple or complex, be compatible with the solvent being employed and that it yield a solution which is ionically conductive. According to the Lewis or electronic concept of acids and bases, many substances which contain no active hydrogen can act as acids or acceptors or electron doublets.
In the U.S. Patent No. 3,542,602 it is suggested that the complex or double salt formed between a Lewis acid and an ionizable salt yields an entity which is more stable than either of the components alone.
Typical Lewis acids suitable for use in the -present invention include aluminum chloride, antimony pcn~ckl~ e, zirconium tetrachloride, phosphorous pent-,. : - . . : -- : . .

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chloride, boron fluoride, boron chloride and boron bromide.
Inoniæable salts useful in combination with the Lewis acids include lithium fluoride, lithium chloride, lithium bromidej lithium sulfide, sodium fluoride, sodium chloride, sodium bromide, potassium fluoride, potassium chloride and potassium bromide.
The double salts formed by a Lewis acid and an inorganic ionizable salt may be used as such or the indivi-dual components may be added to the solvent separately to form the salt. One such double salt, for example, is that formed by the combination of aluminum chloride and lithium chloride to yield lithium aluminum tetrachloride.
In addition to an anode, active cathode depo-larizer and ionically conductive electrolyte, these cells require a current collector.
According to Blomgren, any compatible solid, which is substantially electrically conductive and inert in the cell, will be useful as a cathode collector since the function of the collector is to permit external electrical contact to be made with the active cathode material. It is desirable to have as much surface contact as possible between the liquid cathode and the current collector.
Therefore, a porous material is preférred since it will provide a high surface area interface with the liquid cathode material. The current collector may be metallic : ,:: . :~. .

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.354~1i and may be present in any physical form such as metallic film, screen or a pressed powder. Examples of some sui-tab:e metal current collectors are provided in ~able II of the Auborn Patent. The current collector may also be made S partly or completely of carbon. Examples provided in the Blomgren Patent use graphite.
Electrical separation of current collector and anode is required to insure that cathode or anode reactions do not occur unless electrical current flows through an external circuit. Since the current collector is insoluble in the electrolyte and the anode does not react spontan-eously with the electrolyte, a mechanical separator may be used. Materials useful for this function are described in the Auborn Patent.
Although the varied cells described in the Blom-gren and Auborn Patents may be feasib~e, much of the recent interest is in cells using thionyl chloride as the active cathode depolarizer and electrolyte solvent. This results from thionyl chloride's apparent ability to provide greater energy density and current delivery capability than other o~yhalide systems. Yet even though thionyl chloride cells have proven to be the best performer among the oxyhalides, they have not lived up to expectations on energy density or internal impedance. Furthermore, the thionyl cloride cell is equally if not more dangerous than the sulfur dioxide cell. As a result, all known efforts to co~mercialize cells .

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using this chemistry have failed.
The present invention is based on the discovery that a substantially safer lithium or calcium anode, thionyl chloride active cathode depolarizer cell with the added benefits of higher energy density and lower internal impedance can be made by adding copper to the cell.
Thus, it is an object of this invention to provide an improvement to the known lithium/thionyl chloride cell that renders the cell safer.
It is another object to provide a lithium/thionyl chloride cell having higher energy densities than those reported in the literature.
Finally, it is the object of this invention to provide a lithium/
thionyl chloride cell with low internal impedance.
These and other objects of the invention may be achieved by an electrochemical cell comprising an anode made from either lithium or calcium;
a current collector spaced from said anode; an electrolyte solution disposed between said current collector and anode; and an additive consisting primarily of copper in intimate contact with said electrolyte. The electrolyte solution includes an active cathode depolarizer which may be either phosphoryl chloride, thionyl chloride, or sulfuryl chloride.

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54i) As mentioned previously, the basis of this inven-tion is the discovery that the addition of elemental copper to the cell provides substantial improvements in both performance and safety. While the theoretical explanation of this phenomenon is not clear, and applicant does not intend to be limited to any theory of invention, at least one explanation of the results involves a reaction with the copper and elemental s-ulfur. Some of the several different reactions that could occur in the prior art cells ~there is no conclusive evidence as to which reaction or reactions actually occur) are as follows:
3 SOC12 + 8 Li Li2S03 * 6 LiCl + 2S (1)

4 SOC12 + 8 Li ~i2S2 4 2 2 (2) 4 SOC12 + 8 Li 4 ~iCl + SO2 + S (3) These reactions all release the same amount of electrical energy~ However, equation (1) requires less thionyl chloride. Thus the energy density of this reaction is higher. That is, more electrical energy can be derived from a given volume of chemicals with the reaction of equation (l) than with the reaction of e~uations (2~ or (3).
One possible explanation of the difference in energy of the cell of this invention is that the copper first acts as a catalyst to force the reaction to be a higher energy density reaction such as the reaction of equation (1), and second, combines with the elemental sulfur to form copper sulfide.

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, - - -- - : -~135~t) The significance of the copper sulfur reaction relates to safety. It is widely believed that the elemental sulfur in contact with lithium will explode above a certain temperature and that this temperature may be easily reached by short circuiting, reverse charging, or other electrical conditions, as well as exposure to high ambient tempera-tures. However, copper sulfide does not react explosively with lithium at any temperature likely to be experienced by batteries. Experimental evidence tends to support this in that batteries made pursuant to this invention do not explode under circumstances that would cause prior art batteries to explode.
Test results showing the effect of varying per-centages of copper on energy density and internal impedance are provided in Table I. This data is given by way of ~-examples to enable those persons skilled in the art to more clearly understand and practice the invention. They are intended to be illustrative and representati~e but not limiting to the scope of the invention.
Each of the entries in Table I represents a test cell having a nominal internal volume of .035 cu inches constructed in a typ;cal button configuration with single disc shaped current collector, anode and separator. The electrolyte is a 1.5 molar solution of lithium aluminum tetrachloride in thionyl chloride. The anode is a .680 inch ....j, , :

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diameter disc o .020 inch thick lithium. The separator is a commercially available ceramic paper. The current col-lector is acetylene black. Particulate copper is dispersed in the acetylene black which is then compacted into a pellet. The only variable in the cell is the ratio by weight of carbon to copper.

TABLE I
Ratio ~ Life Load Current Internal 10 C:Cu Cu - mah voltage Impedance 1:1 50 110 3.29 54.8 5.16 2:1 33 170 3.30 55.0 5.56 3:1 25 180 3.29 54~8 5.65 1~ 4:1 20 200 3.28 54.6 5.86 6:1 14 210 3.28 54.6 5.86 8:1 11 205 3.24 54.0 6.6 10:1 9.1 195 3.24 54.0 6.6 12:1 7.7 195 3.22 53.6 7.0 16:1 5.9 195 3.22 53.6 7.~2 -- 0 190 3.15 52.5 8.57 S~

The foregoing results were taken from samples that were tested shortly after their construction. The trends generally indicated by the data in Table I are accentuated as the batteries are stored at elevated temperatures.
It is understood that the preferred embodiment described above does not limit the scope of the invention.
Certainly copper in either a more or less finely divided state would be useful, and other battery geometrics such as spiral wound may also be employed with the present inven-tion.

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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An electrochemical cell consisting essentially of a lithium anode; a carbonaceous current collector spaced from said anode; an ionically conductive electrolyte solution comprising an ionically conductive solute dissolved in thionyl chloride; and copper dispersed in said carbonaceous current collector.

2. The electrochemical cell of claim 1 in which said current collector is a porous body of carbon and said copper is finely divided and intimately dispersed in said carbon.

3. The electrochemical cell of claim 2 in which the ratio by weight of carbon to copper comprises from about one to one to ten to one.

4. The electrochemical cell of claim 2 in which the ratio by weight of carbon to copper is substantially six to one.

5. An electrochemical cell comprising an anode, selected from the group consisting of lithium and calcium, a current collector spaced from said anode and comprising a porous body including intimately dispersed particles of copper and carbon, and an electrolyte solution disposed between said current collector and anode including a cathode depolarizer comprising thionyl chloride.

6. The electrochemical cell of claim 5 in which said anode consists of calcium.

7. An electrochemical cell comprising: an anode selected from the group consisting of lithium and calcium; a carbonaceous current collector spaced from said anode; an ionically conductive electrolyte solution in intimate contact with said current collector and said anode, said electrolyte comprising an ionically conductive solute dissolved in an active cathode depolarizer selected from the group consisting of one or more of the following: phosphoryl chloride, thionyl chloride and sulphuryl chloride; an additive consisting primarily of copper dispersed in said current collector.

8. An electrochemical cell comprising: an anode selected from the group consisting of lithium and calcium; a carbonaceous current collector spaced from said anode; an ionically conductive electrolyte solution in intimate contact with said current collector and said anode, said electrolyte comprising an ionically conductive solute dissolved in an active cathode depolarizer selected from the group consisting of one or more of the following: phosphoryl chloride, thionyl chloride or sulphuryl chloride; an additive consisting primarily of copper dispersed in said current collector.

9. The electrochemical cell of claim 8 wherein said additive is finely divided and dispersed in said current collector.

10. The electrochemical cell of claim 9 wherein said anode is primarily lithium.

11. The electrochemical cell of claim 10 wherein said active cathode depolarizer is thionyl chloride.

12. The electrochemical cell of claim 11 wherein said copper additive and said carbonaceous current collector are in the proportionate range of 1:1 to 10:1 by weight of current collector to additive.

13. An electrochemical cell comprising: an anode selected from the group consisting of lithium and calcium; a current collector spaced from said anode;
an ionically conductive electrolyte solution in intimate contact with said current collector and said anode, said electrolyte comprising an ionically conductive solute dissolved in an active cathode depolarizer selected from the group consisting of phosphoryl chloride, thionyl chloride or sulphuryl chloride;
and an additive consisting primarily of copper in intimate contact with said electrolyte.

14. An electrochemical cell according to claim 13 wherein said current collector is a carbonaceous current collector and wherein said copper is dispensed in said current collector.

15. An electrochemical cell comprising: an anode selected from the group consisting of lithium and calcium; a current collector spaced from said anode;
an electrolyte solution disposed between said current collector and anode, said electrolyte solution including an active cathode depolarizer selected from the group consisting of phosphoryl chloride, thionyl chloride or sulfuryl chloride; and an additive consisting primarily of copper in intimate contact with said electrolyte.