Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Include electrolyte chemically specified and method
Patent
1985-07-08
1986-08-26
LeFevour, Charles F.
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Include electrolyte chemically specified and method
429197, 429220, 429221, H01M 614
Patent
active
046083243
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to an organic electrolyte cell using lithium or a lithium base alloy as an anode active material and having a high energy density, more particularly to an improved cathode active material for the cell.
BACKGROUND OF THE INVENTION
As the cathode active material of the organic electrolyte cell are known various materials such as carbon fluoride and manganese dioxide. Copper oxide (CuO) is also one of the various cathode active materials and has so high a theoretical electric capacity per unit as 4.25 Ah/cc. Particularly a cell comprising a combination of a lithium anode with copper oxide has a discharge voltage of 1.35 to 1.5 Volts and, therefore, such a cell is interchangeable with a silver oxide cell or mercury cell which is a general-purpose cell, and has excellent shelf stability and resistance to liquid leakage as compared with the general-purpose cell. Therefore, such a cell has been noticed as being attractive as an electric source for precision electronic devices, such as an electronic watch.
However, this cell has such a defect in discharge characteristics that there is a transient voltage drop at an initial discharge stage until the voltage is settled in a constant level. This defect is an important problem when the cell is used in the precision electronic devices such as an electronic watch. Such voltage drop phenomenon as mentioned above inherently occurs in a copper oxide-lithium cell and cannot be eliminated with any electrolyte changed.
One of ways for eliminating such voltage drop is considered that an active material having a higher discharge voltage than that of copper oxide is mixed with the copper oxide and the active material mixed undergoes the reaction preferentially at the initial discharge stage.
In this case, of course, the active material mixed should not be reactive with the copper oxide. On the other hand, however, the discharge voltage should not get two different levels. Therefore, the voltage of a cell comprising a combination of the above-mentioned active material with an lithium anode is desirably approximately equal to or slightly higher than that of a copper oxide-lithium cell and, in addition, the active material should have a high theoretical electric capacity.
DESCRIPTION OF THE INVENTION
In accordance with the present invention, chalcopyrite CuFeS.sub.2 is used as an active material to be mixed with copper oxide.
The theoretical electric capacity of the chalcopyrite is 2.9 Ah/cc. and thus smaller than that of copper oxide, but the theoretical electric capacity of a combination of the chalcopyrite and lithium anode, i.e., Li-CuFeS.sub.2 is 1.20 Ah/cc. which is slightly smaller than that of Li-CuO, 1.39 Ah/cc., since the lithium anode occupies a major part of the combination. Furthermore, the chalcopyrite has a higher efficiency of discharge than that of copper oxide and substantially approximately the same electric capacity as that of copper oxide.
Further surprisingly, an effect of improving the efficiency of discharge of copper oxide is obtained by mixing chalcopyrite with copper oxide. That is, the efficiency of discharge of copper oxide itself is raised and the reaction proceeds fully to the center of the thickness of an electrode as the amount of chalcopyrite mixed with the copper oxide is increased, whereas in an electrode of copper oxide only the reaction may proceed insufficiently to the center of the thickness of the electrode when it is thick. This is considered to be contributed to by the preferential discharge of chalcopyrite at the initial stage of the reaction, resulting in the increase of active sites on the surface of copper oxide contacting the chalcopyrite, and necessarily in the increase in the efficiency of discharge of the copper oxide.
As mentioned above, the advantages obtained by incorporating chalcopyrite into copper oxide are remarkable, that is, voltage drop at the initial discharge stage, which is a defect of the copper oxide-lithium cell, is not only reduced, but also the efficiency
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Fujii Takabumi
Iijima Takashi
LeFevour Charles F.
Matsushita Electric - Industrial Co., Ltd.
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