The present invention relates to a battery, and more particularly to a battery which has means which, upon the occurrence of an abnormal phenomenon, such as an overcharge or an external short circuit, rapidly operates a safety mechanism, such as a current breaking valve, to ensure the safety of the battery.
The spread of portable equipment, such as portable telephones, potable information terminal equipment, and personal computers, has led to an increasing demand for batteries having high energy density. This in turn has led to studies on an increase in capacity. On the other hand, with an increase in the energy density of batteries, an improvement in safety has become important. This is for ensuring safety upon the occurrence of abnormal phenomenon derived from wrong use by a user or malfunction of a circuit. For example, a mechanism (current breaking valve) for breaking current in response to a rise in pressure within the battery and a mechanism (rupture) for releasing internal pressure have been developed and put to practical use. Upon a mistake of connection or malfunction of a charge control circuit, these mechanisms break the current or release the internal pressure before the flow of large current or an increase in battery voltage above a predetermined value causes a dangerous state.
The placement of a material capable of evolving a gas within the battery has been proposed to rapidly increase the pressure within the battery upon the occurrence of an abnormal phenomenon. For example, in a rechargeable battery with a nonaqueous electrolysis solution, the addition of lithium carbonate to a positive electrode has been proposed to enable lithium carbonate to be decomposed upon overcharge to evolve carbon dioxide gas which operates the current breaking valve.
Lithium carbonate as the conventional material, however, is decomposed upon an increase in voltage as a result of the overcharge, and cannot respond to the occurrence of an abnormal phenomenon, which lowers voltage, for example, external short circuit. Further, the gas evolved is carbon dioxide which is easily dissolved in the electrolysis solution. Therefore, the pressure rise rate upon the occurrence of abnormal phenomenon is not necessarily satisfactory.
In view of the above problems of the prior art, the present invention has been made, and it is an object of the present invention to provide a battery which has means which, upon the occurrence of an abnormal phenomenon, such as an overcharge or an external short circuit, rapidly operates a safety mechanism, such as a current breaking valve, to ensure the safety of the battery and which, particularly upon the occurrence of an abnormal phenomenon, can surely and stably increase the pressure within the battery.
The above object of the present invention is attained by a battery comprising a positive electrode, a negative electrode, a separator, an electrolysis solution, and a hermetically sealed container,
the hermetically sealed container containing in its interior a compound represented by formula (1):
Xxe2x80x94Oxe2x80x94COxe2x80x94Rxe2x80x83xe2x80x83(1)
wherein X represents a group which, upon decomposition of the compound caused by a rise in temperature, is eliminated to evolve a gas insoluble or slightly soluble in the electrolysis solution; and R represents a group which controls the decomposition temperature of the compound, the group R having, in the form of a compound represented by chemical formula RH1, a hydrogen atom H1 with an acid dissociation equilibrium constant (pKa) of not more than 13.
According to the present invention, the group X in formula (1) preferably represents a substituted or unsubstituted alkyl group having 3 to 7 carbon atoms and is specifically selected from the group consisting of substituted or unsubstituted propyl, butyl, and pentyl groups.
According to a preferred embodiment of the present invention, the hydrogen atom H1 in the compound represented by chemical formula RH1 is bonded to an oxygen or nitrogen atom.
According to the present invention, the decomposition temperature of the compound represented by formula (1) can be regulated in the range of 100 to 150xc2x0 C. by properly selecting the group R.
For example, in formula (1), when the group X represents a tert-butyl group, the compound is rapidly decomposed upon a temperature rise to evolve carbon dioxide, 2-methylpropene, and a compound represented by chemical formula RH1. In this case, since 2-methylpropene has low solubility in both water electrolysis solution and nonaqueous electrolysis solution, the pressure within the battery can be rapidly increased to operate the current breaking valve or the rupture.