1. Field of the Invention
The present invention relates to a secondary battery and a method of generating electric power.
2. Description of the Related Art
A battery is a device that converts chemical energy of a substance into electric energy. Also, batteries can be classified into primary batteries that provide electric power until their chemical energy is exhausted, secondary batteries that can be reused by being charged after exhaustion of their chemical energy so that the chemical energy is restored, and fuel cells that provide electric energy while continuously supplied with a substance having chemical energy from outside the cell. Many kinds of batteries have been developed, which have respectively different advantages and disadvantages with respect to environmental safety, economical efficiency, amount of usable electric energy, portability, storability, adaptability to use environment, and recycling efficiency. Therefore, batteries are selected in accordance with the intended use. Important technical factors common to every battery are the type of chemical reaction, the way of accelerating the reaction, and the form of the reactants during storage, supply, or recovery.
In the batteries, two kinds of chemical substances are used, which are a reducing agent that causes a reducing reaction (yielding an electron to the other reactant or pulling oxygen out of the other reactant) and an oxidizing agent that causes an oxidizing reaction (pulling an electron out of the other reactant or yielding oxygen to the other reactant). Such reactions are caused separately on two different electrodes, so that the energy of the generated electrons is drawn out of the system, while ions produced on both electrodes as a result of the generation of the electrons are neutralized within the battery. The reaction efficiency depends on the kinds of the chemical substances to be used, the manner of the reactions, the electrode materials and their activities, and the reaction environment including the electrolyte. Furthermore, the selection of substances constituting a battery is an element which determines the quality of the battery not only in terms of the quality upon use but also in terms of the characteristics upon production and waste.
For example, a lithium ion secondary battery is excellent in terms of the amount of electric energy and is rechargeable. However, since lithium is a combustible material that is very unstable upon exposure to moisture or oxygen in the air, the packaging or use environment of the battery has to be so designed that safety is sufficiently secured, in order to avert its danger. Further, since collection after use and recycling are indispensable, the entire cost from the production of the battery to the disposal is high. These problems also occur in the cases of other secondary batteries such as lead-acid battery, nickel-cadmium battery, and nickel-hydrogen battery. Also, during repetition of charging and discharging, the memory effect occurs and the electrolyte deteriorates; thus the battery performance becomes lower.
On the other hand, the storable energy of such secondary batteries is limited and charging takes a long time; therefore, they are not suitable batteries for continuously-driven devices. Considering these circumstances, a secondary battery is disclosed which can supply electric power continuously (for example, see Japanese Patent Application Laid-Open No. 7-99707); in this hydrogen fuel cell, produced water is electrolyzed to reproduce hydrogen, which is the fuel. However, since hydrogen is a combustible gas, it is difficult to store or handle hydrogen.