Technical Field
The embodiments herein relate to electrochemical battery systems having high energy storage per unit weight, and more particularly to a battery having multifunctional structures that combine significant load-bearing support in addition to electrochemical energy storage.
Description of the Related Art
In general, a battery is a device that converts the chemical energy contained in its active materials directly into electric energy by means of an electrochemical oxidation-reduction (redox) reaction. This type of reaction involves the transfer of electrons from one material to another through an electric circuit.
The battery cell comprises three major components: anode or negative electrode; cathode or positive electrode; and the electrolyte. The anode or negative electrode, the reducing or fuel electrode, gives up electrons to the external circuit and is oxidized during the electrochemical reaction. The cathode or positive electrode, the oxidizing electrode, accepts electrons from the external circuit and is reduced during the electrochemical reaction. The electrolyte, the ionic conductor, provides the medium for transfer of electrons as ions, inside the cell between the anode and cathode. The electrolyte is typically a liquid, such as water or other solvent, with dissolved salts, acids, or alkalis to impart ionic conductivity. Some batteries use solid electrolytes, which are ionic conductors at the operating temperature of a cell.
In conventional systems, a battery stores energy by employing a reducing agent (e.g., lead) as an anode or negative electrode and an oxidizing agent (e.g., lead dioxide) as the cathode or positive electrode. An electrolytic solution (e.g., sulfuric acid in water) is used between the electrodes. When energy is withdrawn, the reducing agent (e.g., lead) gives up electrons which flow through an external circuit and are received by the oxidizing agent (e.g., lead dioxide) at the positive electrode. Ions (e.g., hydrogen ions and sulfate ions) flow through the electrolytic solution between the electrodes to complete the circuit. Some type of chemical compound (e.g., lead sulfate) is produced as a result of the combination of these processes. The product or discharge compounds are stored usually in a porous structure of one or both of the electrodes.
Energy-storing systems (e.g., primary batteries) are designed to provide maximum energy storage per unit weight of the battery. In other words, these batteries must have a high energy. Other design considerations involve the life of the battery, its cost and, of course, the operating efficiency. Usually, there is some sort of trade-off between these desirable characteristics.
Li—CFx batteries are used in applications where a high specific energy primary power source is needed. See, T. Tan, P. Lam, H. Tsukamoto, M. Hendrickson and E. Plichta, p. 73, Proc. of the 42nd Power Sources Conf., Philadelphia, Pa., June 2006 and S. V. Sazhin, K. Ramaswami, T. J. Gurrie, C. R. Niendorf, and A. Suszko, p. 61, Proc. of the 42nd Power Sources Conf., Philadelphia, Pa., June 2006.
Li—CFx cells have one of the highest practical specific energies of any solid cathode primary battery system, See J. L. Wood, R. B. Badachhape, R. J. Lagow, J. L. Margrave, J. of Physical Chemistry, 73(9), 3139 (1969); N. Watanabe, Kyoto, M Fukuda, U.S. Pat. No. 3,536,532. Li—O2 cells have a theoretical specific energy even higher than Li—CFx cells but a practical specific energy somewhat lower due to cell construction considerations, See, K. M. Abraham and Z. Jiang, J. Electrochem. Soc., 143, 1 (1996); U.S. Pat. No. 5,510,209 (1996). The construction of an electrochemical cell that takes advantage of both the Li—CFx chemistry and the Li—O2 chemistry has not been described or demonstrated before.