Rechargeable Lithium Battery Technology: a Survey GERALD HALPERT & SUBBARAO SURAMPUDI Introduction Lithium cells and batteries offer a number of advantages over existing non-lithium types. The major advantages include: significantly higher specific energy (Wh/kg) and energy density (Wh/1) and longer active shelf-life. These are essential factors for energy storage devices requiring reduced mass and volume. The term lithium cell refers to an electrochemical energy storage device in which lithium metal (or an alloy thereof) serves as the negative electrode (anode on discharge). The opposing electrode can be any one of a number of materials. This paper will concentrate on the rechargeable lithium cell as the basic building block of the battery. As with other electrochemical systems, there are primary (one discharge) lithium cells and secondary (rechargeable) lithium cells. Several types of primary lithium cells are in use today: 13 different versions are described in a NASA document [1]. NASA has used four types of primary lithium batteries in shuttle applications and one type; lithium-sulfur dioxide (Li-SO2) is in the Galileo Probe scheduled for launch to Jupiter in 1989. The Department of Defense has large numbers of Li-SO2 cells in the field. Several types of low rate primary lithium cells are now being used for consumer and original equipment manufacture (OEM) applications. Rechargeable lithium cells, on the other hand, have yet to reach the same technology readiness level. A few have begun to appear commercially in limited quantities and sizes. This paper will describe the types of rechargeable lithium cells, their expected performance and advantages and the status of the technical issues. The role of the rechargeable lithium cell in future NASA applications will also be described. Rechargeable Lithium Cell Operation A rechargeable lithium cell contains a lithium metal or alloy electrode which serves as the anode on discharge. It is the negative electrode during both charge and discharge. During the discharge process, the metallic lithium (Li°) is converted (oxidized) to the ionic form (Li+) at the electrolyte interface and dissolves in the electrolyte. In the process, this electrode supplies electrons to the load. It is referred to as an anode. At the same time, the opposing electrode serves as the cathode and accepts the electrons (is reduced) by one of several processes depending on its composition. It is the positive electrode during both charge and discharge. Each electrode maintains the same Gerald Halpert & Subbarao Surampudi, Electrochemical Power Group, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA.
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