Current Status of Health and Safety Issues of Sodium/Metal Chloride (Zebra) Batteries
or DOE Information Bridge http://www.doe.gov/bridge/home.html Printed on paper containing at least 50% wastepaper, including 10% postconsumer waste iii Preface Sodium/metal chloride (Zebra) batteries are a mid-to long-term candidate technology for electric vehicle (EV) propulsion. Understanding environmental, health, and safety issues associated with sodium/metal chloride batteries is an important step toward their commercialization. This report examines the EH&S issues associated with the use
... f sodium/metal chloride batteries as the energy source in EVs. The Analytic Studies Division (ASD) prepared this report for AEG Zebra Marketing, the primary developer of Zebra batteries. The objectives of this report are to perform secondary research on EH&S issues associated with Zebra batteries for electric vehicles, and to report the results of that research in an EH&S assessment. patiently and candidly answering the numerous (and often esoteric) technical questions I directed toward them. Don Vissers and Laszlo Redey, of ANL, for providing additional technical expertise and peer review comments, as well as contextual information about the development of this technology and its sodium/sulfur antecedent. And Ron Iori (Ford Motor Company), for providing a succinct description of the Q1 certification program. Special acknowledgements are due Andy Altemos (HMT and Associates) for providing key information and recommended wording used in the shipping section, Jim Leyshon (NREL) for providing the pictorial representation of the Zebra cell used in the report, and Laura Vimmerstedt (NREL) for significant bibliographic research and contract management support. Approved for the NATIONAL RENEWABLE ENERGY LABORATORY iv Executive Summary This report addresses environmental, health, and safety (EH&S) issues associated with sodium/ metal chloride batteries, in general, with specific references to unit, developed or being developed by AEG Zebra Marketing. Sodium/metal chloride cells, referred to as Zebra cells or the Zebra system, operate at relatively high temperatures, use a negative electrode composed of liquid sodium, and use a ceramic electrolyte to separate this electrode from the positive electrode. In these respects, they are similar to sodium/sulfur cells. However, sodium/metal chloride cells also include a secondary electrolyte of molten sodium tetrachloroaluminate (NaAlCl 4 ) in the positive electrode section and an insoluble transition metal chloride (FeCl 2 or NiCl 2 ) or a mix of such chlorides, as the positive electrode. The positive electrode is fabricated in the discharged state from a mixture of common salt, nickel, iron, and aluminum. The initial charge oxidizes these metals and decomposes the salt to sodium and chloride ions, with the chloride ions combining with the oxidized metals. Discharge results in the reverse reaction. The positive electrode section of the cell also contains the liquid electrolyte, sodium tetrachloroaluminate, which serves to conduct sodium ions between this electrode and the ceramic electrolyte tube. vi 4. AEG Zebra stresses that a breached cell is very unlikely to release sodium, since any trauma capable of breaching the cell will almost certainly simultaneously fracture the ceramic electrolyte, binding all available sodium into sodium chloride. 2 It also stress that to its knowledge, free sodium has never been released in any of the tests conducted by MIRA. 3 Given this background, it seems that the release of metallic sodium from Zebra cells in an operational battery is unlikely; however, the effects of such an event still remain unclear. Investigation should be undertaken to determine: (1) if there are (relevant) circumstances under which an operating Zebra cell would, in fact, release sodium, and (2) what effects sodium released from a cell or set of cells would have in an operating battery-perhaps via a simulation akin to that conducted for sodium tetrachloroaluminate.