Lithium-ion batteries are promising candidates for hybrid electric vehicles (HEV). Batteries that exceed the requirements for HEV, as set by the Partnership for a New Generation of Vehicles (PNGV), have been designed and built. These batteries are based on thin LiNi0.15O2 cathodes, thin carbonaceous anodes, and a 1 M LiFF6 ethylene carbonate (EC): diethyl carbonate (DEC) (1:1) electrolyte. A major technical barrier is that the batteries lose their high power capability during use or prolonged storage, particularly at elevated temperatures. Electrochemical impedance spectroscopy indicates that the power fade is due to an increase in cathode impedance in cycled and abused cells. X-ray diffraction and hard X-ray absorption spectroscopy clearly shows that the bulk of the cathode material is largely intact. It is conceivable that the power fade is related to electrolyte decomposition products that are formed on the surface of the cathode. The decomposition products from the solid electrolyte interface (SEI) and might affect ionic motion by pore plugging, or could contribute to resistive electrical paths to parts of the cathode structure. Although the presence of a SEI on the cathode has long been suspected, confirmation of such a layer has proved elusive. In order to study the nature of the SEI layer it is important to use structural techniques with some surface sensitivity. We have explored the use of soft X-ray absorption spectroscopy to study the nature of the SEI layers in lithium-ion battery cathodes.
Proceedings Title: Extended abstract/proceedings of the Electrochemical Society Meeting
Conference Dates: April 27-28, 2002
Conference Location: Paris, -1
Conference Title: Electrochemical Society
Pub Type: Conferences
cathode, hybrid electric vehicles (HEV), lithium-ion batteries, solik electrolyte intervace (SEI)