Roll to Roll Processing
Nanocrystallization of LIC002 Cathodes for thin film batteries Utilizing Pulse Thermal Processing (PTP)
One of the major challenges to the improvement of thin film lithium battery technology is the efficient crystallization and sintering of the LiCoO2 cathode thin-films deposited by rf magnetron sputtering. Even though the as-deposited films, which are x-ray amorphous and possible nanocrystalline, can be used as cathodes, when crystallized to grain sizes approaching 100 nm, the cathodes can deliver a power density 10X higher. Typically, the crystallization requires conventional furnace annealing at 550ºC to 700ºC in an oxidizing atmosphere for several hours. Furthermore, the high temperature anneal step limits the choice of substrate materials to those stable at the high temperature oxidizing conditions. Ideally, the substrate for the thin film battery would be as thin, light, flexible, and inexpensive as possible. If the alumina substrates used in current prototype thin film batteries were replaced with Kapton® (polyimide), which can withstand temperatures to 400ºC, the cathode can be properly annealed by Pulse Thermal Processing.
ORNL has a unique revolutionary rapid thermal annealing capability that enables in-situ fabrication of nanoscaled materials. This technique utilizes a high density plasma arc-based technology and a methodology called Pulse Thermal Processing (PTP) that enables the manipulation of materials on the nanoscale. The unique characteristics of PTP with its high power densities (>20,000 W/cm2), short processing time (millisecond regime) and large processing area (up to 1,000 cm2) allows for rapid thermal processing of thin film and nanoparticle material systems on flexible temperature-sensitive substrates such as polymers without thermally affecting the underlying material. This research project will focus on the nanocrystallization of the LiCoO2 cathode thin films on polyimide substrates and evaluate the microstructural evolution and resistance as a function of PTP processing conditions. A significant decrease in the cathode resistance as measured by liquid electrolyte testing correlates to improved capacity and charge and discharge rate of the battery.
ITN Energy Systems, Inc.