Impedance Growth with Lithium Titanate Based Cells; Understanding and Mitigation

SAFT has successfully applied Li-ion electrochemistry to defense, space, and commercial applications which require very high power.  In fact, by optimizing both the electrochemical and electro-mechanical cell design, Saft has developed a range of Li-ion products that can deliver up to 10 kW/kg of power for 10 seconds and over 30 kW/kg of power for a fraction of a second. There are, however, still inherent limitations for high power applications with traditional Li-ion chemistry.  Particularly, even with an optimized cell design, cycle life can be limited for applications which require very rapid charging due to both Lithium plating and electrolyte decomposition on the graphitic negative electrode.  Lithium titanate oxide (LTO), due to operation above both the lithium plating and solvent reduction potentials, minimizes these phenomenon and can potentially provide extremely long cycle life. Saft is working, with DOE/USABC funding, to industrialize LTO based technology for high power applications. Results will be presented including power capability, high temperature impedance growth, capacity fade, and gas generation.  In particular, impedance growth, which is a major obstacle to large scale use of LTO, will be discussed including mechanistic understanding and methods of mitigation.