Scientific Challenges to Develop a Nonaqueous Secondary Li-Air Battery

The 2008 IBM Almaden Research Grand Challenge competition launched a project focused on developing rechargeable Li-air batteries, whose theoretical specific energy (11,700 Wh/kg of Li) potentially offers a significant improvement over the 160 Wh/kg specific energy found in state-of-the-art Li-ion batteries. Despite this enormous potential specific energy, considerable scientific challenges remain to successfully develop a secondary Li-air battery.  This poster will address some of these challenges, with a particular emphasis on two current areas of Li-air research at IBM: electrolyte stability and electrical passivation of the cathode due to electrochemical product formation.

To better understand electrolyte stability in the presence of the working electrochemical cathode reaction (i.e., Li⁺ + O₂ + 2e^- → Li₂O₂), quantitative Differential Electrochemical Mass Spectrometry (DEMS) was used to analyze Li-O₂ cells employing various electrolytes and porous carbon paper as the cathode.  In conjunction with the gas-phase DEMS analysis, electrodeposits formed during discharge were characterized using ex-situ analytical techniques. This poster will outline results which indicate that the reversibility of Li-O₂ electrochemistry is strongly dependent on the choice of solvent employed in the cell.

In addition, lithium-oxygen discharge electrodeposits formed on smooth, glassy carbon electrodes were characterized by both electrochemical and surface analytical techniques.  Ferrocene was used as an in-situ electrochemical redox probe to correlate cell performance with electrical passivation as a result of discharge product formation.  These studies revealed that cell failure during discharge was coincident with exponentially decreasing charge transfer at the cathode surface.  Ex-situ analysis of the electrodeposit using focused ion beam micromachining, combined with conductive atomic force microscopy, yielded results consistent with the in-situ findings.