Do You Really Want an Unsafe Battery?

Many investigations of high potential cathodes in lithium systems have shown evidence of oxygen evolution, which can lead to thermal runaway problems. It will be shown that this is to be expected on the basis of thermodynamic considerations. Experiments involving 10 phases in the Li-Co-O, Li-Fe-O and Li-Mn-O systems were performed in a glove box over a limited range of both oxygen pressure and voltage, and the results interpreted in terms of ternary phase stability diagrams. They showed a linear relation between the logarithm of the equilibrium oxygen pressure and the potential, independent of both the chemical compositions and the crystal structures of the phases involved. Extrapolation to higher potentials indicates very high values of the equilibrium oxygen pressures in high voltage cathode materials. These results shows that the critical issue related to the equilibrium oxygen pressure of high potential cathodes is their potential, not their compositions or crystal structures. (C) 2013 The Electrochemical Society.