Rotating ring-disk electrode measurements on Mn dissolution and capacity losses of spinel electrodes in various organic electrolytes

The Mn dissolution and capacity losses of spinel electrodes in lithium-ion cells with the various electrolyte solutions of LiPF6, LiClO4, LiBF4 and LiCF3SO3, in ethylene carbonate-dimethyl carbonate (EC-DMC) were studied using rotating ring-disk collection experiments. The cyclic voltammograms are similar at high scan rates for all electrolytes. Electrodes with LiPF6 electrolyte show the best cycling performance. Cells with both LiPF6 and LiBF4 electrolyte solutions exhibited a capacity loss of 0.45% per cycle over 200 cycles at high scan rates, and these were slightly lower than the 0.5% per cycle in LiClO4 and LiCF3SO3 electrolytes. The in situ monitoring of Mn dissolution from various electrolytes was carried out under different conditions. Ring cathodic currents of similar shaped were obtained for all electrolytes, which reveal that the Mn dissolution from the spinel LiMn2O4 electrodes exists and the highest Mn dissolution takes place at the top of charge voltage in all of electrolytes. Under both overcharge and overdischarge conditions, the ring current peak at disk potential of 5.0 V in the LiCF3SO3 electrolyte is much larger than that in other electrolytes. Moreover, the increase in ring current with cycle number occurs only in the LiCF3SO3 electrolyte. These results can be attributed to the oxidation of LiCF3SO3 electrolyte due to its voltage breakdown below 5.0 V. (c) 2005 Elsevier B.V. All rights reserved.