Rotating ring-disc electrode measurements of manganese dissolution and capacity loss of Li1+xMn2-xO4 and Li1+xAlyMn2-x-yO4 spinel electrodes for lithium-ion batteries

Three types of spinel-based cathode powders, namely, LiMn2O4, Li1.07Mn1.93O4, and Li1.06Al0.2Mn1.74O4, are examined with rotating ring-disc collection experiments to measure manganese dissolution and capacity losses in lithium-ion cells. The cyclic voltammograms are similar at high scan rates for all three electrodes. Initially, all electrodes rapidly lose capacity during cycling. After about 25 cycles, the electrodes start to exhibit capacity retention, and the performance matches that of the best spinels. The cation-substituted spinel electrodes experience a moderate capacity loss of 0.2% per cycle over 200 cycles, which is half that suffered by a typical spinel electrode (LiMnO4). Manganese (Mn) dissolution from all the spinel-based samples is monitored in situ under various conditions. The ring cathodic currents for the cation-substituted spinel electrodes are similar to those for LiMn2O4, which shows that the Mn dissolution behaviour is the same for all spinel-based cathode powders. The ring currents reach maximum values at the end-of charge (EOC) and end-of discharge (EOD), with the largest peak at EOC. The results suggest that the dissolution of Mn from all spinel-based samples occurs during charge-discharge cycling, especially in a charged state at >4.0 V and in a discharged state at <3.1 V In addition, lower ring cathodic currents are observed in the cation-substituted spinel cathodes and this indicates that the rate of dissolution of Mn has decreased in these materials. (c) 2005 Elsevier B.V. All rights reserved.