Correlation between battery material performance and cooperative electron-phonon interaction in LiCo_yMn_2-yO₄

Abstract

Understanding the basic physics related to archetypal lithium battery material (such as LiCo_yMn_2-yO₄) is of considerable interest and is expected to aid the designing of cathodes of high capacity. The relationship between electrochemical performance, activated-transport parameters, thermal expansion, and cooperativity of electron-phonon-interaction distortions in LiCoyMn2-yO4 is investigated. The first order cooperative-normal-mode transition, detected through coefficient of thermal expansion, is found to disappear at a critical doping (y∼0.16); interestingly, for y≳0.16, the resistivity does not change much with doping, and the electrochemical capacity becomes constant over repeated cycling. The critical doping y∼0.16 results in breakdown of the network of cooperative/coherent normal-mode distortions; this leads to vanishing of the first-order transition, establishment of hopping channels with lower resistance, and enhancing lithiation and delithiation of the battery, thereby minimizing electrochemical capacity fading.