Correlation between battery material performance and cooperative   electron-phonon interaction in LiCo$_y$Mn$_{2-y}$O$_{4}$
  Understanding the basic physics related to archetypal lithium battery material (such as LiCo$_y$Mn$_{2-y}$O$_{4}$) is of considerable interest and is expected to aid designing of cathodes of high capacity. The relation between electrochemical performance, activated-transport parameters, thermal expansion, and cooperativity of electron-phonon-interaction distortions in LiCo$_y$Mn$_{2-y}$O$_{4}$ is investigated. The first order cooperative-normal-mode transition, detected through coefficient of thermal expansion, is found to disappear at a critical doping ($y \sim 0.16$); interestingly, for $y \gtrsim 0.16$ the resistivity does not change much with doping and the electrochemical capacity becomes constant over repeated cycling. The critical doping $y \sim 0.16$ 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. 
Krishna Rao Ragavendran, Prabhat Mandal, and Sudhakar Yarlagadda
cond-mat.str-el