  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.
