Unprecedented superionicity of ultra-low barrier in A_0.5CoO₂ (A=Li, Zn)

The ion conductivity of a solid-state ion conductor generally increases exponentially upon reduction in ion migration barrier. For prevalent cathode material LiCoO₂, the room-temperature ion conductivity and migration barrier are respectively around 10^-4 S/cm and 0.3 eV. In this paper, through first-principles calculations we predict the existence of 1D superionicity as the Li ions in O2 LiCoO₂ are transformed to Zn_0.5CoO₂ or Li_0.5CoO₂ via cation-exchange reaction or deintercalation. The ion migration barriers (0.01-0.02 eV) even lower than room-temperature ~k_BT are reduced by more than an order of magnitude compared with LiCoO₂, which are facilitated by facile transition of mobile ions between two coordination configurations. The room-temperature ion conductivity is estimated to be over 50 S/cm, enhanced by 2-3 orders of magnitude compared with current highest reported value. Such unprecedented superionicity may also exist in other similar layered ion conductors, which may render technical advances and exotic effects such as ultrafast ion batteries and quantized ferroelectricity.