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 LiCoO_2, the room-temperature ion conductivity and migration barrier are respectively around 10^-4 S/cm and 0.3 eV. In this Letter, through first-principles calculations we predict the existence of 1D superionicity as the Li ions in O2 LiCoO_2 are transformed into Zn_0.5CoO_2 or Li_0.5CoO_2 via cation-exchange reaction or deintercalation. The ion migration barriers (0.01-0.02 eV) even lower than room-temperature \simk_\rm BT are reduced by more than an order of magnitude compared with LiCoO_2, 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 the current highest reported value. Such unprecedented superionicity may also exist in other similar layered ion conductors, which may lead to technical advances and exotic effects such as ultrafast ion batteries and quantized ferroelectricity.