Electrochemical synthesis and properties of CoO2, the x = 0 phase of the AxCoO2 systems (A = Li, Na)

TL;DR

This paper reports the successful electrochemical synthesis of pure CoO2, revealing its structural and magnetic properties, and suggesting it is a Pauli-paramagnetic metal with itinerant electrons.

Contribution

It presents the first synthesis of pure CoO2 phase via electrochemical de-intercalation and characterizes its structure and magnetic behavior.

Findings

CoO2 is oxygen stoichiometric with a hexagonal structure.

CoO2 exhibits temperature-independent magnetic susceptibility.

CoO2 is likely a Pauli-paramagnetic metal.

Abstract

Single-phase bulk samples of the "exotic" CoO2, the x = 0 phase of the AxCoO2 systems (A = Li, Na), were successfully synthesized through electrochemical de-intercalation of Li from pristine LiCoO2 samples. The samples of pure CoO2 were found to be essentially oxygen stoichiometric and possess a hexagonal structure consisting of stacked triangular-lattice CoO2 layers only. The magnetism of CoO2 is featured with a temperature-independent susceptibility of the magnitude of 10-3 emu/mol Oe, being essentially identical to that of a Li-doped phase, Li0.12CoO2. It is most likely that the CoO2 phase is a Pauli-paramagnetic metal with itinerant electrons.