Synthesis and properties of CoO2, the x = 0 end member of the LixCoO2 and NaxCoO2 systems

TL;DR

This paper reports the synthesis of pure CoO2, the end member of lithium and sodium cobalt oxide systems, revealing its crystal structure and metallic, Pauli-paramagnetic behavior through electrochemical de-intercalation.

Contribution

It introduces a method to synthesize pure CoO2 and characterizes its structure and magnetic properties, providing new insights into its electronic behavior.

Findings

CoO2 is oxygen-stoichiometric with a layered crystal structure.

CoO2 exhibits Pauli-paramagnetic metallic behavior.

The magnetic susceptibility levels off at higher temperatures.

Abstract

We report here the synthesis of single-phase bulk samples of CoO2, the x = 0 end member of the AxCoO2 systems (A = Li, Na), from a pristine LiCoO2 sample using an electrochemical technique to completely de-intercalate lithium. Thus, synthesized CoO2 samples were found to be oxygen-stoichiometric and possess a crystal structure consisting of stacked triangular-lattice CoO2 layers only. The magnetic susceptibility of the CoO2 sample was revealed to be relatively large in its initial value and then level off as the temperature increases, suggesting that CoO2 is a Pauli-paramagnetic metal with itinerant electrons.