Rapid SECM probing of dissolution of LiCoO2 battery materials in an ionic liquid

Attempts to utilise LiCoO2 as the cathode when the electrolyte is based on an ionic liquid, e.g. 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide, have been severely limited by significant capacity fade. Given that some form of instability of this material in ionic liquids is widely suspected as the principal cause, the aim of the current work is to determine the efficacy of using the scanning electrochemical microscope (SECM), to detect solubilisation of species leaving the LiCoO2 electrode during charging and/or discharging. The SECM microelectrode probe tip was lowered to within 10–20 μm of the platinum substrate electrode, onto which solid LiCoO2 had been coated. This substrate material was charged and discharged to different voltages, whilst probing any solubilised species at the microelectrode tip. The detection of solubilised Co2+ and oxygen during over-charge and more so under deep discharge was observed. Possible mechanisms for degradation of the electrode are proposed. From these preliminary results, strategies are suggested for mitigating the degradation of LiCoO2 when used in a room temperature ionic liquid electrolyte.