Transition metal catalysis in lithium-ion batteries studied by operando magnetometry

Owing to the potential ability of metal nanoparticles to enhance the performance of energy storage devices, their catalytic performance has been studied by many researchers. However, a limited number of suitable characterization techniques does not allow fully elucidating their catalytic mechanism. Herein, high-accuracy operando magnetometry is employed to investigate the catalytic properties of a cobalt oxide electrode for lithium-ion batteries fabricated by magnetron sputtering. Using this technique, the magnetic responses generated by the Co-catalyzed reversible formation and decomposition of a polymer/gel-like film are successfully detected. A series of CoO/Co films are prepared by magnetron sputtering in different environments at various sputtering times to study the influence of Co content and film thickness on their catalytic properties. It is clearly demonstrated that increasing the Co content enhances the magnetic signal associated with the catalysis process. Furthermore, decreasing the electrode thickness increases the area affected by the catalytic reactions, which in turn enhances the corresponding magnetic responses. The obtained results experimentally confirm the catalytic activity of Co metal nanoparticles and provide a scientific guidance for designing advanced energy storage devices. This work also shows that operando magnetometry is a versatile technique for studying the catalytic effects of transition metals.