Study led by Ural Federal University Shows Сonductivity of Individual Particles of a Lithium Battery Cathode
Scientists of the Ural Federal University together with the staff of the Institute of Materials of the University of Aveiro (Portugal) measured the conductivity of individual particles of the lithium battery cathode from Robert Bosch, GmbH using conductive atomic force microscopy. The study was carried out at the Ural Center for Shared Use “Modern Nanotechnologies” of the UrFU using the Russian atomic force microscope NTEGRA Aura.
The results are published in the journal Ultramicroscopy.
The operation of lithium-ion batteries is provided by the movement of free ions through a conductor between two electrodes: a positively charged cathode, a metal oxide, and a negatively charged anode, a porous carbon. During battery charging, ions move from the anode to the cathode, and during discharging, in the opposite direction. In lithium-ion batteries, lithium-manganese spinel is widely used as a cathode, distributed in the form of micron-sized particles in a carbon matrix. At the interface between the carbon and the spinel particle, there is an interfacial layer with increased electrical resistance, through which lithium ions pass when charging and discharging the battery. The study of the conductivity of individual particles of lithium-manganese spinel, as well as their surface layer, is of great importance for the development of more efficient batteries. However, the small grain size complicates such studies.
Conductive atomic force microscopy makes it possible to measure local electrical characteristics with spatial resolution down to tens of nanometers. The microscope scans the sample surface with a probe with a nanometer radius of curvature. During scanning, a conducting probe touches the surface of the sample pointwise, while an alternating voltage is applied to it and the current at the contact point is measured. Thus, scientists measured the conductivity of the surface layer of individual particles of lithium-manganese oxide, while applying an alternating voltage. Local volt-ampere characteristics were obtained, describing the relationship between the applied electric voltage and the current strength. Scientists have found that the surface layer of particles has high resistance and largely determines the dynamics of lithium ions. Moreover, with increasing voltage, the role of the surface layer increases, hindering the movement of ions.
“This study allowed not only to study the dependence of local conductivity on the concentration of lithium on the surface of particles of lithium-ion conductors, but also to measure the distribution of lithium ions with high spatial resolution. The method used and the developed approaches to the analysis of the results can be successfully applied to study a wide range of conductive materials, “concluded one of the authors of the work, director of the UCKP” Modern Nanotechnologies” Ural Federal University Vladimir Shur.