Structural information about battery cathode materials is of great value to the design and discovery of improved energy storage technologies, but this information is particularly challenging to extract from conventional laboratory X-ray powder diffraction experiments for two reasons.  First, the mobile ion of interest is typically Li+ or Na+, both of which are light atoms that scatters X-rays weakly.  Second, the room temperature mobility of these ions (necessary for battery functionality) results in large displacement parameters relative to other ions in the structure, and further reduces the scattering power of these light ions.  Synchrotron and neutron diffraction beamlines are therefore essential resources for obtaining important structural information about battery cathode materials due to their improved sensitivity to light atoms (neutrons) or their improved flux and resolution (synchrotrons).  We demonstrate the position of Li atoms in novel battery systems can readily be resolved even in powder samples with neutron and synchrotron diffraction data, even when only small samples (10 � 100 mg) are available.  Furthermore, there is very good reproducibility between the displacement parameters obtained through neutron and synchrotron measurements, indicating that accurate information about the motion of light atoms is obtained, and that it is plausible to use diffraction methods to effectively probe changes in mobility as the chemical composition of cathode materials are varied by chemical substitution or by oxidation (i.e. delithiation).  Temperature-dependent studies have been used to follow the behavior of ions as a function of temperature, as well as to monitor ion-exchange processes in situ at elevated temperatures.  The information from scattering data, impedance spectroscopy, and theoretical calculations together give a comprehensive picture of ionic motion processes in emerging battery systems.

Monitoring mobile ions: X-ray and neutron diffraction studies of emerging battery materials

248th National Meeting (2014)

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