Advanced Characterization for Studying Ni-rich Cathode Materials for Li-ion Batteries

Abstract

Li-ion batteries (LiBs) are energy storage devices which are able to convert chemical energy into electrical energy. Due to the recent excessive consumption of fossil fuels resulted in the uncontrolled release of carbon dioxide and significant amounts of greenhouse gases into the atmosphere, the need for sustainable energy growth becameevident. Hence, there is a critical need for high-performance energy storage devices exhibiting both high energy and power density to ensure the sustainability and safety of storing renewable energy.

In this thesis, by means of synchrotron radiation facility we explored the most efficient way to Zr bulk doping a Ni-rich layered cathode material upon two different pathways, during lithiation and co-precipitation step. High resolution x-ray diffraction and x-ray absorption spectroscopy measurements revealed, for the coprecipitation step, the absence of every Zr based impurity and a local environment compatible with its inclusion in the cathode host structure. Whereas for the lithiation step, Zr tended to only form extra-phase impurities.

The Zr-doped Ni-rich cathode material synthesized via the co-precipitation method exhibited improved electrochemical performance compared to the undoped sample. To investigate these enhancements, operando high-energy x-ray diffraction and exsitu x-ray absorption spectroscopy were utilized. X-ray diffraction analysis revealed a reduced formation rate of the detrimental H3 phase in the doped samples, while x-ray absorption spectroscopy indicated a decrease in transition metal dissolution from the cathode material. These findings underline the importance of studying trace amount dopants to advance the development of more robust Ni-rich cathode materials.

The undoped material in the operando studies revealed the presence of a phase segregation upon cycling at high voltages. To understand the nature of the phase segregation formation mechanism, a nanobeam approach was involved. An initial operando experiment by means of scanning x-ray diffraction microscopy was carried out to probe multiple single particles and follow the Li+ heterogenities upon cycling. However, the experiment faced challenges due to cell holder instability, and beam damage. Progress continued with further experiments at the IDOl ESRF beamline, allowing successful ex-situ examination of inter- and intra-particle heterogeneities in polycrystalline particles. Up to date, the operando challenges in nanoprobe studies remain a critical area to address in order to advance the research in the field of Li-ion battery materials.