On 26 August at 14.15 Kenneth Tuul will defend his doctoral thesis “Evaluating lithium-ion pouch cells and hydrogen storage materials under extreme conditions using advanced techniques”.
Supervisors:
Associate Prof. Rasmus Palm, PhD, University of Tartu
Prof. Enn Lust, PhD, University of Tartu
Professor Emeritus Jeff R. Dahn, PhD, Dalhousie University, Canada
Oponent:
Assoc. Prof. Johannes Wandt, PhD, University of Agder (Norway)
Summary:
The energy crisis following Russia’s invasion of Ukraine accelerated the EU’s shift toward energy independence and clean energy. Renewable energy is essential for meeting EU climate goals, and sustainable energy storage is key to effectively integrating it into the grid. Li-ion batteries dominate short-term storage due to their energy density and maturity, but face limits in sustainability, raw material sourcing, and long-duration use. These issues can be eased by extended battery lifetimes and second-life use. Hydrogen from renewable-powered electrolysis is a promising option for long-term and seasonal storage, though existing storage technologies face safety, efficiency, and cost challenges.
This thesis explores hydrogen storage in solid sodium alanate (NaAlH₄) and long-lifetime Li-ion batteries. Both systems were first characterized by standard physical and electrochemical methods. Deeper insights came from advanced techniques: neutron powder diffraction monitored in-situ phase transitions in NaAlH₄ composites, while ultra-high precision coulometry (UHPC) with high-temperature aging tests revealed battery degradation behavior.
NaAlH₄ was made into nanoparticles and confined in carbon, enhancing hydrogen storage and release. This reduced the hydrogen release temperature to 100 °C for composites vs 183 °C for bulk material and enabled partial rehydrogenation at 150 °C and 20 bar. Full reversibility remains limited, though a more finely tuned structure for the carbon support and catalysts could improve performance further.
Li-ion cells were tailored for 60–100 °C operation by carefully selecting electrode materials, electrolytes, and additives. Pouch cells performed well, but it was discovered that electrolyte may permeate out of the pouch cell, especially at high temperatures. Metal cylindrical cells showed greater stability. UHPC testing revealed Arrhenius-type degradation, enabling a simple square-root time model to estimate long-term capacity loss. While not yet fully validated and with limitations, this model enables lifetime prediction into decades, extended warranties, and second-life applications.
