electrochemical modeling

To understand the implications of microstructural properties on a system, the underlying chemical and physical problems have to be well understood. Therefore I am also dealing with all kinds of transport and reaction mechanisms occurring in electrochemical systems.

The two main topics I am focusing on are the description of processes in the lithium-graphite system and the lithium-iron phosphate system. Both systems undergo at least one phase transition during lithium intercalation, leading to a flat potential curve over a wide concentration range.

For LiFePO4, the miscibility gap spans almost the whole concentration range. While it has a miserable rate capability in an electrode made of micrometer-sized particles, it exhibits excellent performance if processed as a nano-powder with particles smaller than 100 nm. Naturally, this raises questions on how the charge-transfer reaction works in that material and if diffusion/phase-boundary movement has to be taken into account.

In graphite, the ordered intercalation of lithium leads to multiple phase-transitions, which can be observed as a distinct pattern in the potential curve (also referred to as staging). As the potential of LixC6 is close to that of metallic lithium for x > 0.5 charging (especially at high currents or low temperatures) leads to the risk lithium deposition (plating) instead of intercalation. That happens if the surface potential drops below that of metallic lithium. In order to avoid operating conditions leading to lithium plating, it is essential to understand both, the intercalation and transport mechanisms in the Li-graphite system, and the deposition of metallic lithium at the graphite particles.

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