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Institute of Energy and Climate Research (IEK)

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Battery materials

In particular, the formation of different phases during the reversible cycling of batteries is an important issue, which links electrochemical, thermodynamic and kinetic aspects. Li4Ti5O12 was synthesized via a solid-state reaction and lithiated at 400°C in a custom built galvanostatic cell consisting of a molten LiCl–KCl electrolyte and Li-Al alloy wires as counter and reference electrodes. The material exhibits decreased rate capability at elevated temperatures. Electrochemical lithiation exhibits a discharge profile with both a sloping curve and flat plateau, which is indicative of a solid solution behavior before reaching a two-phase region. This electrochemical behavior has been shown to be correlated with reversible formation of the cubic Li2TiO3 phase. Experimental observations are combined with simulation activities, in particular finite-temperature density functional theory, to predict thermochemical and mechanical properties of electrode materials, to obtain insights into potential battery failure mechanisms.

High temperature galvanostatic cell setupHigh temperature galvanostatic cell setup

As a joint work with IEK-1 we are investigating the mechanical properties of LLZ as solid-state electrolyte, which is doped by Al and Ta to stabilize the highly conducting cubic phase. This material is a promising candidate for an all-solid state battery.

Structure of LLZ doped with aluminiumSchematic presentation of the structure of LLZ doped with aluminium. The indicated atom types are Zr, O, La, Al and Li.

The interface between solid-state electrolytes and in particular Li as metallic electrode is critical for safety and stability of batteries, as Li plating and dendrite formation may develop from this interface. In the framework of the BMBF funded project MEET-HiEnD 2, we have conducted a continuum description of the electrochemical reactions and transport mechanisms occurring at this interface and their influence of its morphological stability. Here it was found that mechanical stresses, which are imposed during battery fabrication involving a protective layer between electrode and electrolyte can be beneficial for the interface stability.

Spectrum of linear stability analysisSpectrum of the linear stability analysis, indicating a stabilisation through the influence of mechanical stresses