arXiv subjects

Theodosios Famprikis

Publications and source records attributed to Theodosios Famprikis.

3 recordsLinked to original sources

arXiv2026

Coupling of Cation and Anion Dynamics in Solid Electrolytes Revealed by Virtual Isotopic Substitution Molecular Dynamics

We characterise the interplay between cation-translational and anion-rotational dynamics on the model system $\rm α\text{-}Li_{2}SO_{4}$ through virtual isotopic substitution molecular dynamics (VISMD) simulations. We independently control in turn the lithium translational- and sufate rotational- diffusivity by varying the masses of lithium and oxygen, respectively, showing that both diffusivities exhibit power-law relationships with the masses of each individual component. Changing either diffusivity produces an effect on the other; i.e. there exists a bidirectional coupling between anion and cation diffusive dynamics. From our variable-temperature/variable-mass dataset we demonstrate that the apparent activation energy for lithium diffusion depends strongly on the isotope mass, decreasing with accelerated sulfate dynamics; an observation which provides clear evidence of mode-coupling between cation and anion dynamics.

cond-mat.dis-nn↗

arXiv2024

Effects of Grain Boundaries and Surfaces on Electronic and Mechanical Properties of Solid Electrolytes

Extended defects, including exposed surfaces and grain boundaries, are critical to the properties of polycrystalline solid electrolytes in all-solid-state batteries (ASSBs). These defects can significantly alter the mechanical and electronic properties of solid electrolytes, with direct manifestations on the performance of ASSBs. Here, by building a library of 590 surfaces and grain boundaries of 11 relevant solid electrolytes $-$including halides, oxides, and sulfides$-$ their electronic, mechanical, and thermodynamic characteristics are linked to the functional properties of polycrystalline solid electrolytes. It is found that the energy required to mechanically ``separate'' grain boundaries can be significantly lower than in the bulk region of materials, which can trigger preferential cracking of solid electrolyte particles in the grain boundary regions. The brittleness of ceramic solid electrolytes, inferred from the predicted low fracture toughnesses at the grain boundaries, contributes to their cracking under local pressure imparted by Lithium or Sodium penetration in the grain boundaries. Extended defects of solid electrolytes introduce new electronic ``interfacial'' states within bandgaps of solid electrolytes. These interfacial states alter and possibly increase locally the availability of free electrons and holes in solid electrolytes. Factoring effects arising from extended defects appear crucial to explain electrochemical and $-$mechanical observations in ASSBs.

cond-mat.mtrl-sci↗

arXiv2022

Dissolution and Recrystallization Behavior of Li3PS4 in Different Organic Solvents

Solid state batteries can be built based on thiophosphate electrolytes such as beta-Li3PS4. For the preparation of these electrolytes, various solvent-based routes have been reported. For recycling of end-of-life solid state batteries based on such thiophosphates, we consider the development of dissolution and recrystallization strategies for the recovery of the model compound beta-Li3PS4. We show that recrystallization can only be performed in polar, slightly protic solvents such as N-methylformamide (NMF). The recrystallization is comprehensively studied, showing that it proceeds via an intermediate phase with composition Li3PS4*2NMF, which is structurally characterized. This phase has a high resistivity for the transport of lithium ions and must be removed in order to obtain a recrystallized product with a conductivity similar to the pristine material. Moreover, the recrystallization from solution results in an increase of the amorphous phase fraction next to crystalline beta-Li3PS4, which results in a decrease of the activation energy to 0.2 eV compared to 0.38 eV for the pristine phase.

cond-mat.mtrl-sci↗