Halide and Sulfide Electrolytes in Cathode Composites for Sodium All-Solid-State Batteries and their Stability.

Sodium all-solid-state batteries may become a novel storage technology overcoming the safety and energy density issues of (liquid-based) sodium ion batteries at low cost and good resource availability. However, compared to liquid electrolyte cells, contact issues and capacity losses due to interface reactions leading to high cell resistance are still a problem in solid-state batteries. In particular, sulfide-based electrolytes, which show very high ionic conductivity and good malleability, exhibit degradation reactions at the interface with electrode materials and carbon additives.

Protective NaSICON Interlayer between a Sodium-Tin Alloy Anode and Sulfide-Based Solid Electrolytes for All-Solid-State Sodium Batteries.

This paper presents a suitable combination of different sodium solid electrolytes to surpass the challenge of highly reactive cell components in sodium batteries. The focus is laid on the introduction of ceramic NaZrSiPO serving as a protective layer for sulfide-based separator electrolytes to avoid the high reactivity with the sodium metal anode. The chemical instability of the anode|sulfide solid electrolyte interface is demonstrated by impedance spectroscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy.

On the Discrepancy between Local and Average Structure in the Fast Na Ionic Conductor NaSbWS.

Aliovalent substitution is a common strategy to improve the ionic conductivity of solid electrolytes for solid-state batteries. The substitution of SbS by WS in NaSbWS leads to a very high ionic conductivity of 41 mS cm at room temperature. While pristine NaSbS crystallizes in a tetragonal structure, the substituted NaSbWS crystallizes in a cubic phase at room temperature based on its X-ray diffractogram.

Anharmonic Lattice Dynamics in Sodium Ion Conductors.

We employ terahertz-range temperature-dependent Raman spectroscopy and first-principles lattice dynamical calculations to show that the undoped sodium ion conductors NaPS and isostructural NaPSe both exhibit anharmonic lattice dynamics. The anharmonic effects in the compounds involve coupled host lattice-Na ion dynamics that drive the tetragonal-to-cubic phase transition in both cases, but with a qualitative difference in the anharmonic character of the transition. NaPSe shows an almost purely displacive character with the soft modes disappearing in the cubic phase as the change in symmetry shifts these modes to the Raman-inactive Brillouin zone boundary.

Ionic Conductivity of the NASICON-Related Thiophosphate Na Ti Ga (PS ).

Inspired by the recent interest in fast ionic conducting solids for electrolytes, the ionic conductivity of a novel ionic conductor Na Ti Ga (PS ) has been investigated. Using X-ray diffraction and impedance spectroscopy the sodium ionic conductivity in this compound was demonstrated, in which bond valence sum analysis suggests a tunnel diffusion for Na . Substitution with Ga leads to an increasing Na content, an expansion of the lattice and an increasing conductivity with increasing x in Na Ti Ga (PS ) .