Defect-Mediated Conductivity Enhancements in Na_3–xPn_1–xW_xS₄ (Pn = P, Sb) Using Aliovalent Substitutions

Abstract

The sodium-ion conducting family of Na 3 PnS 4 , with Pn = P, Sb, has gained interest for the use in solid-state batteries due to their high ionic conductivity. However, significant improvements to the conductivity have been hampered by the lack of aliovalent dopants that can introduce vacancies into the structure. Inspired by the need for vacancy introduction into Na 3 PnS 4 , the solid solutions with WS 4 2− introduction are explored. The influence of the substitution with WS 4 2− for PS 4 3− and SbS 4 3− is monitored using a combination of X-ray diffraction, Raman, and impedance spectroscopy. With increasing vacancy concentration, improvements resulting in a very high ionic conductivity of 13 ± 3 mS•cm −1 for Na 2.9 P 0.9 W 0.1 S 4 and 41 ± 8 mS•cm −1 for Na 2.9 Sb 0.9 W 0.1 S 4 can be observed. This work acts as a stepping-stone toward further engineering of ionic conductors using vacancy injection via aliovalent substituents.

Planting Repulsion Centers for Faster Ionic Diffusion in Superionic Conductors

“…Various lithium and sodium SICs have been reported, including Li 10 GeP 2 S 12 (LGPS), Li 7 P 3 S 11 , Li 7 La 3 Zr 2 O 12 (LLZO), NASICON‐type compounds such as Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 (LATP) and Na 3.4 Sc 0.4 Zr 1.6 Si 2 PO 12 , Na 3 PS 4 , and Na 11 Sn 2 PS 12 . The exceptionally fast ionic diffusion in these SICs, exceeding that of conventional ion‐conducting materials, has motivated numerous studies on its origins .…”

Under Pressure: Mechanochemical Effects on Structure and Ion Conduction in the Sodium-Ion Solid Electrolyte Na3PS4

“…Multiple hypotheses have been proposed including atomic-scale changes in crystal structure and/or in point defect concentrations, microstructural effects (such as grain boundaries), as well as mesostructural parameters such as particle size/shape and associated surface effects 18,22,23 . Both simulations and experiments show that introducing sodium ion defects through aliovalent doping can decisively enhance ion-transport in Na3PS4 9,11,13,[24][25][26][27][28][29][30] . Through novel atomistic simulations, the effect of grain boundaries on ion conduction in β-Na3PS4 has recently been examined 31 , showing that ion transport is not significantly affected by grain boundaries in this material in contrast to sodium phosphate analogues.…”

On the underestimated influence of synthetic conditions in solid ionic conductors

“…7 However, the emergence of superionic solids that could conduct lithium and sodium nearly as well as some liquids brought extreme interest to the concept of the all-solid-state battery. [10][11][12] These materials offer excellent ionic conductivities, 11,[13][14][15] low electronic conductivity saving the cell from self-discharge, 16 a transference number near unity which further can boost the power density of the cells. 11 Typical solid ionic conductors include polymeric materials; 17 oxides such as LISICON (lithium superionic conductor) 18,19 and NASICON (sodium superionic conductor and Li-ion conducting sodium superionic conductor) 20 type phosphates and garnets such as Li 7 La 3 Zr 2 O 12 (LLZO); 21 suldes such as thio-LISICONs 22 and thiophosphates, including the argyrodites Li 6 PS 5 X (X ¼ Cl, Br, I), 13,14,23 Li 10 MP 2 S 12 (LMPS) (M ¼ Si, Ge, Sn) 11,15,24,25 or Na 3 MS 4 (M ¼ P, Sb) 26,27 and its substituted analogues.…”

“…11 Typical solid ionic conductors include polymeric materials; 17 oxides such as LISICON (lithium superionic conductor) 18,19 and NASICON (sodium superionic conductor and Li-ion conducting sodium superionic conductor) 20 type phosphates and garnets such as Li 7 La 3 Zr 2 O 12 (LLZO); 21 suldes such as thio-LISICONs 22 and thiophosphates, including the argyrodites Li 6 PS 5 X (X ¼ Cl, Br, I), 13,14,23 Li 10 MP 2 S 12 (LMPS) (M ¼ Si, Ge, Sn) 11,15,24,25 or Na 3 MS 4 (M ¼ P, Sb) 26,27 and its substituted analogues. 12 Other materials such as the ternary halides, lithium hydride, and lithium nitride also garner interest. [28][29][30] All these materials have been reviewed in-depth in the literature so we suffice it to say here that each class spans a wide range of advantages and disadvantages in various properties: ionic and electronic conductivity, electrochemical stability windows, mechanical soness or brittleness, Michael Ghidiu earned his PhD in Materials science and Engineering in 2018 from Drexel University in Philadelphia characterizing novel 2D materials for energy storage (MXenes), and subsequently moved to Germany for post-doctoral work with Prof. Wolfgang Zeier, focusing on electrolyte development for solid-state batteries.…”