Fast Sodium‐Ion Conductivity in Supertetrahedral Phosphidosilicates

Abstract

Fast sodium‐ion conductors are key components of Na‐based all‐solid‐state batteries which hold promise for large‐scale storage of electrical power. We report the synthesis, crystal‐structure determination, and Na+‐ion conductivities of six new Na‐ion conductors, the phosphidosilicates Na19Si13P25, Na23Si19P33, Na23Si28P45, Na23Si37P57, LT‐NaSi2P3 and HT‐NaSi2P3, based entirely on earth‐abundant elements. They have SiP4 tetrahedra assembled interpenetrating networks of T3 to T5 supertetrahedral clusters and can be hierarchically assigned to sphalerite‐ or diamond‐type structures. 23Na solid‐state NMR spectra and geometrical pathway analysis show Na+‐ion mobility between the supertetrahedral cluster networks. Electrochemical impedance spectroscopy shows Na+‐ion conductivities up to σ (Na+)=4×10−4 S cm−1. The conductivities increase with the size of the supertetrahedral clusters through dilution of Na+‐ions as the charge density of the anionic networks decreases.

Polyanionic Frameworks in the Lithium Phosphidogermanates Li2GeP2 and LiGe3P3 – Synthesis, Structure, and Lithium Ion Mobility

“…With respect to structure chemistry can the SiP 4 8– units in ortho phosphidosilicates Li 8 SiP 4 undergo – in analogy to ortho oxo‐silicate – formally condensation reactions resulting in vertex‐ or edge‐sharing tetrahedra. In consequence dimeric units are observed in Li 10 Si 2 P 6 , polyanionic layers in Li 3 Si 3 P 7 and three dimensional networks in Li 2 SiP 2 and LiSi 2 P 3 …”

“…The phosphide ion exhibits a higher charge compared to oxide and sulfide leading to an increased charge carrier concentration. These efforts resulted in the development of lithium phosphidotetrelates – named for their structural similarity to oxidosilicates – Li 8 SiP 4 , Li 2 SiP 2 , LiSi 2 P 3 , and α‐ and β‐Li 8 GeP 4 , which show conduction values of up to 0.1 mS · cm –1 …”

Na2Ge3P3 and Na5Ge7P5 Comprising Heteroatomic Polyanions Mimicking the Structure of Fibrous Red Phosphorus

“…[1,2] Recently, a new class of materials, sodium phosphidosilicates, has been shown to exhibit good mobilities for Na ions up to 0.4 mS•cm -1 . [3] The compounds Na 19 Si 13 P 25 , Na 23 Si 19 P 33 , Na 23 Si 28 P 45 , Na 23 Si 37 P 57 , LT-NaSi 2 P 3 , and HT-NaSi 2 P 3 consist of supertetrahedra of SiP 4 units, which form three-dimensional channels for ion migration. [3] Fast ion conduction has also been reported for the related Li phosphidosilicates, which could even be further increased by substitution of Si by Ge.…”

“…[3] The compounds Na 19 Si 13 P 25 , Na 23 Si 19 P 33 , Na 23 Si 28 P 45 , Na 23 Si 37 P 57 , LT-NaSi 2 P 3 , and HT-NaSi 2 P 3 consist of supertetrahedra of SiP 4 units, which form three-dimensional channels for ion migration. [3] Fast ion conduction has also been reported for the related Li phosphidosilicates, which could even be further increased by substitution of Si by Ge. [4,5] The highest value for phosphide-based materials of 3 mS•cm -1 was recently reported for Li 9 AlP 4 .…”

Enhancement of bromide ion conductivity in lanthanum oxybromide based solids by doping divalent zinc ion with high electronegativity

“…Solid electrolytes are functional materials where only a single ion species can migrate macroscopically as the charge carrier. Until now, many ions having relatively small ionic-size (Li + [1][2][3], Na + [4][5][6], F − [7][8][9], O 2− [10][11][12] etc.) are known to conduct in the solid lattice smoothly, and some solid electrolytes showing high conductivity are indispensable materials for electronic devices, such as batteries and chemical sensors.…”