Lithium Ion Mobility in Lithium Phosphidosilicates: Crystal Structure, ⁷Li, ²⁹Si, and ³¹P MAS NMR Spectroscopy, and Impedance Spectroscopy of Li₈SiP₄ and Li₂SiP₂

Abstract

The need to improve electrodes and Li-ion conducting materials for rechargeable all-solid-state batteries has drawn enhanced attention to the investigation of lithium-rich compounds. The study of the ternary system Li-Si-P revealed a series of new compounds, two of which, Li SiP and Li SiP , are presented. Both phases represent members of a new family of Li ion conductors that display Li ion conductivity in the range from 1.15(7)×10 Scm at 0 °C to 1.2(2)×10 Scm at 75 °C (Li SiP ) and from 6.1(7)×10 Scm at 0 °C to 6(1)×10 Scm at 75 °C (Li SiP ), as determined by impedance measurements. Temperature-dependent solid-state Li NMR spectroscopy revealed low activation energies of about 36 kJ mol for Li SiP and about 47 kJ mol for Li SiP . Both compounds were structurally characterized by X-ray diffraction analysis (single crystal and powder methods) and by Li, Si, and P MAS NMR spectroscopy. Both phases consist of tetrahedral SiP anions and Li counterions. Li SiP contains isolated SiP units surrounded by Li atoms, while Li SiP comprises a three-dimensional network based on corner-sharing SiP tetrahedra, with the Li ions located in cavities and channels.

Synthesis, Crystal Structure, and Chemical Bonding of Ba2SiP4

“…339.05(8) P-P 222.01(15) P-Si-P (2 ϫ) 96.18(4) P-Si-P (6 ϫ) 116.50 (2) agreement with the single crystal structure determination. The 31 P spectrum reveals additional weak signals from the impurity phases.…”

Synthesis and Structure of the Sodium Phosphidosilicate Na2SiP2

“…The supertetrahedral compounds in the system Na‐Si‐P are rather sodium‐poor and the only known sodium‐rich compound is Na 5 SiP 3 . Therefore we focused on the sodium‐rich part of the system and came across Na 2 SiP 2 which turned out to be structurally quite different from the lithium analogue reported earlier , . Here we report the synthesis, crystal structure, NMR and impedance spectroscopy of Na 2 SiP 2 .…”

“…Fast lithium and sodium ion conductors composed of earth abundant elements as potential components of all solid‐state batteries attract immense interest . Recently, several phosphidosilicates with isolated or condensed SiP 4 tetrahedra have demonstrated lithium or sodium ion conductivity, for example Li 8 SiP 4 , Li 2 SiP 2 ,, LiSi 2 P 3 , and the series Na 23 Si 9 n +19 P 12 n +33 ( n = 0–3) . These compounds have also been studied in the framework of the electrochemical mechanism of SiP 2 /Li anodes , .…”

Relevance of solid electrolytes for lithium-based batteries: A realistic view

“…× 10 −8 S/cm at 0°C and 6(1) × 10 −6 S/cm at 75°C for Li 2 SiP 2 [94]. These few examples already give a flavor of the large range of novel Li solid electrolytes yet to be uncovered, and at the same time highlight the challenges and bottlenecks associated with such endeavors.…”

“…While Li conductivities of 3.5 × 10 −5 S/cm were determined in the dry state, several orders of magnitude higher conductivities were observed when exposed to humid air, albeit at the expense of electrochemical stability [92]. A new family of potentially fast Li solid electrolytes based on phosphidosilicates in the system Li-Si-P was recently discovered by the groups of Johrendt and Fässler [93,94]. Li 2 SiP 2 and LiSi 2 P 3 feature interpenetrating 3D networks of corner-sharing SiP 4 supertetrahedra while the Li ions are located in the cavities and channels of the supertetrahedral networks.…”