Structure and Li+ dynamics of Sb-doped Li7La3Zr2O12 fast lithium ion conductors

Abstract

Antimony-doped lithium stuffed garnets Li(7-x)La3Zr(2-x)Sb(x)O12 (x = 0.2-1.0) prepared using a conventional solid state reaction method are characterized using Powder X-ray Diffraction (PXRD), Scanning Electron Microscopy (SEM), Energy Dispersive Analysis by X-ray (EDAX), AC Impedance spectroscopy, Magic Angle Spinning Nuclear Magnetic Resonance (MAS NMR) and Raman spectroscopic techniques. PXRD confirms the formation of a garnet-like structure with cubic symmetry for the entire selected compositional range. Among the investigated compounds, the compound with an Sb content corresponding to x = 0.4, i.e. Li6.6La3Zr1.6Sb0.4O12 exhibits the maximum total (bulk + grain boundary) ionic conductivity of 7.7 × 10(-4) S cm(-1) at 30 °C. The shape of the imaginary part of the modulus spectra suggests that the relaxation processes are non-Debye in nature. The full width at half maximum (FWHM) for the master modulus curve of Li6.6La3Zr1.6Sb0.4O12 is found to be the smallest among the investigated lithium garnets. The full width at half maximum (FWHM) of the (7)Li MAS NMR spectrum for the composition Li6.6La3Zr1.6Sb0.4O12 is the smallest among the investigated compounds. Raman data collected for the compounds in this series indicates an increase of Li(+) occupancy in the tetrahedrally coordinated site with an associated decrease of Li(+) occupancy in the octahedrally coordinated site during an increase of x in Li(7-x)La3Zr(2-x)Sb(x)O12. The present investigation reveals that the optimal Li(+) concentration required to achieve the maximum room-temperature Li(+) conductivity in Li(7-x)La3Zr(2-x)Sb(x)O12 lithium stuffed garnet is around x = 0.4.

A Tale of Two Sites: On Defining the Carrier Concentration in Garnet‐Based Ionic Conductors for Advanced Li Batteries

“…[16][17][18][19] The prevailing assumption has been that the Li content (i.e., carrier concentration) is responsible for the high Li-ion conductivity. [ 10,16,19 ] However, Ohta et al noted that when the carrier concentration is calculated based on this assumption, it can be found that the conductivity is not increasing linearly with the carrier concentration. Since the carrier concentration (assuming all the ions participate in conduction) does (5 of 9) 1500096 wileyonlinelibrary.com not change enough to explain the increase in conductivity, it was thought that changes to the mobility caused by the dopant must, therefore, be controlling the conductivity.…”

“…[ 23,28 ] Li conducting garnets have been analyzed using the same assumption that all the Li-ions contribute to the conductivity. [ 10,16,19 ] However, recent experimental evidence shows that this assumption is not valid for the garnet family of materials. [ 29 ] Thus, in order to clarify what is the effective carrier concentration in the garnet family of ionic conductors, a compositional series of cubic stabilized garnet ionic Li ion conductors, Li 7− x La 3 Zr 2− x Ta x O 12 (x = 0.5, 0.75, and 1.5), was synthesized and the relationship between site occupancy and effective carrier concentration was determined.…”

“…[ 14,15 ] A maximum in the ionic conductivity at room temperature has been observed for compositions near the critical Li concentration to stabilize the cubic phase. [16][17][18][19] As such, the majority of the work in the literature has focused on understanding how the cubic phase is stabilized at high Li concentrations. [14][15][16][17][18][19][20][21] However, the understanding of the fundamental parameters that control the Li conductivity has Solid electrolytes based on the garnet crystal structure have recently been identifi ed as a promising material to enable advance Li battery cell chemistries because of the unprecedented combination of high ionic conductivity and electrochemical stability against metallic Li.…”

Insights into the Lithium-Ion Conduction Mechanism of Garnet-Type Cubic Li5La3Ta2O12 by ab-Initio Calculations

“…Optimization efforts have focused on obtaining the cubic phase by promoting disorder across the Li sublattice; dopant incorporation is typically employed, targeting the framework cation sites (i.e., La and Zr). Some notable improvements were reported for Te-doped LLZrO (1.02 × 10 −3 S/cm), 15 Tadoped LLZrO (1.0 × 10 −3 S/cm), 16−19 Nb-doped LLZrO (8.0 × 10 −4 S/cm), 20 Sb-doped LLZrO (7.7 × 10 −4 S/cm), 21 and Sr-doped LLZrO (5.0 × 10 −4 S/cm). 22 Simultaneous substitution was also explored in the series Li 7+x−y (La 3−x A x )-(Zr 2−y Nb y )O 12 (where A is an alkali earth metal) and has shown that an optimum lattice parameter at a constant lithium content of 6.5 per formula unit (p.f.u.)…”

Synthesis, crystal structure and conductive properties of garnet-type lithium ion conductor Al-free Li_7&minus;<i>_x</i>La₃Zr_2&minus;<i>_x</i>Ta<i>_x</i>O₁₂ (0 &le; <i>x</i> &le; 0.6)

“…In this decade, the garnet-related type Li 7 La 3 Zr 2 O 12 , which was reported by R. Murugan et al for first time, 1) has been studied from view points of the chemical stability, the conductive properties and the crystal structure in detail. In order to increase the Li-ion conductivity of the garnet-type Li 7 La 3 Zr 2 O 12 , a large number of studies on the chemical substitution using various cation species has been reported.…”