Development of Novel Garnet-Type Solid Electrolytes for Potential Application in Li Ion Batteries

Abstract

The development of promising solid electrolytes having a garnet-like structure has been successfully achieved through solid state (ceramic) method. Various approaches to improve the Li ion conductivity were employed. The first approach involved creating oxide ion vacancies into the crystal structure of parent garnet-like oxide, Li5La3Nb2O12 to create a novel family of compounds with nominal composition, Li5La3Nb2-xYxO12-δ (0 ≤ x ≤ 1). The second approach was Li stuffing into the garnet-like oxides to develop a series of Li stuffed novel Li5+2xLa3Nb2-xYxO12 (0.05 ≤ x ≤ 0.75) and Li6.5La2.5Ba0.5ZrTaO12. Powder X-ray diffraction (PXRD), thermo gravimetric analysis (TGA), scanning electron microscopy (SEM), electron probe microanalysis (EPMA) coupled with a wavelength-dispersive spectrometer (WDS), 7Li nuclear magnetic resonance (Li-NMR), and AC impedance spectroscopy were employed to characterize the structure, morphology, elemental composition, Li ion sites, and Li ion conductivity. Studies have shown that Li5+2xLa3Nb2-xYxO12 have turned out to be promising solid electrolytes with high Li ion conductivity (10-4 Scm-1 at ambient temperatures). In addition, all families of garnets are found to be chemically stable with Li cathode materials (Li2MMn3O8, where M = Fe, Co) up to 400 oC in air. The developed electrolyte materials have the potential to be used in all-solid-state Li ion batteries.