High conductivity of mixed phase Al-substituted Li7La3Zr2O12

Abstract

Al-substituted Li 7 La 3 Zr 2 O 12 (LLZ:Al) was synthesized via conventional solid state reaction. Different dwell times at sintering temperature of 1200°C led to a varying Li content in LLZ:Al which significantly affected the Li-ion conductivity. Electrochemical impedance spectroscopy and X-ray diffraction were used to characterize the sintered pellets which showed a maximum total ionic conductivity of~3 × 10 −4 S cm −1 at room temperature although the samples were composed of cubic and tetragonal LLZ:Al, with the tetragonal phase as its major phase. Inductively coupled plasma optical emission spectroscopy revealed that the Li content steadily decreased from 7.5 to 6.5 Li per formula unit with increasing sintering time. The highest conductivity was observed from the sample with the lowest Li concentration at 6.5 per formula unit. Scanning electron microscopy images revealed the formation of large grains, about 500 μm in diameter, which additionally could be the reason for achieving high total Li-ion conductivity. Electrochemical tests showed that mixed phase LLZ:Al is stable against metallic Li up to 8 V.

Microelectrodes for local conductivity and degradation measurements on Al stabilized Li7La3Zr2O12 garnets

“…In this specific case a bulk conductivity of 3.3 × 10 −4 S cm −1 results. This is within the range typically found for such LLZO samples stabilized with aluminium [8,13,[27][28][29][30][31]. However, literature data reveal a large scattering of bulk or total conductivities, and in a separate paper we will show that a substantial variation also exists between numerous nominally identical samples prepared in our labs.…”

“…The highest value found for a Fig. 4 Impedance spectra of two Ti/Pt microelectrodes with different diameter d, and the corresponding fits (dashed line) based on the equivalent circuit shown above [7,8,31]. Plotting the averaged conductivity for every microelectrode diameter shows a clear trend ( Fig.…”

Al-incorporation into Li7La3Zr2O12 solid electrolyte keeping stabilized cubic phase for all-solid-state Li batteries

“…The highly conductive cubic phase have reported that Al dopants play a key role as cubic-phase stabilizers by replacing lithium lattice sites (e.g. 24d, 48 g, and 96 h) [10,11,14,18,23,25] . Although the exact Al sites replacing Li sites are not experimentally clear, it seems quite certain that Al substitution could produce a stabilized cubic phase and provide fast Li-ion conduction.…”

“…Any solid electrolytes with fast lithium-ion conduction have been considerable attracted as one of the key technologies for the development of next-generation energy storage systems such as all-solid-state Li batteries, Li-S battery and Li-air battery [1][2][3][4][5] . Various types of lithium-ion-conductive solid electrolytes have been reported, such as layered Li 3 N, Li 14 Zn(GeO 4 ) 4 , Li 1 + x Al x Ti 2-x (PO 4 ) 3 (LATP), Li 3 x La (2/3) −x TiO 3 (LLTO) and Li 7 La 3 Zr 2 O 12 (LLZO) [6] . Among them, garnet-type LLZO has been widely studied as a promising lithium-ion solid electrolyte because of its attractive value of ionic conductivity and its low grain boundary resistance [2] .…”

“…The second focus is unstable and reactive surface of cubic phase under air environment [13] and the surface formation of Li 2 CO 3 hinders fast conduction of lithium ion. To overcome all, previous approaches have tried that several dopants could stabilize cubic phase [14][15][16][17][18][19][20][21][22] . Matsui et al [10,11,18] reported that the substituted Al element occupies the Li sites, which enables the phase transformation from the tetragonal phase to the cubic phase by destabilizing the Li ordering in the tetragonal phase.…”