Effect of Simultaneous Substitution of Alkali Earth Metals and Nb in Li7La3Zr2O12 on Lithium-Ion Conductivity

Abstract

Various lithium-ion garnet-like oxides, Li 7+X-Y (La 3−X A X )(Zr 2−Y Nb Y )O 12 , (where A is an alkali earth metal) were prepared by solid-state reaction, and their lithium-ion conductivities and lattice parameters were determined by AC impedance and X-ray diffraction analysis. The La and Zr sites in these materials were simultaneously substituted, and the extent of substitution was varied to optimize both lattice parameter and lithium content associated with the highest possible lithium-ion conductivity. The optimum lattice parameter at a constant lithium content was determined to be between 12.94 and 12.96 Å. Within this range of lattice parameters, higher lithium-ion conductivities were associated with reduced lithium content.

Development of Lithium-Stuffed Garnet-Type Oxide Solid Electrolytes with High Ionic Conductivity for Application to All-Solid-State Batteries

“…Kihira et al (2013) Interestingly, regardless of the substitution element, the highest conductivity in their samples is observed at nearly the same lattice constant of 12.94-12.96 Å, which is close to our results for LLBZT with x = 0-0.10. However, LLBZT with x = 0.20 has lower room temperature conductivity than LLBZT with x = 0.05, although both samples have nearly the same lattice size.…”

“…It has been pointed out that the Li + conductivity of garnettype oxides is strongly influenced by the site occupancy in both LiO4 (24d site) and LiO6 (96h site) polyhedrons. The 24d and 96h site occupancies effect on the number of carriers, and higher σLi is achieved by well-balanced site occupancy (Li et al, 2012b;Kihira et al, 2013;Thangadurai et al, 2014Thangadurai et al, , 2015. We believe that the 24d and 96h site occupancies are influenced not only by the Li + contents in a garnet framework but also by the sizes of both LiO4 and LiO6 polyhedrons.…”

“…Partial substitution of the Zr 4+ site in LLZ by other higher valence cations, such as Nb 5+ (Ohta et al, 2011;Kihira et al, 2013), Ta 5+ (Buschmann et al, 2012;Li et al, 2012b;Logéat et al, 2012;Wang and Wei, 2012;Inada et al, 2014a;Thompson et al, 2014Thompson et al, , 2015 Ren et al, 2015a,b), W 6+ (Dhivya et al, 2013;Li et al, 2015), and Mo 6+ (Bottke et al, 2015) is also reported to be effective in stabilizing the cubic garnet phase, and their conductivity at room temperature is greatly enhanced up to ~1 × 10 −3 S cm −1 by controlling the contents of dopants and optimizing Li + concentration in the garnet framework. Although a demonstration of a solidstate battery with Nb-doped LLZ as SE has been already reported (Ohta et al, 2012(Ohta et al, , 2014, it has also been reported that the chemical stability against a Li metal electrode of Ta-doped LLZ is much superior to a Nb-doped one (Nemori et al, 2015 (Thangadurai and Weppner, 2005;Murugan et al, 2007b;Awaka et al, 2009b;Kihira et al, 2013;Thangadurai et al, 2014Thangadurai et al, , 2015.…”

“…Although a demonstration of a solidstate battery with Nb-doped LLZ as SE has been already reported (Ohta et al, 2012(Ohta et al, , 2014, it has also been reported that the chemical stability against a Li metal electrode of Ta-doped LLZ is much superior to a Nb-doped one (Nemori et al, 2015 (Thangadurai and Weppner, 2005;Murugan et al, 2007b;Awaka et al, 2009b;Kihira et al, 2013;Thangadurai et al, 2014Thangadurai et al, , 2015. Since the ionic radii of Ba 2+ (142 pm) is greater than La 3+ (116 pm), the lattice sizes of LLBZT with fixed Li + concentration per chemical formulae will be changed by the Ba substitution level, which will modify the ionic conducting property.…”

“…In concentration but also by the lattice constant (Thangadurai and Weppner, 2005;Murugan et al, 2007b;Awaka et al, 2009b;Kihira et al, 2013;Thangadurai et al, 2014Thangadurai et al, , 2015. Since the ionic radii of Ba 2+ (142 pm) is greater than La 3+ (116 pm), the lattice sizes of LLBZT with fixed Li + concentration per chemical formulae will be changed by the Ba substitution level, which will modify the ionic conducting property.…”