Benefits and Limitations of 226 Substitutions into Li-La-Ti-O Perovskites

Abstract

Lithium lanthanum titanate solid electrolyte has high bulk conductivity and stability at high potentials but suffers from low grain boundary conductivity and instability at low potentials. In order to mitigate these two limitations, the effect of single partial substitutions on perovskite (Li-La-Ti-O) materials was studied. The X-ray diffraction patterns showed that numerous substituents enable pure-phase perovskite, a feat that could not previously be accomplished in the unsubstituted materials. Bond valence mismatch is used as a simple predictor of the substitution site and shows that remarkably high mismatches can be tolerated by the perovskite structure. The best substitutions had minimal impact on bulk conductivity but induced minor enhancements in the grain boundary conductivity. Some elements, such as Cr and Mn, increased the electronic conductivity producing good candidates for the electrolyte in the composite cathode for an all-solid-state battery. The electrochemical stability limits were also shifted either to higher or lower potentials by substitutions. Cr substitution resulted in the electrolyte becoming a cathode material with a highly reversible redox peak near 3.43 V (vs Li/Li+). A thorough screening, therefore, yields a combination of materials (unsubstituted as the anode/electrolyte and Cr-substituted as the cathode) that represents a strong candidate for the elusive epitaxial battery, an ideal application of this class of materials given the very high bulk conductivities. Some substitutions also extended the low potential stability limit to below 1.5 V, a shift that would allow the use of Li4Ti5O12 and Nb-based anodes without a buffer layer. Overall, this work shows to what extent the properties of LLTO perovskites can be tuned with substitution in order to meet various application requirements.

Improving Li-Ion Anodes with Systematic Elemental Doping in Titanium Niobate

“…Specifically, the samples were made by first dispensing 0.55 M titanium butoxide and ammonium niobate oxalate hydrate, along with stoichiometric quantities of dopants of different precursor concentrations, into alumina cups. The dopant precursors are the same as those used in Jonderian et al 39 Citric acid (3 M) was then added as a chelating agent. These homogeneous precursor solutions then underwent a gelation process by heating at 60, 110, and 200 °C under vacuum.…”

Semiautomated Experiments to Accelerate the Design of Advanced Battery Materials: Combining Speed, Low Cost, and Adaptability

“…The simplest is the sol–gel approach. This method has improved versatility over coprecipitation: doping studies have been performed with up to 52 different dopants on Na-ion cathodes, Li-ion cathodes, and solid electrolytes . The initial step is similar to coprecipitation with mixtures of precursor solutions being mixed, but then a chelating agent such as citric acid is added .…”

“…For XRD data, the McCalla group utilizes automated phase identification and fitting in both commercial and house-written software. This is ideal for cases where crystallographic databases have phases that are similar to the target phase, such as when a small amount of dopant is added and small changes in lattice parameters do not impact phase identification. ,, However, such approaches may be limited when new materials are encountered or if full substitutions are tested, such that phase matching fails. In such cases, supplementing experimental databases with computational ones such as the Materials Project becomes attractive and necessary.…”

Pioneering Combinatorial Investigation to Unlock the Potential of Lithium Borosilicate Glasses as Solid Electrolytes

“…In previous reports, high-throughput methodologies have been successfully employed to investigate the effects of substitutions on cathode and anode materials. Additionally, our laboratory has developed and utilized high-throughput tools to accelerate the screening process of crystalline oxide electrolytes. − These studies develop the composition–structure–property relationships to enable the rational design of electrolytes. The properties screened include ionic conductivity, electronic conductivity, electrochemical stability window, and stability against lithium; all of which are essential to develop viable solid electrolytes .…”