Structural analysis of the LiCoO2 cathodes/garnet-type Li6.5La3Zr1.5Ta0.5O12 solid electrolyte interface

Abstract

The sinterability of oxide cathode LiCoO₂ and garnet-type solid electrolyte Li_7-xLa₃Zr_2-xTa_xO₁₂ (x = 0.5) at 980 and 1080 °C has been studied using an integrated suite of scanning transmission electron microscopy and spectroscopic techniques, with a particular focus on the LiCoO₂/Li_7-xLa₃Zr_2-xTa_xO₁₂ interfaces. Whereas the densification hardly progresses and the interdiffusion is limited to the vicinity of the interface at 980 °C, dramatic densification can be achieved at 1080 °C at the expense of severe interfacial modification. The structural, chemical, and electronic characteristics of the interphases are systematically investigated. Two kinds of interphases are formed: one has a disordered LiCoO₂ structure, thickly forming in contact with LiCoO₂, and the other has a structural and chemical character similar to Li_7-xLa₃Zr_2-xTa_xO₁₂, thinly forming in contact with Li_7-xLa₃Zr_2-xTa_xO₁₂. The former is assumed to play a vital role in the densification of the pellet. Analysis using energy-dispersive spectroscopy and electron energy loss spectroscopy reveals that the disordered LiCoO₂ interphase is somewhat depleted of Li and contaminated with La, Zr, and Ta. These properties are considered less favorable for achieving undisturbed ionic conductivity.