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

The sinterability of oxide cathode LiCoO 2 and garnet-type solid electrolyte Li 7- x La 3 Zr 2- x Ta x O 12 ( 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 LiCoO 2 /Li 7- x La 3 Zr 2- x Ta x O 12 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 LiCoO 2 structure, thickly forming in contact with LiCoO 2 , and the other has a structural and chemical character similar to Li 7- x La 3 Zr 2- x Ta x O 12 , thinly forming in contact with Li 7- x La 3 Zr 2- x Ta x O 12 . 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 LiCoO 2 interphase is somewhat depleted of Li and contaminated with La, Zr, and Ta. These properties are considered less favorable for achieving undisturbed ionic conductivity. • The mixture of LiCoO 2 and Li 7- x La 3 Zr 2- x Ta x O 12 was sintered at high temperatures. • The interfacial microstructures were studied using STEM. • Sintering at 980 °C was insufficient to promote densification of the pellet. • Sintering at 1080 °C promoted densification with forming two interlayer products. • LiCoO 2 -like interlayer product plays a key role in densification.