Microstructure of the LiCoO2 (cathode)/La2/3-xLi3xTiO3 (electrolyte) interface and its influences on the electrochemical properties

Two different types of lithium lanthanum titanate (LLT)/LiCoO2 assemblies were produced by depositing the LiCoO2 cathode on the cleaved or polished surfaces of polycrystalline LLT to investigate the effects of the LLT/LiCoO2 interface structure on the electrochemical properties of the assemblies. The microstructures and electrochemical properties of the assemblies were investigated as a function of charge/discharge cycle number. Cyclic voltammetry indicates that anodic and cathodic peaks shift to higher and lower potentials, respectively, with cycle number for the assembly produced with the cleaved LLT, whereas these potential changes are negligibly small for that produced with the mechanically polished LLT. LiCoO2 is formed epitaxially on LLT with the orientation relationships (110)(LLT)// (11 (2) over bar0)(LiCoO2) and [001](LLT)//[(4) over bar 401](LiCoO2) for both assemblies, but amorphous regions are formed at the interface for the assembly produced with polished LLT. The amorphous region is considered to play an important role in the cycle stability of the assembly upon charging/discharging. (c) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.