Thin Film Battery with Epitaxial LiCoO2 Cathode

Composition-adjusted LiCoO2 films are deposited on donor-doped electron-conductive SrTiO3 single crystal substrates, and (104)- and (001)-orientated epitaxial LiCoO2 thin films can be obtained on (100) and (111) cutting planes of the SrTiO3 substrate, respectively. Deposition of amorphous Li3PO4 solid electrolyte films on LiCoO2 cathode under careful control of substrate bias, as well as succeeding high-rate deposition of metallic Li films at an elevated temperature enables us to assemble thin film batteries showing definite anisotropy in battery performance. The (104)-oriented LiCoO2 cathode shows extremely high-rate discharge capability as contrasted with the low-rate capable (001)-oriented LiCoO2 cathode. Although p-n junction at the interface of p-type LiCoO2 film on n-type SrTiO3 substrate induces rectifying transport behavior with anomalous overpotentials, Pt current collectors connected to LiCoO2 films enable it possible to make an ohmic contact with ignorable resistance at any interfaces.