Two-dimensional (2-D) nanoplates of iron-substituted calcium cobaltite (Ca3Co3FeO9) are synthesized through a simple citrate-gel method. The lithium electroactivity of Ca3Co3FeO9 demonstrates that this is an applicable active anode material. In this study, we focus on the reversible conversion process and internally multi-phasic, nanostructured character occurring in Ca3Co3FeO9 nanoplates. Moreover, we demonstrate that in-situ formation of active/inactive nanocomposite improves the conversion reaction kinetics by accommodating the large volume changes during lithium uptake and removal, thereby achieving outstanding rate capabilities.