Redox Targeting of Anatase TiO2 for Redox Flow Lithium-Ion Batteries

Anatase TiO2 is an extensively studied anode material for lithium-ion batteries because of its superior capability of storing Li+ electrochemically. Here reversible lithium storage of TiO2 is achieved chemically using redox targeting reactions. In the presence of a pair of redox mediators, bis(pentamethylcyclopentadienyl) cobalt (CoCp2*) and cobaltocene (CoCp2) in an electrolyte, TiO2 and its lithiated form LixTiO2 can be reduced and oxidized by CoCp2* and CoCp2+, respectively, which accompany Li+ insertion and extraction, albeit without attaching the TiO2 onto the electrode. The reversible chemical lithiation/delithiation and the involved phase transitions are unambiguously confirmed using density functional theory (DFT) calculations, UV-vis spectroscopy, X-ray photoelectron spectoscopy (XPS), and Raman spectroscopy. A redox flow lithium-ion battery (RFLB) half-cell is assembled and evaluated, which is a critical step towards the development of RFLB full cells.