Mechanistic studies of transition metal-terephthalate coordination complexes upon electrochemical lithiation and delithiation

Abstract

Redox-active organic molecules are intriguing candidates as active electrode materials for next-generation rechargeable batteries due to their structural diversity, environmental friendliness, and solution-phase preparation processes. Recently, a transition metal-organic coordination approach is exploited to construct high capacity anodes for lithium-ion rechargeable batteries. Here, a family of transition metal-organic coordination complexes with terephthalate ligands is synthesized that exhibit reversible capacities above 1100 mA h g(-1). The reaction mechanism to describe the multi-electron redox processes is investigated at the molecular-level via the synchrotron-sourced X-ray absorption spectroscopy and solid-state NMR analyses. The spectroscopic studies reveal that the electrochemical process involves oxidation state changes of the transition metals followed by additional lithium insertion/extraction in the conjugated aromatic ligands. The combined approaches assisted by synthetic organic chemistry and solid-state analysis provide mechanistic insights into excessive lithiation processes that have implications for the design of high-performance anode materials.