Origin of Metal-Specific Reversible Conversion Processes for Metal-Organic Coordination Complexes in Lithium-Ion Batteries

Abstract

Conversion electrode materials exploiting transition-metal redox couples are prominent candidates for high-capacity lithium-ion batteries. Although extensive mechanistic investigations of inorganic host materials have been conducted, little is known about redox-active metal-organic coordination complexes in the context of solid-state reversibility. Herein, we disclose that metal-specific reversible conversion is governed by close spatial proximity between metallic nanoparticles and organic ligands, as verified by combined X-ray absorption spectroscopy and high-resolution transmission electron microscopy studies. Moreover, fully reduced metallic nanoparticles well dispersed in the organic matrix offer electrically conductive paths that allow multi-electron transfer to redox-active ＆pi;-conjugated molecules. We further extend the coordination complex scope by synthesizing cobalt-2,5-thiophenedicarboxylate, which presents distinctive electrochemical performance with a large reversible capacity of ~1100 mA h g-1 over 100 cycles at an exceptionally high current density of 500 mA g-1.