Ultrathin Cobalt-Based Metal–Organic Framework Nanosheets with Both Metal and Ligand Redox Activities for Superior Lithium Storage

The controllable synthesis and structural tailoring of nanostructured metal–organic frameworks (MOFs) is of huge significance in boosting their potential for rechargeable batteries. We herein present the facile synthesis of cobalt-based ultrathin metal–organic framework nanosheets (referred to as “u-CoTDA”) by using 2,5-thiophenedicarboxylic (H₂TDA) as the organic building block through a one-pot ultrasonic method for the first time. The obtained u-CoTDA exhibits high reversible capacity (790 mAh g⁻¹ after 400 cycles at 1 A g⁻¹) and excellent rate capability (694 mAh g⁻¹ at 2 A g⁻¹), which outperforms its bulk counterpart. Moreover, the detailed lithiation/delithiation processes of u-CoTDA were studied by the combination of Co K-edge X-ray absorption near edge structure (XANES), O K-edge soft X-ray spectroscopy (sXAS) and electron paramagnetic resonance (EPR) techniques, which demonstrate that both the Co^II centers and organic ligands of u-CoTDA are involved in the reduction/oxidation processes.