The Application Of Cobalt Based Metal-Organic Framework Anodes In Lithium/Sodium Ion Batteries

Metal–organic frameworks（MOFs）which are consisted of metallic nodes and electron-donating organic linkers have attracted enormous attention for two decades on account of their superior structural flexibility,tunable pore sizes and functionality.Inthispaper,wefirstlyreportaflower-likeCo-TDA（TDA=Thiophenedicarboxylic acid）MOFs suited for sodium ion battery through a versatile hydrothermal method.It delivers a reversible capacity of 328 mAh g^-1 after100 cycles at 50 mA g^-11 for Na-ion batteries.To the best of our knowledge,it is the first time that MOFs are applied as electrode materials in SIBs,and the outstanding performance outperforms most of the carbon-based materials for sodium-ion batteries.On the basis of the research above,we report a cobalt（Ⅱ）-based ultrathin metal-organic framework nanosheets（defined as―u-CoTDA‖,TDA=2,5-thiophenedicarboxylic）as anode material in rechargeable lithium ion battery for the first time.The obtained u-CoTDA with structure advantages（thinner nanosheets,higher specific surface area,etc.）over its bulk counterpart b-CoTDA exhibits high reversible capacity(790 mAh g^-1 after 300 cycles at 1 A g^-1,548 mAh g^-11 after 400cycles at 2 A g^-1),excellent rate capability.The electrochemical performance of our u-CoTDA for LIBs outperforms most of the previous reported MOFs anode materials.Moreover,the electrochemical redox mechanism of u-CoTDA was studied by the combination of X-ray absorption near edge structure（Co K-edge）,synchrotron-based soft X-ray spectroscopy（O K-edge）and electron paramagnetic resonance experiments for the first time.The main results are as follow:（1）The XANES spectrum suggests the occurrence of Co⁰ during the Li⁺insertion process.（2）The ex-situ EPR studies for u-CoTDA demonstrate the occurrence of delocalized conduct electrons.（3）The O K-edge sXAS studies for u-CoTDA prove the rehybridization between Co-3d and O-2p orbitals and the following recovery of the local environment around oxygen ions upon charging.