Supernano Crystals Boost the Initial Coulombic Efficiency and Capacity of Copper Benzene-1,3,5-Tricarboxylate for Li-Ion Batteries

Despite the high capacity of metal-organic framework (MOF) electrodes for Li-ion batteries (LIBs), the low initial Coulombic efficiency (ICE) due to irreversible and massive consumption of lithium ions in the initial cycle hinders their practical application. Nanoscale transition metal oxides (TMOs) can activate the electrochemically stable Li-O bonds and therefore improve the ICE. Hence, copper benzene-1,3,5-tricarboxylate (Cu-BTC) rods with encapsulated supernano CuO were synthesized in a straightforward way using CuO and H₃BTC as the metal source and organic ligand, respectively. By altering the reaction temperature, the size of CuO crystals can be adjusted from 6.98 to 2.72 nm. The CuO-doped Cu-BTC (40 °C) anode delivers an optimal capacity of 990.7 mA h g^-1 (under 0.2 A g^-1) after 100 cycles and the highest ICE of 61.84%, which exceeds the other counterparts. Such superior electrochemical properties are closely related to the size and content of CuO. This strategy introduces supernano CuO into Cu-BTC, which can be generalized to construct other in situ-formed TMO-doped MOF compounds as efficient lithium storage materials.