Facile synthesis of polymetallic Li-MOFs and their synergistic mechanism of lithium storage

Abstract

A simple hydrothermal method was used to synthesize a series of seven polymetallic Li-MOFs (Metal organic frameworks) with the molecular formula Li2(H2O)2M2(H2O)2(BHC) [BHC: benzene-1,2,3,4,5,6-hexacarboxylate; M: Mn, Co, Ni], which are named as MnLi, CoLi, NiLi, MnCoLi, MnNiLi, CoNiLi and MnCoNiLi, respectively. Single crystal X-ray diffractometer (SXRD), powder X-ray diffractometer (PXRD), Scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS) were employed to characterize the structures, phases, morphologies and elemental oxidation states. The seven Li-MOFs have identical structure, all of which belong to monoclinic system, P21/c space group with the similar unit cell parameters. The transition metal ions and lithium ions are coordinated with the carboxyl groups of BHC to form a unique three-dimensional framework. When used as anode materials for lithium ion batteries, MnCoLi exhibited the best electrochemical performance among others with the discharge capacity of 799.4 mAh g−1 after 100 cycles at a current density of 100 mA g−1. The superior electrochemical performance of Li-MOFs shows potential application prospects in the field of electrode materials.