MOF-derived Zn–Mn mixed oxides@carbon hollow disks with robust hierarchical structure for high-performance lithium-ion batteries

Abstract

Hollow metal oxides and carbon hybrids with hierarchical and robust nanoarchitecture hold great potential as high-performance electrode materials. Herein, a relatively unexplored hollow and hierarchical metal–organic framework (MOF) assembled by parallel stacked triangular sub-MOFs were successfully synthesized via a facile co-precipitation method. The hollow MOFs were then converted to binary metal oxides@carbon composites, exemplified herein as Zn–Mn mixed oxides@carbon (Zn_xMnO@C) hybrids. The obtained Zn_xMnO@C inherits the unique hollow hexagonal nanodisks (HHNDs) structure of the MOF precursor, and each triangular plate-like subunit consists of a continuous carbon matrix embedded uniformly within the ultrafine Zn_xMnO nanoparticles. When evaluated as an anode material for lithium ion batteries, the Zn_xMnO@C HHNDs exhibited high specific capacity (1050 mA h g⁻¹ at 0.1 A g⁻¹ after 200 cycles) and remarkable cycling performance up to 1000 cycles. It is believed that besides the protection of the carbon matrix, the unique hierarchically hollow structure with parallel stacked subunits endows the Zn_xMnO@C hybrid with additional capability to withstand lithiation/delithiation strain. Moreover, kinetics-analysis based on cyclic voltammograms (CVs) reveals that the high lithium storage capacity is primarily attributed to fast kinetics originating from pseudocapacitive contribution. This also accounts for the good rate capabilities of Zn_xMnO@C HHNDs (713 and 330 mA h g⁻¹ at 1 and 10 A g⁻¹, respectively). Furthermore, full cells with Zn_0.5MnO@C anodes and LiMn₂O₄ cathodes are assembled and show good cycling stability over 120 cycles. This study demonstrates a new hollow structure of MOFs and its usefulness in developing robust and hierarchical metal oxide/carbon composites for electrochemical storage applications.