Inner-Stress-Optimized High-Density Fe<sub>3</sub>O<sub>4</sub> Dots Embedded in Graphitic Carbon Layers with Enhanced Lithium Storage
Zhaoliang Shi, Qing Zhang, Liyun Zhao, Hua Wang, Wei Zhou
Abstract
The volume variation of electrode materials will lead to poor cyclability of lithium-ion batteries during the lithiation/delithiation process. Instead, inner-stress fragmentation is creatively used to change carbon-layer-capped Fe3O4 particles ∼30 nm in diameter into high-density Fe3O4 dots ∼4 nm in size embedded in ultrathin carbon layers. The optimized structure shows a remarkable 45.2% enhancement of lithium storage from 804.7 (the 10th cycle) to 1168.7 mA h g–1 (the 250th cycle) at 500 mA g–1, even retaining 1239.5 mA h g–1 after another 550 cycles. The electrochemical measurements reveal the enhanced capacitive behavior of the high-density Fe3O4 dots@C layers, which have more extra active sites for the insertion/extraction of Li+ ions, confirmed by the differential capacity plots, leading to remarkably increased specific capacity during cycling. The restructured electrode also shows a superior rate capacity and excellent cycling stability (938.7 and 815.4 mA h g–1 over 2000 cycles at 1000 and 2000 mA g–1, respectively). X-ray photoelectron spectroscopy and transmission electron microscopy characterizations show that the optimized structure has stable structural and componential stability even at large rates. This work presents an MOF-guided synthesis of high-density Fe3O4-dots’ anode material optimized by inner-stress fragmentation, showing a feasible route to design high-efficiency electrode materials.