ABSTRACT
Metal sulfides are attractive anodes for alkali metal ion batteries due to the high theoretical capacity, while their practical implementation is hampered by the inherent poor conductivity and vast volume variation during cycles. Approaching rational designed microstructures with good stability and fast charge transfer is of great importance in response to these issues. Herein, a partial sulfuration strategy for the rational construction of multi-yolk-shell (m-Y-S) structures, from which multiple Fe1- x S nanoparticles are confined within hollow carbon nanosheet with tunable interior void space is reported. As anode materials, the m-Y-S Fe1- x S@C composite can display high capacity and excellent rate capability (134, 365, and 447 mA h g-1 for K+ , Na+ , and Li+ storage at 20 A g-1 ). Remarkably, it exhibits ultra-stable potassium storage up to 1200, 6000, and 20 000 cycles under current densities of 0.1, 0.5, and 1 A g-1 , which is much superior to previous yolk-shell structures and metal-sulfide anodes. Based on comprehensive experimental analysis and theoretical calculations, the exceptional performance of m-Y-S structure can be ascribed to the optimized interior void space for good structure stability, as well as the multiple connection points and conductive carbon layer for superior electron/ion transportation.
ABSTRACT
Transition metal oxides with high theoretical capacities are widely investigated as potential anodes for alkali-metal ion batteries. However, the intrinsic conductivity deficiency and large volume changes during cycles result in poor cycling stability and low rate capabilities. Graphene has been widely used to support metal oxide for enhanced performance, but the cycling life is limited by the aggregation/collapse of active materials on graphene surface. Herein, we significantly improve the battery performance of graphene-metal oxide composite via pore engineering and surface protection. In this architecture, the mesoporous NiFe2O4 is designed for fast ion diffusion and volume accommodation, and the outer graphene protection can further enhance the electrical conductivity and prevent the aggregation during cycle. Thus, as-prepared G@p-NiFe2O4@G composite for lithium storage delivers high capacity (1244 mA h g-1 after 300 cycles at 0.2 A g-1), excellent rate performance (563 mA h g-1 at 4 A g-1), and outstanding cycling life up to 1200 cycles at 1.5 A g-1. For sodium storage, it also displays good cycling stability and superior rate performance. Moreover, the effects of various microstructures on the battery performance, the reaction kinetics of various electrodes, and the reaction mechanism of NiFe2O4 have been systematically investigated in this work.
