Iron encapsulated in single-walled carbon nanotubes for obtaining the evidence of improved coulombic efficiency and improving the lithium battery performance of ZnO anodes

Abstract

Cycling coulombic efficiency including the 1^st cycle is a crucial factor for nano-carbon based anodes. How to improve their coulombic efficiency and further prove whether the additional reversible capacity produced from the SEI film in the 1^st cycle is an obstacle for their possible commercial application in Li ion batteries (LIBs). For this aim, a novel composite of Fe-encapsulated single-walled carbon nanotubes (Fe@SWNTs) with special nano-structure was designed and used as an anode material for LIBs. The resulting Fe@SWNT anode can provide much larger coulombic efficiency of 53.1% in the 1^st cycle than 35.6% for pure SWNTs, implying the value increment reached ∼50%. The Fe@SWNTs can exhibit an reversible capacity of 420 mA h g⁻¹ after 300 cycles and excellent rate performance at room temperature, being obviously better than 275 mA h g⁻¹ for a SWNT anode. The origination of this extra improved reversible capacity can be confirmed to be derived from the reversible reaction of SEI film activated by the Fe catalyst. Meanwhile, the Fe@SWNT anodes exhibited superior low-temperature (at 5 and −15 °C) electrochemical performance, which should be associated with an improved effect of the highly conducting Fe at low temperature, and with the activation of catalyst Fe on the reversible capacity. In addition, when Fe@SWNTs were developed as carriers for attaching ZnO, the ZnO/Fe@SWNTs can deliver much better LIB performance than anodes of pure ZnO and ZnO/SWNTs. Thus, catalyst modification supplied a promising route to obtain improved coulombic efficiency and reversible capacity for LIB nano-carbon based anodes.