Tunnel-type β-FeOOH cathode material for high rate sodium storage via a new conversion reaction

다국어 초록 (Multilingual Abstract)

<P><B>Abstract</B></P> <P>We have investigated a tunnel-type β-FeOOH cathode material for rapid sodium storage. Rietveld refinement of the X-ray diffraction (XRD) data obtained for β-FeOOH indicated that the structure was stabilized into [2 × 2] hollandite tunnel structure, and the adhesion of the β-FeOOH onto carbon nanotubes (CNTs) led to a high electrical conductivity of 3Scm<SUP>−1</SUP>. As a result, the β-FeOOH/CNTs composite electrode showed excellent electrode performance, with a discharge capacity of 205 mAh g<SUP>−1</SUP> and a coulombic efficiency of 88.5% in the voltage range of 1.1–4V during the first cycle, 131 mAh g<SUP>−1</SUP> after 200 cycles, and a capacity retention of 70% over 300 cycles at 10C (1920mAg<SUP>−1</SUP>). Based on the XRD, X-ray absorption, and time-of-flight secondary-ion mass spectroscopy results, we suggest a new conversion mechanism for the β-FeOOH cathode material in Na cells, namely, FeOOH + Na<SUP>+</SUP> + e<SUP>-</SUP> → FeO + NaOH. This conversion reaction produces NaOH as a byproduct, and the reaction is fairly reversible even at 10 C-rates.</P> <P><B>Highlights</B></P> <P> <UL> <LI> β-FeOOH/CNTs composite is suggested as an cathode material for Na-ion batteries. </LI> <LI> β-FeOOH/CNTs composite is activated by a new conversion reaction via Fe<SUP>3+/2+</SUP> redox. </LI> <LI> β-FeOOH/CNTs composite shows a high electric conductivity, 3Scm<SUP>−1</SUP>. </LI> <LI> β-FeOOH/CNTs composite is fairly reversible at high rates for a long term. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>We report on tunnel type β-FeOOH nano-stick particles embedded in carbon nanotubes. The β-FeOOH/CNTs composite represents rapid sodium storage capability via a new conversion reaction, which is fairly reversible at high rates for a long term.</P> <P>[DISPLAY OMISSION]</P>