A Nanostructured SiAl0.2O Anode Material for Lithium Batteries

Silicon monoxide (SiO) is a promising candidate for anodes in lithium rechargeable batteries, because of its large capacity. The initial irreversible reaction and still dissatisfactory capacity retention during cycling, however, hinder its practical application. A nanostructured SiAl0.2O composite material has been developed via mechanochemical synthesis and investigated as an alternative anode. The SiAl0.2O is composed of quantitatively increased silicon nanocrystallites, each of which is less than 10 nm in size, embedded in an amorphous matrix; the compositional structure of the matrix is aluminosilica in which most of Si atoms are neighbored with two Al atoms over oxygen, as confirmed with X-ray diffraction (XRD), solid-state Si-29 and Al-27 nuclear magnetic resonance (NMR), and transmission electron microscopy (TEM). This electrode exhibits enhanced initial Coulombic efficiency of which the relative increase is >10%, compared to SiO, and also demonstrates improved cycling performance, offering a capacity of 800 mAh/g over 100 cycles. These improvements are attributed to the electrochemically inactive alumina component, which not only replaces part of the SiO2 phase that is regarded as an origin of initial irreversible reaction but also provides mechanically reinforcing properties, resulting in little pulverization of particles and less change in the impedance of the SiAl0.2O electrode during cycling.