High Initial Coulombic Efficiency of SiO Enabled by Controlling SiO 2 Matrix Crystallization.

SiO is a promising anode material for practical Li-ion batteries because it can achieve a much higher capacity than graphite and a better capacity retention than Si. However, SiO suffers from poor initial Coulombic efficiency (ICE). Here, we report on a fundamentally different approach to increase the low ICE of SiO while achieving high capacity and long-term cycle stability compared to previous approaches such as electrochemical/chemical pre-lithiation processes. To enhance the ICE, the long-range/short-range orders of amorphous SiO 2 in SiO are increased by the chemical reaction of a small amount of LiOH·H 2 O even at a much lower temperature (900 °C) than the reported. The increased crystallization of SiO 2 substantially reduces the irreversible electrochemical reaction of SiO. As a result, the Li-added SiO shows substantially increased ICE, ∼82.7%, which is one of the highest values. Furthermore, we demonstrate that controlling the crystallization of SiO can enable us to achieve high ICE, high reversible capacity, and superior capacity retention (∼100% at 1C rate for 100 cycles) in SiO simultaneously. The understanding and findings will pave the way to design high-capacity SiO with high ICE and long-term stability for practical high energy density Li batteries.