Atomic investigation on reversible lithium storage in amorphous silicon oxycarbide as a high power anode material

Abstract

Silicon oxycarbide (SiCO) has a remarkable reversible capacity of lithium and is believed to be a promising anode material for the new generation of lithium-ion batteries. Although current experiments have provided some information on lithium storage in SiCO, further study on the origin of reversible capacity needs to be conducted at the atomic scale. In this work, first principles calculations are used to investigate reversible lithium storage in five SiCO structures with different compositions. Based on lithiated structures, the Si–O bond tends to break and Li₂O forms at the beginning of lithiation and then Li_xO and Li_ySi form with increasing Li concentration, which make a major contribution to the Li capacity. The carbon atoms do not attract lithium but form a stable C–C domain to maintain the stability of the lithiated system; this is also verified by the root mean-square deviation of C. The free volume of the structures tends to decrease with increasing carbon content, implying that the void is not the major resource for lithium storage. Stoichiometric glass without free carbon presents very low reversible capacity. The reversible capacity tends to increase with higher carbon concentration; however, it would reach a maximum value and begin to decrease when the carbon content increases further.