Amorphous silicon oxycarbide is considered as a promising anode material for new generation of lithium-ion batteries, and figuring out the lithiation mechanism is crucial for its application. In this work, first principle calculations are performed to study the atomic structures, formation energy and lithiation voltage of homogeneous SiC2/5O6/5. The interpretation of radial distribution, angular distribution and coordinate number suggests that the Si–O bond tends to break and the Li2O will form at the beginning of lithiation, then the LixO and the LiySi form with increasing Li concentration, which makes a major contribution to the capacity of SiC2/5O6/5. By the Li content dependence of the formation energies curve, the theoretical specific capacity of SiC2/5O6/5 is predicted as 1415 mA h g−1, which is comparable to the reversible capacity of 900 mA h g−1 in experiments. Both the formation energies and the voltage curves suggest lithium is preferable in incorporation with SiC2/5O6/5, and this is attributed to the formation of LixO and LiySi.

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 LixO and LiySi 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.

Polymer-derived silicon oxycarbide (SiCO) has a reversible capacity of ∼800 mA h g−1 and is considered as a promising anode material for Li-ion battery. Further study needs to be conducted in terms of energy and structure in atomic scale, which could be very challenging for current experimental technologies. To better understand the mechanism of lithium insertion in SiCO, first principle calculations are performed to study the atomic structures, bonding mechanism, mechanical properties and lithiation voltage of lithiated SiC1/4O7/4. The predominate feature of the lithiated configuration is the presence of several Li involved tetrahedrons with the formation of LiC/LiO bonds. By the calculations of relative volume and bulk modulus, SiC1/4O7/4 presents a considerably better performance in expansion and mechanical property than Si and SiO1/3. The formation energy and voltage curve also show that the lithium is more preferable in incorporation with SiC1/4O7/4 than Si and SiO1/3, which is attributed to the formation of LiO, LiC bonds and corresponding Li involved tetrahedrons. Our calculations are in agreement with the available experiments, and provide a deeper insight into the lithiation mechanism of SiCO anode for Li-ion batteries.

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 LixO and LiySi 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.