High Capacity and Reversibility of Oxygen-Vacancy-Controlled MoO₃ on Cu in Li-Ion Batteries: Unveiling Storage Mechanism in Binder-Free MoO_3−x Anodes

MoO₃ has great potential as an electrode for lithium-ion batteries due to its unique layered structure that can host Li⁺. Despite high theoretical capacity (≈1117 mAh g⁻¹), MoO₃ is not widely used simply because of poor rate capability due to lower electronic conductivity and severe pulverization. The Li-storage mechanism in MoO₃ is also still unclear. Herein, oxygen-vacancy-controlled MoO₃ is used without any additional binders and conductive materials to directly examine the Li-storage mechanism on MoO_3−x. Li-storage capacity based on the reversible formation/decomposition of solid-electrolyte interphase (SEI) films and the transformation of MoO_3−x to amorphous Li₂MoO₃ is demonstrated. The surfaces of MoO_3−x are conjugated with Cu₂O nanoparticles via annealing at 200 °C. Cu₂O acts as an effective catalyst for the formation of SEI films and the reversible reaction of MoO_3−x with Li⁺ ions. As a result, Cu₂O@MoO_3−x exhibits a charge capacity of 1100 mAh g⁻¹ after the second cycle and maintains a high reversible capacity, whereas MoO_3−x exhibits a charge capacity of 900 mAh g⁻¹ and fades to 590 mAh g⁻¹ after 100 cycles at 1 A g⁻¹.