MoO3− x Incorporated Covalent Organic Framework Nanocomposite as an Advanced Anode Material for Li-Ion Batteries: Elucidating Structure−Activity Relationships

Abstract

MoO3 serves as a promising anode material for lithium-ion batteries (LIBs) because of its high theoretical capacity of 1117 mAh g−1 and its layered structure. However, MoO3 has inherently low electronic conductivity and experiences significant volume expansion during the charge−discharge cycles, which limits its ability to achieve substantial capacity and cyclability for practical applications. Generally, oxygen vacancies in MoO3 are considered effective in enhancing conductivity and expanding the lattice distance. On the other hand, covalent organic frameworks (COFs) have recently been used as organic anode materials for LIBs because of their abundance of active sites, large conjugated structures, high surface area, and accessible Li+ transport channels. Despite the several advantages of COF-based nanomaterials, critical issues like poor structural stability and a limited number of redox-active sites impede the extensive use of these nanomaterials in LIBs. In this study, we present a novel nanomaterial design strategy that incorporates oxygen-deficient MoO3−x in the TA COF architecture, fabricated using a simple mechanochemical synthesis procedure. To the best of our knowledge, MoO3−x-TA COF nanocomposites (NCs) as anode materials have been evaluated for LIBs for the first time. The assembled LIBs demonstrate exceptional performance, achieving a specific capacity of 517 mAh g−1 at a current of 0.1 A g−1 and showing cyclic stability of 1100 cycles with roughly 100% retention. A density functional theory (DFT) investigation was conducted, and the results indicate that molybdenum trioxide preferentially binds near the keto site while preserving the overall structure of TA-COF. Furthermore, this modification enhances Li adsorption, as the keto-modified TA-COF remains structurally less distorted and energetically more stable at higher Li loadings compared to the pristine TA-COF. Thus, this strategy of introducing transition metal oxides paves the way for regulating the valence, lattice structure, and even the composition of electrode materials through COF-based nanocomposite preparation. This approach equips these materials with desirable features and offers an alternative solution to meet the demands of energy storage systems.