Large-scale synthesis of Co2V2O7 hexagonal microplatelets under ambient conditions for highly reversible lithium storage

Abstract

Micro-/nanostructured mixed transition metal oxides (MTMOs) with their unique morphologies have attracted much attention due to their potential applications such as lithium-ion batteries (LIBs). Nevertheless, in contrast to active research for the synthesis of MTMOs (A_xB_3−xO₄ (A, B = Co, Ni, Zn, Mn, Fe)), metal vanadates seem to be an unnoticed group, possibly due to the lack of appropriate synthetic methods. In this work, for the first time, we report a structure- and size-controlled synthesis of pseudohexagonal monoclinic Co₂V₂O₇·nH₂O monodisperse hexagonal nanoplatelets (MHNPs) through a facile water bath method via a micelle-assisted assembly-Ostwald ripening process. The amount of hexamethylenetetramine in the reaction was found to be pivotal to the formation of hexagonal nanoplatelets. Additionally, the structure of MHNPs could be retained only in a certain temperature range. By calcination of Co₂V₂O₇·nH₂O in air, mesoporous Co₂V₂O₇ MHNPs composed of numerous nanometer-sized subunits could be harvested. Benefiting from the unique structure and probably synergetic effects of different metal ions, the as-prepared Co₂V₂O₇ MHNPs possess high specific capacity, long-term cycling stability, and good rate capability. Specifically, the Co₂V₂O₇ MHNPs exhibit a reversible capacity as high as 866 mA h g⁻¹ with nearly 100% capacity retention after 150 cycles, making them potential electrode materials for LIBs.