Direct soft-chemical synthesis of chalcogen-doped manganese oxide 1D nanostructures: Influence of chalcogen doping on electrode performance

We have developed a direct nonhydrothermal route to nanostructured chalcogen-doped manganese oxides; K_xMnO₂Q_y (Q = S, Se, and Te). According to combinative diffraction and microscopic analyses, the S- and Se-doped manganese oxides exhibit ID nanowire-type morphology with layered Δ-MnO₂- and α-MnO₂-structures, respectively, whereas the Te-doped compound consists of 3D nanospheres that are amorphous according to X-ray diffraction. X-ray absorption and X-ray photoelectron spectroscopy analyses clearly demonstrate that the doped chalcogen ions exist in the form of hexavalent chalcogenate clusters mainly on the sample surface or grain boundary. According to electrochemical and ex situ X-ray absorption spectroscopy investigations, the Se-doped manganate nanowires show higher structural stability and better electrode performance with excellent rate characteristics compared to the S-/Te-doped and undoped manganate nanostructures. This is attributed to the presence of chemically stable SeO ₄^2- species, leading to enhanced stability of the manganate lattice through the prevention of structural deformation during cycling and/or to the improvement of Li⁺ ion transport through the maintenance of intercrystallite voids. Based on the present experimental findings, we are able to conclude that the present one-pot soft-chemical route with chalcogen dopants can provide a simple method not only to economically synthesize ID nanostructured manganese oxides but also to finely control their electrode performance, crystal structure and morphology, and lattice stability.