Composition-tailored 2D Mn_1-xRu_xO₂ nanosheets and their reassembled nanocomposites: Improvement of electrode performance upon Ru substitution

Composition-tailored Mn_1-xRu_xO₂ 2D nanosheets and their reassembled nanocomposites with mesoporous stacking structure are synthesized by a soft-chemical exfoliation reaction and the subsequent reassembling of the exfoliated nanosheets with Li⁺ cations, respectively. The tailoring of the chemical compositions of the exfoliated Mn_1-xRu_xO₂ 2D nanosheets and their lithiated nanocomposites can be achieved by adopting the Ru-substituted layered manganese oxides as host materials for exfoliation reaction. Upon the exfoliation-reassembling process, the substituted ruthenium ions remain stabilized in the layered Mn_1-xRu_xO₂ lattice with mixed Ru³⁺/Ru⁴⁺ oxidation state. The reassembled Li-Mn_1-xRu_xO₂ nanocomposites show promising pseudocapacitance performance with large specific capacitances of approximately 330 Fg^-1 for the second cycle and approximately 360 Fg^-1 for the 500th cycle and excellent cyclability, which are superior to those of the unsubstituted Li-MnO₂ homologue and many other MnO ₂-based materials. Electrochemical impedance spectroscopy analysis provides strong evidence for the enhancement of the electrical conductivity of 2D nanostructured manganese oxide upon Ru substitution, which is mainly responsible for the excellent electrode performance of Li-Mn _1-xRu_xO₂ nanocomposites. The results underscore the powerful role of the composition-controllable metal oxide 2D nanosheets as building blocks for exploring efficient electrode materials.