MnO2 Nanoflakes Anchored on N-Doped Carbon Nanotubes for Lithium Storage

Abstract

Nano-MnO₂ integrated with conductive carbon has been surfaced as an opportune anode for high-performance lithium ion batteries (LIBs). However, MnO₂ assembled in nanotube form that is more conducive to Li⁺ diffusion has been desperate for a simple and efficient preparation approach. Here, through a straightforward solution method, we construct an innovative sandwich-like architecture based on wide graphitic carbon nanotubes, of which the dual surfaces are anchored by a conductive polymer (polypyrrole, PPy) and MnO₂ nanoflakes layer by layer. The N-doped interior carbon layer derived from annealed PPy favors enhanced conductivity for rapid Li⁺ transport, and benefiting from the wide cavity of nanotubes, nano-MnO₂ is heavily loaded, and the severe volume variation could be effectively suppressed to preserve the anode integrity. As a result, such a hybrid anode with over 65% MnO₂ loading reveals stable cycling capacity, reinforced rate capability, and a long service life, achieving 1401.30 mA h/g in 150th cycle at 100 mA/g and 211.43 mA h/g, with Coulombic efficiency close to 100% after 6000 cycles at 2000 mA/g. Detailed electrochemical measurements confirm the critical role of PPy in facilitating fast lithium storage and rapid Li⁺ diffusion, and the electrochemical behavior of carbon, MnO₂, and their hybrids is also analyzed. Hence, we believe this work would provide valuable insights for the development of next-generation LIBs based on metal oxides.