Abstract

Manganese dioxide (MnO₂) with high theoretical capacity (1230 mAh/g) and low cost is considered as a promising anode material for next generation high energy density lithium-ion (Li⁺) batteries. However, the intrinsic low electric conductivity and volume change during cycling process limit its applications. In this work, a unique δ-MnO₂/C composite has been synthesized through the directed growth of 2D δ-MnO₂ nanosheets on the cabbage-leaf-derived biocarbon. The biocarbon acts as both structure buffer to accommodate the volume expansion and conductive agent to promote electron and ion transport. Moreover, oriented δ-MnO₂ nanosheets are beneficial for increasing contact area between electrode and electrolyte, thus providing more active sites and shortening the Li+ transmission routes. Electrochemical performances show that δ-MnO₂/C displays large reversible capacity (754 mAh/g after 250 cycles at current density of 0.1 A/g), excellent rate capability as well as low charge transfer resistance (17.3 Ω), and high Li⁺ diffusion rate (DLi⁺ = 2.91 × 10⁻¹⁴ cm²/s) during the cycles. Furthermore, the density functional theory calculations reveal the lower Li⁺ migration barrier energies and improved Li+ diffusion kinetics in δ-MnO₂/C hetero-layer. This study provides a novel strategy to design advanced nanocomposites, using natural plant-leaf derivatives as structure-directing agents, for the next generation energy storage and conversion systems.