Sodium-ion batteries are being considered as a promising system for stationary energy storage and conversion, owing to the natural abundance of sodium. It is important to develop new cathode and anode materials with high capacities for sodium-ion batteries. Herein, we report the synthesis of b-MnO 2 nanorods with exposed tunnel structures by a hydrothermal method. The as-prepared b-MnO 2 nanorods have exposed {111} crystal planes with a high density of (1 Â 1) tunnels, which leads to facile

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... um ion (Na-ion) insertion and extraction. When applied as cathode materials in sodium-ion batteries, b-MnO 2 nanorods exhibited good electrochemical performance with a high initial Na-ion storage capacity of 350 mAh g À1 . b-MnO 2 nanorods also demonstrated a satisfactory high-rate capability as cathode materials for sodium-ion batteries.