Low-Temperature Assembly of Ultrathin Amorphous MnO₂ Nanosheets over Fe₂O₃ Spindles for Enhanced Lithium Storage

Carbon coating is an effective method to enhance the lithium storage of metal oxides, which, however, suffers from harsh conditions in high-temperature hydrolysis of organic mass at inert atmosphere and compromised capacity due to the presence of low-capacity carbon. We herein report a direct assembly of ultrathin amorphous MnO 2 nanosheets with thickness less than 3 nm over Fe 2 O 3 nanospindle backbones at 95 °C as a mild-condition, short-process, and upscalable alternative to the classic carbon-coating method. The assembly of the amorphous MnO 2 nanosheets significantly increases the electrical conductivity of Fe 2 O 3 nanospindles. When evaluated as an anode for lithium-ion batteries, the Fe 2 O 3 @amorphous MnO 2 electrode shows enhanced capacity retention compared to that of the Fe 2 O 3 nanospindle electrode. In situ transmission electron microscopy and in situ X-ray diffraction observations of the electrochemically driven lithiation/delithiation of the Fe 2 O 3 @amorphous MnO 2 electrode indicate that the assembled amorphous MnO 2 nanosheets are in situ transformed into a Fe–Mn–O protection layer for better electrical conductivity, uncompromised Li + penetration, and enhanced structural integration. The Fe 2 O 3 @amorphous MnO 2 electrode therefore has a reversible capacity of 555 mAh g –1 after 100 galvanostatic charge/discharge cycles at 1000 mA g –1, comparable with that of the Fe 3 O 4 @C electrode derived via the classic carbon-coating route.