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 MnO2 nanosheets with thickness less than 3 nm over Fe2O3 nanospindle backbones at 95 degrees C as a mild-condition, short process, and upscalable alternative to the classic carbon-coating method. The assembly of the amorphous MnO2 nanosheets significantly increases the electrical conductivity of Fe2O3 nano spindles. When evaluated as an anode for lithium-ion batteries, the Fe2O3@amorphous MnO2 electrode shows enhanced capacity retention compared to that of the Fe2O3 nanospindle electrode. In situ transmission electron microscopy and in situ X-ray diffraction observations of the electrochemically driven lithiation/delithiation of the Fe2O3@amorphous MnO2 electrode indicate that the assembled amorphous MnO2 nanosheets are in situ transformed into a Fe-Mn-O protection layer for better electrical conductivity, uncompromised Li+ penetration, and enhanced structural integration. The Fe2O3@amorphous MnO2 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 Fe3O4@C electrode derived via the classic carbon-coating route.