Low-Temperature Assembly of Ultrathin Amorphous MnO Nanosheets over FeO 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 nanosheets with thickness less than 3 nm over FeO 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 nanosheets significantly increases the electrical conductivity of FeO nanospindles. When evaluated as an anode for lithium-ion batteries, the FeO@amorphous MnO electrode shows enhanced capacity retention compared to that of the FeO nanospindle electrode. In situ transmission electron microscopy and in situ X-ray diffraction observations of the electrochemically driven lithiation/delithiation of the FeO@amorphous MnO electrode indicate that the assembled amorphous MnO nanosheets are in situ transformed into a Fe-Mn-O protection layer for better electrical conductivity, uncompromised Li penetration, and enhanced structural integration. The FeO@amorphous MnO electrode therefore has a reversible capacity of 555 mAh g after 100 galvanostatic charge/discharge cycles at 1000 mA g, comparable with that of the FeO@C electrode derived via the classic carbon-coating route.