Embedding MnO@Mn3 O4 Nanoparticles in an N-Doped-Carbon Framework Derived from Mn-Organic Clusters for Efficient Lithium Storage.

The first synthesis of MnO@Mn3 O4 nanoparticles embedded in an N-doped porous carbon framework (MnO@Mn3 O4 /NPCF) through pyrolysis of mixed-valent Mn8 clusters is reported. The unique features of MnO@Mn3 O4 /NPCF are derived from the distinct interfacial structure of the Mn8 clusters, implying a new methodological strategy for hybrids. The characteristics of MnO@Mn3 O4 are determined by conducting high angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and electron energy loss spectroscopy (EELS) valence-state analyses. Due to the combined advantages of MnO@Mn3 O4 , the uniform distribution, and the NPCF, MnO@Mn3 O4 /NPCF displays unprecedented lithium-storage performance (1500 mA h g-1 at 0.2 A g-1 over 270 cycles). Quantitative analysis reveals that capacitance and diffusion mechanisms account for Li+ storage, wherein the former dominates. First-principles calculations highlight the strong affiliation of MnO@Mn3 O4 and the NPCF, which favor structural stability. Meanwhile, defects of the NPCF decrease the diffusion energy barrier, thus enhancing the Li+ pseudocapacitive process, reversible capacity, and long cycling performance. This work presents a new methodology to construct composites for energy storage and conversion.