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A layered compound, NaxMn2/3Co1/6N1/6O2 (NMCN), prepared by a solid-state reaction, served as a high capacity positive electrode material with the reversible capacity of ca. 200 mA ⋅ h ⋅ g-1 using a Na foil as the counter electrode. A high-resolution synchrotron X-ray diffraction (XRD) analysis revealed that, whereas the NMCN sample had the P3 structure (R3m) when the precursor was heated below 700°C, the P2 structure (P63/mmc) was obtained when heated above 800°C. The latter excels over the former in both capacity and cycle stability; i.e., the initial discharge capacities and potentials of the P2 and P3-NMCN were 216 mA ⋅ h ⋅ g-1, 2.87 V vs. Na+/Na and 206 mA ⋅ h ⋅ g-1, 2.78 V vs. Na+/Na, respectively. The P2-MNCN retained 80% of its initial discharge capacity while the P3-NMCN dropped to 69% after 30 cycles in the potential range of 1.0-4.5 V vs. Na+/Na. An in-situ XRD analysis revealed that the lattice volume of the P2-NMCN contracts and expands by 20% during the charge and discharge (i.e., Na extraction and insertion) without drastically changing its crystallographic structure. [ABSTRACT FROM AUTHOR]

The electrochemical properties of SnC2O4-coated Si materials with various compositions were investigated. Among them, the Si-70 wt%SnC2O4 composite maintained a high capacity of greater than 1000 mAhg-1 after more than 30 cycles. A synchrotron XRD analysis revealed that the SnC2O4 decomposed into Sn and an irreversible product during the first lithiation process. Subsequently, Sn and Si were independently lithiated/de-lithiated to Li17Sn4 and Li15Si4, respectively, during the Li insertion and de-insertion process. A full-cell using LiFePO4 as the positive electrode material was assembled, and the cell exhibited a good cycle performance in which it maintained almost 100% of the initial capacity after 100 cycles in the temperature range of -20-60°C. The 1-Ah class cell showed a high safety during a nail penetration test and an overcharge test; no smoke and flames were observed during these safety tests. [ABSTRACT FROM AUTHOR]