The spinel MgMn2O4, a cathode material with theoretical capacity of 272 mA h g–1, holds promise for future application in high volumetric magnesium-ion batteries. Atomic-resolution imaging of the structure of the spinel and its surface composition would advance our understanding on its electrochemical properties, mass, and charge transport behavior in electrodes. We observe directly, by aberration-corrected scanning transmission electron microscopy (STEM), the atomic structure of cubic spinel MgMn2O4 for the first time. More importantly, we find that a thin stable surface layer of rocksalt MgMnO2 was grown on a bulk cubic spinel phase. The formation of a rocksalt phase was induced by reconstruction of the spinel phase, i.e., the insertion of Mg into the spinel lattice together with Mg/Mn cation exchange and Frenkel-defect-mediated relocation of Mg cations. This new structural analysis provides a critical step toward understanding and tuning the electrochemical performance of spinel oxide in rechargeable Mg-ion batteries.

The development of high energy–density lithium-ion secondary batteries as storage batteries in vehicles is attracting increasing attention. In this study, high-voltage bipolar stacked batteries with a quasi-solid-state electrolyte containing a Li-Glyme complex were prepared, and the performance of the device was evaluated. Via the successful production of double-layered and triple-layered high-voltage devices, it was confirmed that these stacked batteries operated properly without any internal short-circuits of a single cell within the package: Their plateau potentials (6.7 and 10.0 V, respectively) were two and three times that (3.4 V) of the single-layered device, respectively. Further, the double-layered device showed a capacity retention of 99% on the 200th cycle at 0.5 C, which is an indication of good cycling properties. These results suggest that bipolar stacked batteries with a quasi-solid-state electrolyte containing a Li-Glyme complex could readily produce a high voltage of 10 V.

Exploring novel electrode materials is critical for the development of a next-generation rechargeable magnesium battery with high volumetric capacity. Here, we showed that a distinct amorphous molybdenum sulfide, being a coordination polymer of disulfide-bridged (Mo3S11) clusters, has great potential as a rechargeable magnesium battery cathode. This material provided good reversible capacity, attributed to its unique structure with high flexibility and capability of deformation upon Mg insertion. Free-terminal disulfide moiety may act as the active site for reversible insertion and extraction of magnesium.

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A highly safe 100 Wh-class laminated lithium ion battery (LIB) was developed. For ensuring safety of the LIB, a liquid electrolyte was quasi-solidified at silica surfaces. For the liquid electrolyte, a solvate ionic liquid (SIL), which is an equimolar complex of lithium bis(trifluoromethanesulfonyl)amide (LiTFSA) and tetraethylene glycol dimethyl ether (G4), Li(G4)TFSA, was used. For enhancing discharge-rate capability, Li(G4)TFSA was diluted by propylene carbonate (PC). Then, for enhancing cycle life, vinylene carbonate (VC) and hexafluorophosphate anion (PF 6 −)based salt were added for forming an solid-electrolyte interphase (SEI) on the graphite negative electrode and an AlF 3 at the surface of the aluminum current collector of the positive electrode, respectively. The assembled LIB exhibited initial discharge capacity of 32 Ah and coulombic efficiency of 76%. Regardless of high energy-type, the developed battery exhibited high discharge capacity of 26.2 Ah at 2 C. Its retention ratio of discharge capacity at the 118th cycle is high, i.e., 96%. The developed LIB (with energy density of 363 Wh L −1) generated neither fire nor smoke in a nail-penetration test. These results suggest that the developed LIB has high safety compared to a LIB comprised of a conventional organic liquid electrolyte.