Relocation of Cobalt Ions in Electrochemically Delithiated LiCoPO₄ Cathode Materials

Relocation of Cobalt Ions in Electrochemically Delithiated LiCoPO₄ Cathode Material

Exfoliated MoS₂ and MoSe₂ Nanosheets by a Supercritical Fluid Process for a Hybrid Mg–Li-Ion Battery

The ultrathin two-dimensional nanosheets of layered transition-metal dichalcogenides (TMDs) have attracted great interest as an important class of materials for fundamental research and technological applications. Solution-phase processes are highly desirable to produce a large amount of TMD nanosheets for applications in energy conversion and energy storage such as catalysis, electronics, rechargeable batteries, and capacitors. Here, we report a rapid exfoliation by supercritical fluid processing for the production of MoS₂ and MoSe₂ nanosheets. Atomic-resolution high-angle annular dark-field imaging reveals high-quality exfoliated MoS₂ and MoSe₂ nanosheets with hexagonal structures, which retain their 2H stacking sequence. The obtained nanosheets were tested for their electrochemical performance in a hybrid Mg–Li-ion battery as a proof of functionality. The MoS₂ and MoSe₂ nanosheets exhibited the specific capacities of 81 and 55 mA h g^–1, respectively, at a current rate of 20 mA g^–1

Unravelling the Surface Structure of MgMn₂O₄ Cathode Materials for Rechargeable Magnesium-Ion Battery

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

Unravelling the Surface Structure of MgMn₂O₄ Cathode Materials for Rechargeable Magnesium-Ion Battery

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