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Spinel-type MgMn2O4 nanoplates ~10 nm thick were prepared as a positive electrode for magnesium rechargeable batteries by transformation of metal hydroxide nanoplates. Homogeneous coating with a va...

Spinel-type MgMn

Mesocrystals of MgCo2O4 spinel oxide exhibiting porous and single-crystalline structures were synthesized by the reaction of magnesium ions with calcite-type CoCO3 mesocrystal precursors grown in micrometer-sized agar gels. The mesocrystals consisted of single-crystalline porous grains measuring 200–300 nm in diameter with iso-oriented subunits of approximately 10 nm. The single-crystalline porous framework structure of the MgCo2O4 mesocrystals enhanced the discharge capacity and positively shifted the discharge potential compared with MgCo2O4 nanoparticles prepared by the inverse co-precipitation method. These enhancements were attributed to a combination of the high specific surface areas of the mesocrystals and the high connectivity of the magnesium ion diffusion paths in the solid-phase.

Self-organized formation of parallel-banded structures was demonstrated through the twisted growth of K2Cr2O7 in a thin layer of a viscous solution containing poly(acrylic acid) on a glass substrate. Dense branching of the twisted crystals was induced by increasing their growth rate under a controlled flow of nitrogen gas. Periodically banded structures were then obtained by the synchronization of the twist in the parallel branches. Specific structural colors originating from the parallel-banded structures as a diffraction grating were observed on the self-organized patterns of the twisted crystals.

To achieve a sustainable-energy society in the future, next-generation highly efficient energy storage technologies, particularly those based on multivalent metal negative electrodes, are urgently required to be developed. Magnesium rechargeable batteries (MRBs) are promising options owing to the many advantageous chemical and electrochemical properties of magnesium. However, the substantially low working voltage of sulfur-based positive electrodes may hinder MRBs in becoming alternatives to current Li-ion batteries. We proposed halide-free noncorrosive ionic liquid-based electrolytes incorporating Mg[TFSA]2 for high-voltage MRB applications. Upon the complexation of Mg[TFSA]2 with tetraglyme (G4) and strict control of the liquid states, the electrolytes achieved excellent anodic stability up to 4.1 V vs. Mg2+/Mg even at 100 °C. The modest electrochemical activities for magnesium deposition/dissolution in the [Mg(G4)][TFSA]2/ionic liquid electrolyte can be improved by certain modifications to the coordination state of [TFSA]-. Dialkyl sulfone was found to be effective in changing the coordination state of [TFSA]- from associated to isolated (free). This coordination change successfully promoted magnesium deposition/dissolution reactions, particularly in the coexistence of ether ligand. By contrast, the coordination of Mg2+ by strongly donating agents such as dimethyl sulfoxide and alkylimidazole led to the complexes inactive electrochemically, suggesting that interaction between Mg2+ and coordination agents predominates the fundamental electrochemical activity. We also demonstrated that an enhancement in the electrochemical activity of electrolytes contributed to improvements in the cycling ability of magnesium batteries with 2.5 V-class MgMn2O4 positive electrodes.

A structured spinel oxide as a positive-electrode active material for magnesium rechargeable batteries was produced using a propylene-oxide-driven sol–gel method and subsequent vanadium oxide coating. Porous frameworks consisting of MgMn2O4 nanoparticles having diameters of ∼10 nm exhibited a large specific surface area of ∼150 m2 g−1 and interconnected bimodal pores distributed in the micrometer (1–10 μm) and nanometer (10–100 nm) regions. Hierarchical conduction paths constructed by mixing the porous frameworks with carbon nanoparticles reduced the overpotential for the insertion and extraction of magnesium ions and increased the redox capacity in an ionic-liquid electrolyte system. Moreover, the surface coating of vanadium oxide on the spinel oxide nanoparticles enhanced the extraction of magnesium ions and suppressed the decomposition of the electrolyte. The electrochemical properties, such as the capacities, rate capabilities, and cyclabilities, of the positive electrodes were largely improved by the structured spinel oxide frameworks.

Microscale patterns consisting of two-dimensional (2D) dendrites with trunks and branches 1–3 μm wide were precisely controlled through crystal growth in a thin polymer matrix by the use of a dipping technique. A variety of 2D micropatterns, such as orthogonal lattices, bull’s horns, randomly curving weaves, and aligned dots, were homogeneously formed with an aqueous solution of Ba(NO3)2 and poly(vinyl alcohol) in a wide area ranging over several centimeters on flat and rounded substrates. The micrometric dendritic growth that produced these several patterns was tuned by changing the withdrawal rate and the polymer concentration. The crystallographic orientation of the micropatterns was characterized to discuss on the formation mechanism of the specific morphologies. The curving branches were found to be induced by gradual change in the growth direction through low-angle grain boundaries under a highly diffusion-limited condition. This simple, bottom-up patterning process is applicable for various crystal...

Various 2-D patterns of copper sulfate pentahydrate (CuSO4·5H2O) were spontaneously formed through crystal growth in a thin gelatin matrix on a glass plate. The form of the grown crystal changes from polyhedrons to irregularly branching morphologies with increasing the polymer density in the matrix. Characteristic patterns, such as sinuous dendrites and wavy lattices, are obtained under specific intermediate conditions. The formation of periodically curving sinuous trunks is based on the helical growth with a pile of tilted units of CuSO4·5H2O. The wavy microlattices are produced with periodical branching of the sinuous trunks. The characteristic 2-D patterns with the curving trunks and branches are achieved with the controlled growth of the triclinic crystal under a diffusion-limited condition in the polymer matrix.

Mesocrystal nanosheet of rutile TiO2 has been synthesized in an aqueous solution in the absence of any organic molecules at room temperature. In general, it is not easy to tune the morphologies of rutile crystals in two-dimensional structures. The rutile nanosheets 10 nm in thickness and 200–600 nm in width consisted of the oriented nanocrystals 2–3 nm in size. The unit rutile nanocrystals were surrounded by the combination of the (101) and (110) faces or the (111) and (110) faces. Compared to the single crystalline nanosheet, different crystal faces can be exposed on the surface. In addition, a higher specific surface area was achieved on the nanosheet with a mesocrystal interior. The introduction of substrates and a titanium source TiCl3 facilitates the formation of the mesocrystal nanosheets in aqueous solution. The oxidation-preferred face of (111) or (101) and the reduction-preferred face of (110) can be exposed on the surface of the nanosheets. The oxidation reaction preferentially proceeded on the photocatalytic decomposition of an organic dye.

We demonstrate the oscillatory phenomenon for the twisting growth of a triclinic crystal through in situ observation of the concentration field around the growing tip of a needle by high-resolution phase-shift interferometry.

The crystal morphology of pyrene formed in a solution changes from polyhedral shapes surrounded with flat planes into characteristic curving forms, such as sigmoidal and helical architectures, in the presence of polyvinyl pyrrolidone. Dendritic patterns and linear alignments of lozenge units are produced under the intermediate conditions. The formation of hierarchical structures with increasing the polymer concentration is based on a pile of pyrene units. The curving forms are inferred to be constructed through a twisted assembly of asymmetric units under diffusion-limited conditions. Because similar morphological variation was observed in other systems, such as chrysazin–polyvinyl pyrrolidone and pyrene–polystyrene, the controlled growth of organic crystals using the polymer matrix would provide a novel type of functional materials having various curving morphologies.