Enabling an Excellent Ordering-Enhanced Electrochemistry and a Highly Reversible Whole-Voltage-Range Oxygen Anionic Chemistry for Sodium-Ion Batteries.

Though considerable Mg-doped layered cathodes have been exploited, some new differences relative to previous reports can be concluded by doping a heavy dose of Mg via two rational strategies. Unlike the common unit cell of the P63/mmc group by X-ray diffraction, neutron diffraction reveals a large supercell of the P63 group and enhanced ordering for Na11/18Mg1/18[Ni1/4Mg1/9Mn11/18]O2 with Mg occupying both the Na and Mn sites. Compared with only one obvious voltage plateau of Na0.5[Ni0.25Mn0.75]O2 (NNM), Na11/18Mg1/18[Ni1/4Mg1/9Mn11/18]O2 (NMNMM) shows more severe voltage plateaus but with excellent electrochemical performance. Na0.5[Mg0.25Mn0.75]O2 (NMM) with Mg only occupying the Ni site displays a highly reversible whole-voltage-range oxygen redox chemistry and smooth voltage curves without any voltage hysteresis. Cationic Ni2+/Ni4+ couples are responsible for the charge compensations of NNM and NMNMM, while only the oxygen anionic reaction accounts for the capacity of NMM between 2.5 and 4.3 V. Interestingly, the Mn3+/Mn4+ pair contributes all capacity for all cathodes between 1.5 and 2.5 V. All cathodes undergo a double-phase mechanism: an irreversible P2-O2 phase transition for NNM, an enhanced reversible P2-O2 phase transition for NMNMM, and a highly reversible P2-OP4 phase transition for NMM. In addition, the designed cathodes display excellent rate capability and long-term cycling stability but with a large difference in the various voltage ranges of 2.5-4.3 and 1.5-2.5 V, respectively. This work provides a good understanding of ion doping and some new insights into exploiting high-performance materials.

First-Principles Study of Electronic Properties of Substitutionally Doped Monolayer SnP3.

SnP3 has a great prospect in electronic and thermoelectric device applications due to its moderate band gap, high carrier mobility, absorption coefficients, and dynamical and chemical stability. Doping in two-dimensional semiconductors is likely to display various anomalous behaviors when compared to doping in bulk semiconductors due to the significant electron confinement effect. By introducing foreign atoms from group III to VI, we can successfully modify the electronic properties of two-dimensional SnP3. The interaction mechanism between the dopants and atoms nearby is also different from the type of doped atom. Both Sn7BP24 and Sn7NP24 systems are indirect bandgap semiconductors, while the Sn7AlP24, Sn7GaP24, Sn7PP24, and Sn7AsP24 systems are metallic due to the contribution of doped atoms intersecting the Fermi level. For all substitutionally doped 2D SnP3 systems considered here, all metallic systems are nonmagnetic states. In addition, monolayer Sn7XP24 and Sn8P23Y may have long-range and local magnetic moments, respectively, because of the degree of hybridization between the dopant and its adjacent atoms. The results complement theoretical knowledge and reveal prospective applications of SnP3-based electrical nanodevices for the future.

Supramolecular Oligourethane Gel with Multicolor Luminescence Controlled by Mechanically Sensitive Hydrogen-Bonding.

We report a new type of mechanically sensitive multicolor luminescent oligourethane gel (OUA-gel). The conformation of the oligomeric chains can be controlled by changing the strength of hydrogen bonds. The optical properties of the oligomers are highly dependent on the conformations which vary in response to mechanical stresses and phase transitions. The design relies on the introduction of a single mechanical chromophore, aurintricarboxylic acid, with propeller-like, spatially crowded, and highly twisted conformations, and the presence of three carboxyl groups, which provide multidirectional hydrogen-bonding opportunities. Introducing dimethylsulfoxide (DMSO) as an additional H-bond acceptor molecule leads to a viscous OUA-gel which exhibits multiemission colors because of changes in the chain conformation within the matrix, which are induced by different strengths of H bonds. The conformation can be adjusted by mechanical force or temperature, both of which influence the H-bonding. The multifunctional and multicolored mechanochromism of the OUA-gel has great promise in sensing applications. The results represent a substantial step toward understanding the mechanism of polychromism in soft materials and the molecular design of advanced smart materials.