Dual-Ion Intercalation Chemistry Enabling Hybrid Metal-Ion Batteries

To outline the role of dual-ion intercalation chemistry to reach sustainable energy storage, the present Review aimed to compare two types of batteries: widely accepted dual-ion batteries based on cationic and anionic co-intercalation versus newly emerged hybrid metal-ion batteries using the co-intercalation of cations only. Among different charge carrier cations, the focus was on the materials able to co-intercalate monovalent ions (such Li⁺ and Na⁺ , Li⁺ and K⁺ , Na⁺ and K⁺ , etc.) or couples of mono- and multivalent ions (Li⁺ and Mg²⁺ , Na⁺ and Mg²⁺ , Na⁺ and Zn²⁺ , H⁺ and Zn²⁺ , etc.). Furthermore, the Review was directed on co-intercalation materials composed of environmentally benign and low-cost transition metals (e. g., Mn, Fe, etc.). The effect of the electrolyte on the co-intercalation properties was also discussed. The summarized knowledge on dual-ion energy storage could stimulate further research so that the hybrid metal-ion batteries become feasible in near future.

8-Layer Shifted Hexagonal Perovskite Ba8MnNb6O24: Long-Range Ordering of High-Spin d5 Mn2+ Layers and Electronic Structure

A new 8-layer shifted hexagonal perovskite Ba₈MnNb₆O₂₄ has been synthesized in air, featuring unusual long-range B-cation ordering with single octahedral high-spin d⁵ Mn²⁺ layers separated by ∼1.9 nm within the corner-sharing octahedral d⁰ Nb⁵⁺ host, analogous to Ba₈(Zn/Co)Nb₆O₂₄. The large size and charge differences between high-spin Mn²⁺ and Nb⁵⁺, as well as the out-of-center distortion of NbO₆ octahedra associated with the bonding covalence and second-order Jahn-Teller effect of Nb⁵⁺, drive long-range cationic ordering, thus stabilizing Ba₈MnNb₆O₂₄. The Ba₈MnNb₆O₂₄ pellet exhibits a high dielectric permittivity, ε_r ∼ 38, and a large temperature coefficient of resonant frequency, τ_f ∼ 20 ppm/K, but a dielectric loss ( Qf ∼ 987 GHz) and conductivity (∼10^-8-10^-3 S/cm within 473-1173 K) much higher than those of Ba₈ZnNb₆O₂₄. Electronic structures from density functional theory calculations reveal that Ba₈MnNb₆O₂₄ is a Mott insulator in contrast with the charge-transfer insulator nature of Ba₈ZnNb₆O₂₄, and they confirm that the off-center distortion of Nb⁵⁺ contributes to stabilization of the 8-layer ordered shifted structure. The contrast between conductivity and dielectric loss of Ba₈MnNb₆O₂₄ and Ba₈ZnNb₆O₂₄ is understood based on the electronic structure that depends on high-spin d⁵ Mn²⁺ and d¹⁰ Zn²⁺ cations. The hopping of 3d valence electrons in high-spin Mn²⁺ to Nb⁵⁺ 4d conduction bands over a small gap (∼2.0 eV) makes Ba₈MnNb₆O₂₄ more conductive than Ba₈ZnNb₆O₂₄, where the electrons are conducted via the hopping of a lattice O 2p valence electron to the Nb⁵⁺ 4d conduction bands over a larger gap (∼3.9 eV). The high microwave dielectric loss of BMN may be mainly ascribed to the half-filled Mn 3d orbits, which is understood based on the softened infrared modes that increase the lattice vibration anharmonicity as well as the resonant spin excitation of unpaired d electrons.

Facile synthesis of yolk shell Mn2O3@Mn5O8 as an effective catalyst for peroxymonosulfate activation

The Mn₂O₃@Mn₅O₈ catalyst exhibits unique structural properties for catalytic activities and shows efficient performance for the degradation of 4-CP in a PMS system.