Electrode materials for Li + -ion batteries require optimization along several disparate axes related to cost, performance, and sustainability. One of the important performance axes is the ability to retain structural integrity though cycles of charge/discharge. Metal-metal bonding is a distinct feature of some refractory metal oxides that has been largely underutilized in electrochemical energy storage, but that could potentially impact structural integrity. Here LiScMo 3 O 8 , a compound containing triangular clusters of metal-metal bonded Mo atoms, is studied as a potential anode material in Li + -ion batteries. Electrons inserted though lithiation are localized across rigid Mo 3 triangles (rather than on individual metal ions), resulting in minimal structural change as suggested by operando diffraction. The unusual chemical bonding allows this compound to be cycled with Mo atoms below a formally +4 valence state, resulting in an acceptable voltage regime that is appropriate for an anode material.Several characterization methods including potentiometric entropy measurements indicate two-phase regions, which are attributed through extensive first-principles modeling to Li + ordering. This study of LiScMo 3 O 8 provides valuable insights for design principles for structural motifs that stably and reversibly permit Li + (de)insertion.

Shear-phase early transition metal oxides, mostly of Nb, and comprising edge-and corner-shared metal−oxygen octahedra have seen a resurgence in recent years as fast-charging, low-voltage electrodes for Li + -ion batteries. Mo oxides, broadly, have been less well studied as fast-charging electrodes.Here we examine a reduced Mo oxide, Mo 4 O 11 , that has a structure comprising only corner-connected MoO 4 tetrahedra and MoO 6 octahedra. We show that an electrode formed using micrometer-sized particles of Mo 4 O 11 as the active material can function as a high-rate Li + -ion electrode against Li metal, with a stable capacity of over 200 mAh g −1 at the high rate of 5C. Operando X-ray diffraction (XRD), entropic potential measurements, and ex situ Raman spectroscopy are employed to understand the nature of the charge storage. The crystal structure dramatically changes upon the first lithiation, and subsequent cycling is completely reversible with low capacity fade. It is the newly formed and potentially more layered structure that demonstrates high-rate cycling and small voltage polarization. A space group and unit cell for the new structure is proposed. This finding expands the scope of candidate highrate electrode materials to those beyond the expected Nb-containing shear-phase oxide materials.

We report hybrid and all-inorganic, vacancy-ordered double perovskites of d 2 W 4+ with the formula A 2 WCl 6 (A = CH NH 3 3Rb + , and Cs + ). These compounds, which are reddish in color, can be distinguished from structurally similar compounds obtained by hydrothermal methods on the basis of structure, spectroscopic, and magnetic properties. The latter are green and incorporate oxygen, with the actual formula Cs 2 WO x Cl 6−x and distinct optical absorption and emission behavior. The local-moment magnetism of the pure-red d 2 compounds reported here does not correspond to the appropriate Kotani model, suggesting as-yet undiscovered physics in these systems.

The development of new high-performing battery materials is critical for meeting the energy storage requirements of portable electronics and electrified transportation applications. Owing to their exceptionally high rate capabilities, high volumetric capacities, and long cycle lives, Wadsley−Roth compounds are promising anode materials for fast-charging and high-power lithium-ion batteries. Here, we present a study of the Wadsley− Roth-derived NaNb 13 O 33 phase and examine its structure and lithium insertion behavior. Structural insights from combined neutron and synchrotron diffraction as well as solid-state nuclear magnetic resonance (NMR) are presented. Solid-state NMR, in conjunction with neutron diffraction, reveals the presence of sodium ions in perovskite A-site-like block interior sites as well as square-planar block corner sites. Through combined experimental and computational studies, the high rate performance of this anode material is demonstrated and rationalized. A gravimetric capacity of 225 mA h g −1 , indicating multielectron redox of Nb, is accessible at slow cycling rates. At a high rate, 100 mA h g −1 of capacity is accessible in 3 min for micrometer-scale particles. Bondvalence mapping suggests that this high-rate performance stems from fast multichannel lithium diffusion involving octahedral block interior sites. Differential capacity analysis is used to identify optimal cycling rates for long-term performance, and an 80% capacity retention is achieved over 600 cycles with 30 min charging and discharging intervals. These initial results place NaNb 13 O 33 within the ranks of promising new high-rate lithium-ion battery anode materials that warrant further research.

As Li-ion batteries are more widely adopted, it becomes important to identify new battery electrode materials made from a greater diversity of elements while improving stability, extracted power, and the ability to charge and discharge rapidly. Early transition metals, such as Nb and Mo, are relatively earth-abundant elements, with oxides that are candidates for next-generation anode materials. However, Mo oxides are limited as battery electrodes due to their intermediate redox voltages. Lowering this voltage could open the door for high-performance Mo-based oxide anodes. Oxidation of the voltage can be employed by adding redox-inactive cations of electropositive elements. This strategy is named the induction effect and has been proposed as a design principle to increase cathode voltages. However, its use on the anode side appears less common. Here, we compare the ionization energy, electrochemistry, and Li diffusivity of the compound Li2Mo4O13 with MoO3, which both start out as Mo6+ compounds before lithiation. The ionization energy values extracted from ultraviolet photoemission spectroscopy support the hypothesis that the alkali metal cation pushes up the valence band. Electrochemical studies in half-cells against Li/Li+ indicate that Li2Mo4O13 can reversibly take up two additional Li ions in the unit cell. Moreover, the addition of Li to the molybdenum oxide structure lowers the voltage by 300 mV for the Mo6+/5+ couple compared to the same redox couple in MoO3 and retains high Li+ diffusivity. This work, in conjunction with experimental redox voltages extracted from prior literature on Ti4+/3+ and Nb5+/4+ redox couples, demonstrates the utility of using inductive effects to tailor the operating voltage of candidate anode materials.