Rapid and Reversible Lithium Insertion in the Wadsley-Roth-Derived Phase NaNb13O33.

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 NaNb13O33 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. Bond-valence 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 NaNb13O33 within the ranks of promising new high-rate lithium-ion battery anode materials that warrant further research.

Hybrid Layered Double Perovskite Halides of Transition Metals.

Hybrid layered double perovskite (HLDP) halides comprise hexacoordinated 1+ and 3+ metals in the octahedral sites within a perovskite layer and organic amine cations between the layers. Progress on such materials has hitherto been limited to compounds containing main group 3+ ions isoelectronic with PbII (such as SbIII and BiIII). Here, we report eight HLDP halides from the A2MIMIIIX8 family, where A = para-phenylenediammonium (PPDA), 1,4-butanediammonium (1,4-BDA), or 1,3-propanediammonium (1,3-PDA); MI = Cu or Ag; MIII = Ru or Mo; X = Cl or Br. The optical band gaps, which lie in the range 1.55 to 2.05 eV, are tunable according to the layer composition, but are largely independent of the spacer. Magnetic measurements carried out for (PPDA)2AgIRuIIICl8 and (PPDA)2AgIMoIIICl8 show no obvious evidence of a magnetic ordering transition. While the t2g3 MoIII compound displays Curie-Weiss behavior for a spin-only d3 ion, the t2g5 RuIII compound displays marked deviations from the Kotani theory.

Design of Polymeric Zwitterionic Solid Electrolytes with Superionic Lithium Transport.

Progress toward durable and energy-dense lithium-ion batteries has been hindered by instabilities at electrolyte-electrode interfaces, leading to poor cycling stability, and by safety concerns associated with energy-dense lithium metal anodes. Solid polymeric electrolytes (SPEs) can help mitigate these issues; however, the SPE conductivity is limited by sluggish polymer segmental dynamics. We overcome this limitation via zwitterionic SPEs that self-assemble into superionically conductive domains, permitting decoupling of ion motion and polymer segmental rearrangement. Although crystalline domains are conventionally detrimental to ion conduction in SPEs, we demonstrate that semicrystalline polymer electrolytes with labile ion-ion interactions and tailored ion sizes exhibit excellent lithium conductivity (1.6 mS/cm) and selectivity (t + ≈ 0.6-0.8). This new design paradigm for SPEs allows for simultaneous optimization of previously orthogonal properties, including conductivity, Li selectivity, mechanics, and processability.

Metal-Metal Bonding as an Electrode Design Principle in the Low-Strain Cluster Compound LiScMo3O8.

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 LiScMo3O8, 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 Mo3 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 LiScMo3O8 provides valuable insights for design principles for structural motifs that stably and reversibly permit Li+ (de)insertion.

AB2X6 Compounds and the Stabilization of Trirutile Oxides.

The properties of crystalline materials tend to be strongly correlated with their structures, and the prediction of crystal structure from only the composition is a coveted goal in the field of inorganic materials. However, even for the simplest compositions, such prediction relies on a complex network of interactions, including atomic or ionic radii, ionicity, electronegativity, position in the periodic table, and magnetism, to name only a few important parameters. We focus here on the AB2X6 (AB2O6 and AB2F6) composition space with the specific goal of finding new oxide compounds in the trirutile family, which is known for unusual one-dimensional (1D) antiferromagnetic behavior. Through machine learning methods, we develop an understanding of how geometric and bonding constraints determine the crystallization of compounds in the trirutile structure as opposed to other ternary structures in this space. In combination with density functional theory (DFT) calculations, we predict 16 previously unreported candidate trirutile oxides. We successfully prepare one of these and show it forms in the disordered rutile structure, under the preparation conditions adopted here.