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An extended nitro-functionalised 1,2,4-triazole ligand has been used to induce considerable lattice distortion in a 2-D Hofmann framework material via competing supramolecular interactions. Single crystal X-ray diffraction analyses on [Fe3(N-cintrz)6(Pd(CN)4)3]·6H2O (N-cintrz: (E)-3-(2-nitrophenyl)acrylaldehyde) reveal a substantial deviation from a regular Hofmann structure, in particular as the intra- and inter-layer contacts are dominated by hydrogen-bonding interactions rather than the typical π-stacking arrays. Also, the 2-D Hofmann layers show an assortment of ligand conformations and local FeII coordination environments driven by the optimisation of competing supramolecular contacts. Temperature-dependent magnetic susceptibility measurements reveal a two-step spin crossover (SCO) transition. Variable temperature structural analyses show that the two crystallographically distinct FeII centres, which are arranged in stripes (2 : 1 ratio) within each Hofmann layer, undergo a cooperative HS ↔ HS/LS ↔ LS (HS = high spin, LS = low spin) transition without periodic spin-state ordering. The mismatch between crystallographic (2 : 1) and spin-state (1 : 1) periodicity at the HS : LS step provides key insight into the competition (frustration) between elastic interactions and crystallographically driven order. [ABSTRACT FROM AUTHOR]

The P3-type layered oxide Na0.5Ni0.25Mn0.75O2 is a promising manganese-rich positive electrode (cathode) material for sodium ion batteries, with a high working voltage of 4.2–2.5 V vs. Na+/Na and a high capacity of over 130 mA h g−1 when cycled at 10 mA g−1. However, its structural evolution during battery cycling – specifically, the nature of the high-voltage phase above 4 V – has never been fully understood, which has hindered efforts to rationally modify and improve its performance. In this work we use in situ neutron diffraction to show that the phase above 4 V is a modification of the intermediate O3 phase from which all sodium has been removed, and which consequently has a dramatically shorter interlayer distance. We label this fully Na-depleted phase O3s, such that the phase evolution with increasing voltage is P3 → O3 → O3s. Having elucidated its structure, we used first-principles calculations of the electronic structure as a function of sodium content to show that reversible oxygen redox plays a key role in the electrochemical activity of this O3s phase above 4 V. We also calculated the energies of oxygen/transition metal vacancies and found that the O3s phase should be relatively stable against their formation. The results will guide future research aimed at understanding and stabilizing the O3s phase, in order to improve the performance and cycling stability of this material in sodium ion batteries. [ABSTRACT FROM AUTHOR]

High-voltage spinel LiNi0.5Mn1.5O4 (LNMO) is a promising cathode for the next-generation high-performance lithium-ion batteries (LIBs) due to its high energy density (650 W h kg−1), high operating voltage (∼4.7 V vs. Li), low fabrication cost, and low environmental impact. However, the short cycle life of LNMO caused by rapid capacity decay during cycling limits its wide application and commercialization. Intense research effort to improve the electrochemical performance of LNMO has been moderately successful. Accordingly, it is absolutely necessary to revisit and summarize the up-to-date findings and deeper understanding of how to modify LNMO. In this review, the crystallographic structure and electrochemical properties of LNMO spinel, as well as its existing issues and corresponding solutions, are discussed in detail. In addition, the current accomplishments relating to LNMO application in full-cell configurations are also discussed. Finally, some insight into the future prospects for LNMO cathode developments is provided. [ABSTRACT FROM AUTHOR]

High-voltage spinel LiNi0.5Mn1.5O4 (LNMO) is considered a potential high-power-density positive electrode for lithium-ion batteries, however, it suffers from capacity decay after extended charge–discharge cycling, severely hindering commercial application. Capacity fade is thought to occur through the significant volume change of the LNMO electrode occurring on cycling, and in this work we use operando neutron powder diffraction to compare the structural evolution of the LNMO electrode in an as-assembled 18650-type battery containing a Li4Ti5O12 negative electrode with that in an identical battery following 1000 cycles at high-current. We reveal that the capacity reduction in the battery post cycling is directly proportional to the reduction in the maximum change of the LNMO lattice parameter during its evolution. This is correlated to a corresponding reduction in the MnO6 octahedral distortion in the spinel structure in the cycled battery. Further, we find that the rate of lattice evolution, which reflects the rate of lithium insertion and removal, is ∼9 and ∼10% slower in the cycled than in the as-assembled battery during the Ni2+/Ni3+ and Ni3+/Ni4+ transitions, respectively. [ABSTRACT FROM AUTHOR]

The oxygen reduction reaction (ORR) activity of cathodes has to be improved to realize the low-temperature operation of solid-oxide fuel cells (SOFCs). Whilst geometric factors are conventionally accepted to influence the ORR activity of perovskite cathodes, other factors may also contribute and therefore need to be explored. Here, we substituted 20% niobium and tantalum which have similar ionic radii into strontium cobaltites to obtain the two perovskite oxides SrCo0.8Nb0.2O3−δ (SCN20) and SrCo0.8Ta0.2O3−δ (SCT20), respectively. Our study of the isostructural SCN20 and SCT20 allows geometric effects to be separated from other factors, and we observe better cathode performance of SCT20 cathode, which may be related to the lower electronegativity of Ta5+, thus resulting in higher oxygen surface exchange kinetics and diffusivity as compared with Nb5+. [ABSTRACT FROM AUTHOR]

The development of cathode materials with high capacity and cycle stability is essential to emerging electric-vehicle technologies, however, of serious environmental concern is that materials with these properties developed so far contain the toxic and expensive Co. We report here the Li-rich, Co-free Li1+xMO2 (M = Li, Ni, Mn, Fe) composite cathode material, prepared via a template-free, one-step wet-chemical method followed by conventional annealing in an oxygen atmosphere. The cathode has an unprecedented level of cation mixing, where the electrochemically-active component contains four elements at the transition-metal (3a) site and 20% Ni at the active Li site (3b). We find Ni2+/Ni3+/Ni4+ to be the active redox-center of the cathode with lithiation/delithiation occurring via a solid-solution reaction where the lattice responds approximately linearly with cycling, differing to that observed for iso-structural commercial cathodes with a lower level of cation mixing. The composite cathode has ∼75% active material and delivers an initial discharge-capacity of ∼103 mA h g−1 with a reasonable capacity retention of ∼84.4% after 100 cycles. Notably, the electrochemically-active component possesses a capacity of ∼139 mA h g−1, approaching that of the commercialized LiCoO2 and Li(Ni1/3Mn1/3Co1/3)O2 materials. Importantly, our operando neutron powder-diffraction results suggest excellent structural stability of this active component, which exhibits ∼80% less change in its stacking-axis than for LiCoO2 with approximately the same capacity, a characteristic that may be exploited to enhance significantly the capacity retention of this and similar materials. [ABSTRACT FROM AUTHOR]

The water-stable zirconium--tricarboxylate series of frameworks, [Zr6O4(OH)4(X)6(btc)2]⋅nH2O, where X = formate (F), acetate (A), or propionate (P), exhibit tunable porosity by virtue of systematic modulation of the chain length of the monocarboxylate ligand X. This modification not only impacts the pore size of the framework, but provides an important avenue for the construction of mixed-linker MOFs. [ABSTRACT FROM AUTHOR]

Neutron powder diffraction measurements were carried out on the evacuated and CO2-loaded Prussian blue analogue, Fe3[Co(CN)6]2, identifying two distinct CO2 adsorption sites: site A, in which CO2 uniquely bridges between two bare-metal sites, and site B, in which it interacts in a face capping motif. The saturation of site A at low loadings of CO2 demonstrates the favourable nature of the interaction of CO2 with bare-metal sites within the material. [ABSTRACT FROM AUTHOR]