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Thestructure of the nanoporous metal–organic frameworkCu3(BTC)2(BTC = 1,3,5-benzenetricarboxylate)with a variety of molecular guests was studied in situusing single crystal X-ray diffraction. By collecting crystal structuredata for a series of guests within the same host crystal, insightsinto the molecular interactions underpinning guest adsorption processeshave been gained. Adsorption behaviors are influenced strongly byboth enthalpic and entropic thermodynamic, as well as interpore steric(size-exclusion) effects, and we note correlations between guest attributesand these effects. Vapor adsorption measurements revealed a guestuptake capacity inversely proportional to guest size. Correspondingly,structural results show that guests reside in the smallest pores accessibleto them. Interpore steric effects for larger guests cause these tobe excluded from the smallest pores, and this corresponds to lowertotal uptake. Both hydrophilic and lipophilic small guests adsorbfavorably into the 5 Å diameter smallest pore of the material,with the number of guests in these pores dependent on guest size andtheir location, in turn dependent upon both guest–guest interactionsand competition between hydrogen-bonding interactions at the aperturesof the smallest pore and lipophilic interactions at the center ofthe smallest pore. Hydrophilic guests with lone electron pairs interactpreferentially with the coordinatively unsaturated Cu sites of thedesolvated framework, with the number of these depending on stericinteractions between neighboring bound guests and guest flexibility.Guest coordination at the Cu sites has a significant effect on theframework structure, increasing the Cu···Cu distancein the dinuclear unit, with the Cu3(BTC)2unitcell being smaller when guests that do not coordinate with the Cuare present, and in the case of cyclohexane, smaller than for thedesolvated framework. Overall, our comprehensive structural studyreconciles Cu3(BTC)2adsorption properties withthe underlying guest–host and guest–guest interactionsthat gives rise to these. [ABSTRACT FROM AUTHOR]

The favorable combination of fast-ionic conductivity and high electrochemical stability of Li-stuffed garnet type Li7La3Zr2O12 (LLZ) makes this material a promising candidate for applications as a solid-state electrolyte in high-energy-density batteries. However, a widespread technical use of LLZ is impeded by difficulty in reliable formation and densification of the pure fast-ion conducting phase. The present study of the phase-formation process enables rational fabrication procedures to be devised based on a thorough understanding of the complex phase formation of LLZ. In situ neutron powder diffraction monitoring of the phase formation revealed an influence of the partial melting of precursors on the formation of the fast-ion conducting phase, indicating that in the typical synthesis route LLZ is not formed in a solid-state reaction but from a partial carbonate melt that decomposes on further heating. The cooling rate critically influences lithium ordering and ionic conductivity. [ABSTRACT FROM AUTHOR]

With the potential of delivering reversible capacities of up to 300 mAh/g, Li-rich transition-metal oxides hold great promise as cathode materials for future Li-ion batteries. However, a cohesive synthesis-structure-electrochemistry relationship is still lacking for these materials, which impedes progress in the field. This work investigates how and why different synthesis routes, specifically solid-state and modified Pechini sol-gel methods, affect the properties of Li 2 MnO 3 , a compositionally simple member of this material system. Through a comprehensive investigation of the synthesis mechanism along with crystallographic, morphological, and electrochemical characterization, the effects of different synthesis routes were found to predominantly influence the degree of stacking faults and particle morphology. That is, the modified Pechini method produced isotropic spherical particles with approximately 57% faulting and the solid-state samples possessed heterogeneous morphology with approximately 43% faulting probability. Inevitably, these differences lead to variations in electrochemical performance. This study accentuates the importance of understanding how synthesis affects the electrochemistry of these materials, which is critical considering the crystallographic and electrochemical complexities of the class of materials more generally. The methodology employed here is extendable to studying synthesis-property relationships of other compositionally complex Li-rich layered oxide systems.

Development of low-cost and cobalt-free efficient cathode materials for oxygen reduction reaction (ORR) remains one of the paramount motivations for material researchers at a low temperature (<650 °C). In particular, iron-based perovskite oxides show promise as electrocatalysts for ORR because Fe metal is cheaper and naturally abundant, exhibit matched thermal expansion with contacting components such as electrolytes, and show high tolerance in a CO 2 -containing atmosphere. Herein, we demonstrated a new mechanism, the in situ formation of alkali metal carbonates at the cathode surface. This new mechanism leads to an efficient and robust cobalt-free electrocatalyst (Sr 0.95 A 0.05 Fe 0.8 Nb 0.1 Ta 0.1 O 3-δ , SAFNT5, A = Li, Na, and K) for the application of low-temperature solid oxide fuel cells (LT-SOFCs). Our results revealed that the formation of Li\K carbonates boosts the ORR activity with an area-specific resistance as low as 0.12 and 0.18 Ω cm 2 at 600 °C, which show the highest performance of the cobalt-free single-phase cathode that has been ever reported so far. We also find that the chemical stability and tolerance of tested cathodes toward CO 2 poisoning significantly improved with alkali carbonates, as compared to the pristine SrFe 0.8 Nb 0.1 Ta 0.1 O 3-δ (SFNT) at 600 °C. This work demonstrates the conclusive role of alkali carbonates in developing highly efficient and stable cobalt-free cathodes for LT-SOFCs and CO 2 neutralization.

All-solid-state Li-ion batteries with metallic Li anodes and solid electrolytes could offer superior energy density and safety over conventional Li-ion batteries. However, compared with organic liquid electrolytes, the low conductivity of solid electrolytes and large electrolyte/electrode interfacial resistance impede their practical application. Garnet-type Li-ion conducting oxides are among the most promising electrolytes for all-solid-state Li-ion batteries. In this work, the large-radius Rb is doped at the La site of cubic Li 6.10 Ga 0.30 La 3 Zr 2 O 12 to enhance the Li-ion conductivity for the first time. The Li 6.20 Ga 0.30 La 2.95 Rb 0.05 Zr 2 O 12 electrolyte exhibits a Li-ion conductivity of 1.62 mS cm -1 at room temperature, which is the highest conductivity reported until now. All-solid-state Li-ion batteries are constructed from the electrolyte, metallic Li anode, and LiFePO 4 active cathode. The addition of Li(CF 3 SO 2 ) 2 N electrolytic salt in the cathode effectively reduces the interfacial resistance, allowing for a high initial discharge capacity of 152 mAh g -1 and good cycling stability with 110 mAh g -1 retained after 20 cycles at a charge/discharge rate of 0.05 C at 60 °C.

Owing to their high conductivity, crystalline Li 7-3x Ga x La 3 Zr 2 O 12 garnets are promising electrolytes for all-solid-state lithium-ion batteries. Herein, the influence of Ga doping on the phase, lithium-ion distribution, and conductivity of Li 7-3x Ga x La 3 Zr 2 O 12 garnets is investigated, with the determined concentration and mobility of lithium ions shedding light on the origin of the high conductivity of Li 7-3x Ga x La 3 Zr 2 O 12 . When the Ga concentration exceeds 0.20 Ga per formula unit, the garnet-type material is found to assume a cubic structure, but lower Ga concentrations result in the coexistence of cubic and tetragonal phases. Most lithium within Li 7-3x Ga x La 3 Zr 2 O 12 is found to reside at the octahedral 96h site, away from the central octahedral 48g site, while the remaining lithium resides at the tetrahedral 24d site. Such kind of lithium distribution leads to high lithium-ion mobility, which is the origin of the high conductivity; the highest lithium-ion conductivity of 1.46 mS/cm at 25 °C is found to be achieved for Li 7-3x Ga x La 3 Zr 2 O 12 at x = 0.25. Additionally, there are two lithium-ion migration pathways in the Li 7-3x Ga x La 3 Zr 2 O 12 garnets: 96h-96h and 24d-96h-24d, but the lithium ions transporting through the 96h-96h pathway determine the overall conductivity.

The mechanism of capacity fade of the Li2MnO3·LiMO2 (M = Li, Ni, Co, Mn) composite positive electrode within a full cell was investigated using a combination of operando neutron powder diffraction and transmission X-ray microscopy methods, enabling the phase, crystallographic, and morphological evolution of the material during electrochemical cycling to be understood. The electrode was shown to initially consist of 73(1) wt % R3̅m LiMO2 with the remaining 27(1) wt % C2/m Li2MnO3 likely existing as an intergrowth. Cracking in the Li2MnO3·LiMO2 electrode particle under operando microscopy observation was revealed to be initiated by the solid-solution reaction of the LiMO2 phase on charge to 4.55 V vs Li(+)/Li and intensified during further charge to 4.7 V vs Li(+)/Li during the concurrent two-phase reaction of the LiMO2 phase, involving the largest lattice change of any phase, and oxygen evolution from the Li2MnO3 phase. Notably, significant healing of the generated cracks in the Li2MnO3·LiMO2 electrode particle occurred during subsequent lithiation on discharge, with this rehealing being principally associated with the solid-solution reaction of the LiMO2 phase. This work reveals that while it is the reduction of lattice size of electrode phases during charge that results in cracking of the Li2MnO3·LiMO2 electrode particle, with the extent of cracking correlated to the magnitude of the size change, crack healing is possible in the reverse solid-solution reaction occurring during discharge. Importantly, it is the phase separation during the two-phase reaction of the LiMO2 phase that prevents the complete healing of the electrode particle, leading to pulverization over extended cycling. This work points to the minimization of behavior leading to phase separation, such as two-phase and oxygen evolution, as a key strategy in preventing capacity fade of the electrode.