Dual Stabilization and Sacrificial Effect of Na₂CO₃ for Increasing Capacities of Na-Ion Cells Based on P2-Na_<i>x</i>MO₂ Electrodes

Sodium ion battery technology is gradually advancing and can be viewed as a viable alternative to lithium ion batteries in niche applications. One of the promising positive electrode candidates is P2 type layered sodium transition metal oxide, which offers attractive sodium ion conductivity. However, the reversible capacity of P2 phases is limited by the inability to directly synthesize stoichiometric compounds with a sodium to transition metal ratio equal to 1. To alleviate this issue, we report herein the <i>in situ</i> synthesis of P2-Na_<i>x</i>MO₂ (<i>x</i> ≤ 0.7, M = transition metal ions)-Na₂CO₃ composites. We find that sodium carbonate acts as a sacrificial salt, providing Na⁺ ion to increase the reversible capacity of the P2 phase in sodium ion full cells, and also as a useful additive that stabilizes the formation of P2 over competing P3 phases. We offer a new phase diagram for tuning the synthesis of the P2 phase under various experimental conditions and demonstrate, by <i>in situ</i> XRD analysis, the role of Na₂CO₃ as a sodium reservoir in full sodium ion cells. These results provide insights into the practical use of P2 layered materials and can be extended to a variety of other layered phases

Metal–Organic Frameworks Polyurethane Composite Foams for the Capture of Volatile Organic Compounds

Composites of metal–organic frameworks (MOFs) in polyurethane foams (PUF) are reported to adsorb polar or apolar volatile organic compounds (VOCs), avoiding the problems usually found when handling MOFs in the powder form. MOF/PUF composites were prepared using MIL-160(Al) and UiO-66(Zr)-(CF3)2 via one step process where the MOFs particles are incorporated during the foam matrix formation. Under adjusted conditions, the composite materials maintained the shape and characteristics of the MOF material, good mechanical stability, and good accessibility to the pores without significantly compromising the VOCs adsorption capacity for hexane, acetone, methanol, toluene, and acetic acid. This methodology proved the possibility of incorporating high amounts of shaped MOF particles, reaching 200% (w/w) of foam, upon maintaining a considerable open-cell volume percentage (32%). As an application perspective, we demonstrate that the composites can overcome the challenge of acetic acid capture in the presence of ambient moisture with a similar performance to the pure MOF. Thus, VOCs capture through MOF/polyurethane foam composites is a promising environmental technology to eliminate air pollutants

Synthesis of Li-Rich NMC: A Comprehensive Study

Li-rich NMC are considered nowadays as one of the most promising candidates for high energy density cathodes. One significant challenge is nested in adjusting their synthesis conditions to reach optimum electrochemical performance, but no consensus has been reached yet on the ideal synthesis protocol. Herein, we revisited the elaboration of Li-rich NMC electrodes by focusing on the science involved through each synthesis steps using carbonate Ni_0.1625Mn_0.675Co_0.1625CO₃ precursor coprecipitation combined with solid state synthesis. We demonstrated the effect of precursor’s concentration on the kinetics of the precipitation reaction and provided clues to obtain spherically agglomerated NMC carbonates of different sizes. Moreover, we highlighted the strong impact of the Li₂CO₃/NMC carbonate ratio on the morphology and particles size of Li-rich NMC and subsequently on their electrochemical performance. Ratio of 1.35 was found to reproducibly give the best performance with namely a first discharge capacity of 269 mAh g^–1 and capacity retention of 89.6% after 100 cycles. We hope that our results, which reveal how particle size, morphology, and phase composition affect the material’s electrochemical performance, will help in reconciling literature data while providing valuable fundamental information for up scaling approaches

Evidence of New Fluorinated Coordination Compounds in the Composition Space Diagram of FeF₃/ZnF₂–H<i>amtetraz</i>-HF_aq System

The exploration of the composition space diagram of the FeF₃/ZnF₂–H<i>amtetraz</i>-HF_aq system (H<i>amtetraz</i> = 5-aminotetrazole) by solvothermal synthesis at 160 °C for 72 h in dimethylformamide (DMF) has evidenced five new hybrid fluorides (<b>1</b>–<b>5</b>); the structures are characterized from single crystal X-ray diffraction data. [H<i>dma</i>]­·(ZnFe^III(H₂O)₄F₆) (<b>1</b>) and [H<i>dma</i>]­·[H<i>gua</i>]₂­·(Fe^IIIF₆) (<b>2</b>) contain anionic inorganic chains (<b>1</b>) or isolated octahedra (<b>2</b>) weakly hydrogen bonded (Class I hybrids) to dimethylammonium (H<i>dma</i>) and/or guanidinium (H<i>gua</i>) cations which are produced from the tetrazole ligand and solvent decomposition. [H<i>dma</i>]₂­·[H<i>gua</i>]­·[NH₄]­·[ZnFe^IIIF₅(<i>amtetraz</i>)₂]₂ (<b>3</b>), [H<i>dma</i>]₂­·[Zn_1.6Fe^II_0.4Fe^IIIF₆­(<i>amtetraz</i>)₃] (<b>4</b>), and [H<i>dma</i>]­·[Zn₄F₅(<i>amtetraz</i>)₄] (<b>5</b>) are considered as Class II hybrids in which the (<i>amtetraz</i>)⁻ anions are strongly linked to divalent metal cations via N–M bonds. In <b>3</b>, _∞{[NH₄]­·[ZnFe^IIIF₅­(<i>amtetraz</i>)₂]₂} layers are separated by [H<i>dma</i>]⁺ and [H<i>gua</i>]⁺ cations. <b>4</b> and <b>5</b> exhibit three-dimensional (3D) hybrid networks that contain small cavities where [H<i>dma</i>]⁺ cations are inserted. A porous 3D metal–organic framework intermediate is evidenced from the thermogravimetric analysis and X-ray thermodiffraction of <b>5</b>