Search

Owing to their high-voltage stabilities, halide superionic conductors such as Li3YCl6 recently emerged as promising solid electrolyte (SE) materials for all-solid-state batteries (ASSBs). It has been shown that by either introducing off-stoichiometry in solid-state (SS) synthesis or using a mechanochemical (MC) synthesis method the ionic conductivities of Li3-3xY1+xCl6 can increase up to an order of magnitude. The underlying mechanism, however, is unclear. In the present study, we adopt a hopping frequency analysis method of impedance spectra to reveal the correlations in stoichiometry, crystal structure, synthesis conditions, Li+ carrier concentrations, hopping migration barriers, and ionic conductivity. We show that unlike the conventional Li3YCl6 made by SS synthesis, mobile Li+ carriers in the defect-containing SS-Li3-3xY1+xCl6 (0 < x < 0.17) and MC-Li3-3xY1+xCl6 are generated with an activation energy and their concentration is dependent on temperature. Higher ionic conductivities in these samples arise from a combination of a higher Li+ carrier concentration and lower migration energy barriers. A new off-stoichiometric halide (Li2.61Y1.13Cl6) with the highest ionic conductivity (0.47 mS cm-1) in the series is discovered, which delivers exceptional cycling performance (∼90% capacity retention after 1000 cycles) in ASSB cells equipped with an uncoated high-energy LiNi0.8Mn0.1Co0.1O2 (NMC811) cathode. This work sheds light on the thermal activation process that releases trapped Li+ ions in defect-containing halides and provides guidance for the future development of superionic conductors for all-solid-state batteries.

Rare earth (RE) materials have widespread applications and constitute an indispensable part of modern lives. Tailored electrical, optical, and magnetic properties can be achieved by various RE elements in isomorphic structures, providing materials with the desired properties for specific applications. However, the processing of RE materials encounters difficulties in separation and recycling of RE elements due to the similar physical and chemical properties. For better utilization of REs, including mining, recovery, and incorporation into devices, it is essential to have comprehensive knowledge about thermodynamic properties of RE compounds.The present work comprises not only new experimental thermodynamic studies on selected RE compounds but also a fundamental understanding of the energetics of RE compounds. By means of high temperature oxide melt solution calorimetry, formation enthalpies of RE oxycompounds (REOOH, REOF, and REOCl) and ternary sodium fluorides (NaREF4) were measured to provide reliable data for energetic assessments of REs in diverse structures. NaF–NdF3 nanocrystals and Ca1−xRExF2+x solid solutions were also investigated to shed light on the energetics of RE fluoride nanocrystals and solid solutions containing defect clusters. Combining other published thermochemical data, lattice energies of numerous RE compounds were evaluated to reveal the correlations between the energetics and structures of RE materials. RE oxycompounds are important components of RE precipitates and play a key role in the leaching of RE elements. By different synthesis methods, high-purity single-phase REOOH, REOF, and REOCl with various REs were prepared and characterized by powder X-ray diffraction (PXRD). The formation enthalpies from binary components, determined by high temperature oxide melt solution calorimetry, are all negative but become less exothermic from light to heavy RE elements. They confirm the thermodynamic stability of these RE compounds relative to binar

Rare earth (RE) materials have widespread applications and constitute an indispensable part of modern lives. Tailored electrical, optical, and magnetic properties can be achieved by various RE elements in isomorphic structures, providing materials with the desired properties for specific applications. However, the processing of RE materials encounters difficulties in separation and recycling of RE elements due to the similar physical and chemical properties. For better utilization of REs, including mining, recovery, and incorporation into devices, it is essential to have comprehensive knowledge about thermodynamic properties of RE compounds.The present work comprises not only new experimental thermodynamic studies on selected RE compounds but also a fundamental understanding of the energetics of RE compounds. By means of high temperature oxide melt solution calorimetry, formation enthalpies of RE oxycompounds (REOOH, REOF, and REOCl) and ternary sodium fluorides (NaREF4) were measured to provide reliable data for energetic assessments of REs in diverse structures. NaF–NdF3 nanocrystals and Ca1−xRExF2+x solid solutions were also investigated to shed light on the energetics of RE fluoride nanocrystals and solid solutions containing defect clusters. Combining other published thermochemical data, lattice energies of numerous RE compounds were evaluated to reveal the correlations between the energetics and structures of RE materials. RE oxycompounds are important components of RE precipitates and play a key role in the leaching of RE elements. By different synthesis methods, high-purity single-phase REOOH, REOF, and REOCl with various REs were prepared and characterized by powder X-ray diffraction (PXRD). The formation enthalpies from binary components, determined by high temperature oxide melt solution calorimetry, are all negative but become less exothermic from light to heavy RE elements. They confirm the thermodynamic stability of these RE compounds relative to binar

The incorporation of functional building blocks to construct functionalized and highly porous covalent triazine frameworks (CTFs) is essential to the emerging adsorptive-involved field. Herein, a series of amide functionalized CTFs (CTF-PO71) have been synthesized using a bottom-up strategy in which pigment PO71 with an amide group is employed as a monomer under ionothermal conditions with ZnCl2 as the solvent and catalyst. The pore structure can be controlled by the amount of ZnCl2 to monomer ratio. Benefitting from the highly porous structure and amide functionalities, CTF-PO71, as a sulfur cathode host, simultaneously demonstrates physical confinement and chemical anchoring of sulfur species, thus leading to superior capacity, cycling stability, and rate capability in comparison to unfunctionalized CTF. Meanwhile, as an adsorbent of organic dye molecules, CTF-PO71 was demonstrated to exhibit strong chemical interactions with dye molecules, facilitating adsorption kinetics and thereby promoting the adsorption rate and capacity. Furthermore, the dynamic adsorption experiments of organic dyes from solutions showed selectivity/priority of CTF-PO71s for specific dye molecules.

The aligned one-dimensional channels found in covalent organic frameworks offer a unique space for energy storage. However, physical isolation of sulfur in the channels is not sufficient to prevent the shuttle of lithium-sulfide intermediates that eventually results in a poor performance of lithium-sulfur energy storage. Herein, we report a strategy based on imine-linked frameworks for addressing this shuttle issue by covalently engineering polysulfide chains on the pore walls. The imine linkages can trigger the polymerization of sulfur to form polysulfide chains and anchor them on the channel walls. The immobilized polysulfide chains suppress the shuttle effect and are highly redox active. This structural evolution induces multifold positive effects on energy storage and achieves improved capacity, sulfur accessibility, rate capability and cycle stability. Our results suggest a porous platform achieved by pore wall engineering for tackling key issues in energy storage.