Structural and Chemical Compatibilities of Li1- x Ni0.5 Co0.2 Mn0.3 O2 Cathode Material with Garnet-Type Solid Electrolyte for All-Solid-State Batteries.

All-solid-state batteries (ASSBs) based on ceramic materials are considered a key technology for automobiles and energy storage systems owing to their high safety and stability. However, contact issues between the electrode and solid-electrolyte materials and undesired chemical reaction occurring at interfaces have hindered their development. Herein, the chemical compatibility and structural stability of composite mixtures of the layered cathode materials Li1- x Ni0.5 Co0.2 Mn0.3 O2 (NCM523) with the garnet-type solid electrolyte Li6.25 Ga0.25 La3 Zr2 O12 (LLZO-Ga) during high-temperature co-sintering under various gas flowing conditions are investigated. In situ high-temperature X-ray diffraction analysis of the composite materials reveals that Li diffusion from LLZO-Ga to NCM523 occurs at high temperature under synthetic air atmosphere, resulting in the decomposition of LLZO-Ga into La2 Zr2 O7 and the recovery of charged NCM523 to the as-prepared state. The structural stability of the composite mixture at high temperature is further investigated under N2 atmosphere, revealing that Li diffuses toward the opposite direction and involves the phase transition of LLZO-Ga from a cubic to tetragonal structure and the reduction of the NCM523 cathode to Ni metal. These findings provide insight into the structural stability of layered cathode and garnet-type solid-electrolyte composite materials and the design of stable interfaces between them via co-sintering for ASSBs.

Critical Role of Ti4+ in Stabilizing High-Voltage Redox Reactions in Li-Rich Layered Material.

Li-rich layered oxide materials are considered promising candidates for high-capacity cathodes for battery applications and improving the reversibility of the anionic redox reaction is the key to exploiting the full capacity of these materials. However, permanent structural change of the electrode occurring upon electrochemical cycling results in capacity and voltage decay. In view of these factors, Ti4+ -substituted Li2 IrO3 (Li2 Ir0.75 Ti0.25 O3 ) is synthesized, which undergoes an oxygen redox reaction with suppressed voltage decay, yielding improved electrochemical performance and good capacity retention. It is shown that the increased bond covalency upon Ti4+ substitution results in structural stability, tuning the phase stability from O3 to O1' upon de-lithiation during charging compared with O3 to T3 and O1 for pristine Li2 IrO3 , thereby facilitating the oxidation of oxygen. This work unravels the role of Ti4+ in stabilizing the cathode framework, providing insight for a fundamental design approach for advanced Li-rich layered oxide battery materials.

Theoretical Study on the Degree of CO2 Activation in CO2-Coordinated Ni(0) Complexes.

The geometrical characteristic and the degree of CO2 activation of the CO2-coordinated Ni(0) complexes were investigated computationally by quantum chemical means for bidentate and tridentate ligands of PP, PPMeP, and PNP, and sometimes with co-complexing Fe(II) to differently coordinate CO2. We show that the coordination geometry of the central metal is determined by the ligand geometry. The charge and the energy decomposition analyses show that the charge transfer energy through orbital mixing has a strong correlation with CO2 net charge, while the binding energy cannot due to the lack of the coordination number and the deformation energy of the ligand. Among the examined ligands, PNP with negatively charged secondary amine makes Ni(0) an electron-rich atom, which results in an ∼20% higher CO2 activation than those of PP and PPMeP. In particular, Fe(II)-PNP in the CO2-bridged diatomic complex enhances CO2 activation by another ∼20%, partly through the inductive effect of Fe(II), which pulls electron density from Ni-PNP across the CO2-bridge and partly by the backward donation from Fe(II)-PNP. Therefore, the present study encourages us to design a strongly electron-donating ligand and a CO2-bridged diatomic complex to develop more efficient homogeneous catalyst.

Diamine-Functionalization of a Metal-Organic Framework Adsorbent for Superb Carbon Dioxide Adsorption and Desorption Properties.

For real-world postcombustion applications in the mitigation of CO2 emissions using dry sorbents, adsorption and desorption behaviors should be controlled to design and fabricate prospective materials with optimal CO2 performances. Herein, we prepared diamine-functionalized Mg2 (dobpdc) (H4 dobpdc=4,4'-dihydroxy-(1,1'-biphenyl)-3,3'-dicarboxylic acid). (1-diamine) with ethylenediamine (en), primary-secondary (N-ethylethylenediamine-een and N-isopropylethylenediamine-ipen), primary-tertiary, and secondary-secondary diamines. A slight alteration of the number of alkyl substituents on the diamines and their alkyl chain length dictates the desorption temperature (Tdes ) at 100 % CO2 , desorption characteristics, and ΔT systematically to result in the tuning of the working capacity. The existence of bulky substituents on the diamines improves the framework stability upon exposure to O2 , SO2 , and water vapor, relevant to real flue-gas conditions. Bulky substituents are also responsible for an interesting two-step behavior observed for the ipen case, as revealed by DFT calculations. Among the diamine-appended metal-organic frameworks, 1-een, which has the required adsorption and desorption properties, is a promising material for sorbent-based CO2 capture processes. Hence, CO2 performance and framework durability can be tailored by the judicial selection of the diamine structure, which enables property design at will and facilitates the development of desirable CO2 -capture materials.

A catalytic role of surface silanol groups in CO2 capture on the amine-anchored silica support.

A new mechanism of CO2 capture on the amine-functionalized silica support is demonstrated using density functional theory calculations, in which the silica surface not only acts as a support to anchor amines, but also can actively participate in the CO2 capture process through a facile proton transfer reaction with the amine groups. The surface-mediated proton transfer mechanism in forming a carbamate-ammonium product has lower kinetic barrier (8.1 kcal mol-1) than the generally accepted intermolecular mechanism (12.7 kcal mol-1) under dry conditions, and comparable to that of the water-assisted intermolecular mechanism (6.0 kcal mol-1) under humid conditions. These findings suggest that the CO2 adsorption on the amine-anchored silica surface would mostly occur via the rate-determining proton transfer step that is catalyzed by the surface silanol groups.

Assessments of semilocal density functionals and corrections for carbon dioxide adsorption on metal-organic frameworks.

The significant amount of attention that has been directed toward metal-organic frameworks (MOFs) for a wide spectrum of applications can be attributed to their variety and tunability, which are precisely the aspects that computational modeling can offer by systematically exploring the chemical space. In this minireview, we describe density functional theory calculations for gas adsorption on MOFs, mainly focusing on the interaction of CO2 with MOF-74. The generalized gradient approximation (GGA) level of density functional studies seems suited to treat MOFs, owing to the balance between its practical applicability and its useful accuracy, although this method is not without deficiencies such as the lack of nonlocal correlations and self-interactions. We review and analyze the effects of correction schemes to the GGA to amend the latter weaknesses, and the choice of exchange correlation functionals to treat MOFs for gas capture and separation. We also discuss a few topical questions that are currently missing in the present literature and that require further investigations.