Destabilization of Oxidized Lattice Oxygen in Layered Oxide Cathode.

Integrating anion-redox capacity with orthodox cation-redox capacity is deemed as a promising solution for high-energy-density battery cathodes surmounting the present technical bottlenecks. However, the evolution of oxidized oxygen species during the electrochemical or chemical process easily jeopardizes the reversibility of oxygen redox and remains poorly understood. Herein, we showcase the gradual conversion of the π-interacting oxygen (localized hole states on O) to the σ-interacting oxygen upon resting at a high voltage for P3-type Na0.6Li0.2Mn0.8O2 with nominally stable ribbon-like superstructure, accompanied by the O-O dimerization and the local structural reorganization. We further pinpoint an abnormal Li+ migration process from the alkali-metal layer to the transition-metal layer for desodiated P3-Na0.6Li0.2Mn0.8O2, thereby leading to a partial reconstruction of the ribbon superstructure. The high-voltage plateau of oxygen-redox cathodes is concluded to be exclusively controlled by the oxygen stabilization mechanism rather than the superstructure ordering. In addition, there exists a kinetic competition between π and σ interaction during the uninterrupted electrochemical process.

Na2.5 Cr0.5 Zr0.5 Cl6 : A New Halide-Based Fast Sodium-Ion Conductor.

All-solid-state batteries employing solid electrolytes (SEs) have received widespread attention due to their high safety. Recently, lithium halides are intensively investigated as promising SEs while their sodium counterparts are less studied. Herein, a new sodium-ion conductor with a chemical formula of Na2.5 Cr0.5 Zr0.5 Cl6 is reported, which exhibits high room temperature ionic conductivity of 0.1 mS cm-1 with low migration energy barrier of ≈0.41 eV. Na2.5 Cr0.5 Zr0.5 Cl6 has a Fm-3m structure with 41.67 mol.% of cationic vacancies owing to the occupation of Cr (8.33 mol.%) and Zr (8.33 mol.%) ions at Na sites. Supercell calculations show that the lowest columbic energy configuration has Cr/Zr/V (where V is the vacancy) clusters in the structure. Nonetheless, the clusters have mixed effects on the sodium ion conduction pathway, based on the Bond Valence Energy Landscape calculation. A global 3D Na-ion transport percolation network can be revealed in the lowest energy supercell. Effective pathways are connected through the NaCl6 and VCl6 nodes. Besides, Raman spectroscopy and 23 Na solid-state nuclear magnetic resonance spectroscopy further prove the tunable structure of the SEs with different Cr to Zr ratios. The optimization between the concentration of Na+ and vacancies is crucial to create an improved network of Na+ diffusion channels.

4d Lithium-Rich Cathode System Reinvestigated with Electron Paramagnetic Resonance: Correlation between Ionicity, Oxygen Dimers, and Molecular O2.

Layered lithium-rich (Li-rich) oxide cathodes with additional capacity contribution via oxygen redox are promising high energy density cathodes for next generation Li-ion batteries. However, the chemical states of the oxidized oxygen in charged materials are under fierce debate, including the O2- with stable electron holes, O-O dimer (O2)n- (n > 0), molecular O2, and oxygen π redox. Here, we show using electron paramagnetic resonance (EPR) spectroscopy that in the 4d Li-rich ruthenate compounds, Li2Ru0.75Sn0.25O3 and Li2Ru0.5Sn0.5O3, strong covalency between 4d transition metal and oxygen can inhibit the formation of trapped molecular O2 but not suppress the formation of O-O dimer. As the covalent bond of Ru-O weakens and the ionic bond Sn-O becomes dominant in Li2Ru0.25Sn0.75O3, (O2)- will detach from Sn4+, eventually leading to the formation of trapped molecular O2 during the deep oxygen redox. We propose two possible evolution paths of oxidized oxygen as (1) oxygen electron holes → Ru-(O2)m- (m > 1) → Ru-(O2)- or (2) oxygen electron holes → Sn-(O2)m- (m > 1) → Sn-(O2)- → O2, and the species to which they will evolve are related to which metal (O2)- bonds to and whether the ionicity dominates.

A rings-in-pores net: crown ether-based covalent organic frameworks for phase-transfer catalysis.

We herein present a new family of crown ether-based covalent organic frameworks (CE-COFs) for the first time. The CE-COFs show excellent phase-transfer catalytic performance in various nucleophilic substitution reactions.

Unveiling the benefits of potassium doping on the structural integrity of Li-Mn-rich layered oxides during prolonged cycling by dual-mode EPR spectroscopy.

The oxygen redox process in Li- and Mn-rich layered oxides will inevitably lead to the generation of oxygen vacancies on the surface and their subsequent injection into the bulk lattice, which incurs poor kinetics, capacity decrease, and voltage fading. Herein, this predicament is effectively alleviated by bulk doping of K+, which is intrinsically stable in the lattice to inhibit the generation of oxygen vacancies in the deep delithiated state. More importantly, the benefits of K+ doping on the structural reversibility during prolonged cycling were studied by electron paramagnetic resonance (EPR) spectroscopy in both perpendicular and parallel polarization modes and high-resolution transmission electron microscopy. The results elucidate that the migration of transition-metal ions and oxygen vacancies and the reduction of Mn-ions are mitigated after K+ doping. Consequently, the growth of Li-poor nanovoids in the bulk lattice is greatly diminished and the structural transition from layered to spinel phases is effectively delayed.

Low-temperature pseudomorphic transformation of polyhedral MIL-88A to lithium ferrite (LiFe3O5) in aqueous LiOH medium toward high Li storage.

The ability to develop novel nanomaterials, and to precisely manufacture their functional structures at the nano- and microscales would benefit many emerging device applications. Herein, as a first example, we describe the exploration of feasibility for the morphological replacement of an iron-based MOF bearing trimeric FeIII-O clusters, MIL-88A preform, with a polyhedral architecture of around 0.4 × 1.2 µm by a lithium ferrite (LiFe3O5) phase via solid-liquid pseudomorphic transformation reactions in biologically and environmentally favourable aqueous lithium hydroxide (LiOH). The reaction proceeds at 170 °C, and the overall reaction can be described as Fe3O(H2O)2(FMA)3(OH)·nH2O (MIL-88A) + 7OH- + Li+ → LiFe3O5 + 3FMA2- + (n + 6) H2O (FMA = fumarate). It was proposed that through the coordination substitution of a MOF ligand by OH-, follow-up dehydration and dehydroxylation, and final H+/Li+ ionic exchange, the monolithiated iron oxides formed thermodynamically at comparatively low temperatures, which transcribe the global nanostructure morphologies of the polyhedral MOF preforms with the hexagonal symmetry, but were composed of interconnected LiFe3O5 particles (about 16 nm) that crystallize in a typical magnetite-type cubic (Fd3[combining macron]m) structure. Given the characteristic texture and structure of the Li-Fe oxide replica, cubic LiFe3O5 was preferentially employed as a new type of electrode material in rechargeable lithium cells. Notably, from the electrochemical evaluation, this metal oxide system exhibits decent anodic performances by undergoing a nine-electron conversion reaction, showing a substantially high specific capacity with an average potential of 0.8 V versus lithium metal, a long service life (700 cycles), and exceptional high-rate capability (up to 2.0 A g-1). The synthetic paradigms demonstrated that the MIL-88A to LiFe3O5 conversion may be transferable to other advanced inorganic-based electrodes from the parent metal compound such as LiFeO2, LiMn2O4 or LiCoO2 toward sustainable energy fields.

A comprehensive study on the generation of reactive oxygen species in Cu-Aß-catalyzed redox processes.

In the amyloid plaques, a signature of AD, abnormally high Cu2+ concentrations are found bound to Aß. Most of previous studies reported that Cu-Aß could contribute to oxidative stress, as H2O2 and •OH are catalytically generated by Cu-Aß with the assistance of biological reductant, with only one recent report stated that free O2•- is also generated in the Cu-Aß catalyzed processes, where an indirect technique was applied. To comprehensively investigate the free radicals produced during this Cu-Aß-mediated process with a biological reductant, DNA-cleavage assay, an indirect method, and two direct methods including electron paramagnetic resonance (EPR) spectroscopy and transient absorption spectroscopy (TAS), both having qualitative and quantitative power, were employed in this work. All the experimental results obtained from the three methods demonstrated that Cu-Aß in the biological reducing environment was not only able to catalyze the production of H2O2 and •OH, but also to generate free O2•-. The results further indicated that O2•- was the precursor of H2O2 and •OH. It is also important to note that the results obtained from EPR spectroscopy and TAS provided direct evidence for the presence of O2•- and •OH. By virtue of the direct techniques, we also found that the longest peptide fragments of Aß16, Aß40, and Aß42 produced the least radicals with a lowest rate. More interestingly, the fibrillar forms of Aß generated less O2•- and •OH compared with oligomeric and monomeric forms.

One-Pot Synthesis of Co-Based Coordination Polymer Nanowire for Li-Ion Batteries with Great Capacity and Stable Cycling Stability.

Nanowire coordination polymer cobalt-terephthalonitrile (Co-BDCN) was successfully synthesized using a simple solvothermal method and applied as anode material for lithium-ion batteries (LIBs). A reversible capacity of 1132 mAh g-1 was retained after 100 cycles at a rate of 100 mA g-1, which should be one of the best LIBs performances among metal organic frameworks and coordination polymers-based anode materials at such a rate. On the basis of the comprehensive structural and morphology characterizations including fourier transform infrared spectroscopy, 1H NMR, 13C NMR, and scanning electron microscopy, we demonstrated that the great electrochemical performance of the as-synthesized Co-BDCN coordination polymer can be attributed to the synergistic effect of metal centers and organic ligands, as well as the stability of the nanowire morphology during cycling.

Reduction of the 13C cross-polarization experimental time for pharmaceutical samples with long T1 by ball milling in solid-state NMR.

Many pharmaceutical samples have notably long 1H T1 (proton spin-lattice relaxation time), leading to lengthy experiments lasting several days in solid-state NMR studies. In this work, we propose the use of ball milling on the pharmaceutical samples to reduce the 1H T1, which also leads to enhanced sensitivity in {1H}-13C Cross-Polarization (CP) experiments due to reduced particle sizes and increased surface areas of the samples. Experimentally, we determined that depending on the substrates and milling time, the signal-to-noise ratio (S/N) of a 1D 13C CP spectrum can be increased by a factor of 3-6, which means that the experimental time can be shortened by a factor of 9-36. Furthermore, the application of simple ball-milling within a short time avoids the amorphization of the studied samples such that no signal due to amorphous state is observed in the 13C CP spectrum. This simple ball milling method used for sensitivity enhancement can be further applied in the SS-NMR studies of pharmaceutical samples.

Green and Rational Design of 3D Layer-by-Layer MnO x Hierarchically Mesoporous Microcuboids from MOF Templates for High-Rate and Long-Life Li-Ion Batteries.

Rational design and delicate control on the textural properties of metal-oxide materials for diverse structure-dependent applications still remain formidable challenges. Here, we present an eco-friendly and facile approach to smartly fabricate three-dimensional (3D) layer-by-layer manganese oxide (MnO x) hierarchical mesoporous microcuboids from a Mn-MOF-74-based template, using a one-step solution-phase reaction scheme at room temperature. Through the controlled exchange of metal-organic framework (MOF) ligand with OH- in alkaline aqueous solution and in situ oxidation of manganese hydroxide intermediate, the Mn-MOF-74 template/precursor was readily converted to Mn3O4 or δ-MnO2 counterpart consisting of primary nanoparticle and nanosheet building blocks, respectively, with well-retained morphology. By X-ray diffraction, transmission electron microscopy (TEM), scanning electron microscopy, high-resolution TEM, N2 adsorption-desorption analysis and other techniques, their crystal structure, detailed morphology, and microstructure features were unambiguously revealed. Specifically, their electrochemical Li-ion insertion/extraction properties were well evaluated, and it turns out that these unique 3D microcuboids could achieve a sustained superior lithium-storage performance especially at high rates benefited from the well-orchestrated structural characteristics (Mn3O4 microcuboids: 890.7, 767.4, 560.1, and 437.1 mAh g-1 after 400 cycles at 0.2, 0.5, 1, and 2 A g-1, respectively; δ-MnO2 microcuboids: 991.5, 660.8, 504.4, and 362.1 mAh g-1 after 400 cycles at 0.2, 0.5, 1, and 2 A g-1, respectively). To our knowledge, this is the most durable high-rate capability as well as the highest reversible capacity ever reported for pure MnO x anodes, which even surpass most of their hybrids. This facile, green, and economical strategy renews the traditional MOF-derived synthesis for highly tailorable functional materials and opens up new opportunities for metal-oxide electrodes with high performance.

Custom-Made Ceria Nanoparticles Show a Neuroprotective Effect by Modulating Phenotypic Polarization of the Microglia.

The neuroprotective effect of ceria nanoparticles in the context of brain disorders has been explained by their antioxidant effect. However, the in-depth mechanism remains unknown. As resident immune cells in the brain, microglia exert a variety of functional reprogramming termed as polarization in response to stress stimuli. Herein, custom-made ceria nanoparticles were developed and found to scavenge multiple reactive oxygen species with extremely high efficiency. These nanoparticles drove microglial polarization from a pro-inflammatory phenotype to an anti-inflammatory phenotype under pathological conditions. Pretreatment of these nanoparticles changed the microglial function from detrimental to protective for the neuronal cells by blocking the pro-inflammatory signaling. This work not only helps to elucidate the mechanism of ceria-nanoparticle-mediated neuroprotection but also provides a new strategy to rebalance the immuno-environment by switching the equilibrium of the phenotypic activation of microglia.

Exploring the Capacity Limit: A Layered Hexacarboxylate-Based Metal-Organic Framework for Advanced Lithium Storage.

Our previous work suggested that more carboxylate groups might lead to higher energy density for metal-organic frameworks. In this study, we synthesized a layered metal-organic framework (MOF) Ni-BHC by use of 1,2,3,4,5,6-benzenehexacarboxylic acid. After evacuation by thermal treatment, this MOF was employed as an anode for lithium storage. For its rich lithiation sites as well as layered fast-kinetics structure, it delivers a superior reversible capacity of 1261.3 mA h g-1 at 100 mA g-1, far exceeding the performance of previously reported MOF-based anode materials. Density functional theory calculation and O soft X-ray absorption spectroscopy suggest that the luxuriant carboxylate-metal units play an important part in the electrochemical process.

Ultrathin Cobalt-Based Metal-Organic Framework Nanosheets with Both Metal and Ligand Redox Activities for Superior Lithium Storage.

The controllable synthesis and structural tailoring of nanostructured metal-organic frameworks (MOFs) is of huge significance in boosting their potential for rechargeable batteries. We herein present the facile synthesis of cobalt-based ultrathin metal-organic framework nanosheets (referred to as "u-CoTDA") by using 2,5-thiophenedicarboxylic (H2 TDA) as the organic building block through a one-pot ultrasonic method for the first time. The obtained u-CoTDA exhibits high reversible capacity (790 mAh g-1 after 400 cycles at 1 A g-1 ) and excellent rate capability (694 mAh g-1 at 2 A g-1 ), which outperforms its bulk counterpart. Moreover, the detailed lithiation/delithiation processes of u-CoTDA were studied by the combination of Co K-edge X-ray absorption near edge structure (XANES), O K-edge soft X-ray spectroscopy (sXAS) and electron paramagnetic resonance (EPR) techniques, which demonstrate that both the CoII centers and organic ligands of u-CoTDA are involved in the reduction/oxidation processes.

Ultrathin Manganese-Based Metal-Organic Framework Nanosheets: Low-Cost and Energy-Dense Lithium Storage Anodes with the Coexistence of Metal and Ligand Redox Activities.

We herein demonstrate the fabrication of Mn- and Ni-based ultrathin metal-organic framework nanosheets with the same coordination mode (termed "Mn-UMOFNs" and "Ni-UMOFNs", respectively) through an expedient and versatile ultrasonic approach and scrutinize their electrochemical properties as anode materials for rechargeable lithium batteries for the first time. The obtained Mn-UMOFNs with structure advantages over Ni-UMOFNs (thinner nanosheets, smaller metal-ion radius, higher specific surface area) exhibit high reversible capacity (1187 mAh g-1 at 100 mA g-1 for 100 cycles), excellent rate capability (701 mAh g-1 even at 2 A g-1), rapid Li+ diffusion coefficient (2.48 × 10-9 cm2 s-1), and a reasonable charge-discharge profile with low average operating potential at 0.4 V. On the grounds of the low-cost and environmental benignity of Mn metals and terephthalic acid linkers, our Mn-UMOFNs show alluring promise as a low-cost high-energy anode material for future LIBs. Furthermore, the lithiation-delithiation chemistry of Mn-UMOFNs was unequivocally studied by a combination of magnetic measurements, electron paramagnetic resonance, and synchrotron-based soft X-ray spectroscopy (O K-edge and Mn L-edge) experiments, the results of which substantiate that both the aromatic chelating ligands and the Mn2+ centers participate in lithium storage.

Highly reversible lithium storage in cobalt 2,5-dioxido-1,4-benzenedicarboxylate metal-organic frameworks boosted by pseudocapacitance.

Exploiting novel metal-organic frameworks (MOFs) as electrode materials with superior rate capabilities and understanding their electrochemical behaviour in detail are crucial for boosting the application of MOFs in the field of energy storage. Herein, we prepared Co2(DOBDC) (DOBDC=2,5-dioxido-1,4-benzenedicarboxylate) via a hydrothermal method and explored its electrochemical performance as an anode material for lithium-ion batteries. The as-prepared Co2(DOBDC) MOF exhibits a reversible capacity of 526.1mAhg-1 after 200 charge/discharge cycles at a current density of 500mAg-1 and also demonstrates an impressive rate capability, with a high capacity of 408.2mAhg-1 at a high current density of 2Ag-1. Furthermore, synchrotron-based soft X-ray absorption spectroscopy (sXAS) and electron paramagnetic resonance (EPR) spectroscopy have been applied to investigate the spin state of cobalt in the electrodes at different states of charge. Our results suggest that localized electrons in high-spin (S=3/2) Co2+ in pristine Co2(DOBDC) are gradually delocalized after discharging. It was also found that the high rate capability of Co2(DOBDC) is mainly ascribed to an ultrafast ion intercalation pseudocapacitance process, which results from its unique microporous architecture and adequate specific surface that offers sufficient electrode/electrolyte contact and benefits fast Li+ ion diffusion.

Pillared-Layer Metal-Organic Frameworks for Improved Lithium-Ion Storage Performance.

Recently, more and more metal-organic frameworks (MOFs) have been directly used as anodic materials in lithium-ion batteries, but judicious design or choice of MOFs is still challenging for lack of structural-property knowledge. In this article we propose a pillared-layer strategy to achieve improved Li-storage performance. Four Mn(II) and Co(II) MOFs with mixed azide and carboxylate ligands were studied to illustrate the strategy. In these 3D MOFs, layers (1, 3, and 4) or chains (2) with short bridges are linked by long organic spacers. All the MOFs show very high lithiation capacity (1170-1400 mA h g-1 at 100 mA g-1) in the first cycle owing to the rich insertion sites arising from the azide ion and the aromatic ligands. After the formation cycles, the reversible capacities of the anodes from 1, 3, and 4 are kept at a high level (580-595 mA h g-1) with good rate and cycling performance, while the anode from 2 undergoes a dramatic drop in capacity. All the MOFs lose the crystallinity after the first cycle. While the amorphization of the chain-based framework of 2 leads to major irreversible deposit of Li ions, the amorphous phases derived from the pillared-layer frameworks of 1, 3, and 4 still retain rich accessible space for reversible insertion and diffusion of active Li ions. Consistent with the analysis, electrochemical impedance spectra revealed that the pillared-layer MOFs led to significantly smaller charge-transfer resistances than 2. Soft X-ray absorption spectroscopy suggested that no metal conversion is involved in the lithiation process, consistent with the fact that the isomorphous Co(II) (3) and Mn(II) (4) MOFs are quite similar in anodic performance.

A novel coordination polymer based on Co(ii) hexanuclear clusters with azide and carboxylate bridges: structure, magnetism and its application as a Li-ion battery anode.

A novel Co(ii) coordination polymer, [Co(H2O)6][Co6(bpybdc)2(N3)10(H2O)4]·8H2O (bpybdc2- = 1,1'-bis(3,5-dicarboxylatophenyl)-4,4'-bipyridinium), has been synthesized from a rigid zwitterionic tetracarboxylate ligand and azide. In this compound, hexacobalt clusters with mixed µ-1,1-azide, µ3-1,1,1-azide and µ-1,3-carboxylate bridges are linked into chains by µ-1,3-azide bridges, and the chains are interlinked into 2-fold interpenetrated three-dimensional frameworks through the organic ligand and hydrogen bonds mediated by hexaaquacobalt(ii) complex ions. Magnetic analysis suggested that intracluster ferromagnetic and intercluster antiferromagnetic interactions work together to give overall antiferromagnetic ground states for the azide and carboxylate bridged chain. When applied as an anode for lithium-ion batteries, the coordination polymer changes into an amorphous phase and exhibits a relatively high reversible capacity of 510 mA h g-1 with stable cycling behavior and rate performance.

High Anodic Performance of Co 1,3,5-Benzenetricarboxylate Coordination Polymers for Li-Ion Battery.

We report the designed synthesis of Co 1,3,5-benzenetricarboxylate coordination polymers (CPs) via a straightforward hydrothermal method, in which three kinds of reaction solvents are selected to form CPs with various morphologies and dimensions. When tested as anode materials in Li-ion battery, the cycling stabilities of the three CoBTC CPs at a current density of 100 mA g(-1) have not evident difference; however, the reversible capacities are widely divergent when the current density is increased to 2 A g(-1). The optimized product CoBTC-EtOH maintains a reversible capacity of 473 mAh g(-1) at a rate of 2 A g(-1) after 500 galvanostatic charging/discharging cycles while retaining a nearly 100% Coulombic efficiency. The hollow microspherical morphology, accessible specific area, and the absence of coordination solvent of CoBTC-EtOH might be responsible for such difference. Furthermore, the ex situ soft X-ray absorption spectroscopy studies of CoBTC-EtOH under different states-of-charge suggest that the Co ions remain in the Co(2+) state during the charging/discharging process. Therefore, Li ions are inserted to the organic moiety (including the carboxylate groups and the benzene ring) of CoBTC without the direct engagement of Co ions during electrochemical cycling.

Bimetallic coordination polymer as a promising anode material for lithium-ion batteries.

Bimetallic coordination polymers (BiCPs) with Zn and Co were synthesized and applied as anode materials. When the rate was increased to 2 A g(-1), a capacity of 622 mA h g(-1) after 500 cycles could still be maintained.