Enhancing the Kinetic Process in Biphasic Crystalline NiWO4/Amorphous Co-B Electrode Materials toward Energy Storage with Ultrahigh Rate Performance

Here, we report a two-phase crystalline NiWO₄/amorphous Co−B nanocomposite as an electrode material for supercapacitors, which is effectively synthesized via a simple hydrothermal method and chemical precipitation method. The obtained NiWO₄/Co−B exhibits crystal-amorphous contact, which makes it have more active sites than other crystalline-crystalline phase boundaries, thereby enhancing electron transport. The NiWO₄/Co−B electrode with the best mass ratio of crystalline and amorphous exhibits a great specific capacitance and excellent cycle durability. Compared to individual Co−B and NiWO₄, it also shows enhanced rate capability Besides, NiWO₄/Co−B/activated carbon supercapacitor device can provide a good specific capacitance and a maximum energy density of 10.92 Wh kg⁻¹ at 200 W kg⁻¹. This work provides new insights to develop novel electrode materials for energy storage and conversion.     

An Experimental Evidence of a Metal−Metal Bond in μ‐Carbonylhexacarbonyl[μ‐(5‐oxofuran‐2(5H)‐ylidene‐κC,κC)]‐dicobalt(Co−Co)[Co2(CO)6(μ‐CO)(μ‐C4O2H2)]

The orthorhombic crystal structure of [Co₂(CO)₆(μ‐CO)(μ‐C₄O₂H₂)] ( 1 ) was determined at 150 K (Fig. 1). Two C−H⋅⋅⋅O bonds connect the molecules, forming waving ribbons along the b axis. The experimental electron density, determined with the aspherical‐atom formalism, was analyzed with the topological theory of molecular structure. The presence of the Co−Co bond critical point indicates for the first time the existence of a metal−metal bond in a system with bridged ligands. The bond critical properties of the intramolecular bonds and of the intermolecular interactions show features similar to those found in [Mn₂(CO)₁₀], confirming our previously established bonding classification for organometallic and coordination compounds.     

Co−Co Dinuclear Active Sites Dispersed on Zirconium-doped Heterostructured Co9S8/Co3O4 for High-current-density and Durable Acidic Oxygen Evolution

Developing cost-effective and sustainable acidic water oxidation catalysts requires significant advances in material design and in-depth mechanism understanding for proton exchange membrane water electrolysis. Herein, we developed a single atom regulatory strategy to construct Co−Co dinuclear active sites (DASs) catalysts that atomically dispersed zirconium doped Co₉S₈/Co₃O₄ heterostructure. The X-ray absorption fine structure elucidated the incorporation of Zr greatly facilitated the generation of Co−Co DASs layer with stretching of cobalt oxygen bond and S−Co−O heterogeneous grain boundaries interfaces, engineering attractive activity of significantly reduced overpotential of 75 mV at 10 mA cm⁻², a breakthrough of 500 mA cm⁻² high current density, and water splitting stability of 500 hours in acid, making it one of the best-performing acid-stable OER non-noble metal materials. The optimized catalyst with interatomic Co−Co distance (ca. 2.80 Å) followed oxo-oxo coupling mechanism that involved obvious oxygen bridges on dinuclear Co sites (1,090 cm⁻¹), confirmed by in situ SR-FTIR, XAFS and theoretical simulations. Furthermore, a major breakthrough of 120,000 mA g⁻¹ high mass current density using the first reported noble metal-free cobalt anode catalyst of Co−Co DASs/ZCC in PEM-WE at 2.14 V was recorded.     

Influence of the PVdF binder on the stability of LiCoO2 electrodes

We report herein on the effect of the PVdF binder on the stability of composite LiCoO₂ electrodes at elevated temperatures in 1 M LiPF₆ EC/EMC solutions at open circuit conditions. The structure and morphology of composite LiCoO₂ electrodes with different combinations of electrode components (LiCoO₂ active material, PVdF binder, carbon black and current collector) were evaluated by Raman spectroscopy, X-ray diffraction and SEM. The content of Co ions in the electrolyte solutions was determined by ICP. A new effect was discovered, namely, a detrimental impact of the contact between PVdF and LiCoO₂ on the stability of the active mass. The formation of surface Co₃O₄ and dissolution of Co ions at elevated temperatures is accelerated at the contact points between the active mass and the binder. The effect of water content in the electrolyte solutions on the stability of LiCoO₂ was also studied. The presence of water (and/or HF) is a necessary condition for the accelerated dissolution of Co ions from the active mass. LiCoO₂ oxidizes the solvents at elevated temperatures thus forming CO₂.     

Review and prospect of layered lithium nickel manganese oxide as cathode materials for Li-ion batteries

Layered structural lithium metal oxides with rhombohedral α-NaFeO₂ crystal structure have been proven to be particularly suitable for application as cathode materials in lithium-ion batteries. Compared with LiCoO₂, lithium nickel manganese oxides are promising, inexpensive, nontoxic, and have high thermal stability; thus, they are extensively studied as alternative cathode electrode materials to the commercial LiCoO₂ electrode. However, a lot of work needs to be done to reduce cost and extend the effective lifetime. In this paper, the development of the layered lithium nickel manganese oxide cathode materials is reviewed from synthesis method, coating, doping to modification, lithium-rich materials, nanostructured materials, and so on, which can make electrochemical performance better. The prospects of lithium nickel manganese oxides as cathode materials for lithium-ion batteries are also looked forward to.     

Hydrogen Bond Networks Stabilized High-Capacity Organic Cathode for Lithium-Ion Batteries

High-capacity small organic materials are plagued by their high solubility. Here we proposed constructing hydrogen bond networks (HBN) via intermolecular hydrogen bonds to suppress the solubility of active material. The illustrated 2, 7- diamino-4, 5, 9, 10-tetraone (PTO-NH₂) molecule with intermolecular hydrogen (H) bond between O in −C=O and H in −NH₂, which make PTO-NH₂ presents transverse two-dimensional extension and longitudinal π–π stacking structure. In situ Fourier transform infrared spectroscopy (FTIR) has tracked the reversible evolution of H-bonds, further confirming the existence of HBN structure can stabilize the intermediate 2-electron reaction state. Therefore, PTO-NH₂ with HBN structure has higher active site utilization (95 %), better cycle stability and rate performance. This study uncovers the H-bond effect and evolution during the electrochemical process and provides a strategy for materials design.     

Low-Barrier Hydrogen Bonds in Negative Thermal Expansion Material H3[Co(CN)6]

The covalent nature of the low-barrier N−H−N hydrogen bonds in the negative thermal expansion material H₃[Co(CN)₆] has been established by using a combination of X-ray and neutron diffraction electron density analysis and theoretical calculations. This finding explains why negative thermal expansion can occur in a material not commonly considered to be built from rigid linkers. The pertinent hydrogen atom is located symmetrically between two nitrogen atoms in a double-well potential with hydrogen above the barrier for proton transfer, thus forming a low-barrier hydrogen bond. Hydrogen is covalently bonded to the two nitrogen atoms, which is the first experimentally confirmed covalent hydrogen bond in a network structure. Source function calculations established that the present N−H−N hydrogen bond follows the trends observed for negatively charge-assisted hydrogen bonds and low-barrier hydrogen bonds previously established for O−H−O hydrogen bonds. The bonding between the cobalt and cyanide ligands was found to be a typical donor–acceptor bond involving a high-field ligand and a transition metal in a low-spin configuration.     

Insights into the cooperativity between multiple interactions of dimethyl sulfoxide with carbon dioxide and water

Interactions of dimethyl sulfoxide with carbon dioxide and water molecules which induce 18 significantly stable complexes are thoroughly investigated. An addition of CO₂ or H₂O molecules into the DMSO⋯1CO₂ and DMSO⋯1H₂O systems leads to an increase in the stability of the resulting complexes, in which it is larger for a H₂O addition than a CO₂. The overall stabilization energy of the DMSO⋯1,2CO₂ is mainly contributed by the S=O⋯C Lewis acid–base interaction, whereas the O − H⋯O hydrogen bond plays a significant role in stabilizing complexes of DMSO⋯1,2H₂O and DMSO⋯1CO₂⋯1H₂O. Remarkably, the complexes of DMSO⋯2H₂O are found to be more stable than DMSO⋯1CO₂⋯1H₂O and DMSO⋯2CO₂. The level of the cooperativity of multiple interactions in ternary complexes tends to decrease in going from DMSO⋯2H₂O to DMSO⋯1CO₂⋯1H₂O and finally to DMSO⋯2CO₂. It is generally found that the red shift of the O − H bond involved in an O − H⋯O hydrogen bond increases while the blue shift of a C − H bond in a C − H⋯O hydrogen bond decreases when a cooperative effect occurs in ternary complexes as compared to those of the corresponding binary complexes. © 2018 Wiley Periodicals, Inc.     

Synthesis,molecular structure and electrochemistry of cobalt(II) complexes of 2,2′: 6′,2′′-terpyridine macrocycles

The macrocycle L, prepared by template condensation of bis-6,6′′-(α-methylhidrazino)-4′-phenyl-2,2′:6′′,2′-terpyridine with glyoxal, forms a stable crystalline complex of cobalt(II) [Co(L)(H₂O)₂][PF₆]₂ which has been used as a starting material to prepare, for electrochemical studies, a series of seven coordinate cobalt(II) complexes [Co(L)X₂][PF₆]₂ (X=pyridine, 4-cianopyridine, 4-aminopyridine, 4-dimethylaminopyridine, pirazine, imidazole, 1-methylimidazole, 2-methylimidazole, and trimethylphosphite). Cyclic voltammetry of the aquo complex in DMSO show one reversible reduction wave at −1.35 V versus Ag ∣ AgBF₄ reference electrode and controlled potential electrolysis in the presence of trimethylphosphite affords a diamagnetic species which has been assigned as a mononuclear d⁸ Co(I) species. The crystal and molecular structure of [Co(L)(imidazole)₂][PF₆]₂·Me₂CO shows the metal to be in a pentagonal-bipyramidal N₇ environment.     

Antivitamin B12 Inhibition of the Human B12-Processing Enzyme CblC: Crystal Structure of an Inactive Ternary Complex with Glutathione as the Cosubstrate

B₁₂ antivitamins are important and robust tools for investigating the biological roles of vitamin B₁₂. Here, the potential antivitamin B₁₂ 2,4-difluorophenylethynylcobalamin (F2PhEtyCbl) was prepared, and its 3D structure was studied in solution and in the crystal. Chemically inert F2PhEtyCbl resisted thermolysis of its Co−C bond at 100 °C, was stable in bright daylight, and also remained intact upon prolonged storage in aqueous solution at room temperature. It binds to the human B₁₂-processing enzyme CblC with high affinity (K_D=130 nm ) in the presence of the cosubstrate glutathione (GSH). F2PhEtyCbl withstood tailoring by CblC, and it also stabilized the ternary complex with GSH. The crystal structure of this inactivated assembly provides first insight into the binding interactions between an antivitamin B₁₂ and CblC, as well as into the organization of GSH and a base-off cobalamin in the active site of this enzyme.     

Synthesis and electrochemical performance of three-dimensionally ordered macroporous LiCoO2

Three-dimensionally ordered macroporous (3DOM) LiCoO₂ was synthesized by colloidal crystal templating method using poly(methyl methacrylate) with the diameter of 232 nm as the template. The effects of roasting temperature on properties of LiCoO₂ cathode materials were investigated by thermogravimetric analysis (TG-DTG), scanning electron microscope, X-ray diffraction, transmission electron microscopy, and electrochemical measurements. The results indicated that the synthesized 3DOM LiCoO₂ calcined at 700 °C had better crystal framework and electrochemical properties. The 3DOM LiCoO₂ samples presented higher rate capacity compared to commercial LiCoO₂ with a specific discharge capacity of 151.2 mAh g^?1 at a current density of 1 C, and 92 % of the specific discharge capacity was retained after 50 charge–discharge cycling.     

Evaluation of Bond Covalency and Bond Valence in Sr-Doped Perovskite-Type Compounds

Formulas for decomposing of complex crystals to a sum of binary crystals are described and applied to the study of bond covalency in La_1−xSr_xFeO₃ (0.0≤x≤0.9) and Ca_1−xSr_xMnO₃ (0.0≤x≤0.5). The bond valence is treated by bond-valence sums scheme. The results indicate that, for both compounds, with the increasing doping level, the bond covalency and bond valence show the same trend, namely, larger bond covalency corresponds to higher bond valence. For La_1−xSr_xFeO₃, with the increase of doping level, the bond covalency of La−O, Ca−O decreases in the orthorhombic (0.0≤x≤0.2) and rhombohedral (0.4≤x≤0.7) systems, then increases slightly for the cubic (0.8≤x≤0.9) system, but that of Fe−O increases for all crystal systems. A sharp decrease in bond covalency was observed where the crystal changes from orthorhombic to rhombohedral, while a smooth trend was seen for the rhombohedral-to-cubic transition. On the other hand, for orthorhombic Ca_1−xSr_xMnO₃, the bond covalency of Ca−O, Sr−O, and Mn−O (4-coordinate site) decreases with the increasing doping level, that of Mn−O (2-coordinate site) increases.     

Structural and electrochemical characterization of polyaniline/LiCoO2 nanocomposites prepared via a Pickering emulsion

Polyaniline (PANI)/LiCoO₂ nanocomposite materials are successfully ready through a solid-stabilized emulsion (Pickering emulsion) route. The properties of nanocomposite materials have been put to the test because of their possible relevance to electrodes of lithium batteries. Such nanocomposite materials appear thanks to the polymerization of aniline in Pickering emulsion stabilized with LiCoO₂ particles. PANI has been produced through oxidative polymerization of aniline and ammonium persulfate in HCl solution. The nanocomposite materials of PANI/LiCoO₂ could be formed with low amounts of PANI. The morphology of PANI/LiCoO₂ nanocomposite materials shows nanofibers and round-shape-like morphology. It was found that the morphology of the resulting nanocomposites depended on the amount of LiCoO₂ used in the reaction system. Ammonium persulfate caused the loss of lithium from LiCoO₂ when it was used at high concentration in the polymerization recipe. Highly resolved splitting of 006/102 and 108/110 peaks in the XRD pattern provide evidence to well-ordered layered structure of the PANI/LiCoO₂ nanocomposite materials with high LiCoO₂ content. The ratios of the intensities of 003 and 104 peaks were found to be higher than 1.2 indicating no pronounced mixing of the lithium and cobalt cations. The electrochemical reactivity of PANI/LiCoO₂ nanocomposites as positive electrode in a lithium battery was examined during lithium ion deinsertion and insertion by galvanostatic charge–discharge testing; PANI/LiCoO₂ nanocomposite materials exhibited better electrochemical performance by increasing the reaction reversibility and capacity compared to that of the pristine LiCoO₂ cathode. The best advancement has been observed for the PANI/LiCoO₂ nanocomposite 5 wt.% of aniline.     

Disordering and Electronic State of Cobalt Ions in Mechanochemically Synthesized LiCoO2

Mechanical activation (MA) combined with heat treatment at moderate temperatures was used to prepare disordered and highly dispersed LiCoO₂ starting from the mixtures of various cobalt precursors (CoOOH, Co(OH)₂, and Co) and LiOH. X-ray powder diffraction and IR spectroscopy were used to investigate the phase composition and the crystal structure of as-prepared samples, while the electronic state of cobalt ions was characterized by diffuse reflectance electron spectroscopy. MA of the LiOH+CoOOH mixture led to the formation of LT-LiCoO₂ with a cubic spinel-related structure. Heat treatment at 600°C of the latter resulted in the formation of HT-LiCoO₂ with a hexagonal layered structure similar to ceramic LiCoO₂. However, as-prepared HT-LiCoO₂ is characterized by Co³⁺O₆ octahedra less perfect than those of ceramic LiCoO₂. All MA-LiCoO₂ samples are exclusively described by localized d electrons.     

Investigation of regioselectivity on the reaction of 5-bromo-2,4-dichloro-6-methylpyrimidine with ammonia

Regioselective displacement reaction of ammonia with 5-bromo-2,4-dichloro-6-methylpyrimidine was studied by X-ray crystallography analysis and showed the formation of 5-bromo-2-chloro-6-methylpyrimidin-4-amine as a main product. Reaction of the latter compound with secondary amines in boiling ethanol afforded 4-amino-5-bromo-2-substituted aminopyrimidines. The synthesized compound in this paper crystallized in the monoclinic crystal system space group P2₁/n. In the title cocrystal, 5-bromo-2-chloro-6-methylpyrimidin-4-amine·3H₂O, the asymmetric unit contains one crystallographically independent 5-bromo-2-chloro-6-methylpyrimidin-4-amine and three crystallization of water molecules. The typical intramolecular O−H⋯N as well as O−H⋯O hydrogen bond is observed in the crystalline network of the title compound. It is interesting to point out that the crystal structure is further stabilized by O−H⋯O hydrogen bonds created by (H₂O)_∞ clusters.     

Water adsorption on the surface of Ni‐ and Co‐based layer‐structured cathode materials for lithium‐ion batteries

Ni‐based layer‐structured cathode materials are more vulnerable to moisture than conventional LiCoO₂ cathodes, adsorbing more water and easily forming LiOH on the surface. This study investigated the moisture adsorption mechanism on the surface of layer‐structured cathodes. The behavior of water molecules on LiCoO₂ and LiNiO₂ surfaces were simulated and the structural and chemical changes during the adsorption process were analyzed by first‐principles methods. It was found that the adsorption occurs via two types of mechanism: one involving ionic interactions between Li on the crystal surface and O in the adsorbate, and the other involving covalent bonding between the transition metal (TM) on the surface and O in the adsorbate, which restores the coordination of the TM by recovering its broken bonds. The difference between the water adsorption behaviors of Ni‐based and Co‐based layer‐structured cathodes was found to be mainly due to the ionic‐interaction‐driven adsorption on the (003) surface.     

Synergistic effect of fluorinated solvent and Mg2+ enabling 4.6 V LiCoO2 performances

Increasing the charging cut-off potential of lithium cobalt oxide (LiCoO₂, LCO) can effectively improve the energy density of the lithium-ion batteries, which are the mainstream energy storage devices used in 3C electronic products. However, the continuous decomposition of the electrolyte and dissolution of Co from the electrode will occur at high-potential operation, which deteriorate the performances of LCO. Here, a cathode-electrolyte interface (CEI) layer containing MgF₂ is constructed to enhance the electrochemical stability of LCO at 4.6 V (vs. Li⁺/Li). The Mg²⁺ added to the cathode gradually releases into the electrolyte during cycling, which forms a stable MgF₂-rich protective layer. In addition, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropylether (TTE) is added to the electrolyte acting as a F source to increase the content of MgF₂ in the CEI layer. The MgF₂-rich CEI layer effectively suppresses the decomposition of electrolyte components and the dissolution of Co of LCO, which makes the Li||LiCoO₂ (Li||LCO) cell cycled stably at 3∼4.6 V (vs. Li⁺/Li) in 200 cycles with a retention of 83.9%.     

Long-Life,High-Rate Rechargeable Lithium Batteries Based on Soluble Bis(2-pyrimidyl) Disulfide Cathode

Organosulfides are promising candidates as cathode materials for the development of electric vehicles and energy storage systems due to their low-cost and high capacity properties. However, they generally suffer from slow kinetics because of the large rearrangement of S−S bonds and structural degradation upon cycling in batteries. In this paper, we reveal that soluble bis(2-pyrimidyl) disulfide (Pym₂S₂) can be a high-rate cathode material for rechargeable lithium batteries. Benefiting from the superdelocalization of pyrimidyl group, the extra electrons prefer to be localized on the π* (pyrimidyl group) than σ* (S−S bond) molecular orbitals initially, generating the anion-like intermedia of [Pym₂S₂]²⁻ and thus decreasing the dissociation energy of the S−S bond. It makes the intrinsic energy barrier of dissociative electron transfer depleted, therefore the lithium half cell exhibits 2000 cycles at 5 C. This study provides a distinct pathway for the design of high-rate, long-cycle-life organic cathode materials.     

A Cobalt(III)−Hydroxo Complex Bearing a Pentadentate Amidate Ligand as an Electrocatalyst for Water Oxidation

A Co(III)−hydroxo complex, [Co^III(dpaq)OH]ClO₄ ( 1-OH ) bearing a pentadentate ligand, H-dpaq, (H-dpaq=(2-[bis(pyridin-2-ylmethyl)]amino-N-quinolin-8-yl-acetamidate]) catalyses water oxidation in mildly alkaline medium (pH 8.0) at a potential of 1.4 V_NHE with an average Turn-Over-Frequency (TOF_max) of 2.8×10⁴ s⁻¹ and faradaic efficiency of 88 %. Post-electrolysis characterization of the electrode rules out the formation of any heterogeneous electroactive species. Electrochemical results and theoretical calculations confirm the occurrence of both metal and ligand centered PCET processes during anodic scanning. The resulting formally Co(V)−oxo/oxyl intermediate undergoes water nucleophilic attack to install the O−O bond. The role of axial ligand in water oxidation by Co(III)−dpaq system has been examined by comparing the reactivity of the Co-hydroxide complex ( 1-OH ) with that of its chloride-ligated counterpart, [Co^III(dpaq)Cl]Cl ( 1-Cl ). The results confirm the ability of the Co-dpaq complexes to bind water/or water derived ligands over chloride or non-aqueous solvents. The interplay of ligand redox non-innocence and σ-donating ability of the N5-carboxamido ligand helps to store oxidizing equivalents and triggers O−O bond formation.     

Enhanced electrochemical performance of submicron LiCoO<Subscript>2</Subscript> synthesized by polymer pyrolysis method

Submicron LiCoO₂ was synthesized by a polymer pyrolysis method using LiOH and Co(NO₃)₂ as the precursor compounds. Experimental results demonstrated that the powders calcined at 800 °C for 12 h appear as well-crystallized, uniform submicron particles with diameter of about 200 nm. As a result, the as-prepared LiCoO₂ electrode displayed excellent electrochemical properties, with an initial discharge capacity of 145.5 mAh/g and capacity retention of 86.1% after 50 cycles when cycled at 50 mA/g between 3.5 and 4.25 V. When cycled between 3.5 and 4.5 V, the discharge capacity increased to 177.9 mAh/g with capacity retention of 85.6% after 50 cycles.