Dynamic instability of lithiated phosphorene

Li-ion batteries are widely used energy storage units. Although phosphorene delivers a high Li capacity, the transition capacity between the intercalation reaction and the conversion reaction is still not clear. We investigate the structural and electronic properties of Li intercalated phosphorene and graphene/phosphorene/graphene sandwiches by first-principles calculations. The competition to obtain charge from Li between C and P reduces charge depletion on the interlayer P–P bonds, improving stability. Importantly, the sandwiches show higher transition capacities than freestanding phosphorene, confirmed by ab initio molecular dynamics simulations. The trilayer structures show better structural reversibility than the monolayers.

Introduction of C improves transition capacity between intercalation and conversion reactions for multilayer phosphorene.     

Pressure-driven electronic phase transition in the high-pressure phase of nitrogen-rich 1H-tetrazoles

High-energy-density materials (HEDMs) require new design rules collected from experimental and theoretical results and a proposed mechanism. One of the targeted systems is the nitrogen-rich compounds as precursors for possible polymeric nitrogen or its counterpart in a reasonable pressure range. 1H-tetrazole (CH₂N₄) with hydrogen bonds was studied under pressure by both diffraction and spectroscopy techniques. The observed crystal structure phase transition and hydrogen bond-assisted electronic structure anomaly were confirmed by first-principles calculation. The rearrangement of the hydrogen bonds under pressure elucidates the bonding interactions of the nitrogen-rich system in local 3D chemical environments, allowing the discovery and design of a feasible materials system to make new-generation high-energy materials.

Combined high pressure in situ spectra with first-principles calculations, a possible hydrogen-bond assisted phase transition was proposed in tetrazole.     

Boosting Li/Na storage performance of graphite by defect engineering

Regulating material properties by accurately designing its structure has always been a research hotspot. In this study, by a simple and eco-friendly mechanical ball milling, we could successfully engineer the defect degree of the graphite. Moreover, according to the accurate deconstruction of the structure by atomic pair distribution function analysis (PDF) and X-ray absorption near-edge structure analysis (XANES), those structural defects of the ball-milled graphite (BMG) mainly exist as carbon atom vacancies within the graphene structure, which are beneficial to enhance the lithium and sodium storage performance of BMG. Therefore, BMG-30 h exhibits superior lithium and sodium storage performance.

The structural defects of ball-milled graphite (BMG) mainly exist as carbon atom vacancies within the graphene structure, which are proven to be the main source of lithium/sodium storage performance promotion of BMGs.     

Ruthenium complexes of sterically-hindered pentaarylcyclopentadienyl ligands

The synthesis of ruthenium complexes incorporating an overcrowded pentaarylcyclopentadienyl ligand has been investigated, and higher efficiency has been reached using chlorine-functionalised precursors when compared with their brominated counterparts. A new methodology for the preparation of chlorocyclopentadienes has been developed which is well adapted for highly sterically hindered compounds and works with either electron rich or poor systems.

Preparation of chlorine functionalised intermediates has been developed which is well adapted for highly sterically hindered compounds both with either electron rich or poor systems.     

Synthesis of mixed musks via Eschenmoser–Tanabe fragmentation,enyne metathesis and Diels–Alder reaction as key steps

Musk analogues containing different macrocyclic ring systems as well as different annulated ring systems were synthesised by a simple and useful strategy. This strategy includes Eschenmoser–Tanabe fragmentation, enyne metathesis and Diels–Alder reaction as key steps. Starting from easily available (n) macrocyclic ketones, (n + 3) macrocyclic systems were assembled using the basic organic reactions.

Musk analogues containing different macrocyclic ring systems as well as different annulated ring systems were synthesised by a simple and useful strategy.     

Interaction between functionalized graphene and sulfur compounds in a lithium–sulfur battery – a density functional theory investigation

Lithium–sulfur (Li–S) batteries are emerging as one of the promising candidates for next generation rechargeable batteries. However, dissolution of lithium polysulfides in the liquid electrolyte, low electrical conductivity of sulfur and large volume change during electrochemical cycling are the main technical challenges for practical applications. In this study, a systematic first-principles density functional theory calculation is adopted to understand the interactions between graphene and graphene with oxygen containing functional groups (hydroxyl, epoxy and carboxyl groups) and sulphur (S₈) and long chain lithium polysulfides (Li₂S₈ and Li₂S₄). We find the adsorption is dominated by different mechanisms in sulphur and lithium polysulfides, i.e. van der Waals attraction and formation of coordinate covalent Li–O bonds. The adsorption strength is dependent on the inter-layer distance and electron rich functional groups. Through these mechanisms, sulphur and lithium polysulfides can be successfully retained in porous graphene, leading to improved conductivity and charge transfer in the cathode of Li–S batteries.

Functionalized graphene can successfully anchor sulfur compounds via moderate interactions, leading to improved conductivity and charge transfer in the cathode of Li–S batteries.     

Lithium sensors based on photophysical changes of 1-aza-12-crown-4 naphthalene derivatives synthesized via Buchwald–Hartwig amination

Lithium detection is of great significance in many applications. Lithium-sensing compounds with high selectivity are scarce and, if any, complicated to synthesize. We herein report a novel yet simple compound that can detect lithium ions in an organic solvent through changes in absorbance and fluorescence. Naphthalene functionalized with 1-aza-12-crown-4 (1) was synthesized via one step from commercially available 1-bromonaphthalene through Buchwald–Hartwig amination. In order to obtain a structure–property relationship, we also synthesized two other compounds that are structurally similar to 1, wherein the compounds 2 and 3 include an imide moiety (an electron acceptor) and do not include a 1-aza-12-crown-4 unit, respectively. Upon the addition of lithium ions, compound 1 displayed a clear isosbestic point in the absorption spectra and a new peak in the fluorescence spectra, whereas the compounds 2 and 3 indicated miniscule and no spectroscopic changes, respectively. ¹H NMR titration studies and the calculated optimized geometry from density functional theory (DFT) indicated the lithium binding on the aza-crown. The calculated limit of detection (LOD) was 21 μM. The lithium detection with 1 is selective among other alkali metals (Na⁺, K⁺, and Cs⁺). DFT calculation indicated that the lone pair electrons in the nitrogen atom of 1 is delocalized yet available to bind lithium, whereas the nitrogen lone pair electrons of 2 showed significant intramolecular charge transfer to the imide acceptor, resulting in a high dipole moment, and thus were unavailable to bind lithium. This work elucidates the key design parameters for future lithium sensors.

Lithium sensor based on 1-aza-12-crown-4 naphthalene that can detect lithium ions through absorption and emission changes with the detection limit of 21 μM in an organic solvent.     

Novel hard carbon/graphite composites synthesized by a facile in situ anchoring method as high-performance anodes for lithium-ion batteries

In this report, novel hard carbon/graphite composites are prepared by a simple in situ particle anchoring method, followed by carbonization. The effects of loading content of hard carbon on the structure and electrochemical performance of the composites are investigated. The SEM results show that the hard carbon particles are anchored randomly on the surface of graphite. The electrochemical measurements demonstrate that an appropriate loading content of hard carbon can remarkably increase the specific reversible capacity of graphite, which is mainly contributed by lithiation in hard carbon, whereas excessive loading leads to the formation of a thick particle shell onto the surface of graphite, which deteriorates the initial coulombic efficiency drastically. Kinetic tests further show that excessive loading of hard carbon is unfavorable for lithium-ion diffusion probably due to the increased interface distance and decreased electroconductivity. The composite loaded with 10 wt% hard carbon exhibits balanced lithium storage performance with high reversible capacity of 366 mA h g⁻¹, high initial coulombic efficiency (∼91.3%), and superior rate capability and cycling performance. Thus, in this study, we suggest a facile and effective strategy to fabricate a promising graphite anode material for high-performance lithium-ion batteries.

A facile in situ surface anchoring process is proposed for the fabrication of novel hard carbon/graphite composites. Such unique composites can be used as promising anodes for lithium-ion batteries with high performance.     

Investigation on the role of interfacial water on the tribology between graphite and metals

We investigated the role of interfacial water on the atomic-scale tribology of graphite by contact atomic force microscopy. Upon the approach of Au and Pt tips toward graphite in water, the hydration layers on the respective surfaces interact with each other. This results in a discontinuous motion of the metallic tips towards the graphite surface. Snap-in forces measured with Au and Pt tips scale with their respective water adsorption energies. Moreover, we observed significant differences for the atomic-scale friction between the Au and Pt tips and graphite in water. The atomic-scale sliding friction between an Au tip and graphite is characterized by low friction forces (F_f < 1 nN in the range of normal force values F_n = 1–10 nN) and by a periodic stick-slip that corresponds to the honeycomb structure of graphite. With a Pt tip, the sliding friction on graphite in water is characterized by high friction forces (F_f ≈ 5 nN in the range of normal force values F_n = 1–10 nN) and by an atomic-scale stick-slip whose characteristic lengths may correspond to an ordered water adsorption layer between platinum and graphite.

We investigated the role of interfacial water on the atomic-scale tribology of graphite by contact atomic force microscopy.     

Tunable formaldehyde sensing properties of palladium cluster decorated graphene

The ability to tune the adsorption strength of the targeted gas on sensing materials is crucial for sensing applications. By employing first-principles calculations the adsorption and sensing properties of HCHO on small Pd_n (n = 1–6) cluster decorated graphene have been systematically investigated. The adsorption energy is found to depend on the size of the Pd_n cluster and can be tuned in a wide range from −0.68 eV on Pd(111) to −1.98 eV on the Pd₃/graphene system. We also find that the Pd_n/graphene (n = 5 and 6) systems have an appropriate adsorption energy for HCHO gas sensing. The current–voltage curves are calculated by the non-equilibrium Green''s function method for the two-probe nano-sensor devices along both the armchair and zigzag directions. The devices constructed with Pd_n/graphene (n = 5 and 6), having the highest absolute response over 20% at small voltages, should be applicable for HCHO detection. This work provides a theoretical basis for exploring potential applications of metal cluster decorated graphene for gas sensing.

The adsorption strength of formaldehyde gas molecule and sensing response property on palladium cluster decorated graphene can be tuned by controlling the cluster size.     

Quantitative spatially resolved post-mortem analysis of lithium distribution and transition metal depositions on cycled electrodes via a laser ablation-inductively coupled plasma-optical emission spectrometry method

Diminishing the loss of performance of lithium ion batteries (LIBs) is a challenge that is yet to be fulfilled. Understanding of deterioration processes and mechanisms (i.e., so-called aging) requires analytically accurate examination of aged cells. Changes in the distribution of lithium or transition metals in the LIB cells can influence their cycle and calendar life significantly. As electrochemically treated cells and especially their electrodes do not age homogeneously and the local electrochemistry (e.g. deposition patterns) is strongly dependent on surface properties, bulk analysis is not a satisfactory investigation method. Therefore, a surface sensitive method, namely laser ablation-inductively coupled plasma-optical emission spectrometry (LA-ICP-OES) is presented. LIB cells with lithium metal oxide LiNi_1/3Co_1/3Mn_1/3O₂ (NCM111) as cathode material and graphite as anode material are investigated using a 213 nm Nd:YAG laser.

An LA-ICP-OES method was developed and applied to investigate the transition metal dissolution in lithium batteries as well as lithium deposition e.g. in case of short circuits.     

Deciphering the lithium ion movement in lithium ion batteries: determination of the isotopic abundances of 6Li and 7Li

Lithium ion batteries (LIBs) are the energy storage technology of choice in the context of renewable energies and electro-mobility. It is imperative to get a thorough understanding of the aging mechanisms to achieve a prolonged cycle and calendar life. One major drawback of the technology is continuous capacity fading during operation, which is partly attributed to the loss of active lithium, the object of this work''s analysis. While lithium ion battery aging is an intensively researched topic, there is still the need to determine the origin of the lost lithium and the lithium migration into the different cell components over time. To achieve this goal, different plasma-based mass spectrometric techniques in combination with isotope analysis are applied to obtain bulk as well as depth-resolved information about lithium ion movement and distribution of lithium in aged LIB cells. Different aging experiments are performed on NCM622/graphite cells with a ⁶Li-enriched electrolyte with subsequent Li analysis of the cell components. The results show that the charging rate, as well as the cycle number, has an impact on the ⁶Li/⁷Li-abundances and that the overall abundances show a rapid mixing of the isotopic species already after the first charge/discharge cycle for all cell components.

Different aging experiments were performed on NMC622/graphite cells with a ⁶Li enriched electrolyte to unravel the lithium distribution.     

Heterometallic cobalt(ii) calix[6 and 8]arenes: synthesis,structure and electrochemical activity

Heterometallic cobalt p-tert-butylcalix[6 and 8]arenes have been generated from the in situ reaction of lithium reagents (n-BuLi or t-BuOLi) or NaH with the parent calix[n]arene and subsequent reaction with CoBr₂. The reverse route, involving the addition of in situ generated Li[Co(Ot-Bu)₃] to p-tert-butylcalix[6 and 8]arene, has also been investigated. X-ray crystallography reveals the formation of complicated products incorporating differing numbers of cobalt and lithium or sodium centers, often with positional disorder, as well as, in some cases, the retention of halide. The electrochemical analysis revealed several oxidation events related to the subsequent oxidation of Co(ii) centers and the reduction of the metal cation at negative potentials. Moreover, the electrochemical activity of the phenol moieties of the parent calix[n]arenes resulted in dimerized products or quinone derivatives, leading to insoluble oligomeric products that deposit and passivate the electrode. Preliminary screening for electrochemical proton reduction revealed good activity for a number of these systems. Results suggest that [Co₆Na(NCMe)₆(μ-O)(p-tert-butylcalix[6]areneH)₂Br]·7MeCN (6·7MeCN) is a promising molecular catalyst for electrochemical proton reduction, with a mass transport coefficient, catalytic charge transfer resistance and current magnitude at the catalytic turnover region that are comparable to those of the reference electrocatalyst (Co(ii)Cl₂).

Reactions between p-tert-butylcalix[6 and 8]arenes and lithium or sodium reagents led to complex structures often with positional disorder. Such systems are capable of electrochemical proton reduction.     

Accelerated aging and degradation mechanism of LiFePO4/graphite batteries cycled at high discharge rates

The effects of discharge rates (0.5C, 1.0C, 2.0C, 3.0C, 4.0C and 5.0C) on the aging of LiFePO₄/graphite full cells are researched by disassembling the fresh and aged full cells. The capacity degradation mechanism is analyzed via electrochemical performance, surface morphologies and compositions, and the structure of the anode and cathode electrodes. The capacity fade is accelerated with increasing discharge rates. The irreversible loss of active lithium due to the generation of an SEI film is the primary aging factor for the full cells cycled at low discharge rates. However, when the discharge rate is greater than or equal to 4.0C, the performance degradation of the LiFePO₄ electrode is distinct due to structure decay, which is caused by quick and repeated intercalation of lithium ions and elevated temperature during discharging. In addition, the SEI film on the anode tends to be unstable after the rapid extraction of lithium ions at high discharge rates, and this enhances the loss of active lithium. Therefore, it is indicated that the degradation mechanism is changed for the full cells aged at 4.0C and 5.0C. Besides, the high discharge rate also increases the internal resistance of the full cell, which is detrimental to high rate discharge performance.

Effects of different discharge rates on the aging of LiFePO₄/graphite batteries are researched, and changes in degradation mechanism at high discharge rates are investigated.     

Integrating highly active graphite nanosheets into microspheres for enhanced lithium storage properties of silicon

Integrating silicon (Si) and graphitic carbon into micron-sized composites by spray-drying holds great potential in developing advanced anodes for high-energy-density lithium-ion batteries (LIBs). However, common graphite particles as graphitic carbon are always too large in three-dimensional size, resulting in inhomogeneous hybridization with nanosized Si (NSi); in addition, the rate capability of graphite is poor owing to sluggish intercalation kinetics. Herein, we integrated graphite nanosheets (GNs) with NSi to prepare porous NSi-GN-C microspheres by spray-drying and subsequent calcination with the assistance of glucose. Two-dimensional GNs with average thickness of ∼80 nm demonstrate superior lithium storage capacity, high conductivity, and flexibility, which could improve the electronic transfer kinetics and structural stability. Moreover, the porous structure buffers the volume expansion of Si during the lithiation process. The obtained NSi-GN-C microspheres manifest excellent electrochemical performance, including high initial coulombic efficiency of 85.9%, excellent rate capability of 94.4% capacity retention after 50 repeated high-rate tests, and good cyclic performance for 500 cycles at 1.0 A g⁻¹. Kinetic analysis and in situ impedance spectra reveal dominant pseudocapacitive behavior with rapid and stable Li⁺ insertion/extraction processes. Ex situ morphology characterization demonstrates the ultra-stable integrated structure of the NSi-GN-C. The highly active GN demonstrates great potential to improve the lithium storage properties of Si, which provides new opportunity for constructing high-performance anodes for LIBs.

Highly active graphite nanosheets are integrated with Si nanoparticles to prepare porous microspheres by spray-drying and a subsequent annealing process, which demonstrate superior lithium storage properties.     

Expanded graphite/NiAl layered double hydroxide nanowires for ultra-sensitive,ultra-low detection limits and selective NOx gas detection at room temperature

To develop an ultra-sensitive and selective NO_x gas sensor with an ultra-low detection limit, expanded graphite/NiAl layered double hydroxide (EG/NA) nanowires were synthesized by using hydrothermal method with EG as a template and adjusting the amount of urea in the reaction. X-ray diffraction and transmission electron microscopy showed EG/NA3 nanowires with a diameter of 5–10 nm and a length greater than 100 nm uniformly dispersed on the expanded graphite nanosheet (>8 layers). The synergy between NiAl layered double hydroxide (NiAl-LDH) and expanded graphite (EG) improved the gas sensing properties of the composites. As expected, gas sensing tests showed that EG/NA composites have superior performance over pristine NiAl-LDH. In particular, the EG/NA3 nanowire material exhibited an ultra-high response (R_a/R_g = 17.65) with ultra-fast response time (about 2 s) to 100 ppm NO_x, an ultra-low detection limit (10 ppb) and good selectivity at room temperature (RT, 24 ± 2 °C), which could meet a variety of application needs. Furthermore, the enhancement of the sensing response was attributed to the nanowire structure formed by NiAl-LDH in the EG interlayer and the conductive nanonetwork of interwoven nanowires.

Expanded graphite/NiAl-LDH nanowires for ultra-sensitive, ultra-low detection limits and selective NO_x gas detection at room temperature.     

Alkene hydroboration with pinacolborane catalysed by lithium diisobutyl-tert-butoxyaluminum hydride

Here we developed a highly efficient alkene hydroboration protocol, showing that various alkyl boronates can be smoothly obtained in good yields by reacting alkenes with pinacolborane (HBpin) in the presence of 5 mol% lithium diisobutyl-tert-butoxyaluminum hydride. The coordination of aluminate ions with lithium cations allowed for effective hydride transfer during hydroboration, and the obtained boronate ester was further used for C–C coupling, trifluoroboronate salt formation, and oxidation to alcohol.

Here we developed a highly efficient alkene hydroboration protocol, showing that various alkyl boronates can be smoothly obtained in good yields by reacting alkenes with pinacolborane (HBpin) in the presence of 5 mol% lithium diisobutyl-tert-butoxyaluminum hydride.     

Photophysical deactivation behaviour of Rhodamine B using different graphite materials

In the present work, an attempt has been made to elucidate the structural features of synthesized graphite materials, i.e., expanded graphite (EG) and an expanded graphite/silver nanoparticles (EG/AgNPs) nanocomposite. In order to obtain knowledge about the functional groups present, the interlayer spacing between the carbon layers, topographical features, and the characterization of the materials were carried out using Fourier-transformer infrared spectroscopy, X-ray diffraction, Raman spectroscopy, field emission scanning electron microscopy-energy dispersive X-ray spectroscopy and atomic force microscope. Furthermore, the quenching efficiency of the synthesized graphite materials was also compared using Rhodamine B (Rhd B) as a fluorescent probe. The non-linear behaviour of the Stern–Volmer plots suggested that the complex quenching mechanism (a combination of static and dynamic quenching) was responsible for the decrease in photoluminescence intensity. At a lower concentration of the quencher, the static quenching mechanism was dominant whereas at a higher concentration dynamic processes seemed to be more likely. The binding strength of the complexation between the fluorophore and the quencher at lower concentrations was studied in detail for both of the synthesized materials. The analysis showed that the EG/AgNPs exhibited better quenching efficiency and possessed a strong binding strength in comparison to EG. The thermodynamic parameters of this association suggested that the interaction process was spontaneous and exothermic in nature. Thus, this work offers helpful insights into the fluorescence quenching mechanisms of the Rhd B/EG and its composite system.

Graphical representation of varying quenching mechanism of RhD B dye using different graphite materials i.e. EG and EG/AgNPs.     

Featured properties of Li+-based battery anode: Li4Ti5O12

3D ternary Li₄Ti₅O₁₂, a Li⁺-based battery anode, presents an unusual lattice symmetry (triclinic crystal), band structure, charge density, and density of states under first-principles calculations. It is a large direct-gap semiconductor with E^d_g ∼ 2.98 eV. The atom-dominated valence and conduction bands, the spatial charge distribution and the atom- and orbital-decomposed van Hove singularities are available for delicate identifications of multi-orbital hybridizations in Li–O and Ti–O bonds. The extremely non-uniform chemical environment, which induces very complicated hopping integrals, directly arises from the large bonding fluctuations and the highly anisotropic configurations. Also, the developed theoretical framework is very useful for fully understanding cathodes and electrolytes of oxide compounds.

A theoretical framework based on first-principles calculations is developed for the essential properties of the 3D ternary compound Li₄Ti₅O₁₂, a Li⁺-based battery anode.     

Solvent-free synthesis of propargylamines: an overview

Propargylamines are a class of compounds with many pharmaceutical and biological properties. A green approach to synthesize such compounds is very relevant. This review aims to describe the solvent-free synthetic approaches towards propargylamines via A³ and KA² coupling reactions covering the literature up to 2021.

This review focuses on solvent-free methodologies for the synthesis of propargylamines, a versatile class of compounds with numerous applications.