Search

The reaction kinetics, reversibility and long-term stability of Zn anodes are crucial for rechargeable aqueous Zn batteries. Polymer electrolyte additives are low cost and effective to modify the deposition behavior of Zn anodes. Here, an interesting phenomenon appears that cycling stability and Coulombic efficiency of Zn anodes are improved by PEO additive in dilute aqueous electrolytes with different Zn salts, while the overpotential and long-term stability of Zn anodes vary significantly with different anions. Systematic electrochemical analysis coupled with NMR and MD simulation was performed to reveal the crucial role of salt anion in tuning the specific solvation structures and hydrogen bonding network of aqueous electrolytes with PEO additive, and interfacial double layer capacitance structures. The reaction kinetics and stability of Zn anodes were, therefore, intensively tuned by salt anions in aqueous electrolytes with PEO additives. The cycle life of Zn anode can be improved by 7–10 times with significantly reduced overpotential in bulky anion such as TFSI- based aqueous electrolyte than compact anion such as SO42- in PEO containing aqueous electrolytes. This work provides useful and low-cost concepts to effectively improve Zn anodes reaction dynamics and cycle life by choosing optimal electrolyte salts and additives.

The effect of initial rotational states in the reaction of antisymmetric-excited CH4(v3=1,|jNl⟩) with Cl atom was investigated in a crossed-beam, product-imaging experiment over the collisional energy (Ec) range of 2-5 kcal mol(-1). We found that while the initial rotational excitations exert a noticeable effect on total reactivity, they leave little imprint on the more detailed product-state and angular distributions. This finding echoes the previous conclusion in the analogous Cl + CHD3(v1=1,|NK⟩) reaction. However, the rotational enhancement factor is substantial at low Ec and then becomes insignificant at higher Ec, in contrast to the Cl + CHD3 case. A more intriguing finding is the role of the vibrational angular momentum (l) in promoting the reactivity. A heuristic picture is proposed to rationalize the observations.

Lithium-sulfur (Li–S) battery is one of the most promising candidates for the next generation energy storage systems. However, several barriers, including polysulfide shuttle effect, the slow solid-solid surface reaction pathway in the lower discharge plateau, and corrosion of Li anode still limit its practical applications, especially under the lean electrolyte condition required for high energy density. Here, we propose a solution-mediated sulfur reduction pathway to improve the capacity and reversibility of the sulfur cathode. With this method, a high coulombic efficiency (99%) and stable cycle life over 100 cycles were achieved under application-relevant conditions (S loading: 6.2 mg cm−2; electrolyte to sulfur ratio: 3 mLE gs−1; sulfur weight ratio: 72 wt%). This result is enabled by a specially designed Li2S4-rich electrolyte, in which Li2S is formed through a chemical disproportionation reaction instead of electrochemical routes. A single diglyme solvent was used to obtain electrolytes with the optimum range of Li2S4 concentration. Operando X-ray absorption spectroscopy confirms the solution pathway in a practical Li–S cell. This solution pathway not only introduces a new electrolyte regime for practical Li–S batteries, but also provides a new perspective for bypassing the inefficient surface pathway for other electrochemical processes.

Hair growth and morphology are generally regulated by the hair cycle in mammals. Fibroblast Growth Factor 5 (FGF5), which is a hair cycle regulator, has a role in regulating the hair cycle during the transition from the anagen phase to the catagen phase, and a hereditary long hair phenotype has been widely reported when FGF5 is mutated in humans and other species. However, there has been no such report in rabbits. Thus, the first exon of rabbit FGF5 was disrupted by the CRISPR/Cas9 system, and the phenotype of FGF5-/- rabbits was characterized while using hematoxylin and eosin (H&amp, E) staining, immunohistochemistry, quantitative PCR, scanning electron microscopy, and western blotting. The results showed a significant and systemic long hair phenotype in the FGF5-/- rabbits, which indicated that FGF5 is a negative regulator of hair growth. In addition, a decreased diameter of the fiber and a higher area proportion of hair follicle clusters were determined in FGF5-/- rabbits as compared with the WT rabbits. Further investigation verified that prolonging the anagen phase in rabbits, with decreased BMP2/4 pathway signaling and increased VERSICAN pathway signaling, caused the systemic long hair phenotype. Taken together, these results indicate a systemic long hair phenotype by prolonging anagen in FGF5-/- rabbits, which could be widely used for Fur production and an ideal model for studying the mechanism of long hair in the future.

Several aspects of the stereo-specific requirement in the title reaction are systematically investigated in a crossed-beam experiment using a time-sliced, velocity-mapped imaging technique. Specifically, we explored (1) the differential steric effect from pre-aligning two different reagent rotational states and (2) the effect from probing different product rotational states. In the reaction with an aligned JK=10 reagent at E

Despite considerable efforts to stabilize lithium metal anode structures and prevent dendrite formation, achieving long cycling life in high-energy batteries under realistic conditions remains extremely difficult due to a combination of complex failure modes that involve accelerated anode degradation and the depletion of electrolyte and lithium metal. Here we report a self-smoothing lithium–carbon anode structure based on mesoporous carbon nanofibres, which, coupled with a lithium nickel–manganese–cobalt oxide cathode with a high nickel content, can lead to a cell-level energy density of 350–380 Wh kg−1 (counting all the active and inactive components) and a stable cycling life up to 200 cycles. These performances are achieved under the realistic conditions required for practical high-energy rechargeable lithium metal batteries: cathode loading ≥4.0 mAh cm−2, negative to positive electrode capacity ratio ≤2 and electrolyte weight to cathode capacity ratio ≤3 g Ah−1. The high stability of our anode is due to the amine functionalization and the mesoporous carbon structures that favour smooth lithium deposition. Metallic lithium wets a functionalized mesoporous carbon film to create a self-smoothing anode that, in conjunction with a standard lithium nickel–manganese–cobalt cathode, delivers long cycling life, 350 Wh kg−1 high-energy cells under realistic conditions.

The alkali-ion storage in spinel lithium titanate (Li4Ti5O12) is comprehensively investigated in this work. In Li4Ti5O12, Na storage is more dependent on the particle size compared to Li storage. Electrochemical results show a Na-storage capacity from 150 to 16 mAh g−1, with increasing particle size from 50 to 500 nm, whereas the Li-storage capacity appears to be independent of particle size. The Na-storage rate capability in Li4Ti5O12 is much worse than that of Li, probably because of the sluggish Na+ diffusion in Li4Ti5O12. Ab initio molecular dynamics simulations also indicate that this can be attributed to the slow diffusion kinetics of Na+ in spinel Li4Ti5O12.

Nitrogen-doped porous carbon (NPC) and multi-wall carbon nanotubes (MWCNT) have been frequently studied to immobilize sulfur in lithium–sulfur (Li–S) batteries. However, neither NPC nor MWCNT itself can effectively confine the soluble polysufides if cathode thickness e.g. sulfur loading is increased. In this work, NPC was combined with MWCNTs to construct an integrated host structure to immobilize sulfur at a relevant scale. The function of doped nitrogen atoms was revisited and found to effectively attract sulfur radicals generated during the electrochemical process. The addition of MWCNT facilitated the uniform coating of sulfur nanocomposites to a practically thickness and homogenized the distribution of sulfur particles in the pristine electrodes, while NPC provided sufficient pore volume to trap the dissolved polysulfides species. More importantly, the difficulty of electrode wetting, a critical challenge for thick sulfur cathodes, is also mitigated after the adoption of MWCNT, leading to a high areal capacity of ca. 2.5 mA h/cm2 with a capacity retention of 81.6% over 100 cycles.

Lithium sulfur (Li-S) battery has been regaining tremendous interest in recent years because of its attractive attributes such as highgravimetric energy, low cost and environmental benignity. However, it is still not conclusively known how polysulfide ring/chainparticipates in the whole cycling and whether the discharge and charge processes follow the same pathway. Herein, we demonstratethedirectobservationofsulfurradicalsbyusinginsituelectronparamagneticresonance(EPR)technique.Basedontheconcentrationchangesofsulfurradicalsatdifferentpotentialsandtheelectrochemicalcharacteristicsofthecell,itisrevealedthatthechemicalandelectrochemical reactions in Li-S cell are driving each other to proceed through sulfur radicals, leading to two completely differentreaction pathways during discharge and charge. The proposed radical mechanism may provide new perspectives to investigate theinteractions between sulfur species and the electrolyte, inspiring novel strategies to develop Li-S battery technology.© 2015 The Electrochemical Society. [DOI: 10.1149/2.0851503jes] All rights reserved.Manuscript submitted November 17, 2014; revised manuscript received December 31, 2014. Published January 9, 2015.

In order to achieve a more efficient preparation of a specific ro-vibrationally excited reactant state for reactive scattering experiments, we implemented the rapid adiabatic passage (RAP) scheme to our pulsed crossed-beam machine, using a single-mode, continuous-wave mid-infrared laser. The challenge for this source-rotatable apparatus lies in the non-orthogonal geometry between the molecular beam and the laser propagation directions. As such, the velocity spread of the supersonic beam results in a significantly broader Doppler distribution that needs to be activated for RAP to occur than the conventional orthogonal configuration. In this report, we detail our approach to shifting, locking, and stabilizing the absolute mid-infrared frequency. We exploited the imaging detection technique to characterize the RAP process and to quantify the excitation efficiency. We showed that with appropriate focusing of the IR laser, a nearly complete population transfer can still be achieved in favorable cases. Compared to our previous setup-a pulsed optical parametric oscillator/amplifier in combination with a multipass ring reflector for saturated absorption, the present RAP scheme with a single-pass, continuous-wave laser yields noticeably higher population-transfer efficiency.

The transition state, which gates and modulates reactive flux, serves as the central concept in our understanding of activated reactions. The barrier height of the transition state can be estimated from the activation energy taken from thermal kinetics data or from the energetic threshold in the measured excitation function (the dependence of reaction cross-sections on initial collision energies). However, another critical and equally important property, the angle-dependent barrier to reaction, has not yet been amenable to experimental determination until now. Here, using the benchmark reaction of Cl + CHD

Over the past ten years or so, great advances in our understanding of the dynamics of elementary (bimolecular) polyatomic reactions in the gas-phase have occurred. This has been made possible by critical improvements (a) in crossed molecular beam (CMB) instruments with rotating mass spectrometric detection and time-of-flight analysis, especially following the implementation of soft ionization (by tunable low energy electrons or vacuum-ultraviolet synchrotron radiation) for product detection with increased sensitivity and universal detection power, and (b) in REMPI-slice velocity map ion imaging (VMI) detection techniques in pulsed CMB experiments for obtaining product pair-correlated information through high-resolution measurements directly in the center of mass system. The improved universal CMB method is permitting us to identify all primary reaction products, characterize their formation dynamics, and determine the branching ratios (BRs) for multichannel non-adiabatic reactions, such as those of ground state oxygen atoms, O(3P), with unsaturated hydrocarbons (alkynes, alkenes, dienes). The improved slice VMI CMB technique is permitting us to explore at an unprecedented level of detail, through pair-correlated measurements, the reaction dynamics of a prototype polyatomic molecule such as CH4 (and isotopologues) in its ground state with a variety of important X radicals such as F, Cl, O, and OH. In this review, we highlight this recent progress in the field of CMB reaction dynamics, with an emphasis on the experimental side, but with the related theoretical work, at the level of state-of-the-art calculations of both the underlying potential energy surfaces and the reaction dynamics, noted throughout. In particular, the focus is (a) on the effect of molecular complexity and structure on product distributions, branching ratios and role of intersystem crossing for the multichannel, addition–elimination reactions of unsaturated hydrocarbons with O atoms, and (b) on the very detailed dynamics of the abstraction reactions of ground-state methane (and isotopologues) with atoms (F, Cl, O) and diatoms (OH), with inclusion of also rotational mode specificity in the vibrationally excited methane reactions.

The transition state in the Cl + CH4 reaction is of Cl-H-C collinear geometry, which serves as the bottleneck to reaction. When the reactant CH4 is antisymmetrically stretch-excited to ν3 = 1 by absorbing a linearly polarized photon, all four C-H bonds are collectively excited, and any one of the H atoms could be attacked by the Cl atom. At first sight, it is not obvious how an excited spherical-top molecule like CH4 is aligned and what consequences will be on chemical reactivity by polarizing the CH4 reagents. As shown here, an enormous steric effect on reactivity is observed, which depends sensitively on the selected rotational states. By exploiting various rotational branches in optical excitation, we quantify the degree of stereospecificity for a few lowest rovibrational states of the aligned CH4(ν3 = 1) reagents, as well as account for the hyperfine depolarization factor. This information lays the foundation for a full stereorequirement study of the Cl + CH4(ν3 = 1) reaction.

With the rapid development of renewable energy of wind and solar power and realization of future smart grid, the large-scale energy storage system becomes more and more important. Recently, room-temperature sodium-ion batteries re-attract a great deal of attention due to its low cost and potential application in large-scale energy storage. So far, a large amount of electrode materials have been proposed for sodium-ion batteries. In general, the electrochemical performance of electrodes is determined by its crystal structure. In this review, we summarize the crystal structures of present electrodes and intend to provide insightful guides to electrode material design.

Following our previous study on the H + CD4 → HD + CD3 reaction [ Proc. Natl. Acad. Sci. U.S.A. 2010 , 107 , 12782 ], the reaction of H + CH4 → H2 + CH3 at collision energies ranging from 0.72 to 1.99 eV is studied using crossed-beam and time-sliced velocity map ion imaging techniques. The product angular and translational energy distributions at four different collision energies were derived from the measured images. The excitation function was also measured from these images together with a careful calibration of the H atom beam intensities at different collision energies. All of these results are compared with those of the H + CD4 reaction to investigate the isotope effects. The isotope effects are all observed in the product angular distributions, the translational energy distributions, and the excitation function and further confirm the reaction mechanism proposed in the previous study on the H + CD4 reaction.

Exciting a stretching mode of a chemical bond should help its breaking during a chemical reaction, according to conventional wisdom. In several recent studies of the reactions of stretch-excited methane (and isotopologues) with the F atom, counterintuitively, we found that the induced reactant vibrations instead inhibit the bond rupture and slow down the overall reaction rate. This intriguing observation has been qualitatively ascribed to the vibrationally induced steric effects of the reaction in previous reports. However, quantitative determination of the reactivity suppression in terms of reaction cross sections remains lacking. In this report, we scrutinize the physical meaning of this (product) signal depletion phenomenon and fill the gap. Through a systematic investigation we further elucidate the additional reaction dynamics information that can be retrieved from the depletion measurements. The resultant rotationally state-selected reaction cross sections for both the vibrational ground and excited states are presented, and the stereodynamical implications are delineated.

In recent years, zinc has gained significant attention due to its wide availability (fourth-most mined material on the Earth), low-cost nature and recyclability. Moreover, it allows water-based batteries (i.e. Zn/MnO2) that could compete with LIBs for both transportation and stationary applications without safety issues. However, they are not considered rechargeable in practice yet due to the capacity limitation from the cathode materials and the detrimental zinc dendrite formation. Most of the electrode preparations are currently based on the use of fluorine-containing polymer binders, such as polyvinylidene difluoride (PVDF) and poly-tetrafluoroethylene (PTFE) with N-methyl-2-pyrrolidone (NMP) as a solvent/dispersant due to its good electrochemical stability and high adhesion to the electrode materials and current collectors. However, the fluorinated binders are relatively expensive and NMP is considered to be a hazardous and toxic substance. Therefore, switching to alternate electrode processing routes with non-toxic binders is crucial to providing a fully sustainable and environmentally friendly electrochemical energy storage device. In this study, various water-soluble binders have been evaluated in mild aqueous electrolyte conditions for Zn/MnO2 systems and are compared with the conventional MnO2/PVDF systems. We observed water-soluble binders can be stable and offer desirable adhesion at certain pH levels (3.5~5) without any decomposition. Electrochemical data also indicates that higher capacity utilization and lower cell overpotential is achieved in the cells with aqueous binders versus the cells with PVDF binder. In summary, our work suggests that the implementation of water-soluble binders can lead to substantial improvements for efficient and effective aqueous battery systems.

Aqueous rechargeable zinc-manganese dioxide batteries show great promise for large-scale energy storage due to their use of environmentally friendly, abundant, and rechargeable Zn metal anodes and MnO2 cathodes. In the literature various intercalation and conversion reaction mechanisms in MnO2 have been reported, but it is not clear how these mechanisms can be simultaneously manipulated to improve the charge storage and transport properties. A systematical study to understand the charge storage mechanisms in a layered δ-MnO2 cathode is reported. An electrolyte-dependent reaction mechanism in δ-MnO2 is identified. Nondiffusion controlled Zn2+ intercalation in bulky δ-MnO2 and control of H+ conversion reaction pathways over a wide C-rate charge-discharge range facilitate high rate performance of the δ-MnO2 cathode without sacrificing the energy density in optimal electrolytes. The Zn-δ-MnO2 system delivers a discharge capacity of 136.9 mAh g-1 at 20 C and capacity retention of 93% over 4000 cycles with this joint charge storage mechanism. This study opens a new gateway for the design of high-rate electrode materials by manipulating the effective redox reactions in electrode materials for rechargeable batteries.

Along with the rapid development of renewable energy storage such as wind and solar, the large-scale energy storage technologies are highly desired. Among different energy storage solutions, the rechargeable aqueous Zn-MnO2 batteries are very promising due to their low cost, high environmental benignity and high energy, potentially two times high of the lead-acid batteries. However, the widely investigated rechargeable alkaline Zn-MnO2 batteries suffer from limited depth of discharge (DOD), Zn anode passivation and dendrite, and limited cycle life. In this talk, we will introduce the use of mild aqueous-based electrolytes to address the above issues based on the greatly improved rechargeability of both MnO2 cathode and Zn anode in such systems.[1,2] We will also discuss our recent understanding on how to realize and maintain the highly reversible reactions for both zinc metal and cathodes by optimizing the electrolyte and electrode structures in optimal neutral aqueous electrolyte systems to realize the long-term cycling stability for their future practical applications in large-scale energy storage.

A novel characterization technique using the combination of chemical sodiation and synchrotron based in situ X-ray diffraction (XRD) has been detailed illustrated. The power of this novel technique was demonstrated in elucidating the structure evolution of Li4Ti5O12 upon sodium insertion. The sodium insertion behavior into Li4Ti5O12 is strongly size dependent. A solid solution reaction behavior in a wide range has been revealed during sodium insertion into the nanosized Li4Ti5O12 (~44 nm), which is quite different from the well-known two-phase reaction of Li4Ti5O12/Li7Ti5O12 system during lithium insertion, and also has not been fully addressed in the literature so far. On the basis of this in situ experiment, the apparent Na(+) ion diffusion coefficient (DNa+) of Li4Ti5O12 was estimated in the magnitude of 10(-16) cm(2) s(-1), close to the values estimated by electrochemical method, but 5 order of magnitudes smaller than the Li(+) ion diffusion coefficient (D(Li+) ~10(-11) cm(2) s(-1)), indicating a sluggish Na(+) ion diffusion kinetics in Li4Ti5O12 comparing with that of Li(+) ion. Nanosizing the Li4Ti5O12 will be critical to make it a suitable anode material for sodium-ion batteries. The application of this novel in situ chemical sodiation method reported in this work provides a facile way and a new opportunity for in situ structure investigations of various sodium-ion battery materials and other systems.

Layered sodium titanium oxide, Na2Ti3O7, is synthesized by a solid-state reaction method as a potential anode for sodium-ion batteries. Through optimization of the electrolyte and binder, the microsized Na2Ti3O7 electrode delivers a reversible capacity of 188 mA h g(-1) in 1 M NaFSI/PC electrolyte at a current rate of 0.1C in a voltage range of 0.0-3.0 V, with sodium alginate as binder. The average Na storage voltage plateau is found at ca. 0.3 V vs. Na+/Na, in good agreement with a first-principles prediction of 0.35 V. The Na storage properties in Na2Ti3O7 are investigated from thermodynamic and kinetic aspects. By reducing particle size, the nanosized Na2Ti3O7 exhibits much higher capacity, but still with unsatisfied cyclic properties. The solid-state interphase layer on Na2Ti3O7 electrode is analyzed. A zero-current overpotential related to thermodynamic factors is observed for both nano- and microsized Na2Ti3O7. The electronic structure, Na+ ion transport and conductivity are investigated by the combination of first-principles calculation and electrochemical characterizations. On the basis of the vacancy-hopping mechanism, a quasi-3D energy favorable trajectory is proposed for Na2Ti3O7. The Na+ ions diffuse between the TiO6 octahedron layers with pretty low activation energy of 0.186 eV.

Rainbow structures in the scattering angular distribution play an important role in deepening our understanding about the elastic and rotationally inelastic collisions of atoms/molecules. Reported here is the discovery of a rainbow in a chemical reaction. At Ec = 4.3 kcal mol(-1) one of the correlated product pairs in the F + CH3D reaction, (vHF, vCH2D) = (3, 00), displays a distinct bulge in angular distribution. We showed that the bulge originates predominantly from the low-j states of the HF(v = 3) products. Heuristic considerations led us to propose that such a bulge could be regarded as a signature for rainbow scattering. The underlying mechanism for its occurrence in this nearly thermoneutral product pair is ascribed to a delicate interplay of the attractive and repulsive parts of interactions in the vicinity of the transition state. In a sense, the situation bears striking similarity to the more familiar elastic rainbow, thus coined "reactive rainbow".

In rechargeable Li–S batteries, the uncontrollable passivation of electrodes by highly insulating Li2S limits sulfur utilization, increases polarization, and decreases cycling stability. Dissolving Li2S in organic electrolyte is a facile solution to maintain the active reaction interface between electrolyte and sulfur cathode, and thus address the above issues. Herein, ammonium salts are demonstrated as effective additives to promote the dissolution of Li2S to 1.25 M in DMSO solvent at room temperature. NMR measurements show that the strong hydrogen binding effect of N–H groups plays a critical role in dissolving Li2S by forming complex ligands with S2– anions coupled with the solvent’s solvating surrounding. Ammonium additives in electrolyte can also significantly improve the oxidation kinetics of Li2S, and therefore enable the direct use of Li2S as cathode material in Li–S battery system in the future. This provides a new approach to manage the solubility of lithium sulfides through cation coordination ...

Rechargeable aqueous batteries such as alkaline zinc/manganese oxide batteries are highly desirable for large-scale energy storage owing to their low cost and high safety; however, cycling stability is a major issue for their applications. Here we demonstrate a highly reversible zinc/manganese oxide system in which optimal mild aqueous ZnSO4-based solution is used as the electrolyte, and nanofibres of a manganese oxide phase, α-MnO2, are used as the cathode. We show that a chemical conversion reaction mechanism between α-MnO2 and H+ is mainly responsible for the good performance of the system. This includes an operating voltage of 1.44 V, a capacity of 285 mAh g−1 (MnO2), and capacity retention of 92% over 5,000 cycles. The Zn metal anode also shows high stability. This finding opens new opportunities for the development of low-cost, high-performance rechargeable aqueous batteries. Rechargeable aqueous batteries are attractive owing to their relatively low cost and safety. Here the authors report an aqueous zinc/manganese oxide battery that operates via a conversion reaction mechanism and exhibits a long-term cycling stability.

The O((1)D) + CD4 → OD + CD3 reaction was investigated using the crossed molecular beam technique with sliced velocity map imaging at four different collision energies: 1.6, 2.8, 4.6, and 6.8 kcal/mol. The vibrational ground state product CD3 was detected using a (2 + 1) resonance-enhanced multiphoton ionization (REMPI). Remarkably different features were found in the forward and backward scatterings, and gradually changed with the collision energy. These features were attributed to two distinctive reaction mechanisms-insertion and abstraction-that occur on the ground and excited state surfaces, respectively. Contributions from the two mechanisms were extracted from the experiment results, and a positive correlation was found between the abstraction proportion and the collision energy. The threshold for the abstraction pathway was determined and compared with results from calculations.

A Na3V2(PO4)3 sample coated uniformly with a layer of 6 nm carbon has been successfully synthesized by a one-step solid state reaction. This material shows two flat voltage plateaus at 3.4 V vs. Na+/Na and 1.63 V vs. Na+/Na in a nonaqueous sodium cell. When the Na3V2(PO4)3/C sample is tested as a cathode in a voltage range of 2.7–3.8 V vs. Na+/Na, its initial charge and discharge capacities are 98.6 and 93 mAh/g. The capacity retention of 99% can be achieved after 10 cycles. The electrode shows good cycle performance and moderate rate performance. When it is tested as an anode in a voltage range of 1.0–3.0 V vs. Na+/Na, the initial reversible capacity is 66.3 mAh/g and the capacity of 59 mAh/g can be maintained after 50 cycles. These preliminary results indicate that Na3V2(PO4)3/C is a new promising material for sodium ion batteries. Keywords: Na3V2(PO4)3, NASICON structure, Carbon coating, Sodium-ion batteries, Cathode, Anode

A uniform and thin amorphous layer of a C-N compound was coated on porous Li(4)Ti(5)O(12) by pyrolysis of urea on its surface at a rather low temperature of 400 °C in an Ar atmosphere. Such a C-N coating layer greatly improved the electrochemical performance of Li(4)Ti(5)O(12). After coating, Li(4)Ti(5)O(12) showed good rate and excellent cycling performance. Reversible capacities for the coated sample of 134 and 105 mAh g(-1) were obtained at current rates of 5C and 10C, respectively, in the voltage range of 1-2.2 V, which is approximately two and five times higher than those of pristine Li(4)Ti(5)O(12) at the same current rates. Excellent capacity retention of 95.8 % was achieved for the coated sample after 2000 cycles in a half cell at a 2C rate.

The Sb-doped ZnO (ZnO:Sb) and undoped ZnO films with wurtzite structure and (0 0 2) preferred orientation were deposited on Si(1 0 0) substrate at 550 ◦ C. It is deduced from XRD and XPS measurements that the Sb in the as-grown ZnO:Sb has high oxidation state and dopes in the form of oxygen-rich Sb–O clusters, which results in a large inner stress and a great increase of the c-axis lattice constant. After annealing at 750 ◦C under vacuum, the c-axis lattice constant of the ZnO:Sb decreases sharply to near the value of ZnO bulk, the electrical properties change from n-type to p-type and the PL intensity ratio of the visible to ultraviolet emission band goes down greatly, as the Sb content increases from 0 to 2.1 at.%. EDS and XRD measurements indicate that some of Sb dopants escape from the ZnO:Sb films and the oxygen-rich Sb-O clusters vanished after the annealing process. The effect of the change in Sb doping behavior on crystal structure, conductivity and PL is discussed in detail.

Crossed molecular beam experiments and accurate quantum scattering calculations have been carried out for the polyatomic H + CD 4 → HD + CD 3 reaction. Unprecedented agreement has been achieved between theory and experiments on the energy dependence of the integral cross section in a wide collision energy region that first rises and then falls considerably as the collision energy increases far over the reaction barrier for this simple hydrogen abstraction reaction. Detailed theoretical analysis shows that at collision energies far above the barrier the incoming H-atom moves so quickly that the heavier D-atom on CD 4 cannot concertedly follow it to form the HD product, resulting in the decline of reactivity with the increase of collision energy. We propose that this is also the very mechanism, operating in many abstraction reactions, which causes the differential cross section in the backward direction to decrease substantially or even vanish at collision energies far above the barrier height.

B–N codoped ZnO (ZnO:(B,N)) films were grown on quartz substrate by radio-frequency (rf) magnetron sputtering. The influence of post-annealing ambient on electrical and optical properties of ZnO:(B,N) films were investigated using Hall and Photoluminescence (PL) measurement, respectively. Electrical properties studies indicate that both post-annealing ZnO:(B,N) showed p- type conduction. However, compared with ZnO:(B,N) annealed in oxygen, the ZnO:(B,N) annealed in vacuum have low resistivity and high concentration. The PL spectra indicate that two new emission bands located at 3.303 and 3.208 eV originate from the recombination of A 0 X and FA related to N acceptor for the annealed p -ZnO:(B,N) in vacuum, but of A 0 X, FA related to Zn vacancy for the annealed p -ZnO:(B,N) in oxygen. The mechanism of influence of post-annealing on the electrical and optical properties of the ZnO:(B,N) film is discussed in this work.

A series of ZnO 1− x S x alloy films (0 ≤ x ≤ 1) were grown on quartz substrates by radio-frequency (rf) magnetron sputtering of ZnS ceramic target, using oxygen and argon as working gas. X-ray diffraction measurement shows that the ZnO 1− x S x films have wurtzite structure with (0 0 2) preferential orientation in O-rich side (0 ≤ x ≤ 0.23) and zinc blende structure with (1 1 1) preferential orientation in S-rich side (0.77 ≤ x ≤ 1). However, when the S content is in the range of 0.23 x 1− x S x film consists of two phases of wurtzite and zinc blende or amorphous ZnO 1− x S x phase. The band gap energy of the films shows non-linear dependence on the S content, with an optical bowing parameter of about 2.9 eV. The photoluminescence (PL) measurement reveals that the PL spectrum of the wurtzite ZnO 1− x S x is dominated by visible band and its PL intensity and intensity ratio of UV to visible band decrease greatly compared with undoped ZnO. All as-grown ZnO 1− x S x films behave insulating, but show n-type conductivity for w-ZnO 1− x S x and maintain insulating properties for β-ZnO 1− x S x after annealed. Mechanisms of effects of S on optical and electrical properties of the ZnO 1− x S x alloy are discussed in the present work.

Currently, sulfur encapsulation in high surface area, nanoporous conducting carbon is the most widely studied approach to improve the cycling stability of Li-S batteries. However, the relatively large amount of high surface area carbon results in two fundamental problems with this approach. First, a large amount of electrolyte volume to sulfur (E/S) ratio (typically > 20 mlE/gs) is needed to fully wet the porous sulfur cathode. Second, the large amount use of high surface area carbon greatly decreases the overall energy density in the system, especially for volumetric energy density, and makes it difficult to compete with other battery technologies. Here, we found the E/S ratio plays a critical role in the cycling stability of Li-S batteries. Owing to the insulating nature of S/Li2S, lowering E/S ratio increases the charge carrier transfer resistance on the interface, causing poor rechargeability and sustainability of sulfur cathode. An ammonium-based electrolyte additive is identified to effectively address the passivation issue of Li2S under low E/S ratio. To further solve the critical passivation issue of cathode especially under lean electrolyte condition, we proposed a new approach that does not depend on the conventional sulfur encapsulation with high surface area carbon was proposed to reduce electrolyte absorption. The new approach generates a large spherical porous agglomerated particles with self-sustaining structures to avoid cathode passivation, leading ~100% sulfur utilization with good cycling (Nature Energy 2, 813, 2017).

Zn–O–Se alloy films were grown on quartz substrate by radio-frequency (rf)-magnetron sputtering ZnSe single crystal target, with high pure Ar and O2 as working gas. X-ray diffraction and transmission electron microscopy characterizations indicate that the films are amorphous state. Energy disperse spectroscopy and X-ray photoelectron spectroscopy measurements verify the amorphous Zn–O–Se alloy was Se doped ZnO2 (Zn1−xSexO2), in which both Zn and Se atoms are bound with O atom. Absorption spectra exhibit that the optical band gap of Zn1−xSexO2 films are 4–5 eV. After annealing at 673 K in Ar ambient for 15 min, Zn1−xSexO2 film was decomposed to ZnO and SeO2, and SeO2 sublimed while annealed. The band gap energy decreased to the 3.2 eV, which is similar to the value of ZnO film directly deposited on quartz substrate. Room-temperature photoluminescence spectrum of the film after annealed shows NBE emission at 3.26 eV.

Reducing the electrolyte amount is critical for the high specific energy of lithium–sulfur (Li–S) batteries in practice. The reduced electrolyte condition (a so-called “lean electrolyte”) raises a complex situation for sulfur redox reactions since the reactions rely on the electrolyte mediation. The insulating nature of discharge product Li2S and its uncontrollable accumulation (passivation) at the cathode interface is one of the major challenges for stable cycling of a Li–S battery under lean electrolyte condition. In this study, it is presented that the NH4TFSI additive in electrolyte solution greatly alleviates the passivation issue in Li–S batteries under lean electrolyte conditions. The ammonium additive enhances the dissociation of Li2S and largely reduces the insoluble and large Li2S particles in the sulfur cathodes, which facilitate the reversible and sustainable redox reactions of sulfur. Therefore, the cycle life of Li–S batteries under lean electrolyte conditions is significantly improved. In addition, it is found that the morphology of Li anodes is dependent on the cathode structures. An ammonium additive enables homogeneous surface of cathode and Li anode and extended cycle life.

(2 + 1) resonance-enhanced multiphoton ionization (REMPI) detection of methyl radicals, in particular that via the intermediate 3p Rydberg states, has shown to be a powerful method and thus enjoyed a wide range of applications. Methyl has six vibrational modes. Among them—including partially and fully deuterated isotopologs—four out of twenty vibrational frequencies in the intermediate 3p states have so far eluded direct spectroscopic determination. Here, by exploiting the imaging spectroscopy approach to a few judiciously selected chemical reactions, the four long-sought REMPI bands—CHD2(611), CH2D(311), CH2D(511), and CH2D(611)—are discovered, which complete the REMPI identification for probing any vibrational mode of excitation of methyl radical and its isotopologs. These results, in conjunction with those previously reported yet scattered in the literature, are summarized here for ready reference, which should provide all necessary information for further spectral assignments and future studies of chemical dynamics using this versatile REMPI scheme.

The dynamics of the F + SiH(4) --HF + SiH(3) reaction has been studied using the crossed molecular beam technique with slice imaging at collision energies from 1.25 to 8.17 kcal/mol. The product silyl radical, SiH(3)(v(2) = 0-5), was detected using the (2 + 1) resonance enhanced multiphoton ionization technique. The product velocity distributions and angular distributions of this reaction were obtained from the recorded images. Experimental results show that the silyl radical product is mainly forward scattered relative to the silane beam direction, and the majority of the available energy was partitioned into the vibration of the HF product. The state-to-state correlation between the two reaction products, SiH(3) and HF, was also determined. In addition, we found that the reaction cross section goes down as the collision energy increases. From these results, we conclude that the F + SiH(4) --HF + SiH(3) reaction proceeds through a direct abstraction mechanism with little or no reaction barrier.

The unstable interface of lithium metal in high energy density Li sulfur (Li-S) batteries raises concerns of poor cycling, low efficiency and safety issues, which may be addressed by using intercalation types of anode. Herein, a new prototype of Li-ion sulfur battery with high performance has been demonstrated by coupling a graphite anode with a sulfur cathode (2 mA h cm(-2)) after successfully addressing the interface issue of graphite in an ether based electrolyte.

The effect of the rotational excitations of CHD3(v1 = 1, |J,K⟩) in reaction with the Cl atom was investigated in a crossed-beam, product-imaging experiment over the collisional energy (Ec) range 1-6 kcal mol(-1). It was found that the initial J- and K-selections affect only the total reactivity, not the more detailed product-state and angular distributions-a surprising result that defies conventional wisdom. Although the higher reactivity with increasing J states could be understood as a result of a wider range of attack angles near the barrier, the observed K-propensity of σ|J0⟩ < σ|JJ⟩ for J = 1 at Ec < 2 kcal mol(-1), opposite to that reported previously at higher Ec's, is perplexing and yet to be explained.

A fundamental understanding of electrochemical reaction pathways is critical to improving the performance of Li-S batteries, but few techniques can be used to directly identify and quantify the reaction species during disharge/charge cycling processes in real time. Here, an in situ (7)Li NMR technique employing a specially designed cylindrical microbattery was used to probe the transient electrochemical and chemical reactions occurring during the cycling of a Li-S system. In situ NMR provides real time, semiquantitative information related to the temporal evolution of lithium polysulfide allotropes during both discharge/charge processes. This technique uniquely reveals that the polysulfide redox reactions involve charged free radicals as intermediate species that are difficult to detect in ex situ NMR studies. Additionally, it also uncovers vital information about the (7)Li chemical environments during the electrochemical and parasitic reactions on the Li metal anode. These new molecular-level insights about transient species and the associated anode failure mechanism are crucial to delineating effective strategies to accelerate the development of Li-S battery technologies.