Search

Introduction: Aspects of social relationships have variably been associated with suicidal ideation (SI) and suicide attempts (SAs). This study assessed whether social support and social distress measures have general factors versus measure‐specific factors that are associated with suicide risk. Methods: Adults (N = 455, 60.0% female), admitted to psychiatric inpatient units following a recent suicide attempt or active SI, completed assessments of social support (emotional support, instrumental support, friendship, perceived support from significant others, friends, family) and social distress (loneliness, perceived rejection, perceived burdensomeness, thwarted belongingness). Bifactor modeling examined general and specific factors of social support and distress in relation to SI (week prior to hospitalization, via the Beck Scale for SI) and SAs (past 30 days, via the Columbia Suicide Severity Rating Scale). Results: SI was significantly associated with the general social support (B = −1.51), the general social distress (B = 1.67), and the specific perceived burdensomeness (B = 1.57) factors. SAs were significantly associated with the specific Perceived Rejection (OR = 1.05) and Thwarted Belongingness (OR = 0.91) factors. Conclusion: General social support and social distress were associated with SI but not recent SAs. Specific social distress factors were also related to SI and SAs controlling for general social distress, suggesting areas for future interventions. [ABSTRACT FROM AUTHOR]

In this work, a Li-rich layered 0.5Li2MnO3.0.5LiMn1/3Ni1/3Co1/3O2 (LMNCO) pristine cathode material synthesized with a glycine-nitrate combustion method is further coated with silver. The effects of silver coating on the material structure and performance of the as-prepared cathode are systemically studied with X-ray diffraction (XRD), scanning electron microscope (SEM), galvanostatic charge/discharge, cyclic voltammetry (CV), and electrochemical impedance spectra (EIS). Material characterizations and electrochemical measurements show that the surface modification does not lead to the change of crystal lattice parameter and particle morphology. It is found that the rate capability and cyclability can be significantly improved, which could be attributed to the enhancement of electronic conductivity of the particle surface of the cathode. It has been found that the obtained silver-coated LMNCO cathode exhibits excellent electrochemical characteristics. For example, it can deliver a high initial discharge capacity of 290 mAh g−1 between 2.0 and 4.9 V at a rate of 0.05C at room temperature and a discharge capacity of 159 mAh g−1 at 1 C, 128 mAh g−1at 2 C, and 101 mAh g−1 even at 5 C. EIS result shows that Rsf and Rct values of LMNCO are bigger than those of silver-coated LMNCO cathode. [ABSTRACT FROM AUTHOR]

Chemical structures of lithium and tetrabutylammonium (TBA) salt solutions in N,N-dimethylacetamide (DMAc) and N,N-diethylacetamide (DEAc), two high Donor Number organic solvents, have been studied. In LiX salt solutions (where X = PF6-, CF3 SO3-, ClO4- and NO3-), solvation occurs when the Li+ bonds with the solvent's carbonyl group forming Li+[O=C(CH3)N(CH3)2]nX- ion pairs. Infrared and 13C-NMR spectra are consistent with the ion pair being solvent-separated when the anion is PF6-, ClO4- or NO3-, and a contact ion pair in the case of CF3SO3-. Chemical interactions between TBA+ and the solvents to form conducting solutions appeared to be dipolar in nature. Ionic conductivities of TBA+ and Li+ electrolytes were measured and correlated with their viscosities. In 0.1M TBAPF6/DMAc, the O2 solubility and diffusion coefficient (3.09 x 10-6 mol/cm-3 and 5.09 x 10-5 cm²s-1, respectively) measured using microelectrode technique are typical of values measured in several TBA+ solutions. Microelectrode voltammetry revealed steady-state limiting current behavior for oxygen reduction reactions (ORR) in TBAX/DMAc electrolytes indicating a reversible ORR process. Conversely, microelectrode current-voltage data for ORR in LiX/DMAc electrolytes revealed irreversible behavior mainly ascribed to the blockage of the electrode surface by insoluble ORR products. The ORR in DMAc correlated with its high Donor Number and the overall process conformed to the Hard-Soft Acid-Base theory. [ABSTRACT FROM AUTHOR]

The electrochemical activity of a Li-air battery cathode catalyst derived from the lithium rich layered-layered metal oxide of the formula 0.5Li2MnO3.0.5LiMn0.5Ni0.35Co0.15O2 is reported. The catalyst formed in-situ by electrochemically de-lithiating this metal oxide embedded in a high surface area carbon matrix behaved as a bifunctional catalyst for O2 reduction reaction (ORR) and O2 evolution reaction (OER) in a non-aqueous Li-O2 cell. Cyclic voltammetry (CV) in both half and full cells revealed enhanced OER and ORR catalytic activity by: i-) displaying a more positive potential shift during ORR, ii-) stabilizing the initial ORR product LiO2, and iii-) showing an additional potential step in the oxidation of the ORR products. In the CV of catalyzed cells, a reduction peak appeared before the main peroxide (O2- 2) formation peak suggesting that the catalyst stabilizes the superoxide (O- 2) formed prior to the formation of peroxide. Evidence for LiO2 as the initial discharge product was obtained from both the Raman spectrum and X-ray diffraction (XRD) pattern of Li-air cell cathodes after galvanostatic discharge to 2 V. Surface features for the discharged cathodes obtained from Field Emission Scanning Electron Microscope (FESEM) unveiled dissimilar morphologies for the discharge products from catalyzed and uncatalyzed cells, originating from different nucleation mechanisms. The catalyzed cells exhibited longer cycle life than uncatalyzed cells under similar cycling conditions. [ABSTRACT FROM AUTHOR]

We report the results of a comprehensive study of the relationship between electrochemical performance in Li cells and chemical composition of a series of Li rich layered metal oxides of the general formula xLi2MnO3 ⋅ (1-x)LiMn0.33Ni0.33Co0.33O2 in which x = 0,1, 0.2, 0,3, 0.5 or 0.7, synthesized using the same method. In order to identify the cathode material having the optimum Li cell performance we first varied the ratio between Li2MnO3 and LiM)2 segments of the composite oxides while maintaining the same metal ratio residing within their LiMO2 portions. The materials with the overall composition 0.5Li2MnO3 ⋅ 0.5LiMO2 containing 0.5 mole of Li2MnO3per mole of the composite metal oxide were found to be the optimum in terms of electrochemical performance. The electrochemical properties of these materials were further tuned by changing the relative amounts of Mn, Ni and Co in the LiMO2 segment to produce x Li2MnO3 ⋅ (1-x(LiMn0.50Ni0.35Co0.15O2 with enhanced capacities and rate capabilities. The rate capability of the lithium rich compound in which x = 0.3 was further increased by preparing electrodes with about 2 weight-percent multiwall carbon nanotube in the electrode. Lithium cells prepared with such electrodes were cycled at the 4C rate with little fade in capacity for over one hundred cycles. [ABSTRACT FROM AUTHOR]

The influence of lithium salts on O2 reduction reactions (ORR) in 1, 2-dimethoxyethane (DME) and tetraethylene glycol dimethyl ether (TEGDME) has been investigated. Microelectrode studies in a series of tetrabutylammonium salt (TBA salt)/DME-based electrolytes showed that O2 solubility and diffusion coefficient are not significantly affected by the electrolyte anion. The ORR voltammograms on microelectrodes in these electrolytes exhibited steady-state limiting current behavior. In contrast, peak-shaped voltammograms were observed in Li+-conducting electrolytes suggesting a reduction of the effective electrode area by passivating ORR products as well as migration-diffusion control of the reactants at the microelectrode. FT-IR spectra have revealed that Li+ ions are solvated to form solvent separated ion pairs of the type Li+(DME)nPF6- and Li+(TEGDME)PF6- in LiPF6-based electrolytes. On the other hand, the contact ion pairs (DME)mLi+(CF3SO3-) and(TEGDME) Li+(CF3SO3-) appear to form in LiS03CF3- containing electrolytes. In the LiS03CF3-based electrolytes the initial ORR product, superoxide (O2-), is stabilized in solution by forming [(DME)m-1( O2-) Li+(CF3SO3-) and [(TEGDME)(O2- ) Li+(CF3SO3-) complexes. These soluble superoxide complexes are able to diffuse away from the electrode surface reaction sites to the bulk electrolyte in the electrode pores where they decompose to form Li2O2. This explains the higher capacity obtained in Li/O2 cells utilizing LiCF3SO3/TEGDME electrolytes. [ABSTRACT FROM AUTHOR]

Non-aqueous electrolytes play a prominent role in the redox reactions of the oxygen electrode in the non-aqueous Li-air battery. In all electrolytes the initial O2 reduction reaction (ORR) product is superoxide, O2-, whose stability is determined by the Lewis acidity of the ion-pairing cations present in the medium as governed by the Hard Soft Acid Base (HSAB) theory. Our results suggest that depending on the basicity of the solvent as measured by its Donor Number (DN), the superoxide will be stabilized to varying lengths of time before transforming to O22- via a chemical or an electrochemical reaction. Organic solvents decrease the Lewis acidity of Li+ through the formation of solvates, Li+(solvent)n. As a result, high DN solvents such as dimethyl sulfoxide (DMSO), which decrease Li+ acidity more than low DN solvents, provide longer life-time for the soft base O2- by forming the ion pair, Li+(DMSO)n-O2-. In low DN solvents such as 1, 2-dimethoxy ethane (DME) and tetraethyleneglycol dimethyl ether (TEGDME), the LiO2 rapidly decomposes to the peroxide, Li2O2. As the ionic bond strength between the O2 reduction product and the conducting salt cation becomes stronger, its rechargeability becomes poorer. Solvent electron donor property affects ORR catalysis also. [ABSTRACT FROM AUTHOR]

The electrocatalysis of oxygen reduction reactions (ORR) in non-aqueous electrolytes is coupled to the ability of the solvents to modulate the Lewis acidity of Li+. This is accomplished through chemical interactions of Li+ with the solvent to form acid-base complexes of the general formula, Li(solvent)n+, which determine the relative stability of the ORR intermediates and the final products formed. In high Donor Number solvents such as dimethyl sulfoxide (DMSO), the ORR proceeds via an outer Helmholtz plane (OHP) reaction pathway, conforming to a homogeneous catalysis of the reaction, irrespective of the presence of a catalyst in the cathode. In low Donor Number solvents exemplified by tetraethylene glycol dimethyl ether (TEGDME) and CH3CN, catalysts such as cobalt phthalocyanine (CoPC), Pt and Au promote heterogeneous electrocatalysis at the inner Helmholtz plane (IHP) of the electrical double layer on the electrode. The catalysis in this case involve the adsorption of O2 as well as the ORR intermediates on the catalyst surface leading to lower activation energy of the reactions and increases in the discharge voltages of Li-air cells compared to uncatalyzed cells. The heterogeneous catalysis at the IHP may promote the full electrochemical reduction of O2 to O2-. [ABSTRACT FROM AUTHOR]

Here we report the fabrication of a carbon-nanotube (CNT) based lithium ion electrode architecture, consisting of alternating layers of multi-walled carbon nanotubes (MWNT) and lithium ion active material, to significantly increase the aerial power and energy density of lithium ion battery cathodes. The CNT-based architecture aims to address engineering limitations of nanoscale active materials such as poor packing density, electrolyte reactivity, and costly fabrication. The alternating layers create a highly porous and highly conductive scaffolding to enhance ionic and electronic transport pathways within the electrode. The results show that the presented CNT-based architecture yielded excellent rate capability and highly stable cycling of lithium manganese oxide (LiMn2O4) active materials and lithium (Li) rich layered (xLi2MnO3 · (1-x)LiMO2) materials. For LiMn2O4 materials, the CNT-based architecture demonstrates 14-20x higher aerial capacity over standard fabrication electrodes at discharge rates of 10C. For Li-rich layered materials, the CNT-based architecture demonstrates 70% higher aerial capacity over standard fabrication electrodes at discharge rates of C/2. Highly stable cycling for 100 cycles at 15C for LiMn2O4 and 500 cycles at 1C for Li-rich layered materials is also observed using the CNT-based architecture. The effect of the number of layers, layer thickness, and composition of the active material is investigated. [ABSTRACT FROM AUTHOR]

We demonstrate that a microelectrode can be used as a diagnostic tool to optimize the properties of electrolytes for non-aqueous Li-air batteries, and to elucidate the influence of ion-conducting salts on O2 reduction reaction mechanisms. Oxygen reduction/evolution reactions on carbon microelectrode have been studied in dimethyl sulfoxide-based electrolytes containing Li+ and tetrabutylammonium((C4H9)4N+) ions. Analysis of chronoamperometric current-time transients of the oxygen reduction reactions (ORR) in the series of tetrabutylammmonium (TBA) electrolytes, TBAPF6, TBAClO4, TBACF3SO3, TBAN(CF3SO2)2 in DMSO revealed that the anion of the salt exerts little influence on oxygen transport. Whereas steady-state ORR currents(sigmoidal-shaped) were observed in TBA-based electrolytes, peak-shaped current-voltage profiles were seen in the electrolytes containing their Li salt counterparts. The latter response results from the combined effects of the electrostatic repulsion of the superoxide intermediate as it is reduced further to peroxide (O22-) at low potentials, and the formation of passivation films at the electrode. Raman spectroscopic data confirmed the formation of Li2O2 and Li2O on the microelectrode surface at different reduction potentials in Li salt solutions. Out of the four lithium electrolytes, namely LiPF6, LiClO4, LiCF3SO3, or LiN(CF3SO2)2 in DMSO, the LiCF3SO3/DMSO solution revealed the most favorable ORR kinetics and the least passivation of the electrode by ORR products. [ABSTRACT FROM AUTHOR]

A new lithium rich composite positive electrode material of the composition 0.3Li2MnO3.0.7LiNi0.5Co0.5O2 (LLNC) was synthesized using the conventional co-precipitation method. Its crystal structure and electrochemistry in Li cells have been compared to that of the previously known material, 0.3Li2MnO3.0.7LiMn0.33Ni0.33Co0.33O2 (LLNMC). The removal of Mn from the LiMO2 (M = transition metal) segment of the composite cathode material allowed us to determine the location of the manganese oxide moiety in its structure that triggers the layered to spinel conversion during cycling. The new material resists the layered to spinel structural transformation under conditions in which LLNMC does. X-ray diffraction patterns revealed that both compounds, synthesized as approximately 300 nm crystals, have identical super lattice ordering attributed to Li2MnO3 existence. Using X-ray absorption spectroscopy we elucidated the oxidation states of the K edges of Ni and Mn in the two materials with respect to different charge and discharge states. The XAS data along with electrochemical results revealed that Mn atoms are not present in the LiMO2 structural segment of LLNC. Electrochemical cycling data from Li cells further revealed that the absence of Mn in the LiMO2 segment significantly improves the rate capabilities of LLNC with good capacity maintenance during long term cycling. Removing the Mn from the LiMO2 segment of lithium rich layered metal oxides appears to be a good strategy for improving the structural robustness and rate capabilities of these high capacity cathode materials for Li-ion batteries. [ABSTRACT FROM AUTHOR]

We have prepared the Li-rich layered NMC composite cathode material of the composition 0.3Li2MnO30.7LiMn0.33Ni0.33Co0.33O2, (NMC) with 5 wt% Na doping. The latter material with composition of 0.3Li2MnO3.0.7Li0.97Na0.03Mn0.33.33Ni0.33Co0.33O2, synthesized as 200-300 nm size particles, was compared to its counterpart without Na. The discharge rate capability of the Li-rich NMC was greatly improved at both room temperature and 50°C with the Na doping. The Na doped material exhibited significantly higher conductivity than its un-doped analog as evidenced by dc electronic conductivity data and impedance of Li cells. Charge/discharge cycling results of Li cells at 50°C indicated that the voltage decay of Li-rich NMC accompanied by a layer to spinel structural conversion was mitigated with Na doping. XRD analysis revealed that ionic exchange of Na occurs upon contact of the cathode material with the electrolyte and produces a volume expansion of the crystal lattice which triggers a favorable metal (probably Ni) migration to Li depleted regions during oxidation of Li2MnO3 in the first cycle. XANES data showed that Na doped NMC has better Ni reduction efficiency to provide higher rate capability. EXAFS data supported this conclusion by showing that in the case of Na doped NMC, the structure has larger crystal cage allowing for better metal migration into the Li depleted regions located in the layered unit cell of C2/m space group. XANES of Mn K-edge supported by pre-edge analysis also revealed that during charging of the electrode, the Na doped NMC was oxidized to a higher Mn valence state compared to its undoped counterpart. [ABSTRACT FROM AUTHOR]

The full reduction of O2 to Li2O is the ultimate chemistry desired for building a super high energy density Li-air battery. Most investigations to date have identified Li2O2 as the discharge product which limits the specific energy of the Li-air battery to 3500 Wh kg-1, about 67% of the theoretical value. Here, for the first time, we report the full reduction of O2 to Li2O in a Li-air cell using cobalt phthalocyanine catalyzed carbon cathodes. Details of the oxygen reduction reaction mechanism have been discerned through cyclic voltammetry experiments in half cells as well as analysis of discharged Li-air cell cathodes by means of X-ray absorption spectroscopy and X-ray diffraction. The catalyst lowers the activation energy for O2 reduction by forming a complex with superoxide, and enables the reduction of Li2O2 to Li2O. In addition, the catalyst is effective in lowering the gap between the discharge and charge voltage plateaus leading to an increase in the energy efficiency of the Li-air battery. The breakthrough in the discharge chemistry being reported could lead to the realization of the full potential of the Li-air battery. [ABSTRACT FROM AUTHOR]

Dimethyl Sulfoxide (DMSO) was evaluated as a practical solvent for the rechargeable lithium air battery. Redox characteristics of the dissolved oxygen and its reduction products in the presence of lithium hexafluorophosphate (LiPF6) supporting electrolyte were studied via cyclic, rotating disk (RDE) and ring-disk (RRDE) electrode voltammetry. The DMSO medium facilitates reversible reduction and oxidation processes in contrast to other solvent-based electrolytes studied. Galvanostatic discharge-charge cycling of the Li-O2 cells has shown characteristics of rechargeability expected from voltammetric studies. Multiple high-efficiency discharge- charge cycles are possible if the depth of discharge of the carbon cathode is limited to avoid excessive passivation by the discharge products. The discharge voltage of this Li-O2 cell is higher than cells assembled with other non-aqueous organic electrolytes, an attribute ascribed to the stability of superoxide (O2-), the one-electron reduction product of oxygen. [ABSTRACT FROM AUTHOR]

A new Fe-V mixed metal phosphate of the composition, Li2-xFe0.5(VO)0.5(PO4)F0.5, has been synthesized and characterized as a single phase Li insertion/extraction cathode material for rechargeable lithium batteries. Its tetragonal crystal structure revealed from X-ray diffraction and absorption spectral data exhibits little change with Li extraction and subsequent Li insertion. The charge/discharge cycling capacities obtained from Li cells is consistent with the structure. The presence of F in the material is essential to prepare a mixed metal phosphate with equal amounts of Fe and V in the crystal structure and is probably the key to our success in preparing a single-phase metal phosphate cathode material. [ABSTRACT FROM AUTHOR]

The redox behavior and kinetic parameters of five ferrocene derivatives were investigated in IM LiPF6 in 50:50 volume percent EC:EMC, a typical electrolyte used in lithium-ion batteries. Using cyclic voltammetry (CV) and rotating disk electrode voltammetry (ROE) techniques, the effect of electron donating and withdrawing substituents on each derivative was evaluated from the view point of the Hammett substituent constant. We found that electrochemical rate constants of the ferrocene derivatives can be related to the Hammett equation which gives an accurate approximation for predicting the oxidation potential of redox shuttles when changes are desired in their electron donating and electron withdrawing properties by means of functional group substitution. Our results show that the exchange current density and reaction rate for oxidation decrease as the electron withdrawing property of the substituent increases. It is also shown that electron donating and electron withdrawing property of a substituent affect the exchange current density and electrochemical oxidation reaction rate obeying a trend opposite to that of the Hammett substituent constants (σ). The correlations found here are expected to improve the ability to systematically design chemical overcharge protection reagents through judicious substitution of functional groups on redox shuttles. [ABSTRACT FROM AUTHOR]

The Li-ion battery positive electrode materials, α-LiVOPO4, β-LiVOPO4, and Li3V2(PO4)3 have been prepared as individual phases from a common precursor mixture by controlling the synthesis conditions. These phases result because of their distinct crystal symmetries and V oxidation states. The synthesis involves the decomposition of a precursor mixture prepared from NH4VO3, NH4H2PO4, LiF and hexanoic acid which when heat-treated under different conditions produced the three LiwVxOy(PO4)z products. The materials were characterized by means of elemental analysis, X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS) and Li cell data. The Li cycling performance and the accompanying structural effects on α- and β-LiVOPO4 were also studied under normal and deep discharge conditions using XAS to probe the local vanadium environment. XANES and EXAFS confirm reversible changes in the two structures when intercalation does not exceed 1Li/VOPO4. Deeper discharge revealed more disruption to both structures, including an additional 0.25 Å increase to the V=O bond length. A greater range in the VO6 symmetry of α-LiVOPO4 resulted in a more flexible accommodating host, in agreement with its improved low voltage performance compared to β-LiVOPO4. [ABSTRACT FROM AUTHOR]

A rechargeable Li-air cell utilizing an electrolyte composed of a solution of LiPF6 in tetraethylene glycol dimethyl ether, CH3O(CH2CH2O)4CH3 (TEGDME), and an uncatalyzed porous carbon electrode, investigated to elucidate the baseline Li-air battery chemistry, is reported. From the x-ray diffraction patterns of the discharged carbon electrodes, the discharge product of the cell was identified to be Li2O2 during normal discharge to 1.5 V. Discharging the cell to 1.0 V or below produces Li2O as well. The cell can be recharged without a catalyst in the carbon cathode, albeit at low depths of discharge. The high resistance of the discharged carbon cathode is a major impediment to recharging cells displaying a high specific capacity. The cell capacity decreases with continued cycling, which was found to be due to the poor cycling efficiency of the Li anode and the high resistance of the discharge products, which slowly accumulate in the porous electrode. [ABSTRACT FROM AUTHOR]

This paper describes a totally solid-state, rechargeable, long cycle life lithium-oxygen battery cell. The cell is comprised of a Li metal anode, a highly Li-ion conductive solid electrolyte membrane laminate fabricated from glass-ceramic (GC) and polymerceramic materials, and a solid-state composite air cathode prepared from high surface area carbon and ionically conducting GC powder. The cell exhibited excellent thermal stability and rechargeability in the 30-105°C temperature range. It was subjected to 40 charge-discharge cycles at current densities ranging from 0.05 to 0.25 mA/cm2. The reversible charge/discharge voltage profiles of the Li-O2 cell with low polarizations between the discharge and charge are remarkable for a displacement-type electrochemical cell reaction involving the reduction of oxygen to form lithium peroxide. The results represent a major contribution in the quest of an ultrahigh energy density electrochemical power source. We believe that the Li-02 cell, when fully developed, could exceed specific energies of 1000 Wh/kg in practical configurations. [ABSTRACT FROM AUTHOR]

Lithium intercalation into graphite was investigated using a graphite with a spheroidal particle morphology and propylene carbonate (PC)-based electrolytes containing LiPF6, NaPF6, or (C4H10)4NPF6 as the supporting electrolyte. The data from Li/C cells utilizing these electrolytes showed that reduction of PC on the graphite electrode occurs at about 0.9 V vs Li+/Li. The PC reduction potentials showed no dependence on the supporting electrolyte salt present in the electrolyte. Furthermore, there was no evidence of graphite exfoliation in PC electrolyte. This was supported by the observation that graphite electrodes retrieved from the Li/C cells, after PC reduction, and reassembled and tested with standard Li-ion battery electrolyte exhibited Li intercalation capacities identical to those exhibited by fresh graphite electrodes. The potentials at which PC is reduced are very similar to those previously found with graphite electrodes in which PC was reported to cointercalate into graphite as Li+(PC)n, leading to its exfoliation at about the same potentials as found in this study. The data presented here are useful for the systematic design and optimization of electrolytes based on organic carbonate solvents to tailor Li-ion battery performance. [ABSTRACT FROM AUTHOR]