Quantification of the Carbon-Coating Effect on the Interfacial Behavior of Graphite Single Particles.

The effect of carbon coating on the interfacial charge transfer resistance of natural graphite (NG) was investigated by a single-particle measurement. The microscale carbon-coated natural graphite (NG@C) particles were synthesized by the simple wet-chemical mixing method using a phenolic resin as the carbon source. The electrochemical test results of NG@C using the conventional composite electrodes demonstrated desirable rate capability, cycle stability, and enhanced kinetic property. Moreover, the improvements in the composite electrodes were confirmed with the electrochemical parameters (i.e., charge transfer resistance, exchange current density, and solid phase diffusion coefficient) analyzed by a single-particle measurement. The surface carbon coating on the NG particles reduced the interfacial charge transfer resistance (Rct) and increased the exchange current density (i0). The Rct decreased from 81-101 (NG) to 49-67 Ω cm2 (NG@C), while i0 increased from 0.25-0.32 (NG) to 0.38-0.52 mA cm-2 (NG@C) after the coating process. The results suggested both electrochemically and quantitatively that the outer uniformly coated surface carbon layer on the graphite particles can improve the solid-liquid interface and other kinetic parameters, therefore enhancing the rate capabilities to obtain the high-power anode materials.

Untuned broadband spiral micro-coils achieve sensitive multi-nuclear NMR TX/RX from microfluidic samples.

The low frequency plateau in the frequency response of an untuned micro-resonator permits broadband radio-frequency reception, albeit at the expense of optimal signal-to-noise ratio for a particular nucleus. In this contribution we determine useful figures of merit for broadband micro-coils, and thereby explore the parametric design space towards acceptable simultaneous excitation and reception of a microfluidic sample over a wide frequency band ranging from 13C to 1H, i.e., 125-500 MHz in an 11.74 T magnet. The detector achieves 37% of the performance of a comparably sized, tuned and matched resonator, and a linewidth of 17 ppb using standard magnet shims. The use of broadband detectors circumvents numerous difficulties introduced by multi-resonant RF detector circuits, including sample loading effects on matching, channel isolation, and field distortion.

Ceramic-Based Flexible Sheet Electrolyte for Li Batteries.

The increasing demand for high-energy-density batteries stimulated the revival of research interest in Li-metal batteries. The garnet-type ceramic Li7La3Zr2O12 (LLZO) is one of the few solid-state fast-ion conductors that are stable against Li metal. However, the densification of LLZO powders usually requires high sintering temperatures (e.g., 1200 °C), which likely result in Li loss and various side reactions. From an engineering point of view, high-temperature sintering of thin LLZO electrolytes (brittle) at a large scale is difficult. Moreover, the high interfacial resistance between the solid LLZO electrolytes and electrodes is a notorious problem. Here, we report a practical synthesis of a flexible composite Al-doped LLZO (Al-LLZO) sheet electrolyte (75 µm in thickness), which can be mass-produced at room temperature. This ceramic-based flexible sheet electrolyte enables Li-metal batteries to operate at both 60 and 30 °C, demonstrating its potential application for developing practical Li-metal batteries.

Magnesium Storage Performance and Mechanism of 2D-Ultrathin Nanosheet-Assembled Spinel MgIn2 S4 Cathode for High-Temperature Mg Batteries.

Magnesium batteries have the potential to be a next generation battery with large capability and high safety, owing to the high abundance, great volumetric energy density, and reversible dendrite-free capability of Mg anodes. However, the lack of a stable high-voltage electrolyte, and the sluggish Mg-ion diffusion in lattices and through interfaces limit the practical uses of Mg batteries. Herein, a spinel MgIn2 S4 microflower-like material assembled by 2D-ultrathin (≈5.0 nm) nanosheets is reported and first used as a cathode material for high-temperature Mg batteries with an ionic liquid electrolyte. The nonflammable ionic liquid electrolyte ensure the safety under high temperatures. As prepared MgIn2 S4 exhibits wide-temperature-range adaptability (50-150 °C), ultrahigh capacity (≈500 mAh g-1 under 1.2 V vs Mg/Mg2+ ), fast Mg2+ diffusibility (≈2.0 × 10-8 cm2 s-1 ), and excellent cyclability (without capacity decay after 450 cycles). These excellent electrochemical properties are due to the fast kinetics of magnesium by the 2D nanosheets spinel structure and safe high-temperature operation environment. From ex situ X-ray diffraction and transmission electron microscopy measurements, a conversion reaction of the Mg2+ storage mechanism is found. The excellent performance and superior security make it promising in high-temperature batteries for practical applications.

Phosphoric Acid Diethylmethylammonium Trifluoromethanesulfonate-Based Electrolytes for Nonhumidified Intermediate Temperature Fuel Cells.

The present study reports a new series of electrolytes for nonhumidified intermediate temperature fuel cells (IT-FCs). This series of new mixed electrolytes, composed of phosphoric acid (PA) and diethylmethylammonium trifluoromethanesulfonate ([dema][TfO]), was designed as nonhumidified IT-FC electrolytes. The mixed electrolytes show a higher thermal stability than pure PA, which is dehydrated at ITs. The thermal stability of the mixed electrolytes could be explained by the interaction between the triflate group in [dema][TfO] and PA, as indicated by Fourier transform infrared and proton nuclear magnetic resonance (1H NMR) spectroscopies. On the other hand, the ionic conductivity and proton transference number of the mixed electrolytes were similar to those of the pure PA. However, the oxygen reduction reaction (ORR) activity of a platinum catalyst is significantly enhanced in the mixed electrolytes, which was due to the several orders of magnitude increase in oxygen solubility by the addition of [dema][TfO] to PA. Specifically, for the equimolar fraction mixed electrolyte, the diffusion coefficient and the solubility of oxygen were ca. 1.47 × 10-5 cm2 s-1 and ca. 1.28 mmol dm-3 at 150 °C, respectively. The addition of [dema][TfO] to PA could significantly enhance the ORR activity. Therefore, the PA_[dema][TfO] mixed electrolyte can be one of the solutions to develop nonhumidified intermediate FC electrolytes.

Good Low-Temperature Properties of Nitrogen-Enriched Porous Carbon as Sulfur Hosts for High-Performance Li-S Batteries.

Despite the increased attention devoted to exploring cathode construction based on various nitrogen-enriched carbon scaffolds at room temperature, the low-temperature behaviors of Li-S cathodes have yet to be studied. Herein, we demonstrate the good low-temperature electrochemical performances of nitrogen-enriched carbon/sulfur composite cathodes. Electrochemical evaluation indicates that a reversible capacity of 368 mAh g(-1) (0.5 C) over 100 cycles is achieved at -20 °C. After returning to 25 °C, a capacity of 620 mAh g(-1) (0.5 C) is achieved over 350 cycles with a low-capacity attenuation rate (0.071% per cycle) and an initial capacity of 1151 mAh g(-1) (0.1C). This positive electrochemical property was speculated to result from the good surface chemistry of the various amine groups in the nitrogen-enriched carbon materials with enhanced polysulfide immobilization.

Nanoscale visualization of redox activity at lithium-ion battery cathodes.

Intercalation and deintercalation of lithium ions at electrode surfaces are central to the operation of lithium-ion batteries. Yet, on the most important composite cathode surfaces, this is a rather complex process involving spatially heterogeneous reactions that have proved difficult to resolve with existing techniques. Here we report a scanning electrochemical cell microscope based approach to define a mobile electrochemical cell that is used to quantitatively visualize electrochemical phenomena at the battery cathode material LiFePO4, with resolution of ~100 nm. The technique measures electrode topography and different electrochemical properties simultaneously, and the information can be combined with complementary microscopic techniques to reveal new perspectives on structure and activity. These electrodes exhibit highly spatially heterogeneous electrochemistry at the nanoscale, both within secondary particles and at individual primary nanoparticles, which is highly dependent on the local structure and composition.

First-principles density functional calculation of electrochemical stability of fast Li ion conducting garnet-type oxides.

The research and development of rechargeable all-ceramic lithium batteries are vital to realize their considerable advantages over existing commercial lithium ion batteries in terms of size, energy density, and safety. A key part of such effort is the development of solid-state electrolyte materials with high Li(+) conductivity and good electrochemical stability; lithium-containing oxides with a garnet-type structure are known to satisfy the requirements to achieve both features. Using first-principles density functional theory (DFT), we investigated the electrochemical stability of garnet-type Li(x)La(3)M(2)O(12) (M = Ti, Zr, Nb, Ta, Sb, Bi; x = 5 or 7) materials against Li metal. We found that the electrochemical stability of such materials depends on their composition and structure. The electrochemical stability against Li metal was improved when a cation M was chosen with a low effective nuclear charge, that is, with a high screening constant for an unoccupied orbital. In fact, both our computational and experimental results show that Li(7)La(3)Zr(2)O(12) and Li(5)La(3)Ta(2)O(12) are inert to Li metal. In addition, the linkage of MO(6) octahedra in the crystal structure affects the electrochemical stability. For example, perovskite-type La(1/3)TaO(3) was found, both experimentally and computationally, to react with Li metal owing to the corner-sharing MO(6) octahedral network of La(1/3)TaO(3), even though it has the same constituent elements as garnet-type Li(5)La(3)Ta(2)O(12) (which is inert to Li metal and features isolated TaO(6) octahedra).

Properties of composite proton-conducting membranes prepared from three-dimensionally ordered macroporous polyimide matrix and polyelectrolyte.

A new proton-conducting composite membrane has been prepared by use of a three-dimensionally ordered macroporous matrix of polyimide and a proton-conducting gel polymer; the resulting composite membrane exhibited very high conductivity of 1.7 x 10-1 S cm-1 at 60 degrees C under 90% relative humidity.

Effects of omega-functional groups on pH-dependent reductive desorption of alkanethiol self-assembled monolayers.

Self-assembled monolayers (SAMs) of alkanethiols having various terminal groups on their omega-positions were formed on a Au111 electrode, and their reductive desorption was studied by linear sweep voltammetry, focusing on effects of solution pH on the desorption behavior. The peak potentials (Ep) of cathodic waves representing reductive desorption were found to be reflected by the pKa value of the thiol group and were negatively shifted with an increase in pH of the electrolyte solution. The magnitude of the pH dependency of Ep was greatly influenced by the hydrophobicity of the terminal groups. In the cases of alkanethiol SAMs having pH-sensitive terminal groups such as carboxyl and amino groups, their basicity was estimated from bending points appearing in the pH titration profile of Ep. This method allows direct determination of not only the pKa value of the arrayed groups but also that of the groups dissolved in solution simultaneously. The pKa values of the arrayed carboxyl groups in SAMs were larger by ca. 3 pH units than their original ones, while those for amino groups were smaller by ca. 2 pH units.