Synthesis and Electrochemical Performance of Electrostatic Self-Assembled Nano-Silicon@N-Doped Reduced Graphene Oxide/Carbon Nanofibers Composite as Anode Material for Lithium-Ion Batteries.

Silicon-carbon nanocomposite materials are widely adopted in the anode of lithium-ion batteries (LIB). However, the lithium ion (Li+) transportation is hampered due to the significant accumulation of silicon nanoparticles (Si) and the change in their volume, which leads to decreased battery performance. In an attempt to optimize the electrode structure, we report on a self-assembly synthesis of silicon nanoparticles@nitrogen-doped reduced graphene oxide/carbon nanofiber (Si@N-doped rGO/CNF) composites as potential high-performance anodes for LIB through electrostatic attraction. A large number of vacancies or defects on the graphite plane are generated by N atoms, thus providing transmission channels for Li+ and improving the conductivity of the electrode. CNF can maintain the stability of the electrode structure and prevent Si from falling off the electrode. The three-dimensional composite structure of Si, N-doped rGO, and CNF can effectively buffer the volume changes of Si, form a stable solid electrolyte interface (SEI), and shorten the transmission distance of Li+ and the electrons, while also providing high conductivity and mechanical stability to the electrode. The Si@N-doped rGO/CNF electrode outperforms the Si@N-doped rGO and Si/rGO/CNF electrodes in cycle performance and rate capability, with a reversible specific capacity reaching 1276.8 mAh/g after 100 cycles and a Coulomb efficiency of 99%.

Thermoelectrochemical cells based on Li+/Li redox couples in LiFSI glyme electrolytes.

Thermoelectrochemical cells (TECs) provide conspicuous advantages, including a high Seebeck coefficient (Se), design flexibility, and low cost compared with conventional thermoelectric devices. Here, we investigated TECs employing Li metal electrodes (Li-TECs) and a series of glyme (CH3O[CH2CH2O]nCH3, n = 1-4, nG) solvents with 0.5-3.0 M lithium-imide salts (lithium bis [fluorosulfonyl]imide, LiFSI, and lithium bis[trifluoromethane sulfonyl]imide, LiTFSI). The Se value and power performance of Li-TECs markedly depend on the nature of glyme solvents and Li salt concentration. The dependency of Se on the solvation structure of the Li-ions is examined via Raman measurements, and the internal resistance of Li-TECs is analyzed using electrochemical impedance spectroscopy. Notably, a Li-TEC with 1.0 M LiFSI 1G displays about two times higher power density and about eight times higher conversion efficiency than a conventional Cu-TEC utilizing aqueous electrolytes, which is ascribed to the high Se value and low thermal conductivity of the former. In addition, for a Li-TEC with 1.0 M LiFSI 1G, the low-temperature performance is examined to assess its practical feasibility.

Synthesis and Characterization of Silicon/Reduced Graphene Oxide Composites as Anodes for Lithium Secondary Batteries.

Silicon (Si) is one of the most attractive anode materials for lithium secondary batteries because of its large theoretical capacity, high safety, low cost and environmental benignity. However, Si-based anode material needs to overcome the structural change of the solid-electrolyte interphase due to the large volume change during cycling. To resolve these problems of composites by exploiting the superior conductivity, large specific surface area and flexibility of graphene, we have synthesized reduced graphene oxide (rGO)/Si composite electrode via a simple dip-coating method. Nickel foam is used as a current collector and template for the electrode fabrication. At 0.03 wt%, Si concentration, the rGO/Si composite anode presented the excellent cycle performance with large reversible capacity (778 mAh g-1 after 100 cycles). The characteristics of the rGO/Si composites were analyzed by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Raman and X-ray photoelectron spectroscopy (XPS). The improved anode performance of the rGO/Si composite anode is ascribed to the rGO serving as a buffer layer, thereby preventing the volume expansion of Si nanoparticles, and provide facile electron pathways.

Unraveling the Magnesium-Ion Intercalation Mechanism in Vanadium Pentoxide in a Wet Organic Electrolyte by Structural Determination.

Magnesium batteries have received attention as a type of post-lithium-ion battery because of their potential advantages in cost and capacity. Among the host candidates for magnesium batteries, orthorhombic α-V2O5 is one of the most studied materials, and it shows a reversible magnesium intercalation with a high capacity especially in a wet organic electrolyte. Studies by several groups during the last two decades have demonstrated that water plays some important roles in getting higher capacity. Very recently, proton intercalation was evidenced mainly using nuclear resonance spectroscopy. Nonetheless, the chemical species inserted into the host structure during the reduction reaction are still unclear (i.e., Mg(H2O)n2+, Mg(solvent, H2O)n2+, H+, H3O+, H2O, or any combination of these). To characterize the intercalated phase, the crystal structure of the magnesium-inserted phase of α-V2O5, electrochemically reduced in 0.5 M Mg(ClO4)2 + 2.0 M H2O in acetonitrile, was solved for the first time by the ab initio method using powder synchrotron X-ray diffraction data. The structure was tripled along the b-axis from that of the pristine V2O5 structure. No appreciable densities of elements were observed other than vanadium and oxygen atoms in the electron density maps, suggesting that the inserted species have very low occupancies in the three large cavity sites of the structure. Examination of the interatomic distances around the cavity sites suggested that H2O, H3O+, or solvated magnesium ions are too big for the cavities, leading us to confirm that the intercalated species are single Mg2+ ions or protons. The general formula of magnesium-inserted V2O5 is Mg0.17HxV2O5, (0.66 ≤ x ≤ 1.16). Finally, density functional theory calculations were carried out to locate the most plausible atomic sites of the magnesium and protons, enabling us to complete the structure modeling. This work provides an explicit answer to the question about Mg intercalation into α-V2O5.

Lithium ion solvation by ethylene carbonates in lithium-ion battery electrolytes, revisited by density functional theory with the hybrid solvation model and free energy correction in solution.

Complex formation between lithium (Li(+)) ions and electrolyte molecules would affect the ionic conductivity through the electrolyte in lithium-ion batteries (LIBs). We hence revisit the solvation number of Li(+) in the most commonly used ethylene carbonate (EC) electrolyte. The solvation number n of Li(+)(EC)n in the first solvation shell of Li(+) is estimated on the basis of the free energy calculated by the density functional theory combined with a hybrid solvation model where the explicit solvation shell of Li(+) is immersed in a free volume of an implicit bulk solvent. This new hybrid solvation (implicit and explicit) model predicts the most probable solvation number (n = 4) and solvation free energy (-91.3 kcal mol(-1)) of Li(+) in a good agreement with those predicted by calculations employing simpler solvation models (either implicit or explicit). The desolvation (n = 2) of Li(0)(EC)n upon reduction near anodes is also well described with this new hybrid model.

Synthesis and Evaluation of New Generation Cross-Bridged Bifunctional Chelator for (64)Cu Radiotracers.

Bifunctional chelators have been successfully used to construct (64)Cu-labeled radiopharmaceuticals. Previously reported chelators with cross-bridged cyclam backbones have various essential features such as high stability of the copper(II) complex, high efficiency of radiolabeling at room temperature, and good biological inertness of the radiolabeled complex, along with rapid body clearance. Here, we report a new generation propylene-cross-bridged chelator with hybrid acetate/phosphonate pendant groups (PCB-TE1A1P) developed with the aim of combining these key properties in a single chelator. The PCB-TE1A1P was synthesized from cyclam with good overall yield. The Cu(II) complex of our chelator showed good robustness in kinetic stability evaluation experiments, such as acidic decomplexation and cyclic voltammetry studies. The Cu(II) complex of PCB-TE1A1P remained intact under highly acidic conditions (12 M HCl, 90 °C) for 8 d and showed quasi-reversible reduction/oxidation peaks at -0.77 V in electrochemical studies. PCB-TE1A1P was successfully radiolabeled with (64)Cu ions in an acetate buffer at 60 °C within 60 min. The electrophoresis study revealed that the (64)Cu-PCB-TE1A1P complex has net negative charge in aqueous solution. The biodistribution and in vivo stability study profiles of (64)Cu-PCB-TE1A1P indicated that the radioactive complex was stable under physiological conditions and cleared rapidly from the body. A whole body positron emission tomography (PET) imaging study further confirmed high in vivo stability and fast clearance of the complex in mouse models. In conclusion, PCB-TE1A1P has good potential as a bifunctional chelator for (64)Cu-based radiopharmaceuticals, especially those involving peptides.

Low Solvating Power of Acetonitrile Facilitates Ion Conduction: A Solvation-Conductivity Riddle.

Acetonitrile (AN) electrolyte solutions display uniquely high ionic conductivities, of which the rationale remains a long-standing puzzle. This research delves into the solution species and ion conduction behavior of 0.1 and 3.0 M LiTFSI AN and propylene carbonate (PC) solutions via Raman and dielectric relaxation spectroscopies. Notably, LiTFSI-AN contains a higher fraction of free solvent uncoordinated to Li ions than LiTFSI-PC, resulting in a lower viscosity of LiTFSI-AN and facilitating a higher level of ion conduction. The abundant free solvent in LiTFSI-AN is attributed to the lower Li-solvation power of AN, but despite this lower Li-solvation power, LiTFSI-AN exhibits a level of salt dissociation comparable to that of LiTFSI-PC, which is found to be enabled by TFSI anions loosely bound to Li ions. This work challenges the conventional notion that high solvating power is a prerequisite for high-conductivity solvents, suggesting an avenue to explore optimal solvents for high-power energy storage devices.

Thermal stability analysis of nitrile additives in LiFSI for lithium-ion batteries: An accelerating rate calorimetry study.

Although lithium-ion batteries (LIBs) are extensively used as secondary storage energy devices, they also pose a significant fire and explosion hazard. Subsequently, thermal stability studies for LiPF6- and LiFSI-type electrolytes have been conducted extensively. However, the thermal characteristics of these electrolytes with thermally stable additives in a full cell assembly have yet to be explored. This study presents a comprehensive accelerating rate calorimetry (ARC) study. First, 1.2-Ah cells were prepared using a control commercial LiPF6 electrolyte and LiFSI with a specific succinonitrile additive and ethyl-methyl carbonate as a thermally stable electrolyte additive. The kinetic parameters involved in heat generation and their effects on the thermal properties of the ARC module were analyzed from the heat-wait-seek (HWS), self-heating (SH), and thermal runaway (TR) stages. The results indicate that the addition of a succinonitrile additive to the LiFSI electrolyte lowers the decomposition temperatures of the solid electrolyte interface (SEI) owing to polymerization with Li at the anode, while simultaneously increasing the activation energy of reaction temperatures at SEI between the separator and the electrolyte. The maximum thermal-runaway temperature decreased from 417 °C (ΔH = 5.26 kJ) (LiPF6) to 285 °C (ΔH = 2.068 kJ) (LiFSI + succinonitrile). This study provides key insights to the thermal characteristics of LiPF6 and LiFSI during the self-heating and thermal runaway stages and indicates a practical method for achieving thermally stable LIBs.

Long-life potassium metal batteries enabled by anion-derived solid electrolyte interphase using concentrated ionic liquid electrolytes.

Potassium metal batteries (PMBs) show great potential as next-generation energy storage systems yet face challenges such as the dendritic growth of the potassium anode, leading to issues with cycle life and safety. This study reports a potassium salt-concentrated ionic liquid electrolyte (PCIL) consisting of potassium bis(fluorosulfonyl)imide (KFSI) and 1-methyl-1-propyl pyrrolidinium bis(fluorosulfonyl)imide (Pyr13FSI) to achieve long-life and, safe PMBs. PCIL presents several advantages including outstanding oxidation stability (≈5.2 V), decent ionic conductivity (4.0 mS cm-1 at 25 °C), and negligible flammability. Moreover, PCIL promotes the development of anion-derived solid-electrolyte interphase (SEI) with high inorganic content. This not only hinders the growth of potassium dendrites but also facilitates facile interfacial charge transfer kinetics. Benefiting from these advantages, PMBs (K||KVPO4F) employing PCIL exhibit remarkable cycle performances at both ambient and elevated temperatures (capacity retention after 300 cycles: 74.8% at 25 °C and 82.9% at 45 °C), surpassing the performance of conventional carbonate (1 M KPF6 EC/PC) and dilute potassium ionic liquid electrolyte (PIL). This work demonstrates the tangible capability of PCIL in realizing practical PMBs.

Water-Ion Interaction Determines the Mobility of Ions in Highly Concentrated Aqueous Electrolytes.

Solvation engineering plays a critical role in tailoring the performance of batteries, particularly through the use of highly concentrated electrolytes, which offer heterogeneous solvation structures of mobile ions with distinct electrochemical properties. In this study, we employed spectroscopic techniques and molecular dynamics simulations to investigate mixed-cation (Li+/K+) acetate aqueous electrolytes. Our research unravels the pivotal role of water in facilitating ion transport within a highly viscous medium. Notably, Li+ cations primarily form ion aggregates, predominantly interacting with acetate anions, while K+ cations emerge as the principal charge carriers, which is attributed to their strong interaction with water molecules. Intriguingly, even at a concentration as high as 40 m, a substantial amount of water molecules persistently engages in hydrogen bonding with one another, creating mobile regions rich in K+ ions. Our observations of a redshift of the OH stretching band of water suggest that the strength of the hydrogen bond alone cannot account for the expansion of the electrochemical stability window. These findings offer valuable insights into the cation transfer mechanism, shedding light on the contribution of water-bound cations to both the ion conductivity and the electrochemical stability window of aqueous electrolytes for rechargeable batteries. Our comprehensive molecular-level understanding of the interplay between cations and water provides a foundation for future advances in solvation engineering, leading to the development of high-performance batteries with improved energy storage and safety profiles.

New bifunctional chelator for 64Cu-immuno-positron emission tomography.

A new tetraazamacrocyclic bifunctional chelator, TE2A-Bn-NCS, was synthesized in high overall yield from cyclam. An extra functional group (NCS) was introduced to the N-atom of TE2A for specific conjugation with antibody. The Cu complex of TE2A-Bn-NCS showed high kinetic stability in acidic decomplexation and cyclic voltammetry studies. X-ray structure determination of the Cu-TE2A-Bn-NH2 complex confirmed octahedral geometry, in which copper atom is strongly coordinated by four macrocyclic nitrogens in equatorial positions and two carboxylate oxygen atoms occupy the elongated axial positions. Trastuzumab was conjugated with TE2A-Bn-NCS and then radiolabeled with 64Cu quantitatively at room temperature within 10 min. Biodistribution studies showed that the 64Cu-labeled TE2A-Bn-NCS-trastuzumab conjugates maintain high stability in physiological conditions, and NIH3T6.7 tumors were clearly visualized up to 3 days by 64Cu-immuno-positron emission tomography imaging in animal models.

New macrobicyclic chelator for the development of ultrastable 64Cu-radiolabeled bioconjugate.

Ethylene cross-bridged cyclam with two acetate pendant arms, ECB-TE2A, is known to form the most kinetically stable (64)Cu complexes. However, its usefulness as a bifunctional chelator is limited because of its harsh radiolabeling conditions. Herein, we report new cross-bridged cyclam chelator for the development of ultrastable (64)Cu-radiolabeled bioconjugates. Propylene cross-bridged TE2A (PCB-TE2A) was successfully synthesized in an efficient way. The Cu(II) complex of PCB-TE2A exhibited much higher kinetic stability than ECB-TE2A in acid decomplexation studies, and also showed high resistance to reduction-mediated demetalation. Furthermore, the quantitative radiolabeling of PCB-TE2A with (64)Cu was achieved under milder conditions compared to ECB-TE2A. Biodistribution studies strongly indicate that the (64)Cu complexes of PCB-TE2A cleared out rapidly from the body with minimum decomplexation.

Effect of plasma treatments to graphite nanofibers supports on electrochemical behaviors of metal catalyst electrodes.

In the present work, we had studied the graphite nanofibers as catalyst supports after a plasma treatment for studying the effect of surface modification. By controlling the plasma intensity, a surface functional group concentration was changed. The nanoparticle size, loading efficiency, and catalytic activity were studied, after Pt-Ru deposition by a chemical reduction. Pt-Ru catalysts deposited on the plasma-treated GNFs showed the smaller size, 3.58 nm than the pristine GNFs. The catalyst loading contents were enhanced with plasma power and duration time increase, meaning an enhanced catalyst deposition efficiency. Accordingly, cyclic voltammetry result showed that the specific current density was increased proportionally till 200 W and then the value was decreased. Enhanced activity of 40 (mA mg(-1)-catalyst) was accomplished at 200 W and 180 sec duration time. Consequently, it was found that the improved electroactivity was originated from the change of size or morphology of catalysts by controlling the plasma intensity.

Synthesis of tin oxide nanoparticle film by cathodic electrodeposition.

Three-dimensional SnO2 nanoparticle films were deposited onto a copper substrate by cathodic electrodeposition in a nitric acid solution. A new formation mechanism for SnO2 films is proposed based on the oxidation of Sn2+ ion to Sn4+ ion by NO+ ion and the hydrolysis of Sn4+. The particle size of SnO2 was controlled by deposition potential. The SnO2 showed excellent charge capacity (729 mAh/g) at a 0.2 C rate and high rate capability (460 mAh/g) at a 5 C rate.

Three-dimensional network of nitrogen-doped carbon matrix-encapsulated Si nanoparticles/carbon nanofibers hybrids for lithium-ion battery anodes with excellent capability.

Three-dimensionally structured silicon (Si)-carbon (C) nanocomposites have great potential as anodes in lithium-ion batteries (LIBs). Here, we report a Nitrogen-doped graphene/carbon-encapsulated Si nanoparticle/carbon nanofiber composite (NG/C@Si/CNF) prepared by methods of surface modification, electrostatic self-assembly, cross-linking with heat treatment, and further carbonization as a potential high-performance anode for LIBs. The N-doped C matrix wrapped around Si nanoparticles improved the electrical conductivity of the composites and buffered the volume change of Si nanoparticles during lithiation/delithiation. Uniformly dispersed CNF in composites acted as conductive networks for the fast transport of ions and electrons. The entire tightly connected organic material of NG/C@Si and CNF prevented the crushing and shedding of particles and maintained the integrity of the electrode structure. The NG/C@Si/CNF composite exhibited better rate capability and cycling performance compared with the other electrode materials. After 100 cycles, the electrode maintained a high reversible specific capacity of 1371.4 mAh/g.

Effects of a Sodium Phosphate Electrolyte Additive on Elevated Temperature Performance of Spinel Lithium Manganese Oxide Cathodes.

LiMn2O4 (LMO) spinel cathode materials suffer from severe degradation at elevated temperatures because of Mn dissolution. In this research, monobasic sodium phosphate (NaH2PO4, P2) is examined as an electrolyte additive to mitigate Mn dissolution; thus, the thermal stability of the LMO cathode material is improved. The P2 additive considerably improves the cyclability and storage performances of LMO/graphite and LMO/LMO symmetric cells at 60 °C. We explain that P2 suppresses the hydrofluoric acid content in the electrolyte and forms a protective cathode electrolyte interphase layer, which mitigates the Mn dissolution behavior of the LMO cathode material. Considering its beneficial role, the P2 additive is a useful additive for spinel LMO cathodes that suffer from severe Mn dissolution.

Characteristics and electrochemical performances of silicon/carbon nanofiber/graphene composite films as anode materials for binder-free lithium-ion batteries.

We report the interfacial study of a silicon/carbon nanofiber/graphene composite as a potentially high-performance anode for rechargeable lithium-ion batteries (LIBs). Silicon nanoparticle (Si)/carbon nanofiber (CNF)/reduced graphene oxide (rGO) composite films were prepared by simple physical filtration and an environmentally-friendly thermal reduction treatment. The films were used as high-performance anode materials for self-supporting, binder-free LIBs. Reducing graphene oxide improves the electron conductivity and adjusts to the volume change during repeated charge/discharge processes. CNFs can help maintain the structural stability and prevent the peeling off of silicon nanoparticles from the electrodes. When the fabricated Si/CNF/rGO composites were used as anodes of LIBs, the initial specific capacity was measured to be 1894.54 mAh/g at a current density of 0.1 A/g. After 100 cycles, the reversible specific capacity was maintained at 964.68 mAh/g, and the coulombic efficiency could reach 93.8% at the same current density. The Si/CNF/rGO composite electrode exhibited a higher specific capacity and cycle stability than an Si/rGO composite electrode. The Si/CNF/rGO composite films can effectively accommodate and buffer changes in the volume of silicon nanoparticles, form a stable solid-electrolyte interface, improve the conductivity of the electrode, and provide a fast and efficient channel for electron and ion transport.

Why Does Dimethyl Carbonate Dissociate Li Salt Better Than Other Linear Carbonates? Critical Role of Polar Conformers.

The marked difference in the ionic conductivities of linear carbonate (LC) electrolyte solutions despite their similar viscosities and permittivities is a long-standing puzzle. This study unraveled the critical impact of solvent conformational isomerism on salt dissociation in 0.1-3.0 M LiPF6 dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) solutions using Raman and dielectric relaxation spectroscopies. The extent of salt dissociation in the LC solutions, which decreased in the order DMC > EMC > DEC, is closely related to the fraction of polar cis-trans LC conformers, as this conformer participates in Li ion solvation more readily than the nonpolar cis-cis counterpart. Our first-principles calculations corroborated that the cis-trans conformer facilitates free ion formation more than the cis-cis conformer, and the extent of this effect decreased in the order DMC > EMC > DEC. This study provides an avenue for the design of highly conductive electrolytes by exploiting the conformational isomerism of solvent molecules.

Electrolyte Additive Enabling Conditioning-Free Electrolytes for Magnesium Batteries.

Most electrolytes for rechargeable Mg batteries require time-consuming conditioning or precycling process to achieve a fully reversible Mg deposition/dissolution, which hinders the normal operation of Mg batteries. This study details a simple and effective method for eliminating this conditioning behavior using heptamethyldisilazane (HpMS) as an electrolyte additive. It was found that the HpMS additive greatly increases the current density and Coulombic efficiency of Mg deposition/dissolution from the initial cycles in various sulfone and glyme solutions containing MgCl2 or Mg(TFSI)2. The beneficial effect of HpMS was ascribed to its ability to scavenge trace water in the electrolytes and remove Mg(OH)2 and Mg(TFSI)2-decomposition products from the Mg surface. Considering its applicability for a wide range of Mg electrolytes, the use of HpMS is expected to accelerate the development of practical Mg batteries.

Mussel-Inspired Polydopamine Coating for Enhanced Thermal Stability and Rate Performance of Graphite Anodes in Li-Ion Batteries.

Despite two decades of commercial history, it remains very difficult to simultaneously achieve both high rate capability and thermal stability in the graphite anodes of Li-ion batteries because the stable solid electrolyte interphase (SEI) layer, which is essential for thermal stability, impedes facile Li(+) ion transport at the interface. Here, we resolve this longstanding challenge using a mussel-inspired polydopamine (PD) coating via a simple immersion process. The nanometer-thick PD coating layer allows the formation of an SEI layer on the coating surface without perturbing the intrinsic properties of the SEI layer of the graphite anodes. PD-coated graphite exhibits far better performances in cycling test at 60 °C and storage test at 90 °C than bare graphite. The PD-coated graphite also displays superior rate capability during both lithiation and delithiation. As evidenced by surface free energy analysis, the enhanced performance of the PD-coated graphite can be ascribed to the Lewis basicity of the PD, which scavenges harmful hydrofluoric acid and forms an intermediate triple-body complex among a Li(+) ion, solvent molecules, and the PD's basic site. The usefulness of the proposed PD coating can be expanded to various electrodes in rechargeable batteries that suffer from poor thermal stability and interfacial kinetics.