Counterion Lewis Acidity Determines the Rate of Hexafluorophosphate Hydrolysis in Nonaqueous Battery Electrolytes.

The decomposition of LiPF in nonaqueous battery electrolytes is a well-studied, deleterious process that leads to hydrofluoric acid (HF) driven transition metal dissolution at the positive electrode and gas production (H) at the anode, often attributed to the inherent moisture sensitivity of the hexafluorophosphate anion. In this work, we use in situ nuclear magnetic resonance (NMR) spectroscopy to demonstrate that the rate of PF hydrolysis significantly decreases in Na and K systems, where the Lewis acidity of the cation dictates the rate of decomposition according to Li > Na > K. Despite the remarkable stability of Na and K electrolytes, we show that they are still susceptible to hydrolysis in the presence of protons, which can catalyze the breakdown of PF, indicating that these chemistries are not immune from decomposition when paired with solvent/cathode combinations that generate H at high voltage.

Steric stabilization of colloidal UiO-66 nanocrystals with oleylammonium octadecylphosphonate.

We report the synthesis and characterization of octahedral UiO-66 nanocrystals ( = 17-25 nm) terminated with amine, oleate, and octadecylphosphonate ligands. Acetate capped UiO-66 nanocrystals were dispersed in toluene using oleic acid and oleylamine. Ligand exchange with octadecylphosphonic acid produces ammonium octadecylphosphonate terminated nanocrystals with coverages of 2.

Light-Induced Living Polymer Networks with Adaptive Functional Properties.

The advent of covalent adaptable networks (CANs) through the incorporation of dynamic covalent bonds has led to unprecedented properties of macromolecular systems, which can be engineered at the molecular level. Among the various types of stimuli that can be used to trigger chemical changes within polymer networks, light stands out for its remote and spatiotemporal control under ambient conditions. However, most examples of photoactive CANs need to be transparent and they exhibit slow response, side reactions, and limited light penetration.

Correction to "Transition Metal Dissolution Mechanisms and Impacts on Electronic Conductivity in Composite LiNiMnO Cathode Films".

[This corrects the article DOI: 10.1021/acsmaterialsau.2c00060.

Transition Metal Dissolution Mechanisms and Impacts on Electronic Conductivity in Composite LiNiMnO Cathode Films.

The high-voltage LiNiMnO (LNMO) spinel cathode material offers high energy density storage capabilities without the use of costly Co that is prevalent in other Li-ion battery chemistries (e.g., LiNiMnCoO (NMC)).

Phase Transformations and Phase Segregation during Potassiation of Sn P Anodes.

K-ion batteries (KIBs) have the potential to offer a cheaper alternative to Li-ion batteries (LIBs) using widely abundant materials. Conversion/alloying anodes have high theoretical capacities in KIBs, but it is believed that electrode damage from volume expansion and phase segregation by the accommodation of large K-ions leads to capacity loss during electrochemical cycling. To date, the exact phase transformations that occur during potassiation and depotassiation of conversion/alloying anodes are relatively unexplored.

Potassium Fluoride and Carbonate Lead to Cell Failure in Potassium-Ion Batteries.

While Li-ion is the prevailing commercial battery chemistry, the development of batteries that use earth-abundant alkali metals (e.g., Na and K) alleviates reliance on Li with potentially cheaper technologies.

Air-stable, long-length, solution-based graphene nanoribbons.

Within the context of nanoelectronics, general strategies for the development of electronically tunable and air stable graphene nanoribbons are crucial. Previous studies towards the goal of processable nanoribbons have been complicated by ambient condition instability, insolubility arising from aggregation, or poor cyclization yield due to electron deficiency. Herein, we present a general strategy for the elongation of smaller graphene nanoribbon fragments into air-stable, easily processed, and electronically tunable nanoribbons.

Recovery and Reuse of Composite Cathode Binder in Lithium Ion Batteries.

Here, we investigate the recovery and reuse of polyvinylidene fluoride (PVDF) binders from both homemade and commercial cathode films in Li ion batteries. We find that PVDF solubility depends on whether the polymer is an isolated powder or cast into a composite film. A mixture of tetrahydrofuran:N-methyl-2-pyrrolidone (THF : NMP, 50 : 50 v/v) at 90 °C delaminates composite cathodes from Al current collectors and yields pure PVDF as characterized by H nuclear magnetic resonance (NMR), gel permeation chromatography (GPC), wide-angle X-ray scattering (WAXS), and scanning electron microscopy (SEM).

High-performance organic pseudocapacitors via molecular contortion.

Pseudocapacitors harness unique charge-storage mechanisms to enable high-capacity, rapidly cycling devices. Here we describe an organic system composed of perylene diimide and hexaazatrinaphthylene exhibiting a specific capacitance of 689 F g at a rate of 0.5 A g, stability over 50,000 cycles, and unprecedented performance at rates as high as 75 A g.

Reversible Deposition and Stripping of the Cathode Electrolyte Interphase on LiRuO.

Performance decline in Li-excess cathodes is generally attributed to structural degradation at the electrode-electrolyte interphase, including transition metal migration into the lithium layer and oxygen evolution into the electrolyte. Reactions between these new surface structures and/or reactive oxygen species in the electrolyte can lead to the formation of a cathode electrolyte interphase (CEI) on the surface of the electrode, though the link between CEI composition and the performance of Li-excess materials is not well understood. To bridge this gap in understanding, we use solid-state nuclear magnetic resonance (SSNMR) spectroscopy, dynamic nuclear polarization (DNP) NMR, and electrochemical impedance spectroscopy (EIS) to assess the chemical composition and impedance of the CEI on LiRuO as a function of state of charge and cycle number.

Establishing Ultralow Activation Energies for Lithium Transport in Garnet Electrolytes.

Garnet-type structured lithium ion conducting ceramics represent a promising alternative to liquid-based electrolytes for all-solid-state batteries. However, their performance is limited by their polycrystalline nature and inherent inhomogeneous current distribution due to different ion dynamics at grains, grain boundaries, and interfaces. In this study, we use a combination of electrochemical impedance spectroscopy, distribution of relaxation time analysis, and solid-state nuclear magnetic resonance (NMR), in order to understand the role that bulk, grain boundary, and interfacial processes play in the ionic transport and electrochemical performance of garnet-based cells.

Li NMR Chemical Shift Imaging To Detect Microstructural Growth of Lithium in All-Solid-State Batteries.

All-solid-state batteries potentially offer safe, high-energy-density electrochemical energy storage, yet are plagued with issues surrounding Li microstructural growth and subsequent cell death. We use Li NMR chemical shift imaging and electron microscopy to track Li microstructural growth in the garnet-type solid electrolyte, LiLaZrTaO. Here, we follow the early stages of Li microstructural growth during galvanostatic cycling, from the formation of Li on the electrode surface to dendritic Li connecting both electrodes in symmetrical cells, and correlate these changes with alterations observed in the voltage profiles during cycling and impedance measurements.

Niobium tungsten oxides for high-rate lithium-ion energy storage.

The maximum power output and minimum charging time of a lithium-ion battery depend on both ionic and electronic transport. Ionic diffusion within the electrochemically active particles generally represents a fundamental limitation to the rate at which a battery can be charged and discharged. To compensate for the relatively slow solid-state ionic diffusion and to enable high power and rapid charging, the active particles are frequently reduced to nanometre dimensions, to the detriment of volumetric packing density, cost, stability and sustainability.

Understanding Fluoroethylene Carbonate and Vinylene Carbonate Based Electrolytes for Si Anodes in Lithium Ion Batteries with NMR Spectroscopy.

Fluoroethylene carbonate (FEC) and vinylene carbonate (VC) are widely used as electrolyte additives in lithium ion batteries. Here we analyze the solid electrolyte interphase (SEI) formed on binder-free silicon nanowire (SiNW) electrodes in pure FEC or VC electrolytes containing 1 M LiPF by solid-state NMR with and without dynamic nuclear polarization (DNP) enhancement. We find that the polymeric SEIs formed in pure FEC or VC electrolytes consist mainly of cross-linked poly(ethylene oxide) (PEO) and aliphatic chain functionalities along with additional carbonate and carboxylate species.

Sodiation and Desodiation via Helical Phosphorus Intermediates in High-Capacity Anodes for Sodium-Ion Batteries.

Na-ion batteries are promising alternatives to Li-ion systems for electrochemical energy storage because of the higher natural abundance and widespread distribution of Na compared to Li. High capacity anode materials, such as phosphorus, have been explored to realize Na-ion battery technologies that offer comparable performances to their Li-ion counterparts. While P anodes provide unparalleled capacities, the mechanism of sodiation and desodiation is not well-understood, limiting further optimization.

Realistic Atomistic Structure of Amorphous Silicon from Machine-Learning-Driven Molecular Dynamics.

Amorphous silicon ( a-Si) is a widely studied noncrystalline material, and yet the subtle details of its atomistic structure are still unclear. Here, we show that accurate structural models of a-Si can be obtained using a machine-learning-based interatomic potential. Our best a-Si network is obtained by simulated cooling from the melt at a rate of 10 K/s (that is, on the 10 ns time scale), contains less than 2% defects, and agrees with experiments regarding excess energies, diffraction data, and Si NMR chemical shifts.

Identifying the Structural Basis for the Increased Stability of the Solid Electrolyte Interphase Formed on Silicon with the Additive Fluoroethylene Carbonate.

To elucidate the role of fluoroethylene carbonate (FEC) as an additive in the standard carbonate-based electrolyte for Li-ion batteries, the solid electrolyte interphase (SEI) formed during electrochemical cycling on silicon anodes was analyzed with a combination of solution and solid-state NMR techniques, including dynamic nuclear polarization. To facilitate characterization via 1D and 2D NMR, we synthesized C-enriched FEC, ultimately allowing a detailed structural assignment of the organic SEI. We find that the soluble poly(ethylene oxide)-like linear oligomeric electrolyte breakdown products that are observed after cycling in the standard ethylene carbonate-based electrolyte are suppressed in the presence of 10 vol% FEC additive.

Monomeric Polyglutamine Structures That Evolve into Fibrils.

We investigate the solution and fibril conformations and structural transitions of the polyglutamine (polyQ) peptide, DQK (Q10), by synergistically using UV resonance Raman (UVRR) spectroscopy and molecular dynamics (MD) simulations. We show that Q10 adopts two distinct, monomeric solution conformational states: a collapsed β-strand and a PPII-like structure that do not readily interconvert. This clearly indicates a high activation barrier in solution that prevents equilibration between these structures.

Correlating Carrier Density and Emergent Plasmonic Features in CuSe Nanoparticles.

Recently, a wide variety of new nanoparticle compositions have been identified as potential plasmonic materials including earth-abundant metals such as aluminum, highly doped semiconductors, as well as metal pnictides. For semiconductor compositions, plasmonic properties may be tuned not only by nanoparticle size and shape, but also by charge carrier density which can be controlled via a variety of intrinsic and extrinsic doping strategies. Current methods to quantitatively determine charge carrier density primarily rely on interpretation of the nanoparticle extinction spectrum.

Ligand density quantification on colloidal inorganic nanoparticles.

Colloidal inorganic nanoparticles are being used in an increasingly large number of applications ranging from biological imaging to television displays. In all cases, nanoparticle surface chemistry can significantly impact particle physical properties, processing, and performance. The first step in leveraging this tunability is to develop analytical approaches to describe surface chemical features.

Impact of As-Synthesized Ligands and Low-Oxygen Conditions on Silver Nanoparticle Surface Functionalization.

Here, we compare the ligand exchange behaviors of silver nanoparticles synthesized in the presence of two different surface capping agents: poly(vinylpyrrolidone) (MW = 10 or 40 kDa) or trisodium citrate, and under either ambient or low-oxygen conditions. In all cases, we find that the polymer capping agent exhibits features of a weakly bound ligand, producing better ligand exchange efficiencies with an incoming thiolated ligand compared to citrate. The polymer capping agent also generates nanoparticles that are more susceptible to reactions with oxygen during both synthesis and ligand exchange.

Observation of uniform ligand environments and (31)P-(197)Au coupling in phosphine-terminated Au nanoparticles.

Here, we use solution and solid-state (31)P NMR to study the ligand environment of water soluble, phosphine-terminated gold nanoparticles. The resulting spectra indicate that particle-bound phosphine ligands occupy an unexpectedly monodisperse ligand environment. This uniformity then facilitates one of the first descriptions of distinct (31)P-(197)Au coupling in colloidal nanoparticles.

Description and Role of Bimetallic Prenucleation Species in the Formation of Small Nanoparticle Alloys.

We report the identification, description, and role of multinuclear metal-thiolate complexes in aqueous Au-Cu nanoparticle syntheses. The structure of these species was characterized by nuclear magnetic resonance spectroscopy, mass spectrometry, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy techniques. The observed structures were found to be in good agreement with thermodynamic growth trends predicted by first-principles calculations.