The key factor in long-term use of batteries 9 is the formation of an electrically insulating solid layer that 10 allows lithium ion transport but stops further electrolyte 11 redox reactions on the electrode surface, hence solid 12 electrolyte interphase (SEI). We have studied a common 13 electrolyte, 1.0 M LiPF 6 /ethylene carbonate (EC)/diethyl 14 carbonate (DEC), reduction products on crystalline silicon 15 (Si) electrodes in a lithium (Li) half-cell system under 16 reaction conditions. We employed in situ sum frequency 17 generation vibrational spectroscopy (SFG-VS) with inter-18 face sensitivity in order to probe the molecular 19 composition of the SEI surface species under various 20 applied potentials where electrolyte reduction is expected. 21 We found that, with a Si(100)-hydrogen terminated wafer, 22 a Si-ethoxy (Si-OC 2 H 5) surface intermediate forms due to 23 DEC decomposition. Our results suggest that the SEI 24 surface composition varies depending on the termination 25

A phase transition within the ligand shell of core/shell quantum dots is studied in the prototypical system of colloidal CdSe/CdS quantum dots with a ligand shell composed of bound oleate (OA) and octadecylphosphonate (ODPA). The ligand shell composition is tuned using a ligand exchange procedure and quantified through proton NMR spectroscopy. Temperaturedependent photoluminescence spectroscopy reveals a signature of a phase transition within the organic ligand shell. Surprisingly, the ligand order to disorder phase transition triggers an abrupt increase in the photoluminescence quantum yield (PLQY) and full-width at half maximum (FWHM) with increasing temperature. The temperature and width of the phase transition shows a clear dependence on ligand shell composition, such that QDs with higher ODPA fractions have sharper phase transitions that occur at higher temperatures. In order to gain a molecular understanding of the changes in ligand ordering, fourier-transform infrared and vibrational sum frequency generation spectroscopies are performed. These measurements confirm that an order/disorder transition in the ligand shell tracks with the photoluminescence changes that accompany the order disorder ligand phase transition. The phase transition is simulated through a lattice model that suggests that the ligand shell is well-mixed, and does not 1 have completely segregated domains of OA and ODPA. Furthermore, we show that the unsaturated chains of OA seed disorder within the ligand shell.

Fluorinated compounds are added to carbonate-based electrolyte solutions in an effort to create a stable solid electrolyte interphase (SEI). The SEI mitigates detrimental electrolyte redox reactions taking place on the anode's surface upon applying a potential in order to charge (discharge) the lithium (Li) ion battery. The need for a stable SEI is dire when the anode material is silicon as silicon cracks due to its expansion and contraction upon lithiation and delithiation (charge-discharge) cycles, consequently limiting the cyclability of a silicon-based battery. Here we show the molecular structures for ethylene carbonate (EC): fluoroethylene carbonate (FEC) solutions on silicon surfaces by sum frequency generation (SFG) vibrational spectroscopy, which yields vibrational spectra of molecules at interfaces and by ab initio molecular dynamics (AIMD) simulations at open circuit potential. Our AIMD simulations and SFG spectra indicate that both EC and FEC adsorb to the amorphous silicon (a-Si) through their carbonyl group (C═O) oxygen atom with no further desorption. We show that FEC additives induce the reorientation of EC molecules to create an ordered, up-right orientation of the electrolytes on the Si surface. We suggest that this might be helpful for Li diffusion under applied potential. Furthermore, FEC becomes the dominant species at the a-Si surface as the FEC concentration increases above 20 wt %. Our finding at open circuit potential can now initiate additive design to not only act as a sacrificial compound but also to produce a better suited SEI for the use of silicon anodes in the Li-ion vehicular industry.

The interaction of charged particles with condensed water films has been studied extensively in recent years due to its importance in biological systems, ecology as well as interstellar processes. We have studied low energy electrons (3-25 eV) and positive argon ions (55 eV) charging effects on amorphous solid water (ASW) and ice films, 120-1080 ML thick, deposited on ruthenium single crystal under ultrahigh vacuum conditions. Charging the ASW films by both electrons and positive argon ions has been measured using a Kelvin probe for contact potential difference (CPD) detection and found to obey plate capacitor physics. The incoming electrons kinetic energy has defined the maximum measurable CPD values by retarding further impinging electrons. L-defects (shallow traps) are suggested to be populated by the penetrating electrons and stabilize them. Low energy electron transmission measurements (currents of 0.4-1.5 μA) have shown that the maximal and stable CPD values were obtained only after a relatively slow change has been completed within the ASW structure. Once the film has been stabilized, the spontaneous discharge was measured over a period of several hours at 103 ± 2 K. Finally, UV laser photo-emission study of the charged films has suggested that the negative charges tend to reside primarily at the ASW-vacuum interface, in good agreement with the known behavior of charged water clusters.

The cyclability of silicon anodes in lithium ion batteries (LIBs) is affected by the reduction of the electrolyte on the anode surface to produce a coating layer termed the solid electrolyte interphase (SEI). One of the key steps for a major improvement of LIBs is unraveling the SEI's structure-related diffusion properties as charge and discharge rates of LIBs are diffusion-limited. To this end, we have combined two surface sensitive techniques, sum frequency generation (SFG) vibrational spectroscopy, and X-ray reflectivity (XRR), to explore the first monolayer and to probe the first several layers of electrolyte, respectively, for solutions consisting of 1 M lithium perchlorate (LiClO) salt dissolved in ethylene carbonate (EC) or fluoroethylene carbonate (FEC) and their mixtures (EC/FEC 7:3 and 1:1 wt %) on silicon and sapphire surfaces. Our results suggest that the addition of FEC to EC solution causes the first monolayer to rearrange itself more perpendicular to the anode surface, while subsequent layers are less affected and tend to maintain their, on average, surface-parallel arrangements. This fundamental understanding of the near-surface orientation of the electrolyte molecules can aid operational strategies for designing high-performance LIBs.

Water molecules adsorbed on SiO2/Si(100) at 140 K to form amorphous solid water (ASW) layers were utilized as a buffer for assisting the growth of gold nanoclusters. It was shown that the average height and diameter of the clusters deposited on the silicon oxide substrate following the buffer annealing/desorption increase as the buffer layer becomes thicker and as more gold is deposited. The clusters' height and diameter were determined by tapping mode AFM and high-resolution SEM imaging, respectively. Typical heights were between 0.5 and 4.5 nm, and the diameters were in the range of 3-9 nm for ASW layer thickness of 7-100 ML and gold deposition in the range of 0.2-1.2 A. The density of the clusters decreased from 65 x 10(10) to 8 x 10(10) cm (-2) in the same buffer layer thickness range. Significantly different morphology of the clusters is obtained when compared to those formed by direct deposition of gold on the silicon oxide surface and to those grown on top of Xe as buffer material.

Composite-solid electrolytes, in which ion-conducting polymers are combined with superionic ceramics, could revolutionize electrochemical-energy-storage devices enabling higher energy density, providing greater stability during operation and enhanced safety. However, the interfacial resistance between the ceramic and polymer phases strongly suppresses the ionic conductivity and presents the main obstacle to the use of these materials. Here, we emphasize the need for a distinct focus on reducing energy barriers to interfacial ion transport and improving the cation transference number. To achieve this goal, it is essential to develop a fundamental understanding of the parameters that influence the interfacial barriers to ion transport in composite electrolytes, and to understand the effect of the type of ceramic (“active” and “inert”) and its content on ion-transport phenomena. We suggest that adapting the polymer chemistry, mainly directed on polymerized ionic liquids, (PolyILs), and combined with functionalization of the surface of ceramic nanoparticles is a promising route for overcoming the high-energy-barrier challenge. Owing to high content of ion-conducting ceramics and high t+ of PolyILs, the fractional contribution of the migrating cationic species to the total ionic conductivity of polymer-in-ceramic electrolytes via an interfacial percolation path, will be close to unity, thus eliminating complications that might arise from emerging concentration gradients during the operation of solid-state batteries.

Herein, three electrolyte families (liquid, polymer, and ceramic) are compared and their future perspectives in research and application are discussed. First, the transport mechanism for each family is presented, as their beneficial and taxing properties stem from the differences in these mechanisms. Following a discussion of each group, their advantages, and limitations, a clear conclusion can be drawn on the need to focus on research on solid electrolytes, which present brighter prospects in terms of significant future advances in lithium‐based battery systems. Yet, in a more realistic perspective based on current work by companies such as Samsung, Solid Power, and QuantumScape, it is our understanding that the hybridization of polymer and solid electrolytes will likely dominate practical electrolyte chemistries, at least in the near future, given that the synergetic properties of the two families are larger than their single parts. Inevitably, solid‐state electrolytes will dominate, mainly in electric vehicles and future lithium battery chemistries.