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. The formation of branched fragments is further confirmed by C-C correlation NMR experiments. The presence of cross-linked PEO-type polymers in FEC and VC correlates with good capacity retention and high Coulombic efficiencies of the SiNWs. Using Si DNP NMR, we are able to probe the interfacial region between SEI and the Si surface for the first time with NMR spectroscopy. Organosiloxanes form upon cycling, confirming that some of the organic SEI is covalently bonded to the Si surface. We suggest that both the polymeric structure of the SEI and the nature of its adhesion to the redox-active materials are important for electrochemical performance.

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. FEC is first defluorinated to form soluble vinylene carbonate and vinoxyl species, which react to form both soluble and insoluble branched ethylene-oxide-based polymers. No evidence for branched polymers is observed in the absence of FEC.

Silicon monoxide is a promising alternative anode material due to its much higher capacity than graphite, and improved cyclability over other Si anodes. An in-depth analysis of the lithium silicide (Li x Si) phases that form during lithiation/delithiation of SiO is presented here and the results are compared with pure-Si anodes. A series of anode materials is first prepared by heating amorphous silicon monoxide (a-SiO) at different temperatures, X-ray diffraction and 29 Si NMR analysis revealing that they comprise small Si domains that are surrounded by amorphous SiO 2 , the domain size and crystallinity growing with heat treatment. In and ex situ 7 Li and 29 Si solid-state NMR combined with detailed electrochemical analysis reveals that a characteristic metallic Li x Si phase is formed on lithiating a-SiO with a relatively high Li concentration of x = 3.4-3.5, which is formed/decomposed through a continuous structural evolution involving amorphous phases differing in their degree of Si-Si connectivity. This structural evolution differs from that of pure-Si electrodes where the end member, crystalline Li 15 Si 4 , is formed/decomposed through a two-phase reaction. The reaction pathway of SiO depends, however, on the size of the ordered Si domains within the pristine material. When crystalline domains of 5 nm within a SiO 2 matrix are present, a phase resembling Li 15 Si 4 forms, albeit at a higher overpotential. The continuous formation/decomposition of amorphous Li x Si phases without the hysteresis and phase change associated with the formation of c-Li 15 Si 4 , along with a partially electrochemically active SiO 2 /lithium silicate buffer layer, are paramount for the good cyclability of a-SiO.

Compared to nanomaterials exposing nonpolar facets, polar-faceted nanocrystals often exhibit unexpected and interesting properties. The electrostatic instability arising from the intrinsic dipole moments of polar facets, however, leads to different surface configurations in many cases, making it challenging to extract detailed structural information and develop structure-property relations. The widely used electron microscopy techniques are limited because the volumes sampled may not be representative, and they provide little chemical bonding information with low contrast of light elements. With ceria nanocubes exposing (100) facets as an example, here we show that the polar surface structure of oxide nanocrystals can be investigated by applying 17O and 1H solid-state NMR spectroscopy and dynamic nuclear polarization, combined with DFT calculations. Both CeO4-termination reconstructions and hydroxyls are present for surface polarity compensation and their concentrations can be quantified. These results open up new possibilities for investigating the structure and properties of oxide nanostructures with polar facets.

We report the exfoliation of layered Na2Ti3O7, a promising anode material for Na-ion batteries, and restacking using HNO3 and NaOH to form H-[Ti3O7] and Na(x)-[Ti3O7] compositions, respectively. The materials were characterised by a range of techniques (SEM, TEM, solid-state NMR, XRD, PDF). Although the formation of aggregated nanoparticles is favoured under acidic restacking conditions, the use of basic conditions can lead to control over the adherence between the exfoliated layers. Pair distribution function (PDF) analysis confirms that the local TiO6 connectivity of the pristine material is maintained. The lowest sodium-containing Na(1)-[Ti3O7] phase, which is the stable product upon Na + leaching after consecutive washing steps, displays the best performance among the compositions studied, affording a stable reversible capacity of about 200 mAh.g -1 for 20 cycles at a C/20 rate. Washing removes the excess of 'free/reactive' Na + , which otherwise forms inactive Na2CO3 in the insufficiently-washed compositions.

The experimentally observed 31P lineshapes and transversal relaxation of 15% (wt/wt) M13, 30% M13, and 30% tobacco mosaic virus (TMV) are compared with lineshapes and relaxation curves that are simulated for various types of rotational diffusion using the models discussed previously (Magusin, P. C. M. M., and M. A. Hemminga. 1993. Biophys. J. 64:1851-1860). It is found that isotropic diffusion cannot explain the observed lineshape effects. A rigid rod diffusion model is only successful in describing the experimental data obtained for 15% M13. For 30% M13 the experimental lineshape and relaxation curve cannot be interpreted consistently and the TMV lineshape cannot even be simulated alone, indicating that the rigid rod diffusion model does not generally apply. A combined diffusion model with fast isolated motions of the encapsulated nucleic acid dominating the lineshape and a slow overall rotation of the virion as a whole, which mainly is reflected in the transversal relaxation, is able to provide a consistent picture for the 15 and 30% M13 samples, but not for TMV. Strongly improved lineshape fits for TMV are obtained assuming that there are three binding sites with different mobilities. The presence of three binding sites is consistent with previous models of TMV. The best lineshapes are simulated for a combination of one mobile and two static sites. Although less markedly, the assumption that two fractions of DNA with different mobilities exist within M13 also improves the simulated lineshapes. The possible existence of two 31P fractions in M13 sheds new light on the nonintegral ratio 2.4:1 between the number of nucleotides and protein coat subunits in the phage: 83% of the viral DNA is less mobile, suggesting that the binding of the DNA molecule to the protein coat actually occurs at the integral ratio of two nucleotides per protein subunit.

Hydrous materials are ubiquitous in the natural environment and efforts have previously been made to investigate the structures and dynamics of hydrated surfaces for their key roles in various chemical and physical applications, with the help of theoretical modelling and microscopy techniques. However, an overall atomic-scale understanding of the water-solid interface, including the effect of water on surface ions, is still lacking. Herein, we employ ceria nanorods with different amounts of water as an example and demonstrate a new approach to explore the water-surface interactions by using solid-state NMR in combination with density functional theory. NMR shifts and relaxation time analysis provide detailed local structure of oxygen ions and the nature of water motion on the surface: the amount of molecularly adsorbed water decreases rapidly with increasing temperature (from room temperature to 150 °C), whereas hydroxyl groups are stable up to 150 °C; dynamic water molecules are found to instantaneously coordinate to the surface oxygen ions. The applicability of dynamic nuclear polarization for selective detection of surface oxygen species is also compared to conventional NMR with surface selective-labeling: the optimal method depends on the feasibility of enrichment and the concentration of protons in the sample. These results provide new insight into the interfacial structure of hydrated oxide nanostructures which is important for relevant applications.

The high theoretical capacity of Li-O 2 batteries attracts a lot of attention and this field has expanded significantly in the last two decades. In a more general way, the large number of articles being published daily makes it difficult for researchers to keep track of the progress in science. Here we develop a text mining program in an attempt to facilitate the process of reviewing the literature published in a scientific field and apply it to Li-O 2 batteries. We analyze over 1800 articles and use the text mining program to extract reported discharge capacities, for the first time, which allows us to show the clear progress made in recent years. In this paper, we focus on three main challenges of Li-O 2 batteries, namely the stability-cyclability, the low practical capacity and the rate capability. Indeed, according to our text mining program, articles dealing with these issues represent 86% of the literature published in the field. For each topic, we provide a bibliometric analysis of the literature before focusing on a few key articles which allow us to get insights into the physics and chemistry of such systems. We believe that text mining can help readers find breakthrough papers in a field (e.g. by identifying papers reporting much higher performances) and follow the developments made at the state of the art (e.g. by showing trends in the numbers of papers published-a decline in a given topic probably being the sign of limitations). With the progress of text mining algorithms in the future, the process of reviewing a scientific field is likely to become more and more automated, making it easier for researchers to get the 'big picture' in an unfamiliar scientific field.