Multinuclear Solid-state NMR Studies Research Articles

Fine structural features and proton conduction in zwitterionic poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC): Multinuclear solid-state NMR, impedance and FTIR spectroscopy study

The poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC), i.e. one of the most biocompatible synthetic polymer, was synthesized using radical addition-fragmentation chain transfer (RAFT) polymerization and characterized by a wide set of experimental techniques, the 1H, 13C, 15N, 31P NMR, impedance and FTIR spectroscopy among those. The optimized synthesis conditions ensured the high product yield, high purity and narrow molecular weight distribution. The stereochemical content was determined from the complex shaped 13C MAS signal of CH3 group, and the relative content of the adsorbed water - from the 1H MAS spectra. The 1H13C and 1H31P cross-polarization kinetics were measured and processed using the Hirschinger and Raya spin dynamics model. Fine structural details, such as the partial (ca 10%) protonation of the internal PO4− group, the local order and the flexibility of the main chain were deduced. The thermal activation of proton conduction in the wet PMPC was deduced by impedance spectroscopy. The thermal boosting of proton mobility is driven via breaking the cage-like structures of water. This was confirmed by 1H MAS and FTIR spectroscopy. The experimental data for poly[2-(methacryloyloxy)ethyl trimethylammonium chloride] (PMETAC), i.e. cationic proton conducting polymer, which structure is closely related to PMPC, were revisited, compared and discussed.

Extent of disorder in iron-bearing albite and anorthite melts: Insights from multi-nuclear (29Si, 27Al, and 17O) solid-state NMR study of iron-bearing NaAlSi3O8 and CaAl2Si2O8 glasses

Knowledge of the detailed structure of iron-bearing aluminosilicate glasses is essential to unraveling the effects of iron on the macroscopic properties of natural silicate glasses and melts. However, the local structures around the framework cations (such as Al and Si) and the extent of network polymerization in iron-bearing aluminosilicate glasses are not well understood. This is mainly because the high-resolution solid-state NMR - one of the effective probes of the structures of aluminosilicate glasses - has limited utility in delving into the local configurations of oxide glasses with paramagnetic elements (i.e., iron). Here, we use multi-nuclear (29Si, 27Al, and 17O) high-resolution solid-state NMR to investigate the effect of iron content on the local structure around framework cations and oxygen species in Na(Al1-XFeX)Si3O8 glasses with varying X [=Fe/(Al + Fe)] (Fe3+/ΣFe = ~0.8), NaAlSi3O8 glasses with varying Fe2O3 (NaAlSi3O8 + Fe2O3, Fe3+/ΣFe = ~0.5), and CaAl2Si2O8 glasses with varying Fe2O3 (CaAl2Si2O8 + Fe2O3, Fe3+/ΣFe = ~0.3).The NMR results for Na(Al1-XFeX)Si3O8 glasses reveal preferential interaction between Fe3+ and Si-rich framework and thus an extensive mixing between [4]Si and [4]Fe3+. The presence of a small amount of [5]Al in Na(Al0.5Fe0.5)Si3O8 glass suggests that the extent of disorder around Al increases by Al-Fe3+ substitution. The NMR results for NaAlSi3O8 + Fe2O3 glasses suggest that Fe2+ interacts more strongly with Al-rich framework and reveal the presence of a non-negligible fraction of Na-NBO, confirming Fe2+-induced structural disorder. The absence of [5]Al in NaAlSi3O8 + Fe2O3 glasses indicates that Fe3+ is more likely to form a highly-coordinated framework (i.e., [5]Fe3+) when excess Fe3+ is added to charge-balanced glasses. The NMR spectra for CaAlSi2O8 + Fe2O3 glasses showed an iron-induced increase in the [5]Al fraction and confirmed that the overall degree of disorder increases with increasing Fe2O3 content. The noble NMR results for iron-bearing aluminosilicate glasses revealed the nature of diverse aspect of iron-induced structural disorder, mainly characterized by the intermixing between Si and Fe3+, preferential interaction between Al and Fe2+, and formation of highly coordinated [5]Fe3+. The detailed iron-induced structural evolution is largely dependent on the composition of melts as well as the valence state of iron. The observed increase in the extent of structural disorder in charge-balanced Na- and Ca-aluminosilicate glasses with increasing Fe2+ and Fe3+ can account for the iron-induced decrease in viscosity of the corresponding iron-bearing aluminosilicate melts.

The β-Agostic Structure in (C5 Me5 )2 Sc(CH2 CH3 ): Solid-State NMR Studies of (C5 Me5 )2 Sc-R (R=Me, Ph, Et).

Multinuclear solid-state NMR studies of Cp*2 Sc-R (Cp*=pentamethylcyclopentadienyl; R=Me, Ph, Et) and DFT calculations show that the Sc-Et complex contains a β-CH agostic interaction. The static central transition 45 Sc NMR spectra show that the quadrupolar coupling constants (Cq ) follow the trend of Ph≈Me>Et, indicating that the Sc-R bond is different in Cp*2 Sc-Et compared to the methyl and phenyl complexes. Analysis of the chemical shift tensor (CST) shows that the deshielding experienced by Cβ in Sc-CH2 CH3 is related to coupling between the filled σC-C orbital and the vacant πSc⋯HC* orbital.

Multinuclear NMR Study of the Solid Electrolyte Interface Formed in Lithium Metal Batteries.

The composition of the solid electrolyte interphase (SEI) layers formed in Cu|Li cells using lithium bis(fluorosulfonyi)imide (LiFSI) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in 1,2-dimethoxyethane (DME) electrolytes is determined by a multinuclear solid-state MAS NMR study at high magnetic field. It is found that the "dead" metallic Li is largely reduced in the SEI layers formed in a 4 M LiFSI-DME electrolyte system compared with those formed in a 1 M LiFSI-DME electrolyte system. This finding relates directly to the safety of Li metal batteries, as one of the main safety concerns for these batteries is associated with the "dead" metallic Li formed after long-term cycling. It is also found that a large amount of LiF, which exhibits superior mechanical strength and good Li+ ionic conductivity, is observed in the SEI layer formed in the concentrated 4 M LiFSI-DME and 3 M LiTFSI-DME systems but not in the diluted 1 M LiFSI-DME system. Quantitative 6Li MAS NMR results indicate that the SEI associated with the 4 M LiFSI-DME electrolyte is denser than those formed in the 1 M LiFSI-DME and 3 M LiTFSI-DME systems. These studies reveal the fundamental mechanisms behind the excellent electrochemical performance associated with higher concentration LiFSI-DME electrolyte systems.

Multinuclear Solid-State NMR Studies of Polymer-Supported Scandium Triflate Catalysts

Scandium(III) trifluoromethanesulfonate [Sc(OTf)3] is extensively used in organic synthesis to catalyze a wide variety of carbon–carbon bond-forming reactions in aqueous media. It has previously been demonstrated that it is possible to immobilize Sc(OTf)3 in polystyrene (PS) to form the heterogeneous catalysts, microencapsulated (ME) Sc(OTf)3. The ME catalysts are recoverable, reusable, often reduce metal leaching, and have activity similar to that of their homogeneous counterparts. Aside from preliminary scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) imaging studies and solution 45Sc NMR studies, there is little information available about the molecular and bulk structure of the ME catalyst. In this regard, we have conducted a 45Sc solid-state NMR investigation of the Sc environments in the crystalline and ME forms of anhydrous Sc(OTf)3 and hydrated Sc(OTf)3·8H2O. Additional solid-state 1H, 19F, and 13C NMR and powder X-ray diffraction experiments provide information that is complementary to that obtained from the 45Sc NMR spectra, allowing for structural models of ME complexes to be proposed. The principal findings are that Sc(OTf)3 is hydrated upon microencapsulation to form Sc(OTf)3·8H2O. 1H–45Sc TRAPDOR and 1H–19F CP SSNMR experiments and powder X-ray diffraction experiments suggest that Sc is dispersed throughout the polymer within nanocrystalline domains of Sc(OTf)3·8H2O. The approach outlined here should be applicable for the characterization of many other polymer-supported metal-based catalysts.

Nature of Si–H Interactions in a Series of Ruthenium Silazane Complexes Using Multinuclear Solid-State NMR and Neutron Diffraction

Three new N-heterocyclic-silazane compounds, 1a-c, were prepared and employed as bidentate ligands to ruthenium, resulting in a series of [Ru(H){(κ-Si,N-(SiMe2-N-heterocycle)}3] complexes (3a-c) featuring the same RuSi3H motif. Detailed structural characterization of the RuSi3H complexes with X-ray diffraction, and in the case of triazabicyclo complex [Ru(H){κ-Si,N-(SiMe2)(C7H12N3)}3] (3a), neutron diffraction, enabled a reliable description of the molecular geometry. The hydride ligand of (3a) is located closer to two of the silicon atoms than it is to the third. Such a geometry differs from that of the previously reported complex [Ru(H){(κ-Si,N-(SiMe2)N(SiMe2H)(C5H4N)}3] (3d), also characterized by neutron diffraction, where the hydride was found to be equidistant from all three silicon atoms. A DFT study revealed that the symmetric and less regular isomers are essentially degenerate. Information on the dynamics and on the Ru···H···Si interactions was gained from multinuclear solid-state ((1)H wPMLG, (29)Si CP MAS, and 2D (1)H-(29)Si dipolar HETCOR experiments) and solution NMR studies. The corresponding intermediate complexes, [Ru{κ-Si,N-(SiMe2-N-heterocycle)}(η(4)-C8H12)(η(3)-C8H11)] (2a-c), involving a single silazane ligand were isolated and characterized by multinuclear NMR and X-ray diffraction. Protonation of the RuSi3H complexes was also studied. Reaction of 3a with NH4PF6 gave rise to [Ru(H)(η(2)-H -SiMe2)κ-N-(C7H12N3){κ-Si,N-(SiMe2)(C7H12N3)}2](+)[PF6](-)(4aPF6) which was isolated and characterized by NMR spectroscopy, X-ray crystallography, and DFT studies. The nature of the Si-H interactions in this silazane series was analyzed in detail.

Multinuclear Solid-State NMR Studies on the Formation Mechanism of Aluminophosphate Molecular Sieves in Ionic Liquids

In the present work, multinuclear solid-state NMR techniques together with power X-ray diffraction (XRD) and scanning electron microscopy (SEM) were employed to monitor the crystallization process of aluminophosphate AlPO4-11 molecular sieves in 1-ethyl-3-methylimidazolium bromide ([emim]Br) ionic liquids (ILs). The local environments of the selected solid samples were probed by one-dimensional 27Al, 31P, and 19F MAS NMR experiments, and more information was obtained from two-dimensional 27Al→31P heteronuclear correlation (HETCOR) and 27Al triple-quantum MAS (3Q MAS) experiments. It is found that a large amount of amorphous aluminophosphates was formed with the F–Aloct–O–Ppar and Altet–O–Ppar structures in the initial stage of aging. With increasing crystallization time, the partially condensed framework phosphorus species disappeared gradually and became fully condensed. Meanwhile, the octahedral Al was transformed into the pentahedral and tetrahedral Al species with the structures of F–Alpenta–O–Pful and Altet–O–Pful in the AlPO4-11 frameworks. During the crystallization process, [emim] cations acting as the structure-directing agents were occluded into the channels, and F– anions were connected with pentahedral Al in the final AlPO4–11 phase. All of these findings can allow proposing a possible formation mechanism for the synthesis of AlPO4-11 in ionic liquids.

Multinuclear NMR Study of the Solid Electrolyte Interface on the Li-FeSn2 Negative Electrodes for Li-Ion Batteries

The composition of the solid electrolyte interface (SEI) layer on the Li-FeSn2 negative electrode has been determined by a multinuclear solid state NMR study. The strong e-nuclear dipolar and contact interactions between the as-formed superparamagnetic Fe nanoparticles and the SEI layer allows a layer wise observation highly depending on the proximity. Li+ from LiPF6, which is traditionally considered as a postdeposited product from the electrolyte solution,has been observed as presenting different solvation states by 19F → 7Li cross polarization magic angle spinning (CPMAS) NMR. Direct contact between LiOH and LixSn or Fe nanoparticles is suggested by Fermi-Contact shifts of −11 and −2 ppm observed in 7Li and 1H NMR spectra, respectively. The LixSn alloy signal remains invisible to 7Li NMR due to the close proximity to the Fe nanoparticles. Effects of different discharging rates and aging at the discharge state are discussed as well.

Functionalization of SBA-15 Mesoporous Materials using “Thiol–Ene Click” Michael Addition Reaction

Methacrylate-labeled SBA-15 has been successfully synthesized from calcined SBA-15 and commercially available 3-trichlorosilyl propylmethacrylate. This material undergoes efficient thiol–ene “click reaction” with a variety of both thiol and disulfide-containing substrates in aqueous and organic media. The products were thoroughly characterized by a variety of analytical techniques including multinuclear (13C, 29Si) solid-state NMR, TG-DTA, and nitrogen adsorption desorption studies. Disulfide-containing substrates in which the TCEP-mediated reduction of the disulfide bond and its subsequent addition to the methacrylate group anchored in SBA-15 in one-pot were used to synthesize a silica–protein hybrid material composed of biotin-labeled SBA-15 and streptavidin. Electrochemically active material was synthesized from the reaction of ferrocene-containing thiol and the methacrylate-labeled SBA-15. The ease of synthesis for the methacrylate-labeled SBA-15 material together with its ability to undergo efficient chemoselective thiol–ene reaction would make it a very attractive platform for the development of covalently anchored enzymes and sensors.

In VivoInspired Conditions to Synthesize Biomimetic Hydroxyapatite

We present a simple one-pot crystallization method, inspired by biological conditions, for the synthesis of hydroxyapatite (Ca5(PO4)3OH) nanocrystals. The reaction proceeds via NH3 vapor diffusion into a CaCl2−NaH2PO4 mixed solution that is free of any organic additives. The advantage of relying on acidic calcium-phosphate precursors here is, first, that the reaction can be performed at room temperature within a short time and without direct pH control and, second, that it does not produce any secondary phases or byproduct. Furthermore, the addition of NaHCO3 to the salt solution or the introduction of (NH4)2CO3 instead of NH3 lead, respectively, to the precipitation of B- or A-type carbonate-apatite phases according to the FT-IR data. Multinuclear solid state NMR studies and especially 13C CP experiments allow an in-depth characterization showing the presence of A/B substitutions in carbonated samples as well and indicate a close similarity to deproteinated bovine compact bone. A precipitation mechanism accounting for the precipitation of mainly A- or B-type carbonated apatite under the respective experimental conditions is proposed.

Probing the local structures and protonic conduction pathways in scandium substituted BaZrO3 by multinuclear solid-state NMR spectroscopy

A comprehensive multinuclear solid-state NMR study of scandium-substituted BaZrO3 is reported. Static low field and MQMAS very high field 45Sc NMR data revealed the presence of both 5- and 6-coordinated scandium atoms, 5-coordinated scandium arising from Sc nearby an oxygen vacancy. 17O NMR spectra showed the presence of up to three different chemical oxygen environments assigned to Zr–O–Zr, Zr–O–Sc and Sc–O–Sc. From the ratios of these different oxygen sites, the distribution of the scandium cations was close to random but indicated that the maximum scandium incorporation was lower than expected, consistent with the observation of Sc2O3 impurities at substitution levels of 30% Sc for Zr. 1H and 45Sc NMR data on the hydrated materials revealed the presence of scandium next to protonic defects. Finally, variable temperature 1H NMR showed the presence of at least two different proton environments in between which proton transfer occurs at ambient temperatures (300 K).

Multinuclear solid-state NMR studies on phase transition of mesostructured aluminophosphate

The phase transition process from a hexagonal to a lamellar mesostructured aluminophosphate was studied by multinuclear solid-state NMR techniques in combination with low-angle XRD and elemental analysis measurements. The XRD result showed that after hydrothermal treatment for 9 h, the initial hexagonal phase began to transform to a lamellar phase. It was also found by NMR that some initially formed aluminophosphate was hydrolyzed during the earliest 2 h of the hydrothermal treatment, and the inorganic aluminophosphate framework became more and more condensed during the phase transition. The organic surfactant mainly has a gauche conformation in the hexagonal phase, whereas it mainly has a trans conformation in the lamellar phase and is packed more compactly. The Br− anion is found to be involved in the phase transition and likely enters into the interface to compensate the lost of negative charges that generated by the condensation of the aluminophosphate. Finally, a mechanism for the phase transition is proposed.

Impact of Reduction on the Properties of Metal Bisdithiolenes: Multinuclear Solid-State NMR and Structural Studies on Pt(tfd)2 and Its Reduced Forms

Transition-metal dithiolene complexes have interesting structures and fascinating redox properties, making them promising candidates for a number of applications, including superconductors, photonic devices, chemical sensors, and catalysts. However, not enough is known about the molecular electronic origins of these properties. Multinuclear solid-state NMR spectroscopy and first-principles calculations are used to examine the molecular and electronic structures of the redox series [Pt(tfd)(2)](z-) (tfd = S(2)C(2)(CF(3))(2); z = 0, 1, 2; the anionic species have [NEt(4)](+) countercations). Single-crystal X-ray structures for the neutral (z = 0) and the fully reduced forms (z = 2) were obtained. The two species have very similar structures but differ slightly in their intraligand bond lengths. (19)F-(195)Pt CP/CPMG and (195)Pt magic-angle spinning (MAS) NMR experiments are used to probe the diamagnetic (z = 0, 2) species, revealing large platinum chemical shielding anisotropies (CSA) with distinct CS tensor properties, despite the very similar structural features of these species. Density functional theory (DFT) calculations are used to rationalize the large platinum CSAs and CS tensor orientations of the diamagnetic species using molecular orbital (MO) analysis, and are used to explain their distinct molecular electronic structures in the context of the NMR data. The paramagnetic species (z = 1) is examined using both EPR spectroscopy and (13)C and (19)F MAS NMR spectroscopy. Platinum g-tensor components were determined by using solid-state EPR experiments. The unpaired electron spin densities at (13)C and (19)F nuclei were measured by employing variable-temperature (13)C and (19)F NMR experiments. DFT and ab initio calculations are able to qualitatively reproduce the experimentally measured g-tensor components and spin densities. The combination of experimental and theoretical data confirm localization of unpaired electron density in the pi-system of the dithiolene rings.

A Multinuclear Solid-State NMR Study of Alkali Metal Ions in Tetraphenylborate Salts, M[BPh4] (M = Na, K, Rb and Cs): What Is the NMR Signature of Cation−π Interactions?

We report a multinuclear solid-state ( (23)Na, (39)K, (87)Rb, (133)Cs) NMR study of tetraphenylborate salts, M[BPh 4] (M = Na, K, Rb, Cs). These compounds are isostructural in the solid state with the alkali metal ion surrounded by four phenyl groups resulting in strong cation-pi interactions. From analyses of solid-state NMR spectra obtained under stationary and magic-angle spinning (MAS) conditions at 11.75 and 21.15 T, we have obtained the quadrupole coupling constants, C Q, and the chemical shift tensor parameters for the alkali metal ions in these compounds. We found that the observed quadrupole coupling constant for M (+) in M[BPh 4] is determined by a combination of nuclear quadrupole moment, Sternheimer antishielding factor, and unit cell dimensions. On the basis of a comparison between computed paramagnetic and diamagnetic contributions to the total chemical shielding values for commonly found cation-ligand interactions, we conclude that cation-pi interactions give rise to significantly lower paramagnetic shielding contributions than other cation-ligand interactions. As a result, highly negative chemical shifts are expected to be the NMR signature for cations interacting exclusively with pi systems.

MVS-derived palladium nanoparticles deposited on polydimethylphosphazene as recyclable catalysts for Heck-type reactions: Preparation, structural study, and catalytic activity

Palladium nanoparticles, obtained by the metal vapor synthesis (MVS) technique, were deposited on polydimethylphosphazene (PDMP). The Pd/PDMP system showed high catalytic activity in the Heck C C coupling of iodobenzene and methyl acrylate, with greater activity than commercially available catalysts such as Pd(OAc) 2 and Pd on carbon. The Pd/PDMP is soluble in the reaction solvent, 1-methyl-2-pyrrolidinone, and can be quantitatively recovered at the end of the reaction by precipitation without loss of metal. When reused, the recovered Pd/PDMP retains its catalytic activity. A multinuclear ( 31P, 13C, 15N) solid-state NMR study identified and characterized the strong structural and dynamic modifications induced by Pd nanoparticles on PDMP. Moreover, solid-state NMR studies and HRTEM analyses, performed on the pristine catalyst and on the catalyst recovered after the reaction, highlighted the almost complete structural invariability of the Pd/PDMP, pointing out the high stability toward agglomeration of the palladium nanoparticles in such a system. Pd/PDMP in the presence of triphenylphosphine was also active in the alkylative cyclization of 7-octen-1-ynes, an important C C coupling reaction to obtain substituted 1,2-bis(alkylidene)cyclohexanes, which are valuable building blocks in fine chemistry.

The First Aluminophosphonate Cluster Analogue of the 4=1 SBU of Zeolites: Structure and Multinuclear Solid-State NMR Study, Including 1H NMR

The first Al−O−P analogue of the so-called 4=1 Secondary Building Unit (SBU) of zeolites is presented and characterized by single-crystal X ray diffraction (compound 1). The 4=1 building unit structure is very rarely encountered in zeolites and microporous materials. Compound 1 was carefully studied by 31P and 27Al solid-state MAS NMR, resulting in the precise spectroscopic description of the phosphorus and aluminium sites. Unusual 27Al quadrupolar parameters were measured. Moreover, we also present a high-resolution solid-state 1H NMR study of 1 at 600 MHz and 33 kHz MAS; a remarkable improvement in resolution is observed, allowing definite assignments. The new opportunities offered by very high speed 1H NMR at high field were further demonstrated with the study of a cubane-shaped Al−O−P cluster (compound 2) and of phenylphosphonic acid. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Synthesis and Characterisation of Mu-26 a Fluorinated All-Silica Zeolite with the STF Framework Topology: Evidence for a Triclinic Symmetry

Abstract X-ray powder diffraction pattern analysis and multinuclear solid state NMR studies performed on the as-synthesised Mu-26 solid, a fluorinated all-silica zeolite with the STF framework topology, have revealed unambiguously a triclinic unit cell and space group P1 for this material.

Multinuclear Solid-State NMR, DSC, and Conductivity Studies of Solid Polymer Electrolytes Based on Polyurethane/Poly(dimethylsiloxane) Segmented Copolymers

Solid polymer electrolytes based on polyurethane/poly(dimethylsiloxane) segmented copolymers (PS55) have been characterized by differential scanning calorimetry (DSC), ionic conductivity, and multinuclear solid-state NMR measurements. The results of DSC measurements indicate the formation of transient cross-links between Li+ ions and the ether oxygens on complexation with LiClO4, resulting in an increase in the soft segment Tg. However, the soft segment Tg remains almost invariant at high salt concentration. There is a conductivity jump at around 310−330 K that the behavior of ionic conductivity changes from Arrehnius- to Vogel−Tamman−Fulcher (VTF)-type behavior. Below this jump temperature, the conductivity follows Arrehnius-like behavior, implying a diffusing mechanism for transport of the charge carriers where the charge carriers are decoupled from the segmental motion of the polymer chain. By contrast, the diffusion of charge carrier is assisted by the segmental motions of the polymer chains above the...

Synthesis and characterization of a novel cyclic aluminophosphinate: structure and solid-state NMR study.

We present the structure and a multinuclear solid-state NMR study of a new cyclic aluminophosphinate. The crystallographic structure of [Al(2)(HC(6)H(5)PO(2))(2)(C(4)H(9)OH)(8)]Cl(4) (compound 1) was obtained at low temperature (a = 11.830(7) A, b = 14.216(6) A, c = 17.790(6) A, beta = 91.25(4) degrees, monoclinic, P21/c, Z = 2). (13)C IRCP (inversion recovery cross polarization) and NQS (non quaternary suppression) NMR experiments allowed the complete assignment of the quaternary carbon atom of the phenyl ring and the precise determination of the isotropic /(1)J(P-C)/ coupling constant. (31)P CP MAS dynamics was carefully studied by varying the contact time. Dipolar oscillations even at slow MAS were observed. Up to 11 kHz, these oscillations were more pronounced, and the P-H distance was easily extracted. (27)Al NMR quadrupolar parameters for 1 were obtained with very good accuracy, and unusual satellite transition splitting was observed. Furthermore, the isotropic lines of the inner and outer transitions were clearly observable, leading to the unambiguous determination of the quadrupolar parameters.

Electrochemical and multinuclear solid-state NMR studies of tin composite oxide glasses as anodes for Li ion batteries

Electrochemical and multi-nuclear solid-state NMR studies of various tin oxide and two tin composite oxide (TCO Sn1.0Al0.42B0.56P0.40O3.6 and Sn-rich TCO Sn1.5Al0.42B0.56P0.40O4.2) samples are described, which give a coherent picture of the different processes occurring within these systems. 6,7Li NMR results demonstrate that the agglomeration of Li–Sn domains is inhibited in TCO; in contrast, in SnO, the aggregation of particles is observed. This difference results in part from the facile back-reaction between Sn and O. The interfacial energy of the most highly divided particles (TCO) allows the "back-reaction" of lithium with oxygen to be reversible at a lower potential than predicted from simple thermodynamic considerations that exclude surface energy contributions. Thus, the proximity and availability of oxygen in the host matrix may indirectly enhance the reversibility and cyclability of the cell in these materials, by "trapping the Sn particles". Aggregation may also be limited in TCO owing to the participation of the matrix observed by 27Al, 31P, and 11B NMR, where reversible changes in the coordination environment are observed during lithium uptake and removal. The size-limiting role of the matrix ions is key to the enhanced electrochemical properties of the TCO glass. The initial rearrangement of the glass network is kinetically limited, as demonstrated by galvanostatic intermittent titration technique (GITT) experiments. The combined results of this study demonstrate the unique nature of the reaction between lithium and TCO.