All-solid-state lithium-sulfur battery based on a nanoconfined LiBH₄ electrolyte

In this work we characterize all-solid-state lithium-sulfur batteries based on nano-confined LiBH4in mesoporous silica as solid electrolytes. The nano-confined LiBH4has fast ionic lithium conductivity at room temperature, 0.1 mScm-1, negligible electronic conductivity and its cationic transport number (t+= 0.96), close to unity, demonstrates a purely cationic conductor. The electrolyte has an excellent stability against lithium metal. The behavior of the batteries is studied by cyclic voltammetry and repeated charge/discharge cycles in galvanostatic conditions. The batteries show very good performance, delivering high capacities versus sulfur mass, typically 1220 mAhg-1after 40 cycles at moderate temperature (55°C), 0.03 C rates and working voltage of 2 V. © The Author(s) 2016

Dielectric Relaxation Spectroscopy for Evaluation of the Influence of Solvent Dynamics on Ion Transport in Succinonitrile-Salt Plastic Crystalline Electrolytes

Influence of succinonitrile (SN) dynamics on ion transport in SN-lithium perchlorate (LiClO4) electrolytes is discussed here via dielectric relaxation spectroscopy. Dielectric relaxation spectroscopy (similar to 2 x 10(-3) Hz to 3 MHz) of SN and SN-LiClO4 was studied as a function of salt content (up to 7 mol % or 1 M) and temperature (-20 to +60 degrees C). Analyses of real and imaginary parts of permittivity convincingly reveal the influence Of trans gauche isomerism and solvent-salt association (solvation) effects on ion transport. The relaxation processes are highly dependent on the salt concentration and temperature. While pristine SN display only intrinsic dynamics (i.e., trans-gauche isomerism) which enhances with an increase in temperature, SN-LiClO4 electrolytes especially at high salt concentrations (similar to 0.04-1 M) show salt-induced relaxation processes. In the concentrated electrolytes, the intrinsic dynamics was observed to be a function of salt content, becoming faster with an increase in salt concentration. Deconvolution of the imaginary part of the permittivity spectra using Havriliak-Negami (HN) function show a relaxation process corresponding to the above phenomena. The permittivity data analyzed using HN and Kohlrausch-Williams-Watta (KWW) functions show non-Debye relaxation processes and enhancement in the trans phase (enhanced solvent dynamics) as a function of salt concentration and temperature

Time-Temperature Scaling of Conductivity Spectra of Organic Plastic Crystalline Conductors

Organic plastic crystalline soft matter ion conductors are interesting alternatives to liquid electrolytes in electrochemical storage devices such as Lithium-ion batteries. The solvent dynamics plays a major role in determining the ion transport in plastic crystalline ion conductors. We present here an analysis of the frequency-dependent ionic conductivity of succinonitrile-based plastic crystalline ion conductors at varying salt composition (0.005 to 1 M) and temperature (-20 to 60 degrees C) using time-temperature superposition principle (TTSP). The main motivation of the work has been to establish comprehensive insight into the ion transport mechanism from a single method viz, impedance spectroscopy rather than employing cluster of different characterization methods probing various length and time scales. The TTSP remarkably aids in explicit identification of the extent of the roles of solvent dynamics and ion-ion interactions on the effective conductivity of the orientationally disordered plastic crystalline ion conductors

Ionic conductivity of bis(2-cyanoethyl) ether-lithium salt and poly(propylether imine)-lithium salt liquid electrolytes

We report here a multiple-nitrile based lithium-salt liquid electrolyte. The ionic conductivity of poly (propyl ether imine) (abbreviated as PETIM) lithium salt dendrimer liquid electrolyte was observed to be a function of dendrimer generation number, n = 0 (monomer)−3. While the highest room temperature ionic conductivity value (∼ 10⁻¹ Sm⁻¹) was recorded for the bis-2cyanoethyl ether monomer (i.e. zeroth generation; G₀-CN), conductivity decreased progressively to lower values (∼ 10⁻³ Sm⁻¹) with increase in generation number (G₁-CN → G₃-CN). The G₀-CN and higher dendrimer generations showed high thermal stability (≈150 to 200 °C), low moisture sensitivity and tunable viscosity (∼10⁻² (G₀-CN) to 3 (G₃-CN) Pa s). The linker ether group was found to be crucial for ion transport and also eliminated a large number of detrimental features, chiefly moisture sensitivity, chemical instability associated typically with prevalent molecular liquid solvents. Based on the combination of several beneficial physicochemical properties, we presently envisage that the PETIM dendrimers especially the G₀-CN electrolytes hold promise as electrolytes in electrochemical devices such as lithium-ion batteries

Brillouin Scattering Investigation of Solvation Dynamics in Succinonitrile-Lithium Salt Plastic Crystalline Electrolytes

Temperature dependent Brillouin scattering studies have been performed to ascertain the influence of solvent dynamics on ion-transport in succinonitrile-lithium salt plastic crystalline electrolytes. Though very rarely employed, we observe that Brillouin spectroscopy is an invaluable tool for investigation of solvent dynamics. Analysis of various acoustic (long wavelength) phonon modes observed in the Brillouin scattering spectra reveal the influence of trans-gauche isomerism and as well as ion-association effects on ion transport. Although pristine SN and dilute SN-LiClO(4) samples show only the bulk longitudinal-acoustic (LA) mode, concentrated SN-LiClO(4) (similar to 0.3-1 M) electrolytes display both the bulk LA mode as well as salt induced brillouin modes at ambient temperature. The appearance of more than one brillouin mode is attributed to the scattering of light from regions with different compressibilities (''compactness''). Correspondingly, these modes show a large decrease in the full width at half-maximum (abbreviated as nu(f)) as the temperature decreases. Anomalous temperature dependent behavior of nu(f) with addition of salt could be attributed to the presence of disorder or strong coupling with a neighbor. The shape of the spectrum was evaluated using a Lorentzian and Fano line shape function depending on the nature and behavior of the Brillouin modes

Brillouin Light Scattering Study of Microscopic Structure and Dynamics in Pyrrolidinium Based Ionic Liquids

Pyrrolidinium based ionic liquids are known to be good ionic conductors even in solid-state around room temperature, which is attributed to the highly disordered plastic crystalline phase. Moreover, these ionic liquids are characterized by multiple phase transitions which include plastic, structural glass, and glassy crystal phases with varying levels of molecular disorder. Temperature-dependent Brillouin light scattering is used to investigate the phase transitions in a series of alkylmethylpyrrolidinium Bis(trifluoromethanesulfonyl) imides (P1nTFSI, n=1,2,4). Brillouin spectral features such as the number of acoustic modes, their shape, and linewidth provide the picture of different disordered phases resultant of dynamics at the microscopic scale. The longitudinal and transverse acoustic velocities in different phases are determined from the corresponding acoustic mode frequencies (Brillouin shift). Extremely low acoustic velocities in the solid phase of P11TFSI and P12TFSI are a consequence of a high degree of disorder and plasticity present in the system. Anomalous temperature-dependent behavior of linewidth and asymmetric (Fano) line shape of acoustic modes observed in certain phases of P1nTFSI could be due to the strong coupling between the Brillouin central peak and the acoustic phonons. The present results establish that the Brillouin light scattering technique can be efficiently used to understand the complex phase behavior, microscopic structure, and dynamics of ionic liquids.</p

Study of solvent relaxation of pristine succinonitrile and succinonitrile-salt mixtures using quasielastic neutron scattering

Succinonitrile (SN) has been demonstrated as an excellent organic plastic crystalline ``solid-like'' solvent for dissolution of large variety of salts at ambient temperatures. The SN-salt electrolytes are highly conducting only in the plastic phase of SN. We discuss here the study of solvent dynamics of SN in the plastic crystalline state both in the absence and presence of salts using high resolution quasielastic neutron scattering (QENS, IN16 spectrometer at ILL-Grenoble). Elastic scan versus temperature for SN, 1 M SN-LiClO4 (SN-lithium perchlorate), 1 M SN-(LiClO4)(0.95)(LiTESI)(0.05) (SN-lithium perchlorate-lithium bis(trifluoromethane-sulfonyl)imide) revealed a sharp order-disorder transition at 233 K. Significant quasielastic broadening was observed above 233 K. The obtained QENS data (T = 245 K) displayed relaxations approximate to 100 ps which is localized and can be accounted on the basis of a one-molecule mathematical model proposed by Bee et al. (assuming all possible molecular conformations in its unit cell). The SN rotational dynamics which determines ionic conductivity is observed to be faster in the SN-salt mixtures than the pristine SN. The high resolution QENS data also revealed the localized diffusion of the whole molecule (which includes the coordinated Li-ion and the counter anion(s)) around its nearest neighbors. Assuming that this molecular diffusion is confined under a potential of spherical symmetry, the estimated value of the radius of the domain for whole molecule diffusion and the corresponding diffusion coefficients are extracted. While the time scale for whole molecular diffusion for pristine SN and 1 M SN-LiClO4 is found to be very similar, the whole molecular diffusion for SN-(LiClO4)(0.95)(LiTFSI)(0.05) is much slower, probably due to increased mass. (C) 2015 Elsevier B.V. All rights reserved