Hybrid organic-inorganic nano-composites for solid-state battery electrolytes

Desired properties of solid electrolytes are high ionic conductivity and transference number, high shear modulus to prevent dendrite growth, chemical compatibility with electrodes, and ease of fabrication into thin films. Especially, elastic stiffness and ionic mobility are opposing attributes in a homogenous material, and a composite approach towards designing novel electrolytes is therefore advisable. We use a two-step sol-gel method to synthesize silica-based hybrid organic-inorganic materials for this application. First, a continuous porous silica structure is created that provides electrochemical stability and mechanical rigidity. This network also contains unreacted epoxy groups. In step 2, single-sided amine-functionalized polyethene glycol (PEG-NH2) infiltrates the pores via fluid exchange. As PEG-NH2 fills the pores, the amine groups react with the epoxy groups and anchor the polymer to the silica network, which provides highly conductive pathways. IR spectroscopy, Raman and Brillouin light scattering, impedance spectroscopy, small angel x-ray scattering (SAXS), charge-discharge cell testing is performed to identify the structural and chemical origins that underlie the performance of these hybrid electrolytes. A room temperature ionic conductivity in excess of 10-5 S/cm is reached (Fig. 1). Please click Additional Files below to see the full abstract

Computational and Phenomenological Modeling of Atomic-Scale Transport Processes in Glasses and Glass-Forming Liquids

This work focuses on the computational investigation and phenomenological model development of atomic-scale transport properties in glasses and glass forming liquids. Specifically, we study ion diffusion and viscous processes as they arise from phenomenologically similar elementary mechanisms. A greater understanding of ionic mobility in glasses can elucidate important materials design criteria for the development of solid-state electrolyte batteries while improvements in viscosity modeling of glass formers is vital to advancing the development and manufacturing of novel glasses. These endeavors work toward providing insight into essential characteristics of the glass transition phenomenon. We begin with a study of diffusivity in a simple two-component model solid electrolyte using molecular dynamics (MD) simulations. This model system is composed of lattice elements, forming a covalent support structure for solute particles that exhibit weaker non-bonding interactions with the network. The solute species size is systematically varied, while the network atoms are unchanged and a constant system volume is maintained. The atomic mobility increases by orders of magnitude in conjunction with cohesive rupture between solute and network and enhanced anharmonicity, as revealed by analyzing the internal pressure, compressibility, and vibrational spectra as a function of solute size. This finding inspires using ion-exchange to enhance ionic mobility in oxide glasses. Replacing cesium in a MD simulation-generated melt-quench cesium silicate glass with the smaller sodium cation results in a 4.5 to 6-fold increase in diffusivity compared to the melt-quenched sodium silicate control. This increase results from a greater free volume of the ion-exchanged glass. Similarly, subjecting the control glass to isotropic volumetric strains, a sodium mobility increase is observed, peaking at 25% strain, which corresponds to the tensile limit of the simulated glass. Expansion causes the potential energy topography to flatten, allowing sodium to readily access transition pathways between neighboring sites. Greater strain causes cavitation of the silica network, creating non-traversable gaps for sodium migration. A hallmark of thermally activated transport processes in glass forming materials is the non-Arrhenius temperature dependence above Tg. This applies to ionic conductivity and viscoelasticity. Conjecturing that this behavior is rooted in a variable free energy topography associated with structural changes occurring in a system upon traversing the glass transition regime, we juxtapose the complex mechanical modulus of a sodium borate melt measured at GHz frequencies and its zero Hz viscosity. Modifying the Maxwell-Wiechert model to account for a temperature dependent activation free energy, the high-frequency and steady-state quantities are perfectly reconcilable with one another, thus validating the underlying atomic scale mechanisms. Expanding on this framework, we develop a workflow for analyzing steady-state viscosity data of 847 oxide glass formers using our new variable activation free energy (VAFE) model in case the adiabatic complex mechanical modulus is not available. We compare the performance of the VAFE model with those of the established VFT and MYEGA equations and find our model to be more robust to extrapolation and possessing more reasonable behavior in the infinite-temperature. Furthermore, our model encodes a relationship between fragility and the temperature-dependent change in the ground-state potential energy associated with structural changes in glass formers between the glassy and liquid states. It also allows one to estimate the number of atoms onto which the activation energy is imparted per elementary viscous dissipation event.PhDChemical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/178029/1/cbeg_1.pd

Cocrystals of 10-Methylphenthiazine and 1,3-Dinitrobenzene: Implications for the Optical Sensing of TNT-Based Explosives

The evaporation of an ethanol solution containing an equimolar mixture of 10-methylphenothiazine and 1,3-dinitrobenzene gave red-purple crystals. The diffuse reflection spectrum for the cocrystals showed a low reflectance from the UV through the visible spectrum until the reflectance increased at the red end of the visible spectrum. The crystal structure showed alternating π stacking of the electron-rich 10-methylphenothiazine and the electron-poor 1,3-dinitrobenzene. There were also hydrogen bonding interactions between the nitro groups from 1,3-dinitrobenzene and the aromatic hydrogen atoms from 10-methylphenothiazine. The infrared spectrum showed a shift to lower wavenumbers for the symmetric and antisymmetric stretching modes for the nitro groups. Thin films containing 10-methylphenothiazine in polystyrene were exposed to 1,3-dintrobenzene vapor, and spectroscopic ellipsometry showed an average increase in the refractive index of 0.006 through the entire range of wavelengths from 1000 to 300 nm

Cocrystals of 10-Methylphenthiazine and 1,3-Dinitrobenzene: Implications for the Optical Sensing of TNT-Based Explosives

The evaporation of an ethanol solution containing an equimolar mixture of 10-methylphenothiazine and 1,3-dinitrobenzene gave red-purple crystals. The diffuse reflection spectrum for the cocrystals showed a low reflectance from the UV through the visible spectrum until the reflectance increased at the red end of the visible spectrum. The crystal structure showed alternating π stacking of the electron-rich 10-methylphenothiazine and the electron-poor 1,3-dinitrobenzene. There were also hydrogen bonding interactions between the nitro groups from 1,3-dinitrobenzene and the aromatic hydrogen atoms from 10-methylphenothiazine. The infrared spectrum showed a shift to lower wavenumbers for the symmetric and antisymmetric stretching modes for the nitro groups. Thin films containing 10-methylphenothiazine in polystyrene were exposed to 1,3-dintrobenzene vapor, and spectroscopic ellipsometry showed an average increase in the refractive index of 0.006 through the entire range of wavelengths from 1000 to 300 nm