Jae-Deok Jeon

Solvent-Free Polymer Electrolytes I. Preparation and Characterization of Polymer Electrolytes Having Pores Filled with Viscous P ( EO ‐ EC ) ∕ Li C F 3 S O 3

We have attempted to combine a typical gel (hybrid liquid-solid system) and a typical solvent-free polymer electrolyte (solid system) through the concept of the pore-filling polymer electrolyte; instead of organic solvents, a viscous polymer complexed with a Li salt is filled into the pores of a porous membrane. The viscous polymer, poly(ethylene oxide-ethylene carbonate) copolymer [P(EO-EC)] with a low molecular weight (Mw = 1800) and amorphous nature is synthesized using ethylene carbonate (EC) and its viscosity is found to be independent of shear rate, which is a characteristic of a Newtonian fluid. Porous membranes consisting of poly(vinylidene fluoride-co-hexafluoropropylene) [P(VdF-HFP)] and P(EO-EC) are prepared by a phase inversion method and examined by means of 1 H solid-state nuclear magnetic resonance and field emission-scanning electron microscopy. From these results, it is confirmed that they are homogenous on a scale of a few tens of nanometers and the existence of P(EO-EC) in membranes makes much larger pore size and higher porosity than the pure P(VdF-HFP) membrane. This implies that the relative composition of P(EO-EC) plays a critical role in determining the membranes morphology and porosity. The temperature dependence of the ionic conductivity for the polymer electrolytes is well fitted to the Arrhenius equation. The highest conductivity of 3.7 X 10 - 5 S cm - 1 at 25°C and 1.6 X 10 - 4 S cm - 1 at 55°C is obtained for E-V6E4. Cyclic voltammetry on stainless steel electrodes shows that the polymer electrolyte is electrochemically stable up to at least 5.0 V vs Li/Li + .

Carbide-derived carbon/sulfur composite cathode for multi-layer separator assembled Li-S battery

To improve the electrochemical performance of Li-S rechargeable batteries, tunable porous carbon materials, which are known as carbide-derived carbons (CDCs), are employed as adsorbents and conductive matrices for the cathodic sulfur materials. A new assembly for Li-S cells was developed by introducing multi-layer membranes as separators. The use of the multi-layer membranes enables the minimization of the shuttle effect by expanding the distance between the separators and blocking the penetration of the polysulfide. The best discharge capacity and cycle life were obtained with ten layers of PP membrane in a sulfur-CDC@1200 composite cathode, resulting in a discharge capacity of 670 mA h g−1 and a minimal gap in the charge-discharge capacity during cell cycling.