Donald Foster

Oxygen Transport Properties of Organic Electrolytes and Performance of Lithium/Oxygen Battery

The oxygen transport properties of several organic electrolytes were characterized through measurements of oxygen solubility and electrolyte viscosity. Oxygen diffusion coefficients were calculated from electrolyte viscosities using the Stokes-Einstein relation. Oxygen solubility, electrolyte viscosity, and oxygen partial pressure were all directly correlated to discharge capacity and rate capability. Substantial improvement in cell performance was achieved through electrolyte optimization and increased oxygen partial pressure. The concentration of oxygen in the electrode under discharge was calculated using a semi-infinite medium model with simultaneous diffusion and reaction. The model was used to explain the dependence of cell performance on oxygen transport in organic electrolyte.

Nano-scale Cu6Sn5 anodes

Abstract Nano-scale ( 5 Sn 6 powders were prepared by a chemical method that used a NaBH 4 solution to reduce the metal ions. A significant improvement in capacity retention was obtained in the nano-scale Cu 6 Sn 5 alloy, compared to the alloy having micron-sized particles. The volumetric capacity of the nano-scale Cu 6 Sn 5 alloy at 100 cycles was almost twice the theoretical capacity of graphite.

Experimental confirmation of the model for microcracking during lithium charging in single-phase alloys

Abstract Indentation fracture toughness measurements yielded a K IC for Li 4.4 Sn equal to 0.8±0.2 MPa m 1/2 . From K IC , a critical crack length of 0.005 nm was determined for the stress generated due to the volume expansion as a result of Li charging into the Li 4.4 Sn alloy. The critical crack length was in excellent agreement with the predicted critical grain size for microcracking. This suggests that the model for predicting the critical grain size for microcracking during Li charging into brittle single-phase alloys is correct.

The effect of the Mn-ion oxidation state on propylene carbonate decomposition

Abstract Cyclic voltammetry revealed that the oxidation voltage of propylene carbonate (PC) containing 1 M LiClO 4 on MnO, Mn 2 O 3 and MnO 2 is approximately 4.7 V. This suggests that the oxidation of PC is independent of the Mn-ion oxidation state. Gas chromatography results support the voltammetry results. CO 2 is the major gas evolved from the decomposition of PC on MnO, Mn 2 O 3 and MnO 2 . Reducing the oxidation state of the Mn-ion does not eliminate CO 2 gas formation in the Li/MnO 2 system.