J. Wolfenstine

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.

The Limits of Low‐Temperature Performance of Li‐Ion Cells

The results of electrode and electrolyte studies reveal that the poor low‐temperature (<−30°C) performance of Li‐ion cells is mainly caused by the carbon electrodes and not the organic electrolytes and solid electrolyte interphase, as previously suggested. It is suggested that the main causes for the poor performance in the carbon electrodes are (i) the low value and concentration dependence of the Li diffusivity and (ii) limited Li capacity.

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.

Electron microscopy characterization of hot-pressed Al substituted Li7La3Zr2O12

Hot-pressing was used to prepare a dense (97% relative density) cubic Al substituted Li7La3Zr2O12 material at temperatures lower than typically used for solid-state and/or liquid phase sintering. Electron microscopy analysis revealed equiaxed grains, grain boundaries, and triple junctions free of amorphous and second phases and no Al segregation at grain boundaries. These results suggest that Al2O3 and/or Al cannot act as a sintering aid by reducing grain boundary mobility. If Al2O3 acts as a sintering aid its main function is to enter the lattice as Al to increase the point defect concentration of the slowest moving species.

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.

High-temperature deformation and defect chemistry of (La1−xSrx)1−yMnO3+δ

The creep behavior of (La{sub 1{minus}x}Sr{sub x}){sub t{minus}y}MnO{sub 3+{delta}} has been studied as a function of oxygen partial pressure (P{sub O{sub 2}}) and Sr concentration. Polycrystalline samples (x = 0.1, 0.2, 0.3) were deformed at 1,523 K in constant-crosshead-speed compression tests in various atmospheres (10{sup {minus}2} {le} P{sub O{sub 2}} {le} 10{sup 5} Pa). The material deformed by grain-boundary sliding accommodated by lattice diffusion with some possible cavitation and/or interface reaction control. The defect-chemistry model which is standard in the literature could not explain the dependence of the stress on P{sub O{sub 2}} and the Sr concentration. A modified defect-chemistry model shows that cation vacancies controlled the creep rate at P{sub O{sub 2}} {le} 10{sup 5} Pa for x = 0.3 and at low P{sub O{sub 2}} for x = 0.1 and 0.2, and that oxygen vacancies were rate-controlling at high P{sub O{sub 2}} for x = 0.1 and 0.2.

Deformation of perovskite electronic ceramics — a review

Steady-state deformation of several important electronic ceramics, all having a perovskite structure, is reviewed and discussed in terms of their common prominent features. Of particular importance are the ferroelectric BaTiO{sub 3}, a leading candidate for electrodes in solid-oxide fuel cells, (La{sub 1-y}Sr{sub y}){sub 1-x}MnO{sub 3-{delta}} and the high-temperature superconductor YBa{sub 2}Cu{sub 3}O{sub x}. In all cases, deformation occurs by grain-boundary sliding accommodated by diffusion. Cations are the rate-controlling species and their diffusivities can be calculated and compared to existing tracer diffusion data. In some cases, the tracer diffusion coefficients have not been measured, but measurements of steady-state creep can provide these values.

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.

Cycling behavior of nanophase Cu/sub 6/Sn/sub 5/ anodes

Alloy anodes offer the advantages of higher capacity and enhanced safety compared to graphite. One alloy that has received attention is Cu/sub 6/Sn/sub 5/. A major problem with Cu/sub 6/Sn/sub 5/ and alloys in general is their poor capacity retention upon cycling. It was observed that a nanophase Cu/sub 6/Sn/sub 5/ alloy produced by a chemical method has increased cycle life compared to Cu/sub 6/Sn/sub 5/ alloys produced by conventional melting and mechanical alloy.

High-temperature deformation and defect chemistry of (La{sub 1{minus}x}Sr{sub x}){sub 1{minus}y}MnO{sub 3+{delta}}

The creep behavior of (La{sub 1{minus}x}Sr{sub x}){sub t{minus}y}MnO{sub 3+{delta}} has been studied as a function of oxygen partial pressure (P{sub O{sub 2}}) and Sr concentration. Polycrystalline samples (x = 0.1, 0.2, 0.3) were deformed at 1,523 K in constant-crosshead-speed compression tests in various atmospheres (10{sup {minus}2} {le} P{sub O{sub 2}} {le} 10{sup 5} Pa). The material deformed by grain-boundary sliding accommodated by lattice diffusion with some possible cavitation and/or interface reaction control. The defect-chemistry model which is standard in the literature could not explain the dependence of the stress on P{sub O{sub 2}} and the Sr concentration. A modified defect-chemistry model shows that cation vacancies controlled the creep rate at P{sub O{sub 2}} {le} 10{sup 5} Pa for x = 0.3 and at low P{sub O{sub 2}} for x = 0.1 and 0.2, and that oxygen vacancies were rate-controlling at high P{sub O{sub 2}} for x = 0.1 and 0.2.