Kathrin Freedman

Tissue-like Silicon Nanowires-Based Three-Dimensional Anodes for High-Capacity Lithium Ion Batteries

Here, we report on the scalable synthesis and characterization of novel architecture three-dimensional (3D) high-capacity amorphous silicon nanowires (SiNWs)-based anodes with focus on studying their electrochemical degradation mechanisms. We achieved an unprecedented combination of remarkable performance characteristics, high loadings of 3-15 mAh/cm(2), a very low irreversible capacity (10% for the 3-4 mAh/cm(2) anodes), current efficiency greater than 99.5%, cycle stability (both in half cells and a LiFePO4 battery), a total capacity of 457 mAh/cm(2) over 204 cycles and fast charge-discharge rates (up to 2.7C at 20 mA/cm(2)). These SiNWs-based binder-free 3D anodes have been cycled for over 200 cycles, exhibiting a stable cycle life. Notably, it was found that the growth of the continuous SEI layer thickness, and its concomitant increase in resistivity, represents the major reason for the observed capacity loss of the SiNWs-based anodes. Importantly, these NWs-based anodes of novel architecture meet the requirements of lithium batteries for future portable, and electric-vehicle, applications.

To the electrochemistry of pyrite in Li/solid composite-polymer-electrolyte battery

The purpose of this work is the study of the charge–discharge mechanism in the all-solid-state lithium/composite-polymer-electrolyte/ pyrite battery operating at 120 8C. Effects on the charge–discharge mechanism of particle size, type of binder and cathode preparation method of the pyrite-based cathode are addressed. Analysis of the experimental XRD, XPS and electrochemical data suggests that creation of sulfur vacancies in pyrite suppresses a sudden jump of charge voltage, which is associated with slow mass transport of iron(II) cations through the Li2FeS2 phase. We believe that our experimental findings show considerable promise of creating sulfur-deficient pyrite structures for cathodes to be used in high-energy-density all-solid-state lithium batteries. The nature and exact composition of a 1.2–1.3 V discharge plateau is still unclear. To clarify the composition of this low-voltage phase synchrotron X-ray absorption measurements were performed on a series of cells cycled more than 100 times. The results will be presented in a forthcoming publication. # 2003 Elsevier Science B.V. All rights reserved.