Investigation of Primary Li-Si/FeS sub 2 Cells

摘要

The factors that limit the performance of thermally activated Li-Si/FeS sub 2 batteries were defined through the use of electrochemical characterization tests and post-test examinations. For the characterization tests, 82 individual cells were instrumented with multiple voltage sensors and discharged under isothermal and isobaric conditions. The voltage data for the sensors were recorded to determine the ohmic and electrochemical impedances of each cell component at different levels of discharge. The data analysis completed to date has demonstrated that this approach can successfully differentiate the influence of various operating parameters (e.g., temperature, current density), electrode structures (e.g., FeS sub 2 particle size), and additives on cell capacity, specific energy, and power capability. Thirty cells selected from these tests and additional tests at SNL were examined using optical and scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffraction. These analyses documented microstructural and compositional changes in the active materials and electrolyte. In general, the electrochemical impedance of the FeS sub 2 electrode limited cell performance. Several methods (including use of fine FeS sub 2 particle size, graphite additions, and higher operating temperatures) produced measurable reductions in this impedance and yielded significant improvements in specific energy and power. Additions of KCl to the negative electrode extended the low-temperature capacity of this electrode by counterbalancing gradients in electrolyte composition that develop during discharge. (ERA citation 12:030679)