| Description |
The research can be broadly divided into three parts: (i) design of an in-situ electrochemical cell that can be used for neutron diffraction studies of small-volume electrodes in Li-ion batteries, (ii) development of Si (100) electrode with microporous columnar architecture to achieve high energy storage capacity, and (iii) neutron diffraction investigation of lithiation phenomenon in microporous columnar Si (100) electrode using the in-situ cell. The first part of the work is concerned with the design and performance of a novel in- situ electrochemical cell that greatly facilitates the neutron diffraction study of complex phase transitions in small volume electrodes of Li-ion cells. The unique aspect of cell design is that it uses single crystal Si (100) sheets as casing material and planar cell configuration, giving an improved signal-to-noise ratio relative to other casing materials. Diffraction patterns of high quality that are Rietveld-refinable could be obtained simultaneously for all the electrodes in graphite/LiCoO2 and graphite/LiMn2O4 cells during cycling. It is shown that most of the finer details of the phase transitions, and the associated changes in crystallographic parameters of electrode phases, can be captured. The second part of the work is concerned with microstructure engineering Si electrode, to produce columnar microporous structure, which can achieve high energy storage capacity. It is shown that this electrode provides a highly reversible specific Li- storage capacity (~1250 mAh/g), and the highest total Li-storage capacity (~1.25 iv mAh/cm2) relative to other Si electrodes. The most exciting finding of this study is that the volume expansion caused during lithiation is accommodated within the pores and the pore walls do not crumble even after a large number of cell cycles, mitigating the Si cracking issues. The present findings reveal a new pathway for architecturing Si electrodes for much larger and highly reversible total charge-storage capacities for on- chip Li-ion cells. The third part of this research, focused on understanding the crystallographic and phase transformation aspect that leads to a high degree of reversible lithiation in the single layer microporous Si electrode, has been performed to understand the lithiation and phase transformation aspects. The results indicate that lithiation induces mosaicity during lithiation. |
