In Situ Measurements of Stress-Potential Coupling in Lithiated Silicon

Abstract

An analysis of the dependence of electric potential on the state of stress of a lithiated-silicon electrode is presented. Based on the Larch\'e and Cahn chemical potential for a solid solution, a thermodynamic argument is made for the existence of the stress-potential coupling in lithiated-silicon; based on the known properties of the material, the magnitude of the coupling is estimated to be ca. 60 mV/GPa in thin-film geometry. An experimental investigation is carried out on silicon thin-film electrodes in which the stress is measured in situ during electrochemical lithiation and delithiation. By progressively varying the stress through incremental delithiation, the relation between stress change and electric-potential change is measured to be 100 - 120 mV/GPa, which is of the same order of magnitude as the prediction of the analysis. The importance of the coupling is discussed in interpreting the hysteresis observed in potential vs. state-of-charge plots, and the role of stress in modifying the maximum charge capacity of a silicon electrode under stress.Comment: 21 pages, 5 figure

Li15Si4Formation in Silicon Thin Film Negative Electrodes

“…These results imply that the Li 15 Si 4 phase may be a consequence of particle aggregation; however, the variance in threshold size among Si morphologies raises questions. In particular, the suppression of Li 15 Si 4 formation in thin films that are microns thick is startling.…”

“…Furthermore, crystalline Li 15 Si 4 has been shown to form during the lithiation of silicon when the voltage becomes less than 50 mV. 1 Acoustic emission studies and imaging techniques have indicated that this phase transition can result in high internal stresses, leading to particle fracture and cell fade.…”

“…2 To overcome the issues associated with Li 15 Si 4 phase formation and volume expansion during cycling, researchers have demonstrated high cycle life in Li cells by using Si in the form of nanoparticles, 3,4 nanowires, 5,6 nanopillars, 7,8 thin films, 9,10 and in alloys with inactive or active phases. 11,12 These studies have reported various threshold sizes for nanoparticles (150 nm), 3,4 nanowires (300 nm), 13 and amorphous thin films (2.5 μm), 14 below which Li 15 Si 4 formation does not occur. These results imply that the Li 15 Si 4 phase may be a consequence of particle aggregation; however, the variance in threshold size among Si morphologies raises questions.…”

“…11,12 These studies have reported various threshold sizes for nanoparticles (150 nm), 3,4 nanowires (300 nm), 13 and amorphous thin films (2.5 μm), 14 below which Li 15 Si 4 formation does not occur. These results imply that the Li 15 Si 4 phase may be a consequence of particle aggregation; however, the variance in threshold size among Si morphologies raises questions. In particular, the suppression of Li 15 Si 4 formation in thin films that are microns thick is startling.…”

Chemomechanics of ionically conductive ceramics for electrical energy conversion and storage

“…Reproduced from [55] by permission of the Royal Society of Chemistry change surface reactivity by engineering strain (or the conjugate stress) within or among lithium intercalation compounds. Sethuraman et al investigated the stress-potential coupling in lithiated silicon through experimental measurements of changes in substrate curvature during electrochemical lithiation and delithiation [178]. They found that the strength of the coupling was on the order of 100 mV/GPa, corresponding to a major contribution to energy dissipation during charge/discharge cycles that resulted from plastic flow associated with stresses arising within the film.…”