Activation Energies of Crystallization Events in Electrochemically Lithiated Silicon

Abstract

Li/Si coin cells were assembled using crystalline Si as a negative electrode material. The Si was electrochemically lithiated and delithiated to various states of charge. Differential scanning calorimetry studies at heating rates varying from 1 • C/min to 20 • C/min were performed and analyzed to yield activation energies for crystallization reactions occurring in lithiated Si with increasing temperatures. Activation energies requiring mainly the diffusion of Li atoms were near or below 150 kJ/mol while activation energies requiring the reworking of Si bonds were near or above 300 kJ/mol. Avoiding the formation of Li 15 Si 4 did not significantly impact the DSC signals of delithiated a-Li x Si samples.

In Situ Mechanistic Elucidation of Superior Si‐C‐Graphite Li‐Ion Battery Anode Formation with Thermal Safety Aspects

“…Mainly, silicon has buildup of thicker LiF layer and other reaction products on its surface and for similar capacities, silicon composite will have lesser contact area with electrolyte, which leads to slower reaction . It is also reported that compared to conventional graphite with similar moles of lithium, the lithiated silicon shows lower reactivity between 100 °C and 350 °C . This suggest that the synergistic effect of each ingredient of the composite results in lowering the exothermic heat released during thermal runaway reactions.…”

“…It is observed that between 155-165 °C there is an endothermic peak which results from the melting of the polypropylene (PP) separator and gasket of the coin cell. [47,53,55] This suggest that the synergistic effect of each ingredient of the composite results in lowering the exothermic heat released during thermal runaway reactions. Around 170-175 °C, binder meltdown and reaction with lithiated material occurs, [51] generating very high exothermic peaks observed after 180 °C.…”

Core-shell Si@TiO2 nanosphere anode by atomic layer deposition for Li-ion batteries

“…4b-c, which could be assigned to the lithiation of crystalline Si into an amorphous Li x Si phase with a progressively increasing Li content at lower voltage [25]. While the corresponding charge slopes below 0.50 V are related to the Li extraction [10], via de-alloying of amorphous Li y Si phase with different composition [49]. The weak discharge slopes starting at around 1.5 V should be attributed to the formation of solid electrolyte interphase (SEI) film on the surface of the active particles [50], which become less important in the following cycles, leading to some irreversible electrochemical reactions on the surface in the first reduction scan [51,52].…”

Measuring Mechanical Properties during the Electrochemical Lithiation of Silicon

“…The literature provides a consistent picture for the phases that are formed during electrochemical lithiation of crystalline Si (c‐Si), although the observed phases are completely different from those shown in the equilibrium phase diagram. For example, the (111) surfaces of silicon form an amorphous Li 3.5 Si phase on decreasing the voltage from the open cell voltage (OCV) to circa 130 mV vs. Li/Li + at room temperature, rather than the stable intermediate phases that are expected from the binary phase diagram . Below 50 mV a metastable crystalline Li 15 Si 4 phase is formed, which reacts with the electrolyte as soon as the potential of the electrode is no longer controlled .…”

“…Forexample,the (111) surfacesofsilicon form an amorphous Li 3.5 Si phase on decreasing the voltage from the open cell voltage (OCV) to circa1 30 mV vs.L i/Li + at room temperature,r ather than the stable intermediate phases that are expected from the binary phase diagram. [1,[5][6][7][8][9][10][11][12][13][14][15] Below 50 mV am etastable crystalline Li 15 Si 4 phase is formed, which reacts with the electrolyte as soon as the potential of the electrode is no longer controlled. [1,[8][9][10][11][12][13] Tr ansmission electron microscopy (TEM) diffraction patterns show that Li 15 Si 4 has an anocrystalline microstructure when formed by in situl ithiation of nanowires and nanoparticles using as olid LiO 2 electrolyte.…”