Microstructure Study of Electrochemically Driven Li_xSi

Abstract

We report the direct observation of microstructural changes of LixSi electrode with lithium insertion. HRTEM experiments confirm that lithiated amorphous silicon forms a shell around a core made up of the unlithiated silicon and that fully lithiated silicon contains a large number of pores of which concentration increases toward the center of the particle. Chemomechanical modeling is employed in order to explain this mechanical degradation resulting from stresses in the LixSi particles with lithium insertion. Because lithiation‐induced volume expansion and pulverization are the key mechanical effects that plague the performance and lifetime of high‐capacity Si anodes in lithium‐ion batteries, our observations and chemomechanical simulation provide important mechanistic insight for the design of advanced battery materials.

Microstructural evolution induced by micro-cracking during fast lithiation of single-crystalline silicon

“…2, in which only an amorphous Li x Si phase was observed. Thus, we believe that the Li 15 Si 4 phase is amorphized during the TEM sample preparation process as a result of gallium ion bombardment [24,40]. In contrast, the XRD pattern for the {110} silicon wafer shows a very weak peak at 23° suggesting the presence of a very small amount of crystalline Li 15 Si 4 , and broad peak around 43°.…”

“…Although silicon transforms to several distinct silicon-lithium crystalline phases at elevated temperature [10], it is well known that electrochemical lithiation of silicon at room temperature results in an amorphous phase of lithiated silicon [5,12,[22][23][24]. Obrovac et al [5] suggested that the lithiation of crystalline silicon is a two-phase reaction in which a reaction front separates the growing amorphous lithiated phase from pristine crystalline silicon.…”

Structural Study of Electrochemically Lithiated Si(111) by using Soft X‐ray Emission Spectroscopy Combined with Scanning Electron Microscopy and through X‐ray Diffraction Measurements

“…By inserting Li into the Si substrate from the < 111 > direction, which is the non-preferential directiono fv olume expansion, pulverization and fracture might be prevented. Recently,e lectrochemically lithiated Si (EC-LiSi)h as been intensively studied, [5][6][7][8][9][10][11][12][13][14][15][16][17][18] but its detailedu nderstanding is still unclear.…”

“…Structural analyses of EC-LiSi have reported different results. Severalg roups [5][6][7][8][9] reported that crystalline Li 15 Si 4 (c-Li 15 Si 4 )w as formed througha na morphous Li x Si (a-Li x Si)p hase formation, but others [10][11][12][13][14][15][16] suggested that only the a-Li x Si phase was formed. Reasonsf or such ad ifference are as follows.…”

Mitigating irreversible capacity losses from carbon agents via surface modification

“…TEM samples are prepared using our FIB air-lock system, descripted in the previous work [23]. A typical TEM sample preparation sequence follows: (1) Pt deposition for the protection of the desired surface area.…”