In situ measurements of stress evolution in silicon thin films during electrochemical lithiation and delithiation

Abstract

V. A. Sethuraman); Pradeep_Guduru@Brown.edu (P. R. Guduru)We report in situ measurements of stress evolution in a silicon thin-film electrode during electrochemical lithiation and delithiation by using the Multi-beam Optical Sensor (MOS) technique. Upon lithiation, due to substrate constraint, the silicon electrode initially undergoes elastic deformation, resulting in rapid rise of compressive stress. The electrode begins to deform plastically at a compressive stress of ca. -1.75 GPa; subsequent lithiation results in continued plastic strain, dissipating mechanical energy. Upon delithiation, the electrode first undergoes elastic straining in the opposite direction, leading to a tensile stress of ca. 1 GPa; subsequently, it deforms plastically during the rest of delithiation. The plastic flow stress evolves continuously with lithium concentration. Thus, mechanical energy is dissipated in plastic deformation during both lithiation and delithiation, and it can be calculated from the stress measurements; we show that it is comparable to the polarization loss. Upon current interrupt, both the film stress and the electrode potential relax with similar time-constants, suggesting that stress contributes significantly to the chemical potential of lithiated-silicon.

Evaluating the performance of nanostructured materials as lithium-ion battery electrodes

“…In addition, Si suffers from a large (± 400%), volume change during the (de)alloying process, the strain of which potentially leads to pulverisation of the local structure and electrical disconnect from the current collector; such an effect results in a marked loss of capacity and cycle performance [15]. Numerous examples in the literature have demonstrated the associated volume change on the local structure of the Si anode [16][17][18]. Nanostructured forms, however, may accommodate much of the strain associated with such alloying processes due to an increase in the surface to volume ratio associated with their reduced dimensions.…”

“…Ab initio calculations revealed a preference for Li + diffusion in Si nanowires with a <110> growth direction [17], where Li + insertion occurs via layer-by-layer diffusion, originating from the surface of the nanowire (Li + interaction at surface sites is energetically favourable), through to the core of the nanowire with increasing energy [17]. Following Li + insertion, a core-shell structure develops consisting of crystalline Si and an amorphous LixSi shell, where an abrupt change in Li + concentration at the core-shell interface induces a chemical strain [21]; the amorphous shell relaxes by plastic flow [18], while the crystalline core suffers elastic deformation, potentially leading to fracturing of the local structure [21].…”

Variation of stress with charging rate due to strain-rate sensitivity of silicon electrodes of Li-ion batteries

“…Fortunately, this mechanical damage can be mitigated by nanostructuring the silicon anodes, as has been successfully demonstrated in nanowires [6,7], thin films [8][9][10][11][12], nanoporous structures [13,14], and hollow nanoparticles [15,16]. Specifically, recent experiments and theories indicate that one can prevent fracture by taking advantage of lithiation-induced plasticity [11,[17][18][19][20][21][22].…”

“…A number of studies have examined plastic deformation in Li x Si [5,12,18,[20][21][22][23][24][25][26][27][28][29][30][31][32][33][34]. Sethuraman et al measured stresses during cycling of Li x Si electrodes, finding plastic flow, which results in dissipation of energy comparable to that of polarization losses [18].…”

“…Sethuraman et al measured stresses during cycling of Li x Si electrodes, finding plastic flow, which results in dissipation of energy comparable to that of polarization losses [18]. Zhao et al suggested that plastic flow in a-Li x Si reduces the energy release rate (i.e., the crack driving force), thus preventing fracture in nano-sized (~100 nm) electrodes [20].…”