Orientation-Dependent Interfacial Mobility Governs the Anisotropic Swelling in Lithiated Silicon Nanowires

Abstract

Recent independent experiments demonstrated that the lithiation-induced volume expansion in silicon nanowires, nanopillars, and microslabs is highly anisotropic, with predominant expansion along the <110> direction but negligibly small expansion along the <111> direction. The origin of such anisotropic behavior remains elusive. Here, we develop a chemomechanical model to study the phase evolution and morphological changes in lithiated silicon nanowires. The model couples the diffusive reaction of lithium with the lithiation-induced elasto-plastic deformation. We show that the apparent anisotropic swelling is critically controlled by the orientation-dependent mobility of the core-shell interface, i.e., the lithiation reaction rate at the atomically sharp phase boundary between the crystalline core and the amorphous shell. Our results also underscore the importance of structural relaxation by plastic flow behind the moving phase boundary, which is essential to quantitative prediction of the experimentally observed morphologies of lithiated silicon nanowires. The study sheds light on the lithiation-mediated failure in nanowire-based electrodes, and the modeling framework provides a basis for simulating the morphological evolution, stress generation, and fracture in high-capacity electrodes for the next-generation lithium-ion batteries.

Mesoporous silicon sponge as an anti-pulverization structure for high-performance lithium-ion battery anodes

“…In fact, the observed expansion for the whole particle along the o0114 direction perpendicular to the pore channels is only B7.8%. The small expansion observed along the pore direction (that is, o1004 direction) is also consistent with the previous reports 39,40 . As a result, the MSS studied in this work exhibits the preferred pore orientation and pore structure which can effectively absorb the volume expansion inside of its nanostructure and prevent the particle from pulverization.…”

“…Further increase in pore size could lead to a decrease in the volumetric capacity of the electrode. It is well-known that Si shows significant anisotropic expansion upon lithiation, with an elongation of B200% along the family of o0114 directions 39,40 . Si particles with sizes 4200 nm will pulverize during the lithiation process 4,5 .…”

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

“…Such fracturing leads to poor cycle performance and thus requires an adequate understanding. The crystallographic orientation of the Si nanowire has been identified as one important aspect in governing the nature of anisotropic swelling [17,21]. 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].…”

“…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].…”

Electrical contacts to single nanowires: a scalable method allowing multiple devices on a chip. Application to a single nanowire radial p-i-n junction

“…In the last few years, part of the scientific and technological interest in nanowires has been moved to energy harvesting such as photovoltaic [4][5][6][7][8][9][10][11][12][13], thermoelectric devices [14][15][16][17] and batteries [18][19][20][21][22]. Most of these devices are linked to the external world via electrical contacts.…”