Abstract
Mechanical degradation and resultant capacity fade in high-capacity electrode materials critically hinder their use in high-performance rechargeable batteries. Despite tremendous efforts devoted to the study of the electro–chemo–mechanical behaviours of high-capacity electrode materials, their fracture properties and mechanisms remain largely unknown. Here we report a nanomechanical study on the damage tolerance of electrochemically lithiated silicon. Our in situ transmission electron microscopy experiments reveal a striking contrast of brittle fracture in pristine silicon versus ductile tensile deformation in fully lithiated silicon. Quantitative fracture toughness measurements by nanoindentation show a rapid brittle-to-ductile transition of fracture as the lithium-to-silicon molar ratio is increased to above 1.5. Molecular dynamics simulations elucidate the mechanistic underpinnings of the brittle-to-ductile transition governed by atomic bonding and lithiation-induced toughening. Our results reveal the high damage tolerance in amorphous lithium-rich silicon alloys and have important implications for the development of durable rechargeable batteries.
Highlights
Mechanical degradation and resultant capacity fade in high-capacity electrode materials critically hinder their use in high-performance rechargeable batteries
The above experimental and modelling results underscore the notion of the high damage tolerance of amorphous Li-rich Si alloys and have important implications for the design of durable Si-based anodes for next-generation Lithium-ion batteries (LIBs)
Lithiation experiments have been conducted with amorphous Si (a-Si) nanoparticles with a wide range of diameters up to 870 nm[18], as well as with a-Si pillars of a few microns in diameter[37]
Summary
Mechanical degradation and resultant capacity fade in high-capacity electrode materials critically hinder their use in high-performance rechargeable batteries. In the development of next-generation LIBs, mechanical degradation in high-capacity electrode materials arises as a bottleneck Such high-capacity electrode materials usually experience large volume changes (for example, up to about 280% for silicon (Si)), leading to high mechanical stresses and fracture of electrodes during electrochemical cycling[13,14,15,16,17,18,19,20,21,22]. The result reveals a direct contrast between the low fracture resistance in the brittle core of pristine Si and the high damage tolerance in the ductile shell of fully lithiated Si. We conducted systematic measurements of the fracture toughness of lithiated Si thin films with nanoindentation. At the end of the lithiation process, the diameter of the unlithiated c-Si core was 85 nm; the thicknesses of the a-Li3.75Si shell and the layer of lithiated surface oxide (LiySiOz) were 47 and 17 nm, respectively
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