Mechanical mismatch-driven rippling in carbon-coated silicon sheets for stress-resilient battery anodes

Abstract

High-theoretical capacity and low working potential make silicon ideal anode for lithium ion batteries. However, the large volume change of silicon upon lithiation/delithiation poses a critical challenge for stable battery operations. Here, we introduce an unprecedented design, which takes advantage of large deformation and ensures the structural stability of the material by developing a two-dimensional silicon nanosheet coated with a thin carbon layer. During electrochemical cycling, this carbon coated silicon nanosheet exhibits unique deformation patterns, featuring accommodation of deformation in the thickness direction upon lithiation, while forming ripples upon delithiation, as demonstrated by in situ transmission electron microscopy observation and chemomechanical simulation. The ripple formation presents a unique mechanism for releasing the cycling induced stress, rendering the electrode much more stable and durable than the uncoated counterparts. This work demonstrates a general principle as how to take the advantage of the large deformation materials for designing high capacity electrode.

Fig. 1

Physical and electrochemical characterization of 2DSi-based anodes. a SEM images of 2DSi with high and low magnifications. b A TEM image of 2DSi@C, inset shows the typical SAED patterns of polycrystalline Si. c A high magnification TEM image, showing 5–10 nm amorphous carbon layers coated on the 2DSi. d–h The side-by-side comparison of half-cell electrochemical performance between 2DSi and 2DSi@C electrodes on initial galvanostatic voltage profiles (d, inset: surface area results of 2DSi, 2DSi@C, and SiNP), capacity retention at 0.2 C-rate (e), rate capability at different C-rate from 0.2 C to 20 C for each 5 cycles (f), long-term stability at 1 C-rate (g), and capacity retention of full-cell paired with LiCoO₂ cathode (h), respectively. Scale bars, 100 nm and 5 μm (a); 500 nm (Inset: 2 1/nm) (b); and 5 nm (c)

Fig. 2

Electrochemical and chemomechanical behavior of the 2DSi@C. a–e The time-lapse in situ TEM images and corresponding SAED patterns of 2DSi@C for two cycles of lithiation and delithation. f Snapshots of chemomechanical modeling of 2DSi@C corresponding to the in situ TEM results. Scale bars, 500 nm for TEM images and 2 1/nm for SAED patterns (a–e)

Fig. 3

Large deswelling ratio induced rippling in 2DSi@C. a An ex situ TEM image of 2DSi@C after the first cycle. b The change in dimension versus SOC calculated from the chemomechanical modeling. c Illustrations of mechanical mismatch induced internal stress and rippling morphology in 2DSi@C during lithiation/delithiation process. Scale bar = 500 nm (a)

Fig. 4

Comparisons of the morphological evolution between 2DSi and 2DSi@C by the chemomechanical modeling. Snapshots of deformation morphologies predicted by the chemomechanical model, showing a–c lithium concentration and b–d the first principal stress of 2DSi and 2DSi@C, respectively

Fig. 5

The morphology changes in a single sheet. A series of SEM images of a–c 2DSi and d–f 2DSi@C after 1, 10, and 100 cycles, respectively (Inset: schematic illustration of each morphology and high magnification SEM images). Scale bars are 1 μm