Sandwich-Lithiation and Longitudinal Crack in Amorphous Silicon Coated on Carbon Nanofibers

Abstract

Silicon-carbon nanofibers coaxial sponge, with strong mechanical integrity and improved electronic conductivity, is a promising anode structure to apply into commercial high-capacity lithium ion batteries. We characterized the electrochemical and mechanical behaviors of amorphous silicon-coated carbon nanofibers (a-Si/CNFs) with in situ transmission electron microscopy (TEM). It was found that lithiation of the a-Si coating layer occurred from the surface and the a-Si/CNF interface concurrently, and propagated toward the center of the a-Si layer. Such a process leads to a sandwiched Li(x)Si/Si/Li(x)Si structure, indicating fast Li transport through the a-Si/CNF interface. Nanocracks and sponge-like structures developed in the a-Si layer during the lithiation-delithiation cycles. Lithiation of the a-Si layer sealed in the hollow CNF was also observed, but at a much lower speed than the counterpart of the a-Si layer coated on the CNF surface. An analytical solution of the stress field was formulated based on the continuum theory of finite deformation, explaining the experimental observation of longitudinal crack formation and general mechanical degradation mechanism in a-Si/CNF electrode.

Review—Promises and Challenges of In Situ Transmission Electron Microscopy Electrochemical Techniques in the Studies of Lithium Ion Batteries

“…149 Nevertheless, damage in the form of surface roughness progressively accumulated on the coating film with long-term charge/discharge cycling. 149,161 Nanocracks and sponge-like structures formed in the amorphous Si films inside and outside of the CNF led to sandwich-lithiation and longitudinal cracks during the lithiation-delithiation cycles. 161 The irreversible chemomechanical degradation is the main question in exploring of a high-capacity electrode material for the next generation of LIBs.…”

“…149,161 Nanocracks and sponge-like structures formed in the amorphous Si films inside and outside of the CNF led to sandwich-lithiation and longitudinal cracks during the lithiation-delithiation cycles. 161 The irreversible chemomechanical degradation is the main question in exploring of a high-capacity electrode material for the next generation of LIBs. The detrimental effect of the swelling may be mediated by formation of a coating like nickel (Ni) on silicon nanotubes (SiNTs), Si nanopillars, or yolk-shell-structured Si NPs.…”

Influence of Y2O3-SiC-Mo and Ce-Al-Ni amorphous alloy on laser melting deposition stellite matrix composites

“…It is known that a series of amorphous alloys have high glass forming ability in Si, Fe, Zr and Y based alloy systems [18][19][20][21]. Thus, it was speculated that a lot of amorphous phases were able to be produced in such LMD coating.…”

“…Nanocomposites differ from the conventional composites due to the particularly high surface-to-volume ratio of ceramic reinforcement [3][4][5][6]. Amorphous materials have also attracted an increasing amount of attention due to their unique physical, mechanical and chemical properties [7][8][9][10]. LMD is a promising approach to producing the amorphous--nanocrystalline composites on metals.…”

Failure Prediction of High-Capacity Electrode Materials in Lithium-Ion Batteries

“…6,7 For instance, Si has the highest theoretical specific capacity in the phase of Li 22 Si 5 (up to 4200 mA h g −1 ), which is nearly ten times higher than that of fully-lithiated graphite in LiC 6 (372 mA h g −1 ). 8,9 Other electrode materials such as Ge and Sn also have considerable theoretical specific capacities (1623 mA h g −1 for Li 22 Ge 5 and 700 mA h g −1 for Li 22 Sn 5 ). 4,7,10 However, the large number of Li-ions inserting into high-capacity electrode materials may result in a huge volume change (400% for full lithiation of Si), 6 and a series of shortcomings: fracture or pulverization of active materials, breakage of a conduction path for electrons and lose of electrical contact, and destruction of solid electrolyte interphase formed by the reaction between active materials and electrolyte.…”