Insights into the Li Diffusion Mechanism in Si/C Composite Anodes for Lithium-Ion Batteries

Abstract

Recently, Si/C composite materials have attracted enormous research interest as the most promising candidates for the anodes of next-generation lithium-ion batteries, owing to their high energy density and mechanical buffering property. However, the fundamental mechanism of Li diffusion behavior in various Si/ C composite materials remains unclear, with our understanding limited by experimental techniques and continuum modeling methodologies. Herein, the atomic behavior of Li diffusion in the Si/C composite material is studied within the framework of density functional theory. Two representative structural mixing formats, that is, simple mixture mode and core−shell mode, are modeled and compared. We discover that the carbon material increases Li diffusion in silicon from 7.75 × 10 −5 to 2.097 × 10 −4 cm 2 /s. The boost is about 50% more obvious in the mixture mode, while the core−shell structure shows more dependence on the atomic structures of the carbon layer. These results offer new insights into Li diffusion behavior in Si/C composites and unlock the enhancing mechanism for Li diffusion in Si/C. This understanding facilitates the modeling of batteries with composite anodes and will guide the corresponding structure designs for robust and high-energy-density batteries.

Influence of the Silicon–Carbon Interface on the Structure and Electrochemical Performance of a Phenolic Resin-Derived Si@C Core–Shell Nanocomposite-Based Anode

“…In the first cycles, the difference of Si2/C and Si3/C in capacity is huge compared to Si1@C, Si2@C, and Si3@C, as the Li ions can directly form an alloy with Si without diffusion through the carbon shell first. 40 However, degradation effects become visible fast, which lead to fast cell failure. Therefore, the surface modification itself is not the reason for stable cycling, but the interaction with the carbon shell, which leads to a stable core−shell material especially at high current densities.…”

“…For core−shell particles, Li atoms are forced to pass through the carbon layer first before they diffuse into the Si core. 40 However, Li diffusion not only depends on the thickness and the structure of the carbon layer but also on the C−Si interface and its resistance. 40 Here, most of the differences seem to be a result of the surface modification itself.…”

Constructing a Sheet-Stacked Si/C Composite by Recycling Photovoltaic Si Waste for Li-Ion Batteries

“…The past 30 years have witnessed the immense progress of lithium-ion batteries (LIBs). Graphite anodes, which are the widely used anode materials, cannot satisfy the ever-growing demand for energy density of LIBs because they present only 372 mA h g –1 . , Si-based anodes, which express a profound theoretical capacity of 3579 mA h g –1 (at room temperature), are deemed as an upcoming anode material for LIBs. , However, low conductivity and the tremendous volume variation of Si anodes limit their application. − During the repeated discharge–charge processes, Si anodes suffer huge volume expansion, resulting in particle fracture, failure of electrical contact, and the formation of solid electrolyte interphase (SEI) films on account of the continuous depletion of the electrolyte, thus leading to fast structure degradation and capacity decay. , To resolve the problems, proper modifications are essential such as reducing the particle size, , carbon coating, , constructing special morphology, , introducing buffer matrix, − and so forth. In the early stage, the Si waste suffers purification and then is modified like common Si sources to relieve its inherent defects.…”

“…8−10 During the repeated discharge−charge processes, Si anodes suffer huge volume expansion, resulting in particle fracture, failure of electrical contact, and the formation of solid electrolyte interphase (SEI) films on account of the continuous depletion of the electrolyte, thus leading to fast structure degradation and capacity decay. 9,11 To resolve the problems, proper modifications are essential such as reducing the particle size, 10,12 carbon coating, 13,14 constructing special morphology, 15,16 introducing buffer matrix, 17−19 and so forth. In the early stage, the Si waste suffers purification and then is modified like common Si sources to relieve its inherent defects.…”

A Novel Tin-Bonded Silicon Anode for Lithium-Ion Batteries

“…Owing to the widespread use of lithium-ion batteries (LIBs) in plethoras of portable consumer electronic devices and electric vehicles, tremendous efforts have been made to meet the increasing demands for high energy and power density output in energy storage systems. − …”