The Effects of Native Oxide Surface Layer on the Electrochemical Performance of Si Nanoparticle-Based Electrodes

Abstract

This study controllably reduces the silicon dioxide (SiO 2 ) layer on Si nanoparticles and evaluates its effect on the performance of Si nanoparticle-based electrodes in Li-ion batteries. Various thicknesses of this native oxide are present on Si nanoparticles generated by chemical vapor deposition (CVD) due to the process conditions and exposure to oxygen during storage. This layer can be effectively reduced by hydrofluoric acid (HF) etching, which results in improved electrochemical performance over as-received samples. As-received Si sample has a higher first-cycle capacity loss than that of the etched Si samples, when the capacity loss is normalized to the surface area of the Si particles. Spectroscopic analysis reveals that when the Si electrode is held at a low potential, the oxide layer can be converted to a more stable silicate form due to the irreversible consumption of lithium species in the cell. The thick SiO 2 surface layer also isolates the Si core from lithium-ion alloying; therefore, the as-received Si nanoparticles deliver a lower specific capacity than their etched counterpart. Incomplete lithiation of the as-received Si particles is confirmed by transmission electron microscopy, which shows that nanocrystalline Si domains remain after cycling. The surface insulating effects of SiO 2 also cause high impedance in the Si electrode.

Fracture and debonding in lithium-ion batteries with electrodes of hollow core–shell nanostructures

“…In fact, a lower lithiation capacity due to an incomplete surface reaction has been observed in recent experiments [15,52,53].…”

Investigation of the Electron Transfer at Si Electrodes: Impact and Removal of the Native SiO2Layer

“…40 The reason for the rather small electron transfer rate constant was the native SiO 2 surface layer of the Si electrode ( Figure 1b) which causes high impedance also evident from electrochemical impedance spectroscopy (EIS). 41 The ME current i T was locally increased at the edge of the upper left pillar in Figure 2a at x = 20 μm/y = 220 μm (circle symbol), because i T amounted to 2.8 nA and was even 0.5 nA larger than i T,∞ ≈ 2.3 nA. Therefore, it can be concluded that the local electron transfer rate constant at this position was much larger than at all other positions of the Si pillars.…”

Challenges and Recent Progress in the Development of Si Anodes for Lithium‐Ion Battery

“…Besides, we should concern more about increased and accelerated native oxide surface derived from nanosized silicon materials with large surface area, which can affect the electrochemical performance and induce the inevitable use of hydrofluoric acid (HF). [43,44] The first-cycle Coulombic efficiency of silicon anode is typically in the range of 65-85%, far below that of commercial graphite anodes (90-94%). Below we will summarize the recent progress to achieve high initial Coulombic efficiency from three aspects, including secondary structure design, prelithiation, and electrolyte additive.…”