Nanosilicon Electrodes for Lithium-Ion Batteries: Interfacial Mechanisms Studied by Hard and Soft X-ray Photoelectron Spectroscopy

Abstract

Largely based on its very high rechargeable capacity, silicon appears as an ideal candidate for the next generation of negative electrodes for Li-ion batteries. However, a crucial problem with silicon is the large volume expansion undergone upon alloying with lithium, which results in stability problems. Means to avoid such problems are largely linked to the understanding of the interfacial chemistry during charging/discharging. This is especially of great importance when using nanometric silicon particles. In this work, the interfacial mechanisms (reaction of surface oxide, Li−Si alloying process, and passivation layer formation) accompanying lithium insertion/ extraction into Si/C/CMC composite electrodes have been scrutinized by Xray photoelectron spectroscopy (XPS). A thorough nondestructive depthresolved analysis was carried out by using both soft X-rays (100−800 eV) and hard X-rays (2000−7000 eV) from two different synchrotron facilities compared with in-house XPS (1487 eV). The unique combination utilizing hard and soft X-ray photoelectron spectroscopy accompanied with variation of the analysis depth allowed us to access interfacial phase transitions at the surface of silicon particles as well as the composition and thickness of the SEI (electrode/electrolyte interface layer).

A hard X-ray photoelectron spectroscopy study on the solid electrolyte interphase of a lithium 4,5-dicyano-2-(trifluoromethyl)imidazolide based electrolyte for Si-electrodes

“…A lot of work has been done to understand the SEI on graphitic negative electrodes while the field of SEI formation on silicon is still a young area with only a rather small number of publications. [4,[7][8][9][10][11][12][13][14][15][16][17][18][19] Philippe et al have…”

“…successfully used different kinds of photoelectron spectroscopy (PES) to analyze the SEI formation on Si-electrodes [7,8,16]. Results suggest that the LiPF 6 salt decomposes to form HF that reacts with the silicon oxide to form new compounds [7,8], possibly detrimental to the cycling of Si.…”

Photoluminescence Studies of Li-Doped Si Nanocrystals

“…It has been shown recently that Li doping can considerably affect the surface layer in Li electrodes for batteries [24]. However, these electrodes have typical sizes of around 50nm with a 2nm thick native oxide layer and our nanocrystals are much smaller (diameters around 3nm) with only one or two oxide monolayers.…”

Synthesis of Li₂SiO₃ using novel water-assisted solid state reaction method

“…10),11) Among of them, alkali metasilicate Li 2 SiO 3 has been actively investigated as luminescent material, 12),13) lithium battery materials, 14), 15) and optical wave guides. 16) Li 2 SiO 3 is generally synthesized by a conventional solid state reaction (SSR) method at high temperature.…”