Role of the LiPF6 salt for the long-term stability of silicon electrodes in Li-ion batteries - A photoelectron spectroscopy study

B. Philippe (1, 2, 3) , Rémi Dedryvère (1, 3) , M. Gorgoi , H. Rensmo (2, 3) , Danielle Gonbeau (3, 4, 1) , K. Edström (5, 2, 3)

1 IPREM - Institut des sciences analytiques et de physico-chimie pour l'environnement et les materiaux
2 Uppsala Universitet [Uppsala]
3 ALISTORE-ERI - Advanced Lithium Energy Storage Systems - ALISTORE-ERI
4 RS2E - Réseau sur le stockage électrochimique de l'énergie
5 Department of Materials Chemistry - The Angstrom Laboratory

Silicon presents a very high theoretical capacity (3578 mAh/g) and appears as a promising candidate for the next generation of negative electrodes for Li-ion batteries. An important issue for the implementation of silicon is the understanding of the interfacial chemistry taking place during charge/discharge since it partly explains the capacity fading usually observed upon cycling. In this work, the mechanism for the evolution of the interfacial chemistry (reaction of surface oxide, Li-Si alloying process, and passivation layer formation) upon long-term cycling has been investigated by photoelectron spectroscopy (XPS or PES). A nondestructive depth resolved 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. The results are compared with those obtained with an in-house spectrometer (1486.6 eV). The important role played by the LiPF6 salt on the stability of the silicon electrode during cycling has been demonstrated in this study. A partially fluorinated species is formed upon cycling at the outermost surface of the silicon nanoparticles as a result of the reaction of the materials toward the electrolyte. We have shown that a similar species is also formed by simple contact between the electrolyte and the pristine electrode. The reactivity between the electrode and the electrolyte is investigated in this work. Finally, we also report in this work the evolution of the composition and covering of the SEI upon cycling as well as proof of the protective role of the SEI when the cell is at rest.

Mots clés: Soft X-ray; Surface oxide; Theoretical capacity; Alloys; Cerium alloys; Electrochemical cells; Electrodes; Electrolytes; Lithium; Photoelectron spectroscopy; Potential energy surfaces; Seebeck effect; Surface reactions; Synchrotrons; X ray photoelectron spectroscopy; Silicon; Alloying process; At rests; Capacity fading; Charge/discharge; Depth-resolved analysis; Hard X ray; Li-ion batteries; Lithium-ion battery; Long term stability; Negative electrode; Non destructive; Partially fluorinated; Passivation layer; PES; SEI; Silicon electrode; Silicon nanoparticles

Domaines: Matériaux; Chimie théorique et/ou physique

B. Philippe, Rémi Dedryvère, M. Gorgoi, H. Rensmo, Danielle Gonbeau, et al.. Role of the LiPF6 salt for the long-term stability of silicon electrodes in Li-ion batteries - A photoelectron spectroscopy study. Chemistry of Materials, 2013, 25 (3), pp.394-404. ⟨10.1021/cm303399v⟩. ⟨hal-01560421⟩