Probing the in-depth distribution of organic/inorganic molecular species within the SEI of LTO/NMC and LTO/LMO batteries: A complementary ToF-SIMS and XPS study
Résumé
Spinel Li4Ti5O12 (LTO) is an attractive candidate for negative electrode materials of Li-ion batteries because of its outstanding safety characteristics. In this paper, the influence of common high voltage cathodes, LiNi3/5Co1/5Mn1/5O2 (NMC) and LiMn2O4 (LMO), upon the electrochemical performances of LTO/LMO and LTO/NMC cells, in relation with the Solid Electrolyte Interphase (SEI) properties formed over the LTO surface, is studied. After cycling, the electrodes were analyzed by ToF-SIMS and XPS with two X-ray sources (Ag and Al) to investigate both the chemical composition and the in-depth distribution of specific SEI species at the electrode surface. Facing both counter-electrodes, LTO electrodes are covered by surface layers due to the degradation of electrolyte components inducing an irreversible capacity loss, more important for LTO/LMO cells. The chemical composition of both layers is similar: organic and inorganic species but the SEI formed on LTO electrode cycled facing LMO electrode is thicker and contains small amounts of manganese compounds from the positive electrode. Moreover, 3D mappings reconstructed from ToF-SIMS depth-profile experiments, display different in-depth spatial distributions of SEI species, which are in agreement with XPS results. Consequently, the impact of interactions between electrodes on the formation of surface films is discussed.
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