Impact of the cycling temperature on electrode/electrolyte interfaces within Li4Ti5O12 vs LiMn2O4 cells

Reliable development of Li-ion Batteries requires a good understanding of the correlation between electrochemical performances and accurate aging interfaces phenomena. The present study focuses on the SEI characterization formed at both electrodes surface in LiMn2O4/Li4Ti6O12 (LMO/LTO) cells, depending on the cycling temperature, which is one of the major stress factors for batteries. LMO/LTO cells were cycled at 25 degrees C, 40 degrees C and 60 degrees C over 100 cycles and the chemical composition of surface layers was investigated by XPS, SAM and ToF-SIMS at the end of the 100th cycles. LTO electrodes are covered by surface layers since the first cycle (inducing an irreversible capacity loss) and the SEI thickness increases with the cycling temperature; moreover, organic (alkyl-carbonates, polyethylene oxides, oxalates) and inorganic species (LiF and (fluoro)-phosphates) of the solid interphase are present in different proportions depending on the temperature; more fluorophosphates are especially observed at 60 degrees C due to a higher chemical degradation of LiPF5 salt. Finally, small amounts of manganese, heterogeneously spread over the LTO electrode surface, are found at different oxidation states at higher temperatures; for the first time, metallic Mn-0 was detected at the LTO surface after cycling at 60 degrees C which could explain the important capacity loss of the system at this temperature.