<i>Operando</i> Time-Slicing Neutron Reflectometry Measurements of Solid Electrolyte Interphase Formation on Amorphous Carbon Surfaces of a Li-Ion Battery
H. Kawaura, Masashi Harada, Yasuhito Kondo, Mamoru Mizutani, Naoko Takahashi, Norifumi L. Yamada
Abstract
Abstract A solid-electrolyte interphase (SEI) is widely recognized to improve the safety and durability of lithium ion batteries. In this work, we investigate the structure and chemistry of the carbon electrode and SEI in operando during two-cycle battery operation for further understanding of the electrochemical reactions, and the effect of the hysteresis using in situ neutron reflectivity (NR) and ex situ hard X-ray photoelectron spectroscopy (HAXPES). The results revealed the structural evolution of the electrode and SEI layer, such as the change in the thickness and scattering length density (SLD) in connection with the chemical composition during the lithiation/delithiation processes. Next, the HAXPES results at the point before and after the charging/discharging process revealed the change in the chemical composition of the SEI layer due to the chemical reactions on the formation/degradation. Based on the combination of these analyses, the results showed that the SLDs of the SEI layer evaluated by NR analysis were consistent with those determined by HAXPES. Concerning the difference in the first and second cycles, the structure of the amorphous carbon electrode exhibited hysteresis due to lithiation/delithiation, whereas the chemical composition of the SEI layer after charge/discharge was almost independent of the number of cycles.