Operando Neutron Reflectometry

First operando Neutron Reflectometry of Lithiation/Delithiation Process of Crystalline Silicon Anode

Anodes consisting of alloys of lithium and silicon have high specific capacity (4200 mAh/g). They are discussed as replacements e.g. for the graphite anodes in Li-ion batteries. In collaboration with colleagues from TU Clausthal, we succeeded in monitoring a lithium-silicon half-cell with unprecedented spatial and temporal resolution during charging and discharging.[1] Using operando neutron reflectometry, we were able to precisely track the migration of lithium ions into the silicon electrode. As displayed in the right Figure, an approximately 20-nm thick layer was formed near the interface to the electrolyte possessing an extremely high lithium concentration. A second adjacent layer contained only one lithium atom for ten silicon atoms. After the second charging cycle both layers were less than 100 nm thick in total. After discharge, about one lithium ion per silicon atom remained in the silicon layer next to the electrolyte. Therefore, extremely thin layers of silicon would be sufficient to maximize the load of lithium. The capacity of anodes in lithium-ion batteries thus may in principle be increased theoretically by six times by using silicon instead of graphite.

[1] B. K. Seidlhofer, B. Jerliu, M. Trapp, E. Hüger, S. Risse, R. Cubitt, H. Schmidt, R. Steitz, M. Ballauff, Lithiation of Crystalline Silicon As Analyzed by Operando Neutron Reflectivity ,ACS Nano 10 (2016) 7458

SLD-profile

Time- and space-resolved lithiation of a crystalline silicon anode investigated with neutron reflectometry. An approximately 20-nm thick layer was formed near the interface to the electrolyte possessing an extremely high lithium concentration. A second adjacent layer contained only one lithium atom for ten silicon atoms.