Study of Prelithiated Silicon As Anode in Lithium-Ion Cells

NASA is developing Ultra High Energy (UHE) lithium ion (Li-ion) cell designs and batteries for future exploration mission under NASA Advanced Space Power System project [1]. Development of silicon (Si) as an advanced anode is part of the effort for UHE Li-ion cell designs since Si is regarded as one of the most promising anode due to its high theoretical capacity (~10 times of graphite [2,3]) and its abundance on earth. However, there are challenges associated with using Si as a Li-ion anode mainly due to the significant volume change in Si particles upon Li alloying/de-alloying process. The volume change during the cycling results in degradation of the solid-electrolyte interphase (SEI) layer and/or disintegration of the Si anode electrode, causing significant irreversible capacity loss at initial few cycles and subsequent rapid capacity fade [4]. The formation of SEI layer on Si is slow and difficult to form during the initial few cycles [5], and SEI formation process consumes lithium, which results in partial capacity loss irreversibly . As Si anode is incorporated into the Li-ion full-cell , the irreversible capacity loss at the initial few cycles is significantly higher, and subsequent capacity fade is much faster than those in the corresponding half-cell , which is due to the limited Li in the full-cell . In addition, the Si anode voltage rises quickly at the end of discharge because of the depletion of Li, as shown in Figure 1, which causes the higher cathode voltage cut-off, results in lower utilization of cathode and reduces the overall cell specific capacity. It is expected that the prelithiation of Si anode can help to overcome the initial irreversible capacity loss, lower the voltage rise at the end of discharge, reduce the capacity fade and extend the cycling life. In this report, the impact of a prelithiated Si anode on SEI formation, the first cycle irreversible capacity loss and the capacity fade has been studied. Various prelithiation methods, including to apply stabilized lithium metal powder (SLMP) on top of Si anode by spray method has been investigated. Electrochemical techniques such as cyclic voltammetry and electrochemical impedance spectroscopy in combination with SEM and other spectroscopy techniques are used to study the SEI formation of prelithiated Si anode vs. non-prelithiated Si anode. Full-cell with reference electrode is constructed to monitor Si anode voltage profile during the cycling and help to understand how prelithiated Si anode help to reduce the irreversible Li loss and extend the cycling life. References: [1] Mercer C. et al., “Energy Storage Technology Development for Space Exploration”, NASA/TM— 2011 -216964 [2] Besenhard, J. O.; Yang, J.; Winter, M. J. Power Sources 1997 , 68, 87. [3] Wen, C. J.; Huggins, R. A. J. Solid State Chem. 1981 , 37, 271. [4] Boukamp, B. A.; Lesh, G. C.; Huggins, R. A. J. Electrochem. Soc. 1981 , 128, 725-729. [5] Wu, J. J. and Bennett, W. R. “Fundamental Investigation of Silicon Anode in Lithium-Ion Cells”, NASA/TM, 2012 -217739, E-18484