Calendar Vs. Cycle Aging of Lithium-Ion Cells with Silicon Anode

Silicon has been investigated for decades, as an alternative to the graphite used in lithium-ion battery anodes, because of its high theoretical capacity. However, the large volume change of Si during electrochemical cycling (cycle-aging) deteriorates the solid electrolyte interphase (SEI) layer on the particles, resulting in increased electrolyte reduction reactions and associated capacity decay. Capacity fade is also observed in cells that are not cycled but simply held at voltage for extended periods of time (calendar-aging). [1] Here we report the calendar and cycle-aging behavior of cells with a Si anode that is paired with a NMC532 cathode (Figure 1). The tests were conducted in coin cells and in cells with a reference electrode (prepared by in-situ lithiation of a 25 mm Cu wire). This reference electrode allowed us to determine changes in the individual electrode profiles during aging and to examine impedance changes that were monitored via hybrid pulse power characterization (HPPC) tests. [2] Our various experiments have revealed the following: (i) capacity-fade is greater during cycle-aging than during calendar-aging; (ii) the capacity fade is associated with shifts in both positive and negative electrode potentials; (iii) parasitic currents are observed during the calendar-life hold, which indicate ongoing electrolyte reduction reactions at the silicon electrode; (iv)both electrodes contribute to the significant impedance rise observed during cell aging. To further examine sources of the observed performance degradation we conducted experiments with cells with the Si paired with LiFePO 4 . These data, along with the probable mechanisms of cell aging, will also be discussed during the presentation. References Kalaga et al., Acta 2018, 280, 221-228. Klett et al., Electrochem. Soc. 163 (2016) p. A875. Acknowledgments : M.L. acknowledges the generous grants from the U.S. National Science Foundation with the award numbers of CMMI-1660572 and IIP-1918991 that enabled her research at Argonne National Laboratory. The electrodes and electrolytes used in this study are from Argonne’s Cell Analysis, Modeling and Prototyping (CAMP) Facility. We are grateful to Andrew Jansen, Bryant Polzin, and Steve Trask for their assistance during this study. Figure 1