Increasing EV pack size and customer expectations are necessitating the push towards higher charger rates, culminating in what the Department of Energy Vehicle Technology Office deems “Extreme Fast Charge” (XFC), which is charging to 80% of the battery capacity in 10 minutes. Though charge rates have generally increased over the last 10 years, cell development has kept pace because moderate charge rates have not introduced new degradation mechanisms. However, with XFC rates approaching 4C, lithium plating has been commonly observed.[1] Sandia National Labs is uniquely qualified to characterize this phenomenon, particularly from the perspectives of early detection and impact on abuse response / safety.

This talk will describe Sandia’s work to better characterize lithium plating over several variables, including cell chemistry, charge rate, and temperature. High precision cycling, a result of partnership with Arbin, Ford Motor Company, and Montana Tech, will be used to accurately measure cell efficiency and identify markers of lithium plating.[2] While similar approaches have been reported in the past,[3] Sandia’s high precision tester offers extreme levels of Measurement Precision (25ppm), Timing Precision (5ppm), and control accuracy (< 0.003%) to derive earlier and more accurate Li plating evidence. [4] We will also report results a Rapid EIS technique, which completes scans in under 10 seconds, to identify impedance-related markers for lithium plating. The technique allows fast EIS scans during applied fast-charge loads, providing a window into electrode interface events as they occur.

In additional to early detection of lithium plating, Sandia is uniquely qualified to assess the safety impacts of XFC and potential lithium plating. Abuse response of cells will be characterized after varying degrees of fast charge, including initiation points of thermal runaway and changes in EUCAR ratings. Lithium plating will be quantified, and any unique safety implications of molten lithium during safety events will be discussed, especially any increases in thermal runway sensitivity.

Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia LLC, a wholly owned subsidiary of Honeywell International Inc. for the U.S. Department of Energy?s National Nuclear Security Administration under contract DE-NA0003525.

[1] S. Ahmed et al., J. Power Sources, 367, p. 250 (2017).

[2] A. Masias, "Electrochemical Prozac: Relieving Battery Anxiety through Life and Safety Research,” in Frontiers of Engineering: Reports on Leading-Edge Engineering from the 2014 Symposium, p. 25, The National Academies Press, Washington, DC (2015).

[3] A. J. Smith, J. C. Burns, S. Trussler, J. R. Dahn, J. Electrochem. Soc., 157 (2), A196 (2010).

[4] Arbin Instruments HP Tester Specifications, http://www.arbin.com/products/coulombic-efficiency/ (2016).