Elizabeth Allan-Cole1,Chuntian Cao2,Roberts Lacey1,Julian Mars1,Michael Toney1
University of Colorado Boulder1,Brookhaven National Laboratory2
Elizabeth Allan-Cole1,Chuntian Cao2,Roberts Lacey1,Julian Mars1,Michael Toney1
University of Colorado Boulder1,Brookhaven National Laboratory2
Enabling fast charging in lithium-ion batteries (LIBs) is critical for future electric vehicles, with the U.S. goal of charging to 80% of full capacity in 15 minutes by 2023 <sup>[1]</sup>. Fast charge rates induce irreversible lithium (Li) plating that adversely impacts battery performance and safety. External stack pressure can improve electrical contact, minimize delamination, and an understanding of the impact of pressure on capacity fade can provide insight into the degradation mechanisms <sup>[2,3]</sup>. In this work, we investigate the extreme fast charging (XFC) regime, focusing on cell degradation and parasitic Li plating using single-layer pouch cells with graphite anodes, LiNi<sub>0.8</sub>Mn<sub>0.1</sub>Co<sub>0.1</sub>O<sub>2</sub> (NMC811) cathodes, and 1.2 M LiPF<sub>6</sub> in 3:7 weight % ethylene carbonate and diethyl carbonate. Cells are tested between 10 – 150 psi, and the cells cycled at higher pressures show a strong reduction in capacity fading after 150 cycles. We performed synchrotron radiation-based <i>operando</i> XRD and <i>in situ</i> 2D XRD mapping in a novel pressure cell during fast charge to study Li plating, parasitic reactions, and Li intercalation into graphite under controlled, uniform pressure. This was complemented with e<i>x situ </i>XPS to study the composition of parasitic reaction products and corrosion to correlate local Li plating to pressure and heterogeneity. Our data reveals the emergence of Li<sub>x</sub>C<sub>6</sub> and Li metal during cycling at XFC, with a reduction in plated parasitic Li at elevated pressure. These results show that the observed improvement on performance is due to more homogenous reaction conditions across the anode and less polarization through the electrode thickness. We emphasize the importance of electrode stack pressure in XFC batteries and quantify Li plating and intercalation yielding critical insight into the degradation mechanisms that cause capacity fade for better battery engineering.<br/><u>References</u><br/>[1] USABC Goals – Lithium Electrode Based Cell and Manufacturing for Automotive Traction Applications, USABC (United States Advanced Battery Consortium), http://www.uscar.org/guest/article_view.php?articles_id=85<br/>[2] C. Cao et al. Influence of Controlled Pressure on Fast-Charging Li-ion Batteries (<i>in preparation</i>)<br/>[3] J. Cannarella and C. B. Arnold, <i>J. Power Sour</i>ce, 2014, 245, 745-751.