Recovery of Unwanted Lithium from Graphite Anodes Via Thermal Gradient

Abstract

Thermal management is a known design consideration for safe and stable cycling of Li-ion batteries. Active thermal management systems attempt to maintain isothermal control to limit thermal excursions that can lead to premature cell performance loss and safety failures. Low temperature cycling is one example of unsafe Li-ion battery operation, which has been shown to limit cycle life by lithium plating and can also lead to dendrite nucleation and growth that can cause internal short circuits and battery failure. However, it can be assumed that these engineering controls cannot consistently maintain the safe isothermal condition and localized thermal gradients will develop within cells. We previously showed that the application of an external thermal gradient has a profound effect on cell electrochemical processes. For lithium metal symmetric cells, the direction of an interelectrode thermal gradient dictates lithium plating morphology and determines whether unstable, dendrite growth or stable plating occurs (1). We have also demonstrated that applying a thermal gradient (cold anode, warm cathode) allows plating lithium on graphite on-demand, dramatically reducing cell capacity by loss of lithium inventory (2). In this way, a thermal gradient rapidly incites realistic cell failure modes, accelerating testing to battery failure to enable improved understanding of battery failure. This talk focuses on the utility of reversing the direction of interelectrode thermal gradients to strip lithium from the graphite electrode. We use post mortem materials characterization techniques including X-ray diffraction (XRD), scanning electron microscopy (SEM), and Raman spectroscopy to characterize texture and morphology of the plated and lithium metal on graphite and confirm its recovery. A thermal gradient effectively restores battery health by modulating plating to recover lithium inventory and battery capacity; this thermal gradient reversal prevents internal short circuits from dendrite growth and ultimately extends battery lifetime in NMC|graphite cells. In addition to post mortem materials characterization, we use electrochemical impedance spectroscopy (EIS) and incremental capacity analysis to monitor lithium plating and stripping modulation. References A. Mistry, C. Fear, R. Carter, C. T. Love and P. P. Mukherjee, ACS Energy Letters, 4, 156 (2018).R. Carter and C. T. Love, ACS Appl Mater Interfaces (2018).