Detrimental Effects of Chemical Cross-Talk in Rechargeable Lithium Metal Batteries

Abstract

The energy density of conventional Li-ion batteries (LIBs) has eventually reached their theoretical limit. Increasing worldwide efforts have been made towards the next generation of energy storage systems including batteries using Li metal anode in combination with various cathodes, including intercalation compounds (such as NMC) or conversion materials (such as oxygen (O2) and sulfur (S)). For a full demonstration of new battery chemistries, the interfacial stability is essential to long cycle lifespan and battery performance. In general, batteries suffer from “cross-talk” processes upon cycling by the crossover of parasitic chemicals through the electrolyte media [1]. Indeed, "cross-talk" phenomena in Li-ion batteries, such as Mn2+ crossover from the cathode and contaminate graphite anode has been well established [2]. Li-S and Li-O2 batteries also have the shuttle issues of soluble redox-active materials, polysulfides and superoxide radical anions, respectively. However, the similar characteristics in Li metal batteries (LMBs) with conventional Li ion intercalation cathodes have rarely been studied. Therefore, an in-depth understanding of how a Li metal anode affects the cathode interface chemistry is critical to ensure the long-term cycling stability of LMBs. Here, we report the cathode failure triggered by the chemical “cross-talk” between the electrode pair in rechargeable LMBs. In sharp contrast to LIBs, the cathode in LMBs suffers more significant and irreversible capacity fade during cycling, and its capacity cannot be fully recovered in spite of repeated replacement with new Li metal in the successive cycling. In-depth characterizations of the cathode surface reveal severe deterioration of cathode electrolyte interphase related to the significant accumulation of highly resistive polymeric components and lithium fluoride. Extensive salt-anion decomposition at Li metal surface can cause the chemical aging of the electrolyte allowing the migration of soluble byproducts toward the cathode side, resulting in the severe deterioration of cathode and separator surfaces. A selective Li-ion permeable separator with polydopamine coating has been developed to mitigate the detrimental chemical crossover and enhance the cathode stability. [1] Mikhaylik, Y. V.; Akridge, J. R., Polysulfide Shuttle Study in the Li/S Battery System. J. Electrochem. Soc. 2004, 151 (11), A1969-A1976 [2] Vetter, J.; Novák, P.; Wagner, M. R.; Veit, C.; Möller, K. C.; Besenhard, J. O.; Winter, M.; Wohlfahrt-Mehrens, M.; Vogler, C.; Hammouche, A. Ageing mechanisms in lithium-ion batteries. J. Power Sources 2005, 147 (1), 269-281. Figure 1