Sulfur (S) is attractive for energy storage as cathode of Lithium/Lithium-ion (Li/Li-ion) batteries due to its low cost, high abundance, and above all 6-10 times higher theoretical capacity of the state-of-the-art transition metal oxides and phosphates cathodes.[1] Despite these attractive attributes of Li-S batteries, however, there are still challenges pertaining to cathode, electrolyte and anode, which are typically associated with poor cycling stability, low Coulombic efficiency, self-discharge and potential safety concerns.[1] In particular, most of these issues are related to lithium metal anode, which causes unavoidable polysufides shuttle and continuous consumption of active sulfur species, and potentially leads to formation of unsafe Li dendrite.[2] Efforts have been attempted to address these challenges by using electrolyte additives, coating on Li metal, hybrid Li anode, barrier layer and solid state electrolyte to relieve or prevent direct reaction of Li metal with polysulfide species. [3,4] To understand interphase behavior of Li metal anode and its influence on the battery performance, we studied Li half-cell with significant portion of Li stripping/deposition under high current densities by using commercial Li nickel cobalt aluminum oxide (NCA) cathodes with an areal capacity of ca. 2 mAh cm-2 for the counter electrodes. As a result, quick accumulation of thick interphase on Li metal was found to be the direct and major reason for fast capacity decay of the batteries employing Li metal as anode, especially under conditions of high charge (Li deposition) rates.[5] Quick growth of interphase is also observed on Li anode in Li-S battery with high sulfur mass loading, which indicates similar failure mechanism of Li-S batteries. To address issues of Li metal for high energy Li-S battery applications, our strategy is to suppress the reactions of Li metal with both electrolyte and polysulfides by utilizing new types of electrolytes or switching to anode materials other than Li. Significant improvement of sulfur batteries was achieved in terms of cycling stability and charge/discharge efficiency. Detailed results from study of electrolytes, non-Li anodes, and compatibility between them will be presented at the meeting.

Challenges in high-energy Li-sulfur batteries: Failure mechanism on lithium metal anode

249th National Meeting (2015)

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