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Toward in-situ protected sulfur cathodes by using lithium bromide and pre-charge

: Wu, Feixiang; Thieme, Sören; Ramanujapuram, Anirudh; Zhao, Enbo; Weller, Christine; Althues, Holger; Kaskel, Stefan; Borodin, Oleg A.; Yushin, Gleb N.


Nano energy 40 (2017), pp.170-179
ISSN: 2211-2855
Bundesministerium für Bildung und Forschung BMBF
01DM14003; StaLiS
Journal Article
Fraunhofer IWS ()
electrolyte additive; lithium bromide; polysulfide; core-shell nanoparticles; Sulfur

Lithium-sulfur (Li-S) batteries suffer from the dissolution of its intermediate charge products (polysulfides) in organic electrolytes, which limits the utilization, rate performance and cycling stability of S cathode materials. Formation of protective surface coatings on S cathodes may effectively overcome such a challenge. Here, we explored a simple, low cost, and widely applicable method that offers in-situ formation of a protective coating on the S-based cathode by using lithium bromide (LiBr) as a novel electrolyte additive. Quantum chemical (QC) studies suggested that pre-cycling a S cathode at high potentials is needed to oxidize the Br- and induce formation of DME(-H) radicals, which are involved in the formation of a polymerized protective layer of a solid electrolyte interphase (SEI) on a S cathode at high potentials. Experimental studies with a LiBr additive confirmed that 3 pre-cycles in a voltage range of 2.5–3.6 V are sufficient to achieve the formation of a robust Li ion permeable SEI on the cathode, effectively preventing the dissolution of polysulfides into electrolyte. As a result, almost no degradation was observed within 200 cycles, compared to more than 40% of capacity loss in the benchmark control cells without LiBr or the pre-cycles. Post-mortem analysis on both the cathode and anode sides of the LiBr-comprising cells further provided evidence for the in-situ SEI formation on the cathode and the lack of polysulfides’ re-precipitation. In addition, such studies showed smooth surface on the cycled Li metal anode, in contrast to the rough Li SEI with dendrites and polysulfides in the benchmark cells.