Solid-state lithium-sulfur batteries (SSLSBs) are considered one of the most promising battery types to meet the requirements of specific applications such as all-electric aviation, due to its high energy density and improved safety. However, polymer-based SSLSBs show rapid degradation during operation over repeated cycles, mainly attributed to the polysulfide shuttle effect. Recently, it has been demonstrated for conventional liquid-electrolyte LSBs that aromatic amide additives such as aramids can effectively inhibit the polysulfide shuttle.
In our contribution, novel concepts and investigations on solid electrolytes (SEs) and composite cathodes for SSLSBs are presented.
Firstly, the influence of aramid additives on the performance and properties of solid electrolytes based on a crosslinked pentaerythritol tetraacrylate (PETEA)-triethylene glycol (TEG) copolymer was investigated. The aramid fibers were functionalized with a silane ligand prior to their integration into the PETEA-TEG matrix. Incorporation of aramid into the PETEA-TEG-based SEs resulted in a significant increase in ionic conductivity up to 2.1∙10-3 S cm-1 at 20 °C. However, after combination with commercial sulfur-carbon cathodes the electrochemical cycling performance revealed severe capacity fading, showing that the integration of aramids into copolymer SEs alone is not sufficient to inhibit the shuttle effect. Therefore, we subsequently investigated an enhancement of the sulfur-carbon composite cathodes by further integrating aramid additives into the PETEA-TEG copolymer-based solid electrolyte binders (catholytes). Consequently, SSLSB coin cells using Li-anodes, PETEA-TEG-aramid SEs, and S-C cathodes with 5 wt.% aramid additives were fabricated and exhibited improved cycle stability with substantially improved capacity retention capacity after 100 cycles.
Thus, from these studies, the integration of aramids into copolymer-based solid electrolytes and S-C composite cathodes has improved the performance and enabled room temperature operation. Currently, we are working on improving material compatibility to increase long-term cycle stability, which promises practical applications for solid-state lithium-sulfur batteries.