Sulfurized carbonized polyacrylonitrile (S-CPAN) is a promising cathode material for Li−S batteries owing to the absence of polysulfide dissolution phenomena in the electrolyte solutions and thus the lack of a detrimental shuttle mechanism.^1,2 However, challenges remain in achieving high performance at practical loading because of large volume expansion of S-CPAN electrodes and lithium anode degradation at high current densities. To take advantage of the unique charge-discharge mechanisms of S-CPAN electrodes at high sulfur loadings, we introduce a novel cell design through the application of polyacrylic acid (PAA) binder to S-CPAN electrodes using alkyl carbonate based electrolyte solutions with fluoroethylene carbonate (FEC) as an additive. PAA based binders were found to be superior over PVdF in a previous work, in terms of excellent adhesion and cohesion properties of composite electrodes. FEC is considered a ‘magic’ additive/co-solvent in Li salt electrolyte solutions, working with Li metal or Li-Si anodes and high voltage Li insertion cathodes or S-C composite cathodes as its surface reactions lead to polymerization and formation of effectively passivating surface films. We found that Li-S cells comprising S-CPAN cathodes with PAA binder resolve the inherent problems of cathode structure fragmentation through hydrogen bonding of S-CPAN-PAA and S-CPAN-PAA-Al₂O₃, which strengthen the cathode structure.³ A major advantage of using FEC-containing solutions is the stabilization of the lithium metal anodes by formation of passivating surface films.⁴ The combination of these three components — S-CPAN, PAA, and FEC — resulted in outstanding electrochemical performance of practically loaded sulfur cathodes with stable cycle life. We demonstrated pouch cells,⁵ which contained 100 mAh S-CPAN cathodes with a specific capacity around 3 mAh cm^-2, which exhibited very stable.

References

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