Fabrication of sulfur cathodes by wet-powder spraying and the understanding of degradation

• Homogenous sulfur-composite layers were fabricated by wet powder-spraying.
• Li–S batteries were tested over 1000 cycles with constant coulombic efficiency (100%).
• Solid amorphous phases were revealed and semi-quantified by operando XRD.
• Structural changes of carbon black and degradation of PVDF occurs after cycling.

In this work, wet powder spraying is presented as an alternative method for the fabrication of sulfur/carbon composite cathodes. The high dispersion and homogeneity of the cathode layer result in high capacity Li/S batteries. Additional use of LiNO3 as additive improved the discharge capacity to 800 Ah kgS−1, 400 Ah kgcathode−1 (at 0.18 C) and 410 Ah kgS−1, 205 Ah kgcathode−1 (at 2 C) after 50 cycles. The shuttle mechanism is reduced and a coulombic efficiency of around 100% is reached and maintained constant until 1000 cycles. To understand more the degradation mechanisms of the battery, Thermogravimetry combined with gas analysis (TG/MS) as well X-ray diffraction (operando and mappings) were applied. The formation of an amorphous phase during cycling that remains nearly stable in the later cycles is considered to be one of the main factors affecting capacity decay. Moreover, others processes are identified as contributors of battery degradation like PVDF decomposition, structural changes of carbon black, and reduction of sulfur content on the bulk of the electrode. These new insights on the degradation processes may contribute to the further understanding, selection of materials, and improvement of this battery.