Lithium-sulfur (Li-S) battery represents an attractive alternative to the state-of-the-art Li-ion batteries to meet the urgent demand of high-efficient and cost-effective energy storage technologies. This is due to low cost, high abundance, and above all 6-10 times higher theoretical capacity of sulfur than conventional oxide and phosphate cathode materials.1 However, these promising prospects are hindered to market penetration due to practically low accessible energy density and poor long-term cycle life of Li-S batteries. Recent attempts in improving performance of Li-S battery have been focused on development of nanostructured sulfur host materials and novel electrode structure designs. However, most of those studies are based on sulfur electrodes with either small fraction of sulfur in carbon composite or low sulfur loading in the whole electrode (less than 2 mg cm-2).2 For practical applications, instead, areal capacity of sulfur cathode should be at least 3-7 mAh cm-2 to compete or outperform commercial Li-ion batteries. This is quite challenging in practical because of intrinsically low electronic and ionic conductivities of sulfur and Li2S/Li2S2. One widely used strategy to improve performance of high mass loading electrode is to use thick and porous cathode structures or free-standing carbon nanofiber (CNF)/nanotube (CNT) papers as sulfur host. These methods help to improve sulfur utilization rate, yet unfortunately sacrifice energy density of the system, because large content of carbon materials increases parasitic weight but does not contribute capacity at all. A more detrimental issue is that the ultra-thick and porous electrode or additional thick carbon interlayers not only reduces volumetric energy density but also lowers gravimetric capacity when sucking excess volume of electrolyte for full electrode wetting. To pursue high cell performance, particularly for high volumetric energy density, it is critical to control the electrode thickness/porosity, which however decreases active material utilization rate and cell cycling life. In our recent research, significant benefits as well as detrimental influences of reducing electrode porosity on cell performance were systematically investigated based on sulfur electrode with mass loading above 4 mg cm-2. At the meeting, we will present our recent progresses on the development of high energy density sulfur cathode including material development, electrolyte modification, and device fabrication.

Enhanced performance of high volumetric energy density sulfur cathode for Li-sulfur batteries

253rd National Meeting (2017)

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