(Invited) High Lithium Sulfide-Loading Electrode for Practical Li/S Cells

The development of the Li-ion battery (LIB) has led to a portable electronics revolution during last couple of decades, however, the traditional LIB seems to be insufficient for practical application in some emerging markets due to the limited specific energy of the cell. For mass market conversion to electric vehicles, high specific energy (> 300 Wh kg -1 ) rechargeable battery systems of low-cost for energy storage are required. Among all alternatives, the lithium/sulfur cell has been considered most promising due to its low cost, high abundance, ultrahigh theoretical specific energy (2,566 Wh kg -1 ) and theoretical energy density (4,260 Wh L -1 ) which far exceed those of conventional lithium-ion cells. Nevertheless, after extensive study of both sulfur cathodes and lithium sulfide cathodes, neither of these technologies has been commercialized due to poor long-term cycle life and low demonstrated specific energy of lithium/sulfur cells. Practical applications require high sulfur loading electrodes together with the lowest “dead weight” possible in the cell while maintaining good performance. This is quite challenging because commercial current collectors have mechanical limitations in electrode loading and sulfur utiliation. Due to the insulating nature of S and Li 2 S, the addition of a significant amount of a conductive additive into the high loading electrodes is required and introduces more surface area, and thus more electrolyte is needed which further leads to more dead weight. Recently, lithium sulfide was proposed to be a more desirable electrode material because it permits the cell to be assembled in discharged state and avoids problems associated with volume expansion of sulfur during discharge. Disadvantages of lithium sulfide include challenging issues due to its sensitivity toward moisture and solubility in many organic solvents. In order to achieve high specific energy, we have developed a novel Li 2 S/KB@Cf electrode (Li 2 S content: 74 %,) using a robust 3-dimensional (3-D) current collector with a high Li 2 S loading up to 11.29 mg cm -2 (S loading: 7.85 mg cm -2 ), which can deliver an areal capacity of 7 mAh cm -2 after 50 cycles with an Electrolyte/Sulfur ratio of 5.5 (see Fig. 1). We will present our recent progress in high S loading cells and more detailed information about active material development, electrode composition and modifications of the electrolyte and cell configuration. Figure 1