A Dual-Phase Cathode and a Si/SiOx Anode for Li-Sulfur Batteries

The lithium-sulfur battery is one of the most promising high-energy-density electrochemical energy storage systems for emerging applications such as power storage systems for renewable energy plants and the powering of sustainable electric vehicles.¹ The natural abundance and low cost of sulfur, coupled with the high theoretical energy density of sulfur-based cathodes, namely, 1675 mAh g^-1 and 3500 Wh kg^-1, are the major advantages of this sulfur battery.² However, the insulating nature of sulfur, leads to low active material utilization, and sulfur electrodes have low stability, arising from the formation of soluble lithium polysulfide during cell operation; these problems, have so far limited the commercialization of this battery.³ There has been consistent progress recently toward optimizing the sulfur electrode.⁴ Recently, several research groups have reported that the addition of lithium polysulfide to the electrolyte could improve the performance of the Li/S battery in terms of cycle performance and energy density.⁵

Another major concern regarding the lithium-sulfur battery system is its use of a lithium metal anode, which is well known to have some critical problems including chemical reactivity in commonly used organic electrolytes and dendritic growth of lithium during cycling, leading to poor cycle performance and safety problems. In addition, when coupled with a sulfur cathode, the lithium metal anode reacts with lithium polysulfide to form an insoluble Li₂S phase on the lithium surface, leading to the loss of lithium metal and eventually causing poor cycle performance of the system. It should be also noted that an excess amount of lithium metal is needed to construct the full cell to secure its long cycle life, which might lead to degradation of both the energy density and the safety of the full cell.

Herein, we demonstrated a lithium-ion sulfur cell configuration using a newly designed dual-type sulfur cathode and a lithiate Si/SiO_x nanosphere anode with optimized liquid electrolyte. Our dual-type sulfur cathode system delivered maximum capacity on the order of 1,300 mAh g^-1as referred to the mass of the overall sulfur content; that is to say, the mass of sulfur both in the solid cathode and in the dissolved lithium polysulfide. The lithiated Si/SiOx nanosphere anode used showed highly stable cycling behavior over 100 cycles, with a capacity as high as 800 mAh g^-1and cycling efficiency approaching 100%. The full lithium-ion sulfur cell presented herein delivered a capacity on the order of about 750mAhg^-1. We believe that these results might advance the practical development of the lithium-ion sulfur battery, particularly for use in emerging markets including electric vehicles and large-scale power storage systems for use with renewable energy systems.

References

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2. E. Peled, A. Gorenshtein, M. Segal, Y. Sternberg, J. Power Sources, 26, 269 (1989).

3. Y-V. Mikhaylik, J. R. Akridge, J. Electrochem. Soc., 151, A1969 (2004)

4. X. Ji, K-T. Lee, L. F. Nazar, Nat Mater., 8, 500 (2009).

5. R. D. Cakan, M. Morcrette, Gangulibabu, A. Guéguen, R. Dedryvère, J-M. Tarascon, Energy Environ. Sci., 6, 176 (2013).