Highly-efficient conversion of SF6 via an eight-electron transfer process in lithium batteries

• Published in: Nano energy Vol. 72; p. 104679
• Main Authors: He, Huajin, Ren, Fucheng, Zhu, Jianping, Xiang, Yuxuan, Zheng, Bizhu, Li, Sheng, Chen, Shijian, Li, Yixiao, Wu, Qi-Hui, Yang, Yong
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.06.2020
• Subjects: Gas conversion; Lithium sulfide; Lithium-SF6 batteries; Porous carbon; Sulfur hexafluoride; Lithium-SF6 batteries; Gas conversion; Porous carbon; Sulfur hexafluoride; Lithium sulfide
• ISSN: 2211-2855
• DOI: 10.1016/j.nanoen.2020.104679

Li-SF6 battery has been proposed as a novel energy conversion device for both reducing greenhouse-effect SF6 and potentially providing large specific energy. However, the real discharge process of SF6 remains ambiguous with fast cathode passivation and large polarization. Here we report that the Li-SF6 chemistry is able to deliver an unprecedented capacity of >20,000 mA h gc−1 with reduced polarization and excellent rate capability by using a low-cost, high-surface-area porous carbon as cathode host. More importantly, by adjusting the SF6 atmosphere, an approximately eight-electron transfer process with predominant products of LiF and Li2S is realized via two voltage steps, whereas previously only a little Li2S could be found with one plateau appearing. The eight-electron process leads to a high energy density about 2,300 W h kg−1 based on the mass of carbon and discharge products, which sheds light on SF6 as a promising high-energy-density cathode. The high-surface-area porous carbon provides sufficient active sites for SF6 absorption and reduction. The limited SF6 avoids the cathode passivation by LiF, thereby maximizing the reduction to Li2S. Combination of both leads to the full reduction of SF6 in lithium batteries with significantly improved discharge capacity and voltage. [Display omitted] •The gas electrode is optimized for the first time in Li-SF6 batteries.•Li-SF6 cells based on high-surface-area Ketjen Black gas electrode deliver great enhanced discharge capacities and voltages.•Firstly disclosing that the eight-electron reduction of SF6 to Li2S involves two voltage plateaus in Li-SF6 batteries.