Identification and Catalysis of the Potential-Limiting Step in Lithium-Sulfur Batteries

Journal Article · 23 March 2023 · Journal of the American Chemical Society

DOI: https://doi.org/10.1021/jacs.2c13776 · OSTI ID:1974181

Zhong, Yiren ^[1]; Wang, Qian  ^[2]; Bak, Seong-Min  ^[3]; Hwang, Sooyeon  ^[4]; Du, Yonghua ^[3]; Wang, Hailiang  ^[2]

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1. Yale University, New Haven, CT (United States); Southeast University, Nanjing (China)
2. Yale University, New Haven, CT (United States)
3. Brookhaven National Laboratory (BNL), Upton, NY (United States). National Synchrotron Light Source II (NSLS-II)
4. Brookhaven National Laboratory (BNL), Upton, NY (United States). Center for Functional Nanomaterials (CFN)

The Li-S chemistry is thermodynamically promising for high-density energy storage but kinetically challenging. Over the past few years, many catalyst materials have been developed to improve the performance of Li-S batteries and their catalytic role has been increasingly accepted. However, the classic catalytic behavior, i.e., reduction of reaction barrier, has not been clearly observed. Crucial mechanistic questions, including what specific step is limiting the reaction rate, whether/how it can be catalyzed, and how the catalysis is sustained after the catalyst surface is covered by solid products, remain unanswered. Herein, we report the first identification of the potential-limiting step of Li-S batteries operating under lean electrolyte conditions and its catalysis that conforms to classic catalysis principles, where the catalyst lowers the kinetic barrier of the potential-limiting step and accelerates the reaction without affecting the product composition. After carefully examining the electrochemistry under lean electrolyte conditions, we update the pathway of the Li-S battery reaction: S₈ solid is first reduced to Li₂S₈ and Li₂S₄ molecular species sequentially; the following reduction of Li₂S₄ to a Li₂S₂-Li₂S solid with an almost constant ratio of 1:4 is the potential-limiting step; the previously believed Li₂S₂-to-Li₂S solid-solid conversion does not occur; the recharging reaction is relatively fast. We further demonstrate that supported cobalt phthalocyanine molecules can effectively catalyze the potential-limiting step. After Li₂S₂/Li₂S buries the active sites, it can self-catalyze the reaction and continue driving the discharging process.

• Research Organization: Brookhaven National Laboratory (BNL), Upton, NY (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES); National Science Foundation (NSF); China Scholarship Council
• Grant/Contract Number: SC0012704; CBET-1903342
• OSTI ID: 1974181
• Report Number(s): BNL-224404-2023-JAAM
• Journal Information: Journal of the American Chemical Society, Vol. 145, Issue 13; ISSN 0002-7863
• Publisher: American Chemical Society (ACS)Copyright Statement
• Country of Publication: United States
• Language: English