Group at BIT Published Research Outcome on Regulating Li-S Battery Kinetics on Chem

       Beijing Institute of Technology, Nov 8th, 2020: Recently, Cell Press’s flagship chemistry magazine Chem (impact factor 19.7) reported the latest progress of Huang Jiaqi’s group in manipulating regulating the sulfur redox kinetics of lithium-sulfur batteries. The group is from the Advanced Research Institute of Multidisciplinary Science, Beijing Institute of Technology (BIT). The related research product has been published online with the title of “An Organopolysulfide Comediator for Accelerating Sulfur Redox Kinetics in Lithium–Sulfur Batteries”. 
       The first author of this work is Meng ZhaoZhao Meng, a doctoral student at BIT, and the corresponding author is Professor professor Jiaqi HuangHuang Jiaqi at  Beijing Institute of TechnologyBIT.
Figure 1. Schematic Illustration of the Reaction Pathway of Li–S Batteries
(A) Schematic illustration of the polysulfide-mediated reaction pathway for routine Li–S batteries.
(B) Schematic of the redox comediated reaction pathway. Bold arrows indicate faster reaction kinetics.
(C) Chemical reaction equation of redox comediator with lithium polysulfides.
       Lithium-sulfur (Li–S) battery affords an ultrahigh theoretical energy density of 2,600 Wh kg-1 as a promising next-generation energy storage technique, whose actual performance is heavily dependent on the sulfur redox kinetics. Lithiumpolysulfide intermediates play a decisive role on the complex sulfur redox reactions but are unfortunately insufficient to afford rapid kinetics, rendering reduced specific capacity especially at high rates. Generally, the deposition/dissolution behavior of Li2S is regulated by soluble lithium polysulfides. Serving as intrinsic redox mediator (RM), lithium polysulfides participate in the chemical comproportionation and disproportionation processes (referring to the redox mediation process) parallel to their electrochemical reduction and oxidation and directly determine the deposition rate and growth dimension of Li2S on conductive substrates. However, the intrinsic RM of lithium polysulfide is restricted to the dynamic battery evolution regarding its species and concentration and therefore fails to execute the mediated process timely and thoroughly, especially at the end of charge or discharge (Figure 1A). Therefore, to achieve a stable cycling of high energy density Li-S batteries, a new strategy or method is of urgency to increase the redox comediation capacity of intrinsic Li2S.
       Inspired by the mechanism of coenzyme in bio-systems, a redox comediation strategy is proposed to accelerate the sulfur redox kinetics for high-performance Li–S batteries in this contribution. Compared with coenzyme that interacts with corresponding enzyme to promote the catalytic activity, a redox comediator (coRM) chemically modulates the intrinsic lithium polysulfide RMs to promote their redox mediation capability with faster kinetics (Figure 1B). As a proof of concept, an organopolysulfide, di-t-butyl disulfide (DtbDS), is introduced as a coRM. Concretely, chemically reactive DtbDS spontaneously reacts with lithium polysulfides to generate lithium t-butyl polysulfide (LitbPS) species through the reaction indicated in Figure 1C. The LitbPSs serve as active RMs possess enhanced redox mediation capability compared with the original lithium polysulfide RMs manifested with significantly improved sulfur redox kinetics. In addition, the introduction of DtbDS coRM regulates the deposition of Li2S from 2D to 3D through strengthened chemical decomposition/disproportionation pathway.
       Redox comediation strategy enhances the ability of intrinsic L2S mediation to improve sulfur cathodes’ redox kinetics, and significantly increase the capacity and rate performance of the battery. Under a high discharge rate of 4C (1 C = 1,675 mA gs-1), the Li-S cells with DtbDS maintained high discharge capacity of 566 mAh gs-1. With both high-sulfur-loading (5 mgs cm-2) and low electrolyte/sulfur (E/S) ratio of 5μL mgs-1, the battery was evaluated to have a stable cycling ability. The same group assembled a 1.5 Ah-level Li—S pouch cell with DtbDS, which achieved an energy density of 300 Wh kg-1 at the cell level and maintained stable cycling for 4000 cycles. This work demonstrated a redox comediation strategy, which can significantly help Li-S cells to regulate the redox kinetics; and might inspire further exploration of redox comediators for advanced energy-related systems. 
       More details about the paper: Meng Zhao, Bo-Quan Li, Xiang Chen, Jin Xie, Hong Yuan, Jia-Qi Huang*. Redox comediation with organopolysulfides in working lithium-sulfur batteries, Chem 2020, 10.1016/j.chempr.2020.09.015.
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       Huang Jiaqi, professor and graduate student tutor at Advanced Research Institute of Multidisciplinary Science, BIT, member of Jiusan Society; has published papers more than one hundred research work on Angew. Chem. Int. Ed., J. Am. Chem. Soc., Adv. Mater., Adv. Funct. Mater., Sci. al, with a h-factor of 75, and over forty pieces are ESI highly cited. He has been selected to the first session of China Association for Science and Technology Youth Talent Promotion Project, Outstanding Youth in Particuology of Chinese Society of Particuology, National Special Support Program for High-level Personnel Recruitment (The National “Ten-thousand Talents Program”), highly cited scientist in 2018 and 2019 by Clarivate Analytics, etc..