Homogeneous Organometallic Catalysts for Improved Electrochemical Kinetics of Li–S Batteries

Abstract

The dissolution of polysulfides into electrolytes and sluggish electrochemical conversion kinetics primarily impede the practical realization of Li–S batteries. Homogeneous catalysis is an effective strategy to overcome the challenges involved under lean electrolyte conditions. Metallocenes, a class of organometallic compounds, hold promise to anchor and catalyze polysulfides. In this study, we used first-principles density functional theory (DFT) simulations to understand the role of metallocenes (using titanocene (TiCp2) as an archetypical example) as homogeneous catalysts in the electrolyte medium to suppress the shuttle effect and promote the reaction kinetics. The calculated electrochemical stability window of TiCp2 reveals that the composition is electrochemically inactive in the operating potential range of Li–S batteries and can thus be leveraged as an additive to expedite the reduction kinetics of soluble lithium polysulfides (LiPSs). We studied the detailed characteristic behavior of LiPS interactions with TiCp2 in both gas and solvent phases and the kinetics of elementary sulfur reduction reactions (SRRs). We found that TiCp2 provides adequate binding toward various LiPSs to mitigate the shuttle effect, and the structural integrity of LiPSs is well retained without any chemical decomposition. The catalyzing effect of TiCp2 is evident from the observed significant reduction in the SRR barriers, particularly for the rate-determining step, which is expected to favorably promote the deposition of Li2S on the cathode surface. We further propose a mechanistic scheme of TiCp2 homogeneous catalyst-boosted sulfur redox cycles. Overall, our simulations predicted moderate binding and improved kinetics of polysulfide chemistry with the metallocene-based homogeneous catalyst and are expected to lead to a paradigm shift in the design of organometallic additives for achieving high-performance metal–sulfur batteries.

First‐Principles Investigations to Evaluate NiCl2/NiF2 as Cycle‐Catalyzed Electrolyte Additives to Improve Li–S Batteries’ Performance

“…We used the B3LYP hybrid functional along with the 6–31 + G* basis set for the C/H/O/Cl/F and LALN2DZ effective core potentials (ECPs) for the Ni atom for all of the calculations, which were widely used to calculate the organo‐sulfides. [ 23 ] The optimized structures were thermally stable without negative frequency. The solvation model based on density (PCM) [ 25 ] was performed to describe the solvent environment of 1,2‐dimethoxythane (DME) and 1,3‐dioxolane (DOL).…”

“…At this time, catalysis is introduced into the electrolyte additives. [ 20–22 ] Rahul Jayan et al [ 23 ] proposed a mechanism scheme of sulfur oxidation reduction cycle promoted by homogeneous TiCp 2 catalyst. During discharge, TiCp 2 has a higher chemical affinity for LiPSs than 1,2‐dimethoxy‐ethane (DME), resulting in the formation of TiCp 2 @LiPSs clusters and contributing to the overall sulfur reduction reaction dynamics of the LSB.…”

Synergistic design of core–shell V3S4@C hosts and homogeneous catalysts promoting polysulfide chemisorption and conversion for Li–S batteries

“…21 Different from the heterogeneous catalysts constructed on sulfur host materials, HCs could dissolve in the electrolyte and completely contact LPSs, meaning a higher efficiency for the catalytic transformation of LPSs. 21–23 For example, the nickel( ii ) chloride dimethoxymethane adduct (NiCl 2 ·DME), which could release DME during the discharging process, showed great shuttle effect suppression because of the high adsorption capacity for LPSs, and this could be reversed during the charging process. 21…”

“…21 Different from the heterogeneous catalysts constructed on sulfur host materials, HCs could dissolve in the electrolyte and completely contact LPSs, meaning a higher efficiency for the catalytic transformation of LPSs. [21][22][23] For example, the nickel(II) chloride dimethoxymethane adduct (NiCl 2 $DME), which could release DME during the discharging process, showed great shuttle effect suppression because of the high adsorption capacity for LPSs, and this could be reversed during the charging process. 21 Herein, we have devised a unique hierarchical core-shell structure (denoted as V 3 S 4 @C), i.e., a 1D porous carbon nanorods (NRs) core in situ decorated with a V 3 S 4 NSs shell by vulcanizing a vanadium-based metal-organic framework of MIL-47as (MIL stands for Materials of Institute Lavoisier), which was transformed from 2D vanadium carbides (V 2 CT x ) by a simple hydrothermal method.…”

Bifunctional Fluorinated Anthraquinone Additive for Improving Kinetics and Interfacial Chemistry in Rechargeable Li–S Batteries

“…Due to the appealing advantages, including ultrahigh energy density (2600 Wh kg –1 ), abundant sulfur resources and environmental benignity, lithium–sulfur (Li–S) batteries are regarded as a competitive choice for next-generation secondary batteries. − Nevertheless, the serious lithium polysulfide (LiPS) shuttling, large volume changes encountered during repeated lithiation/delithiation process, and dendritic lithium growth remain as main barriers to the application of Li–S batteries. − Therefore, through rational design such as electrode configuration, − electrolyte modification, , or electrode–electrolyte interface modification, − more stable Li–S batteries are highly anticipated. For example, Yao et al developed a dual-functional conductive framework (TiN-VN@CNFs) by electrospinning method, in which the flexible carbon nanofibers were integrated with TiN-VN heterostructures.…”