Optimizing Redox Reactions in Aprotic Lithium–Sulfur Batteries

Abstract

The lithium–sulfur battery is regarded as one of the promising energy‐storage devices beyond lithium‐ion battery due to its overwhelming energy density. The aprotic Li–S electrochemistry is hampered by issues arising from the complex solid–liquid–solid conversion process. Recently, tremendous efforts have been made to optimize the electrochemical reaction in Li–S batteries through rationally designing compositions and structures of cathodes. However, a deep and comprehensive understanding of the actual mechanisms of Li–S batteries and their impact on the performance is still insufficient. The vigorous development of various electrochemical analysis and in situ techniques establish a bridge between the microstructure of components and the macroscopic electrochemical performance, thus providing more scientific guidance for the optimal design of Li–S batteries. In this review, based on insights into the mechanism of aprotic Li–S electrochemistry with the aid of in situ characterization and electrochemical methods, the advanced innovations in optimizing Li–S batteries are systematically summarized, including the materials design, cathode configurations optimization, and electrolyte engineering, with the aim to gain a comprehensive understanding of cathodic redox processes and thus achieve high‐performance Li–S batteries. The current status and possible future directions of the field are accordingly outlined.

Ion‐Inserted Metal–Organic Frameworks Accelerate the Mass Transfer Kinetics in Lithium–Sulfur Batteries

“…[4][5][6] Among those studies, most attentions were paid on the strategies for dendrite suppression, [7][8][9] or methods to suppress shuttle effect [10,11] and accelerate conversion kinetics of lithium polysulfides (LiPSs). [12][13][14] Generally, the introduction of porous materials with highly exposed adsorption and catalytic sites has been demonstrated to be one of the most effective ways to promote the Li-S battery performances. [15] As a unique porous material, metal-organic framework (MOF) is suitable for applications in mass transfer property across the interlayers.…”

Engineering Functional Interface with Built‐in Catalytic and Self‐Oxidation Sites for Highly Stable Lithium–Sulfur Batteries

“…Moreover, it could also harvest a high specific capacity of 320.0 mAh g À 1 with the distinct voltage platforms even at a high C rate of 8.0, which is comparable to many reported literatures (Figure and Table S1). [51][52][53][54][55][56][57][58][59][60] This superior rate performance is ascribed to the accelerated kinetic conversion of intermediates and the strong affinity with LiPS due to the G@MC modified layer in a working LiÀ S battery (Figure S14). The specific capacity of the battery could also be recovered to 1106.6 mAh g À 1 , when the C rate switched backed to low current of 0.1 C. Its capacity retention is much higher in comparison with the cased of the batteries with pristine and commercial MnCO 3 modified separator, respectively (Figure S11 and S12).…”

“…With the chemical deposition of LiPS, the corresponding Li element is also detected on the surface of G@MC layer due to the chemically redox reaction of intermediates (Figure 3d). Meanwhile, the positive Li + ions would simultaneously bond with the negative CO 3 2À ions because of the electrostatic interaction, providing the extra traps for anchoring polysulfides [51][52][53][54][55][56][57][58][59] and mitigating their shuttle in electrolyte. Moreover, it is worth noting that the additional characteristic peaks located at 162.5 and 163.5 eV of S element correspond to the conversion reaction from long-chain to short-chain LiPS on the active surface of G@MC layer (Figure 3e).…”

Understanding the Impedance Response of Lithium Polysulfide Symmetric Cells

“…Despite the proposed various strategies, a fundamental understanding on the mechanism of LiPS conversion reactions is still inadequate. [ 9 ] Electrochemical impedance spectroscopy (EIS) is an effective tool to analyze complex LiPS conversion reactions with the advantages of high accuracy and rich information. [ 10 ] By applying an alternating current (AC) perturbation to the electrochemical system and detecting the output signal in a wide frequency range, the involved electrochemical processes will exhibit characteristic impedance responses according to their typical relaxation time scales.…”