An Effective Lithium Sulfide Encapsulation Strategy for Stable Lithium–Sulfur Batteries

Abstract

attributed to the insulating nature of sulfur and its discharge product, Li 2 S; (ii) fast capacity decay due to activematerial loss in the form of soluble polysulfide species; and (iii) potential safety hazards arising with the use of lithium metal as an anode.To mitigate the safety concerns of metallic lithium, one approach is to start with Li 2 S and couple it with a lithium-free anode (silicon, tin, or graphite). [14] When employed as a cathode, Li 2 S encounters less volume expansion in the first cycle; however, similar to its sulfur cathode counterpart, it also requires efficient electron transport pathways around the insulating Li 2 S particles and an effective encapsulation to reduce polysulfide dissolution. [15] In 2014, Seh et al. performed pioneering work that successfully encapsulated Li 2 S with a nanocomposite strategy consisting of 2D layered transition-metal disulfides that offered high conductivity and affinity for polysulfides. [16] The nanocomposite cathodes exhibited enhanced activity in LiS batteries as revealed by a lower charging overpotential, and improved cycling stability up to 400 cycles. However, the process utilized nanosized Li 2 S particles and a complex processing scheme requiring hightemperature annealing of the reacted product, among other preparation steps. In addition, hierarchical carbon structures have also been used to encapsulate Li 2 S forming nanocomposites; [17,18] however, their long-term cycling stability remains a concern considering the nonpolar nature of carbon and its lower affinity for polysulfide species with high polarity. [19,20] To date, a low-cost design of a stable, conductive encapsulation architecture for Li 2 S is yet to be realized.In this work, we build an encapsulation layer comprised of transition-metal sulfide on the surface of Li 2 S bulk particles via a facile strategy employing a surface chemical reaction between Li 2 S and an electrolyte additive containing the transition-metal salt. It is demonstrated that the surface ionization energy of the encapsulation layer determines the initial charging overpotential of Li 2 S. Moreover, while most additives generate encapsulation layers in the open-circuit configuration that are unstable during cycling, it is shown that at least one transition-metal additive, containing manganese, forms a stable encapsulation layer consisting of MnS via a chemical reaction with Li 2 S. The stability of such an in-situ-formed encapsulation layer is a result of the MnS compound being chemically inactive within the cycling window. Through this mechanistic analysis, we With a high theoretical capacity of 1162 mA h g −1 , Li 2 S is a promising cathode that can couple with silicon, tin, or graphite anodes for next-generation energy storage devices. Unfortunately, Li 2 S is highly insulating, exhibits large charge overpotential, and suffers from active-material loss as soluble polysulfides during battery cycling. To date, low-cost, scalable synthesis of an electrochemically active Li 2 S cathode remains a challenge. This work ...

Anode Interface Engineering and Architecture Design for High‐Performance Lithium–Sulfur Batteries

“…Unfortunately, Li 2 S is a poor ion conductor, highly reactive to moisture and oxygen, and requires an activation process at high potentials . Some attempts have been made to improve the electrochemical performance of Li 2 S‐based cathodes, including accelerating the electrical transport by designing Li 2 S composite cathode with conducting material, lowering the activation potential using a redox mediator, and forming a protection layer on the Li 2 S surface using electrolyte additives . However, the preparation and manipulation of Li 2 S cathodes still face great difficulties.…”

Metal Sulfide‐Decorated Carbon Sponge as a Highly Efficient Electrocatalyst and Absorbant for Polysulfide in High‐Loading Li2S Batteries

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serious issues with conventional Li-S batteries, such as the large volume expansion (≈79 vol%), insulating property of sulfur, and Li dendrites formed on the surface of the lithium-metal anode. [20][21][22][23][24] However, the high initial charge barrier, low conductivity, soluble intermediate lithium polysulfide (LiPS) dissolution into the organic liquid electrolyte, and sluggish kinetics during the Li-S redox reaction remain a serious challenge that must be solved for the practical application of the Li 2 S cathode. [20][21][22][23][24] However, the high initial charge barrier, low conductivity, soluble intermediate lithium polysulfide (LiPS) dissolution into the organic liquid electrolyte, and sluggish kinetics during the Li-S redox reaction remain a serious challenge that must be solved for the practical application of the Li 2 S cathode.

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“…[15][16][17][18][19] Owing to its high theoretical specific capacity (1166 mA h g −1 ) and particularly its ability to be paired with a lithium-metal-free anode, Li 2 S has been regarded as a more attractive and safer cathode for nextgeneration advanced Li-S batteries. [20][21][22][23][24] However, the high initial charge barrier, low conductivity, soluble intermediate lithium polysulfide (LiPS) dissolution into the organic liquid electrolyte, and sluggish kinetics during the Li-S redox reaction remain a serious challenge that must be solved for the practical application of the Li 2 S cathode. [25][26][27][28] To address such issues, several strategies have been pursued in the literature.…”

Electrolyte Additives for Lithium Metal Anodes and Rechargeable Lithium Metal Batteries: Progress and Perspectives

“…Another approach to improving the utilization of Li 2 Si s through its encapsulation by conductive and protective surface layers.T he encapsulation layer on Li 2 Sbulk particles should be conductive,able to effectively retain PS species,and robust enough to sustain repeated Li + transport. [127,131] Recently,Manthiram and co-workers [127] built astable encapsulation layer on the surface of micrometer-sized Li 2 Sb ulk particles through as urface chemical reaction between Li 2 S and an electrolyte additive containing at ransition-metal salt (Figure 17 b). Of the transition-metal salts tested, 10 wt % manganese(II) acetylacetonate proved to be robust over the cycling voltage,w hich was attributed to the generated MnS surface species (electrochemically inactive within the cycling voltage window), and led to adownshifted main anodic peak at 2.9 Vi nt he first charge.T he electronic band structure of the generated encapsulation layer is critical to decrease the initial charge resistance of the bulk Li 2 Sbulk particles.…”

“…Reproducedf rom Ref [119]. with permission.C opyright 2017 American Chemical Society.S chematic representation of the proposed b) Li 2 Sencapsulation and c) reaction mechanism as well as resultant particle morphology for the Li 2 S/Mn cell (i)before and (ii)after charging with astable surface layer.R eproducedf rom Ref [127]. with permission.C opyright 2017 Wiley-VCH.…”