Li Polysulfides Research Articles

MXene@PBA heterostructures via end-group-directed self-assembly strategy for effective inhibition of shuttle effect in lithium–sulfur batteries

The commercialization of lithium-sulfur batteries (LSBs) has been hindered by the shuttle effect and slow sluggish conversion kinetics. This study developed MXene and Prussian blue analogue (PBA) heterostructures using an end-group-directed self-assembly strategy. MXene@PBA heterostructures were synthesized through layer-by-layer stacking and in situ growth of Mn-PBA, driven by the electrostatic interactions between Mn2+ and the polar terminal groups of MXene. The dual-metal synergistic adsorption of Mn2+ and Fe3+ within PBA framework significantly enhances both the adsorption capacity and cycling stability of the composite. Furthermore, the in-situ growth of PBA not only reinforces the structural integrity but also increases the number of active sites, mitigates the collapse of the accordion-like layered structure, alleviates volume expansion, and accelerates rapid ion diffusion. Theoretical calculations confirm the composite's superior adsorption capacity for Li polysulfides (LiPSs). As a S host, MXene@PBA facilitates the solid-liquid phase transformation of polysulfides, improving reaction kinetics and delivering exceptional electrochemical performance. MXene@PBA composite exhibited an initial discharge capacity of 1220 mAh g−1 at 0.1 C. Its cycle stability is equally remarkable, with a minimal decay rate of 0.062 % per cycle after 500 cycles at 0.5 C. The construction of these layered heterostructures as S hosts presents an effective strategy to mitigate the shuttle effect and enhance the reaction kinetics of LSBs.

Tri-sulfur radical trapping in lithium–sulfur batteries

Lithium-sulfur (Li–S) batteries have emerged as a next-generation battery technology owing to their prospects of high capacity and energy density. They, however, suffer from rapid capacity decay due to the shuttling of reaction intermediate species: Li polysulfides (LiPSs). One of the more important and intriguing PSs is the tri-sulfur radical (S3•−), observed mainly in high-donor number (DN) solvent-based electrolytes. Although this radical has been proposed to be crucial to full active material (AM) utilization, there is currently no direct evidence of the impact of S3•− on cycling stability. To gain more insight into the role of the S3•−, we studied the use of radical traps in low and high DN solvent-based electrolytes by operando Raman spectroscopy. The traps were based on nitrone and iminium cation, and S3•− was indeed successfully trapped in ex situ analysis. However, it was the ionic liquid-based trap, specifically pyridinium, that effectively suppressed S3•− during battery operation. Overall, the PS formation was altered in the presence of the traps and we confirmed the impact of S3•− formation on the Li–S battery redox reactions and show how the trapping correlates with Li–S battery performance. Therefore, stabilization of the S3•− might be a path to improved Li–S batteries.

Coordination Microenvironment Regulation in Carbon−Based Atomically Dispersed Metal Catalysts for Clean Energy−Conversion

AbstractEmerging atomically dispersed metal catalysts (ADCs), especially carbon−based ADCs have arguably received enormous attention in diverse electrochemical energy conversion processes. Such catalysts have well−defined active centers, and their geometric and electronic structures depend greatly on their coordination microenvironments, which, in turn, govern the performances in the realm of electrocatalysis. In this review, it is focused on the state−of−the−art synthesis strategies for carbon−based ADCs, with particular emphasis on their microenvironment modulations. The advances in characterizing the microenvironment alongside understanding the synthetic pathway are outlined, and exemplified in electrochemical applications, including electrocatalytic H2 evolution, O2 evolution/reduction, CO2 reduction, and Li polysulfides conversion reactions. Rather than focusing on the catalysis metrics, this review delved deeply into the underly science and the associated reaction mechanisms of these catalysts in diverse electrochemical systems. The fundamental impacts of the microenvironments of the catalysts on electrocatalytic activities, selectivities, and stabilities are discussed. In the end, it is concluded by highlighting the current issues of the microenvironment engineering of these carbon−based ADCs and propose the prospects for future opportunities and challenges.

The electrochemistry of stable sulfur isotopes versus lithium

Sulfur in nature consists of two abundant stable isotopes, with two more neutrons in the heavy one (34S) than in the light one (32S). The two isotopes show similar physicochemical properties and are usually considered an integral system for chemical research in various fields. In this work, a model study based on a Li-S battery was performed to reveal the variation between the electrochemical properties of the two S isotopes. Provided with the same octatomic ring structure, the cyclo-34S8 molecules form stronger S-S bonds than cyclo-32S8 and are more prone to react with Li. The soluble Li polysulfides generated by the Li-34S conversion reaction show a stronger cation-solvent interaction yet a weaker cation-anion interaction than the 32S-based counterparts, which facilitates quick solvation of polysulfides yet hinders their migration from the cathode to the anode. Consequently, the Li-34S cell shows improved cathode reaction kinetics at the solid-liquid interface and inhibited shuttle of polysulfides through the electrolyte so that it demonstrates better cycling performance than the Li-32S cell. Based on the varied shuttle kinetics of the isotopic-S-based polysulfides, an electrochemical separation method for 34S/32S isotope is proposed, which enables a notably higher separation factor than the conventional separation methods via chemical exchange or distillation and brings opportunities to low-cost manufacture, utilization, and research of heavy chalcogen isotopes.

Surface Adaptive Dual‐Layer Protection of Li‐metal Anode for Extending Cycle‐Life of Li–Sulfur Batteries with Lean Electrolyte

AbstractBuilding a lithium–sulfur (Li–S) battery with lean electrolytes is essential to far exceed the energy density of today's Li‐ion. However, earlier electrolyte depletion triggered by Li‐metal anodes (LMAs) causes sluggish Li–S redox kinetics and poor S utilization, resulting in a short cycle lifespan. To retard the electrolyte loss effectively, sustainable protection of LMAs is necessary against the dynamic interfacial evolution between LMA and protective layers (PLs). This study elucidates two critical parameters in securing the interfacial adaptivity of PLs upon local Li pitting: surface free energy (SFE) and Young's modulus through solid‐mechanic simulations and experiments using three different PL models. To alleviate the PL delamination at the early stage, a dual‐layer structured, adaptive protective layer (APL) is introduced to adapt the Li pitting‐driven structural evolution of the PL|LMA interfaces. The APL consists of a high‐ SFE polymer as an inner layer, reducing the interfacial energy in contact with LMA surface, and a highly stretchable polymer for outer shield, serving as a physical barrier for the electrolyte and Li polysulfides. APL‐coated LMA demonstrates stable cycling of Li–S cells, achieving a twofold extension of cycle‐life compared to unprotected LMA, even superior to other single‐layer PLs.

Regulating Electron Filling and Orbital Occupancy of Anti-Bonding States of Transition Metal Nitride Heterojunction for High Areal Capacity Lithium-Sulfur Full Batteries.

The commercialization of lithium-sulfur (Li-S) battery is seriously hindered by the shuttle behavior of lithium (Li) polysulfide, slow conversion kinetics, and Li dendrite growth. Herein, a novel hierarchical p-type iron nitride and n-type vanadium nitride (p-Fe2N/n-VN) heterostructure with optimal electronic structure, confined in vesicle-like N-doped nanofibers (p-Fe2N/n-VN⊂PNCF), is meticulously constructed to work as "one stone two birds" dual-functional hosts for both the sulfur cathode and Li anode. As demonstrated, the d-band center of high-spin Fe atom captures more electrons from V atom to realize more π* and moderate σ* bond electron filling and orbital occupation; thus, allowing moderate adsorption intensity for polysulfides and more effective d-p orbital hybridization to improve reaction kinetics. Meanwhile, this unique structure can dynamically balance the deposition and transport of Li on the anode; thereby, more effectively inhibiting Li dendrite growth and promoting the formation of a uniform solid electrolyte interface. The as-assembled Li-S full batteries exhibit the conspicuous capacities and ultralong cycling lifespan over 2000 cycles at 5.0 C. Even at a higher S loading (20mg cm-2) and lean electrolyte (2.5µL mg-1), the full cells can still achieve an ultrahigh areal capacity of 16.1 mAh cm-2 after 500 cycles at 0.1 C.

Optimization of the Form Factors of Advanced Li-S Pouch Cells.

Lithium-sulfur (Li-S) batteries hold immense promise as next-generation energy storage due to their high theoretical energy density (2600Whkg⁻¹), low cost, and non-toxic nature. However, practical implementation faces challenges, primarily from Li polysulfide (LiPS) shuttling within the cathode and Li dendrite growth at the anode. Optimized electrodes/electrolytes design effectively confines LiPS to the cathode, boosting cycling performance in coin cells to up to hundreds of cycles. Scaling up to larger pouch cells presents new obstacles, requiring further research for long-term stability. A 1.45Ah pouch cell, with optimized sulfur loading and electrolyte/sulfur ratio is developed, which delivers an energy density of 151Whkg-1 with 70% capacity retention up to 100 cycles. Targeting higher energy density (180Whkg-1), the developed 1Ah pouch cell exhibits 68% capacity retention after 50 cycles. Morphological analysis reveals that pouch cell failure is primarily from Li metal powdering and resulting polarization, rather than LiPS shuttling. This occurs for continuous Li ion stripping/plating during cycling, leading to dendrite growth and formation of non-reactive Li powder, especially under high currents. These issues increase ion diffusion resistance and reduce coulombic efficiency over time. Therefore, the study highlights the importance of a protected Li metal anode for achieving high-energy-dense batteries.

Lithium Sulfur Batteries: Insights from Solvation Chemistry to Feasibility Designing Strategies for Practical Applications

Rechargeable lithium–sulfur (Li–S) batteries, featuring high energy density, low cost, and environmental friendliness, have been dubbed as one of the most promising candidates to replace current commercial rechargeable Li‐ion batteries. However, their practical deployment has long been plagued by the infamous “shuttle effect” of soluble Li polysulfides (LiPSs) and the rampant growth of Li dendrites. Therefore, it is important to specifically elucidate the solvation structure in the Li–S system and systematically summarize the feasibility strategies that can simultaneously suppress the shuttle effect and the growth of Li dendrites for practical applications. This review attempts to achieve this goal. In this review, we first introduce the importance of developing Li–S batteries and highlight the key challenges. Then, we revisit the working principles of Li–S batteries and underscore the fundamental understanding of LiPSs. Next, we summarize some representative characterization techniques and theoretical calculations applied to characterize the solvation structure of LiPSs. Afterward, we overview feasible designing strategies that can simultaneously suppress the shuttle effect of soluble LiPSs and the growth of Li dendrites. Finally, we conclude and propose personal insights and perspectives on the future development of Li–S batteries. We envisage that this timely review can provide some inspiration to build better Li–S batteries for promoting practical applications.

All-in-one Janus covalent organic frameworks separator as fast Li nucleator and polysulfides catalyzer in lithium-sulfur batteries

The shuttle effect, sluggish conversion kinetics, and uncontrollable lithium dendrites seriously hinder the practical application of lithium-sulfur (Li-S) batteries. Among many modified materials, covalent organic frameworks (COFs) stand out for their excellent ability to inhibit the shuttle effect, while their role in promoting lithium nucleation and catalyzing the conversion of sulfur species has been largely ignored. In this study, an integrated COF separator (TpPa@2400) is developed as a rapid lithium nucleator and sulfur species catalyst in fast-charging Li-S batteries. According to the adsorption energy and Bader charge results, Li atoms preferentially adsorb onto the surface of the TpPa@2400 separator, and the larger Bader charge value (0.52 |e|) of the TpPa@2400 separator also signifies faster lithium transport, promoting the nucleation of Li ions. Furthermore, density functional theory (DFT) theoretically demonstrates that the TpPa@2400 separator exhibits lower free energy for sulfur species interconversion. As a result, the TpPa@2400 separator enables the Li-Li symmetric cell with an extended cycle life of 6000 h at a current density/capacity of 10 mA cm-2/10 mAh cm-2. The Li-S battery assembled using the TpPa@2400 separator delivers a high capacity of 1636.4 mAh/g at 0.1C and a rapid sulfur species conversion capacity of 513.8 mAh/g at 2C.

A gel polymer electrolyte functionalized separator for high-performance lithium-sulfur batteries.

Lithium-sulfur (Li-S) batteries, featuring ultrahigh specific theoretical energy density with low-cost raw materials, have been deemed one of the most promising candidates for next-generation energy storage and conversion devices. However, the shuttle effect of soluble Li polysulfides (LiPSs) has seriously hindered their practical deployment. Herein, we report that tris(pentafluorophenyl)borane (TPFPB) is used to modify the separator (TPFPB/Al2O3) for suppressing the shuttle effect of LiPSs. In detail, the introduction of TPFPB induces 1,3-dioxolane solvent ring-opening polymerization to form a gel layer between the S cathode and separator for suppressing the shuttle effect of Li polysulfides, effectively improving the electrochemical performance of Li-S batteries. The Li-S batteries using the TPFPB/Al2O3 separator demonstrate outstanding cycling stability and high capacity retention rates. This work provides a useful guideline for separator modification using a functional interface layer to design high-performance Li-S batteries.

Dual chemifunctional tin(IV) oxide/nanoperforated graphene interlayer as a polysulfide adsorbent for use in high-performance lithium–sulfur batteries

The development of Li–S batteries is limited by their levels of rapid capacity decay owing to polysulfide dissolution and diffusion in organic electrolytes. We addressed this critical issue by fabricating a dual chemifunctional interlayer comprising SnO2 nanoparticles and nanoperforated graphene (NPG) that could function as a polysulfide adsorbent. The synergistic effects of SnO2 and the high-density functional groups of NPG on polysulfide capture were conceptually confirmed. NPG not only supported the adsorption of Li polysulfides but also provided pathways for simple Li-ion motion within the SnO2/NPG interlayer. A cell assembled with the SnO2/NPG interlayer displayed a high rate capability and initial discharge capacity and good reversible capacity. The excellent high-rate cycling performance of the cathode could mainly be attributed to the strong chemical bonds formed between SnO2/NPG and the polysulfides, rapid electron transfer, and optimized ion diffusion pathways derived from the well-organized structure of the composite. Synthesizing dual chemifunctional interlayers using a composite of metal oxides and NPG may lead to the development of advanced Li–S batteries with numerous practical applications in the near future.

An oxygen-vacancy-boosted heterostructured catalyst with synergistically integrated dual transition-metal oxides for high-performance lithium-sulfur batteries

The practical use of high-energy–density Li–S batteries (LSBs) is significantly hampered by the severe dissolution of soluble Li polysulfides (LiPSs) and their sluggish redox kinetics. To address these issues, a novel heterostructured electrocatalyst comprising nano-RuO2-decorated hexagonal CeO2 (NRHC) was developed in this study. The hetero-growth of RuO2 on the plate-shaped HC induced beneficial oxygen vacancies (OVs), which provided positively charged sites and free electrons owing to the lattice disorder between RuO2 and CeO2, thereby boosting the ability of the NRHC to adsorb LiPSs, exhibit enhanced conversion kinetics, and facilitate Li+ transport. Moreover, the NRHC heterostructure comprising RuO2 (a polar but highly conductive material) and CeO2 (a polar and surface-OV-rich material) effectively improved the “trapping–diffusion–conversion” process to transform LiPSs into Li2S on its surface. Benefiting from the synergistic catalytic attributes of the NRHC, an LSB with the NRHC-modified separator exhibited superior cyclability (844.7 mAh/g after 1000 cycles with a low-capacity decay rate of 0.029% per cycle) at a high current density of 1 C. Even at a high sulfur loading (6.4 mg cm−2), the LSB achieved a high areal capacity of over 4.5 mAh cm−2 at 0.1 C, highlighting its practical applicability.

NiAs-type vanadium sulfides: Topological surface and abundant electroactivity as a bi-functional material in Mg/Li batteries

Rechargeable Mg battery (RMB) is a new type of next-generation secondary battery. The unique NiAs-type V3S4 is capable of achieving high electrochemical performance due to its bi-functional effect of electroactive and anchoring ability to the discharge products of polysulfides. Herein, the first-principles calculations were conducted to explore the electronic properties, dynamic and absorption behavior of Mg/Li-ions in the bulk and crystal plane of V3S4 to reveal the bi-functional mechanism in Mg/Li batteries. First, the stable surface adsorption and rapid diffusion kinetics of Mg/Li ions render the high-rate capability for V3S4. Second, the Mg/Li polysulfides could effectively anchor on the V3S4 (111) plane and retain their structural stability during the discharge–charge process for Mg/Li batteries. Even after Li2Sn/MgSn adsorption, the metallic property of V3S4 is still preserved to realize the redox electrochemistry of Li2Sn/MgSn and ameliorates the effect of the insulated low-order polysulfides. Meanwhile, the low Gibbs energy differences for Mg and Li polysulfides on V3S4 (111) plane gives the evidence of electrocatalytic property. As bi-functional material, the V3S4 has striking characteristics of low diffusion barrier, benificial adsorption and preeminent electrocatalytic ability of Li/Mg species, which can be leveraged for designing vanadium sulfides as high-conductivity cathode materials for RMBs.

Electrolyte Design for Improving Mechanical Stability of Solid Electrolyte Interphase in Lithium–Sulfur Batteries

AbstractPractical lithium–sulfur (Li−S) batteries are severely plagued by the instability of solid electrolyte interphase (SEI) formed in routine ether electrolytes. Herein, an electrolyte with 1,3,5‐trioxane (TO) and 1,2‐dimethoxyethane (DME) as co‐solvents is proposed to construct a high‐mechanical‐stability SEI by enriching organic components in Li−S batteries. The high‐mechanical‐stability SEI works compatibly in Li−S batteries. TO with high polymerization capability can preferentially decompose and form organic‐rich SEI, strengthening mechanical stability of SEI, which mitigates crack and regeneration of SEI and reduces the consumption rate of active Li, Li polysulfides, and electrolytes. Meanwhile, DME ensures high specific capacity of S cathodes. Accordingly, the lifespan of Li−S batteries increases from 75 cycles in routine ether electrolyte to 216 cycles in TO‐based electrolyte. Furthermore, a 417 Wh kg−1 Li−S pouch cell undergoes 20 cycles. This work provides an emerging electrolyte design for practical Li−S batteries.

Electrolyte Design for Improving Mechanical Stability of Solid Electrolyte Interphase in Lithium-Sulfur Batteries.

Practical lithium-sulfur (Li-S) batteries are severely plagued by the instability of solid electrolyte interphase (SEI) formed in routine ether electrolytes. Herein, an electrolyte with 1,3,5-trioxane (TO) and 1,2-dimethoxyethane (DME) as co-solvents is proposed to construct a high-mechanical-stability SEI by enriching organic components in Li-S batteries. The high-mechanical-stability SEI works compatibly in Li-S batteries. TO with high polymerization capability can preferentially decompose and form organic-rich SEI, strengthening mechanical stability of SEI, which mitigates crack and regeneration of SEI and reduces the consumption rate of active Li, Li polysulfides, and electrolytes. Meanwhile, DME ensures high specific capacity of S cathodes. Accordingly, the lifespan of Li-S batteries increases from 75 cycles in routine ether electrolyte to 216 cycles in TO-based electrolyte. Furthermore, a 417 Wh kg-1 Li-S pouch cell undergoes 20 cycles. This work provides an emerging electrolyte design for practical Li-S batteries.

Performance Stabilization of Lithium-Sulfur Batteries Containing Sulfolane-based Electrolyte and Microporous Cathode by Controlling Working Voltage Range

For lithium-sulfur (Li-S) batteries, high-concentration electrolyte that inhibits the dissolution of Li polysulfide has been widely studied; one such electrolyte contains sulfolane. This study investigates the conditions under which a microporous activated carbon cathode, derived from azurmic acid, operates stably in a sulfolane-based electrolyte. We expected this cathode to maintain a stable capacity in a sulfolane-based electrolyte because its micropores stabilize the S species. However, Li-S batteries containing this cathode and electrolyte exhibit significant capacity decay during cycling. The cutoff voltage during charge-discharge cycling is varied to suppress the capacity decay. At a discharge voltage of 1.4 V or lower, the cycle life of the Li-S batteries is significantly reduced. Conversely, increasing the cutoff voltage during discharge suppresses the capacity decay of Li-S batteries. On the other hand, increasing the upper voltage limit during charging increases the reversible capacity. Thus, the operating voltage range is optimized. This study indicates that the voltage range of Li-S batteries should be carefully determined depending on the type of cathode material and electrolyte.

In Situ Trapping Strategy Enables a High-Loading Ni Single-Atom Catalyst as a Separator Modifier for a High-Performance Li-S Battery.

The poor electrochemical reaction kinetics of Li polysulfides is a key barrier that prevents the Li-S batteries from widespread applications. Ni single atoms dispersed on carbon matrixes derived from ZIF-8 are a promising type of catalyst for accelerating the conversion of active sulfur species. However, Ni favors a square-planar coordination that can only be doped on the external surface of ZIF-8, leading to a low loading amount of Ni single atoms after pyrolysis. Herein, we demonstrate an in situ trapping strategy to synthesize Ni and melamine-codoped ZIF-8 precursor (Ni-ZIF-8-MA) by simultaneously introducing melamine and Ni during the synthesis of ZIF-8, which can remarkably decrease the particle size of ZIF-8 and further anchor Ni via Ni-N6 coordination. Consequently, a novel high-loading Ni single-atom (3.3 wt %) catalyst implanted in an N-doped nanocarbon matrix (Ni@NNC) is obtained after high-temperature pyrolysis. This catalyst as a separator modifier shows a superior catalytic effect on the electrochemical transitions of Li polysulfides, which endows the corresponding Li-S batteries with a high specific capacity of 1232.4 mA h g-1 at 0.3 C and an excellent rate capability of 814.9 mA h g-1 at 3 C. Furthermore, a superior areal capacity of 4.6 mA h cm-2 with stable cycling over 160 cycles can be achieved under a critical condition with a low electrolyte/sulfur ratio (8.4 μL mg-1) and high sulfur loading (4.85 mg cm-2). The outstanding electrochemical performances can be attributed to the strong adsorption and fast conversion of Li polysulfides on the highly dense active sites of Ni@NNC. This intriguing work provides new inspirations for designing high-loading single-atom catalysts applied in Li-S batteries.

Sulfide-Bridged Covalent Quinoxaline Frameworks for Lithium-Organosulfide Batteries.

The chelating ability of quinoxaline cores and the redox activity of organosulfide bridges in layered covalent organic frameworks (COFs) offer dual active sites for reversible lithium (Li)-storage. The designed COFs combining these properties feature disulfide and polysulfide-bridged networks showcasing an intriguing Li-storage mechanism, which can be considered as a lithium-organosulfide (Li-OrS) battery. The experimental-computational elucidation of three quinoxaline COFs containing systematically enhanced sulfur atoms in sulfide bridging demonstrates fast kinetics during Li interactions with the quinoxaline core. Meanwhile, bilateral covalent bonding of sulfide bridges to the quinoxaline core enables a redox-mediated reversible cleavage of the sulfursulfur bond and the formation of covalently anchored lithium-sulfide chains or clusters during Li-interactions, accompanied by a marked reduction of Li-polysulfide (Li-PS) dissolution into the electrolyte, a frequent drawback of lithium-sulfur (Li-S) batteries. The electrochemical behavior of model compounds mimicking the sulfide linkages of the COFs and operando Raman studies on the framework structure unravels the reversibility of the profound Li-ion-organosulfide interactions. Thus, integrating redox-active organic-framework materials with covalently anchored sulfides enables a stable Li-OrS battery mechanism which shows benefits over a typical Li-S battery.

Single and multilayer composite electrolytes for enhanced Li-ion conductivity with restricted polysulfide diffusion for lithium–sulfur battery

Lithium–sulfur battery is a promising energy source to achieve high energy density at low cost, but its commercialization has been being impeded by a few huddles associated with Li dendrite growth, polysulfide shuttle, and flammability, due to the utilization of liquid electrolytes. In this study, the single- and multi layered flexible composite electrolytes comprising organic poly(arylene ether sulfone)-g-poly(ethylene glycol) and inorganic Li6PS5Br nanoparticles are designed. Both composite electrolyte membranes exhibit excellent mechanical flexibility and thermal stability up to 200 °C. The single-layer composite electrolyte illustrates high ionic conductivity of 2.4 ⅹ 10−3 S/cm because of the self-assembled poly(ethylene glycol) domains accommodating large amount of free charge carriers. Even though the multilayer electrolyte membrane shows slightly lower conductivity of 8.7 ⅹ 10−4 S/cm, it provides quite high lithium-ion transference number of 0.81 with self-extinguishing ability and effective suppression of Li dendrite growth and polysulfide diffusion because of the highly selective Li6PS5Br layer. Accordingly, the Li/S cell assembled with multilayer composite electrolyte shows outstanding cyclic stability retaining 99.2% after 100 cycles at 0.1 C-rate. Those results demonstrate the application possibility of the prepared solid electrolytes for high safety and high performance lithium–sulfur battery.

Building Better Lithium‐Sulfur Batteries—A Reassessment of the Working Mechanism

AbstractLithium‐sulfur (Li−S) batteries have captured global attention and in‐depth research interest. Nevertheless, its massive commercialization has been bothered by the “shuttle effect” caused by the soluble Li polysulfides (LiPSs) and unremitted growth of Li dendrites originated from unstable solid electrolyte interphase (SEI) film. Over the few decades have witnessed the remarkable progress of Li−S batteries, while several controversial views on the working mechanism have emerged in recent three years, which are challenging for previous related research. In this perspective, we give a brief review on the latest studies and reassess the working mechanism of Li−S batteries. With this regard, we start with a simple introduction to emphasize the significance of developing Li metal batteries. Then, we specifically elucidate the formation process and composition of SEI film. Next, we detailly discuss LiPSs cation as the dominant species in Li−S battery. Subsequently we review the case that contend no LiPSs intermediates formation in Li−S battery using γ‐S as the cathode. Afterwards, we conduct a discussion between dry SEI film vs. wet SEI film on the surface of Li metal anode, followed by the strategies to design rational electrolytes for engineering stable Li metal anodes. Finally, we propose personal insights and perspectives on the development direction of Li−S batteries. We hope this timely perspective will be of great interest to the numerous scientific researchers focusing on Li−S batteries.