Soluble Lithium Polysulfides Research Articles

Ultrafine Co-Species Interspersed g-C3N4 Nanosheets and Graphene as an Efficient Polysulfide Barrier to Enable High Performance Li-S Batteries.

Lithium-sulfur (Li-S) batteries are regarded as one of the promising advanced energy storage systems due to their ultrahigh capacity and energy density. However, their practical applications are still hindered by the serious shuttle effect and sluggish reaction kinetics of soluble lithium polysulfides. Herein, g-C3N4 nanosheets and graphene decorated with an ultrafine Co-species nanodot heterostructure (Co@g-C3N4/G) as separator coatings were designed following a facile approach. Such an interlayer can not only enable effective polysulfide affinity through the physical barrier and chemical binding but also simultaneously have a catalytic effect on polysulfide conversion. Because of these superior merits, the Li-S cells assembled with Co@g-C3N4/G-PP separators matched with the S/KB composites (up to ~70 wt% sulfur in the final cathode) exhibit excellent rate capability and good cyclic stability. A high specific capacity of ~860 mAh g-1 at 2.0 C as well as a capacity-fading rate of only ~0.035% per cycle over 350 cycles at 0.5 C can be achieved. This bifunctional separator can even endow a Li-S cell at a low current density to exhibit excellent cycling capability, with a capacity retention rate of ~88.4% at 0.2 C over 250 cycles. Furthermore, a Li-S cell with a Co@g-C3N4/G-PP separator possesses a stable specific capacity of 785 mAh g-1 at 0.2 C after 150 cycles and a superior capacity retention rate of ~84.6% with a high sulfur loading of ~3.0 mg cm-2. This effective polysulfide-confined separator holds good promise for promoting the further development of high-energy-density Li-S batteries.

Accelerating electrochemical reactions in Li-S batteries through better dispersion of sulfur and the robust catalytic effect upon the vanadium nitride decorated hollow carbon spheres

Li-S battery has been regarded as one of the most promising energy storage technologies due to the remarkable increase in energy density and desirable low cost when comparing with the commercial lithium-ion battery, yet the shuttling effect of soluble lithium polysulfide (LiPS) and the sluggish reaction kinetics during the reactions have hampered its further development. Here, we develop the vanadium nitride-decorated hollow carbon sphere (VNHCS) as advantageous sulfur host aiming to address these issues. Preferential distribution of nano sulfur around the layer region of VNHCS rather than aggregating into particles within the core is demonstrated as a result of the desirable chemical bonding effect of VN nanoparticles, which helps boost the electron and ion transport rates and inhibit shuttling of LiPS simultaneously. Furthermore, the accelerated reaction kinetics towards LiPS conversion are demonstrated by the favorable catalytic behavior of VNHCS, which are verified by the theoretical simulation results. Benefiting from these merits, the S@VNHCS cathode has exhibited advantageous electrochemical performances including the high initial discharge capacity of 1453 mA h g−1 at 0.1C and the ultralow capacity fading rate of 0.0293 % per cycle at 2C, outperforming most of the reported results of nitride compound-based sulfur cathodes.

Synthesis of CoP@B,N,P co-doped porous carbon by a supramolecular gel self-assembly method for lithium-sulfur battery separator modification.

Lithium-sulfur batteries (LSBs) are regarded as promising next-generation batteries due to their high abundance and high theoretical energy density. However, the commercial application of LSBs is hindered by the shuttle effect of soluble lithium polysulfides (LiPSs). Hence, we synthesised B, N, P co-doped three-dimensional hierarchical porous carbon materials, uniformly dispersed with CoP nanoparticles, and utilized them as the coating material for the PE separator. The catalytic and adsorption capacity of the composite material was significantly enhanced by CoP. Both experimental and theoretical calculations show that the LiPS adsorption capacity of the composite material is significantly enhanced after the introduction of B atoms. As a result, the assembled LSBs with the CoP@BNPC/PE separator show excellent long-term stability (940.8 mA h g-1 after 500 cycles at 1.0 C, and only a 0.026% decay rate per cycle) and superior rate performance (613.6 mA h g-1 at 5.0 C). Our work further proves that a modified separator is an effective strategy to promote the commercialization of LSBs.

Core-shell titanium nitride/silicon nitride modified separators as polysulfide shuttling barriers for lithium-sulfur batteries via a facile and recyclable molten-salt route

Lithium–Sulfur battery is deemed as one of the most promising next-generation energy storage systems. Identifying the reduction of soluble lithium polysulfides (LiPSs) is critical for rational material designs for Lithium–Sulfur batteries. In this work, a simple molten-salt method is applied to synthesize titanium nitride/silicon nitride (TiN–Si3N4) core-shell nanoparticles to inhibit soluble polysulfides shuttling. This Ti-reacted strategy has outstanding advantages such as facile and recyclable preparation process, tunable TiN morphology, and good polysulfide adsorption. With the modified separator, Li–S cells exhibit an outstanding initial capacity of 1243 mA h g−1 at 0.5C, good rate capacity of 782 mA h g−1 at 2C, and high capacity retention of 49.2% after 500 cycles. This low-cost and eco-friendly Ti-reacted strategy provides a practical route for the actual application of separator modification in the field of lithium-sulfur battery.

Synergistic effect of porous carbon shell confinement and catalytic conversion of nickel nanoparticle cores for improved lithium-sulfur batteries.

Lithium-sulfur batteries (LSBs) are some of the most promising energy storage systems to break the ceiling of Li-ion batteries. However, the notorious shuttle effect and slow redox kinetics give rise to low sulfur utilization and discharge capacity, poor rate performance, and fast capacity decay. It is proved that the reasonable design of the electrocatalyst is one of the important ways to improve the electrochemical performance of LSBs. Here, a core-shell structure with gradient adsorption capacity for reactants and sulfur products was designed. The Ni nanoparticles core coated with graphite carbon shell was prepared by one-step pyrolysis of Ni-MOF precursors. The design takes advantage of the principle that the adsorption capacity decreases from the core to the shell, and the Ni core with strong adsorption capacity is easy to attract and capture soluble lithium polysulfide (LiPS) during the discharge/charging process. This trapping mechanism prevents the diffusion of LiPSs to the outer shell and effectively inhibits the shuttle effect. In addition, the Ni nanoparticles within the porous carbon, as the active center, expose most of the inherent active sites to the surface area, thus achieving a rapid transformation of LiPSs, significantly reducing the reaction polarization, and improving the cyclic stability and reaction kinetics of LSB. Therefore, the S/Ni@PC composites exhibited excellent cycle stability (a capacity of 417.4 mA h g-1 for 500 cycles at 1C with a fading rate of 0.11%) and outstanding rate performance (1014.6 mA h g-1 at 2C). This study provides a promising design solution of Ni nanoparticles embedded in porous carbon for high-performance, safe and reliable LSB.

Facile one-pot synthesis of biomass-derived activated carbon as an interlayer material for a BAC/PE/Al2O3 dual coated separator in Li-S batteries.

Lithium-sulfur batteries (LSB) are an attractive alternative electrochemical energy storage device compared to conventional lithium-ion batteries due to their higher theoretical capacity and energy density. Despite these advantages, it is still difficult to commercialize LSB because of poor electrochemical performance caused by the dissolution of soluble lithium polysulfides (LiPS). To solve these critical issues, a multi-functional separator was prepared using biomass-derived activated carbon (BAC) and a ceramic layer on the polyethylene (PE) separator. For this purpose, BAC was synthesized by a facile one-pot synthesis method by a specifically designed furnace using various forms of milk waste. The multi-functional separator suppresses the effect of LiPS dissolution and increases the Li+ diffusion kinetics. BAC was able to absorb the LiPS shuttle, as confirmed by UV-vis measurements and X-ray photoelectron spectroscopy (XPS). LSB cells assembled using this multi-functional separator show a higher discharge capacity of 1092.5 mA h g-1 at 0.1 C-rate, while commercial PE separators deliver a specific capacity of 811.8 mA h g-1. These novel separators were also able to suppress lithium dendrites during cycling. This work offers a novel and simple approach for streamlining the synthesis process of BAC and applying it to LSB, aiding in the development of sustainable energy sources.

Highly active rare earth sulfur oxides used for membrane modification of lithium sulfur batteries

How to solve the shuttle effect of soluble lithium polysulfide (LiPS) and the reversible conversion of solid LixS is an important challenge to realize the practical application of lithium sulfide battery (LSB), and the selection, preparation and design of adsorption-conversion materials have always been an important topic in the research of LSB. In this work, based on the adsorption sites of LiPS and the transport path of lithium ion, we propose that metal sulfur oxides containing both metal-O and metal-S bonds in their molecular structure may be ideal adsorption-conversion materials. Therefore, La2O2S as an air stable metal sulfur oxides is selected as the target material. With La-BTC nanorod as the precursor, by adjusting the heat treatment temperature and the use of sulfur source, we achieved the preparation of La2O2S-C composite under relative low heat treatment conditions. Through DFT theoretical calculation, XPS and electrochemical test of button simulation batteries, we find that compared with La2O3 and La2S3, La2O2S has moderate adsorption energy and the largest Gibbs free energy, which is more suitable for the adsorption-conversion material of lithium sulfur battery. The button cell with La2O2S-C/PP retained a capacity of 664 mAh g−1 after 300 cycles at the discharge current of 1C.

Electrocatalytic and Conductive Vanadium Oxide on Carbonized Bacterial Cellulose Aerogel for the Sulfur Cathode in Li-S Batteries

Many transition-metal-oxide-based catalysts have been investigated to chemically bind soluble lithium polysulfides and accelerate their redox kinetics in lithium-sulfur (Li-S) battery chemistry. However, the intrinsic poor electrical conductivities of these oxides restrict their catalytic performance, consequently limiting the sulfur utilization and the rate performance of Li-S batteries. Herein, we report a freestanding electrocatalytic sulfur host consisting of hydrogen-treated VO2 nanoparticles (H-VO2) anchored on nitrogen-doped carbonized bacterial cellulose aerogels (N-CBC). The hydrogen treatment enables the formation and stabilization of the rutile VO2(R) phase with metallic conductivity at room temperature, significantly enhancing its catalytic capability compared to the as-synthesized insulative VO2(M) phase. Several measurements characterize the electrocatalytic performance of this unique H-VO2@N-CBC structure. In particular, the two kinetic barriers between S8, polysulfides, and Li2S are largely reduced by 28.2 and 43.3 kJ/mol, respectively. Accordingly, the Li-S battery performance, in terms of sulfur utilization and charge/discharge rate, is greatly improved. This work suggests an effective strategy to develop conductive catalysts based on a typical transition metal oxide (VO2) for Li-S batteries.

Customizing Component Regulated Dense Heterointerfaces for Crafting Robust Lithium‐Sulfur Batteries

AbstractLithium–sulfur (Li–S) batteries hold great promise for the next‐generation energy storage system. However, their commercial applications are severely hindered by myriads of drawbacks such as poor electrical conductivity of sulfur, sluggish redox reaction kinetics of sulfur species, “shuttling effect” of soluble lithium polysulfides (LiPSs) and uncontrollable dendritic Li growth. Herein, it is conceptually demonstrated that sluggish conversion kinetics of LiPSs is markedly stimulated by exquisite heterointerface modulation at nanoscale level over transition metal carbides and nitrides. In this scenario, N‐doped carbon coupled with molybdenum nitride/carbide (Mo2N‐MoC/NC) hybrid nanocomposites are designed through a one‐step carbonization‐nitridation process, wherein component regulation induced dense heterointerfaces are in situ produced. Benefiting from high electrical conductivity, strong chemical adsorption, and superior catalytic activity afforded by dense heterointerfaces, the Mo2N‐MoC/NC modified separators significantly restrict the soluble LiPSs shuttling and simultaneously suppress the Li dendrite generation. The assembled Li–S batteries with Mo2N‐MoC/NC modified separators exhibit remarkable electrochemical performance. Integrated experimental and theoretical results substantiate the boosted chemisorption and catalytic conversion of LiPSs endowed by such dense heterointerfaces. The work will open a new vista for rationally constructing multifarious heterostructured materials for the communities of Li‐S batteries.

Molybdenum‐Based Catalytic Materials for Li–S Batteries: Strategies, Mechanisms, and Prospects

Lithium–sulfur (Li–S) batteries are regarded as promising candidates for high‐energy storage devices because of their high theoretical energy density (2600 Wh kg−1). However, their practical applications are still hindered by a multitude of key challenges, especially the shuttle effect of soluble lithium polysulfides (LiPSs) and the sluggish sulfur redox kinetics. To address these challenges, varieties of catalytic materials have been exploited to prevent the shuttle effect and accelerate the LiPSs conversion. Recently, molybdenum‐based (Mo‐based) catalytic materials are widely used as sulfur host materials, modified separators, and interlayers for Li–S batteries. They include the Mo sulfides, diselenides, carbides, nitrides, oxides, phosphides, borides, and metal/single atoms/clusters. Here, recent advances in these Mo‐based catalytic materials are comprehensively summarized, and the current challenges and prospects for designing highly efficient Mo‐based catalytic materials are highlighted, with the aim to provide a fundamental understanding of the sulfur reaction mechanism, and to guide the rational design of cathode catalysts for high‐energy and long‐life Li–S batteries.

Porous TiO2-x/C Nanofibers with Axially Aligned Tunnel Pores as Effective Sulfur Hosts for Stabilized Lithium-Sulfur Batteries.

Hierarchically porous TiO2-x/C nanofibers (NFs) with axially aligned cylindrical tunnel pore channels were synthesized as a sulfur (S) host for lithium-sulfur batteries (LSBs) by a microemulsion electrospinning method. We explored a synergistic chemical trapping reinforced by coordinatively unsaturated Ti3+ nuclei with oxygen deficiency (or more broadly via polar O-Ti-O units) in combination with physical trapping in both narrow pores (<5 nm) and larger ordered pore tunnels (20-100 nm) separated by thin walls to allow for a large volume of active material and rapid diffusion within the channels while effectively blocking out the diffusion of soluble lithium polysulfides. Due to this unique architecture and enhanced conductivity, the prepared materials enabled a high S loading (∼72 wt %) and significantly reduced the shuttle effect. Hence, the composite TiO2-x/C@S cathodes exhibited a high utilization of active materials, excellent rate performance, and promising cycling stability (retention of up to ∼1010 mAh g-1 after 150 cycles for the aerial capacity of 1.5 mAh cm-2, with very stable performance even for the high S loading of 2.5 mg cm-2). By designing control nanomaterials that lack either the pore tunnels or the desired chemical compositions, we elucidated the importance of the synergistic effect of both factors. This work demonstrates a successful exploration of oxide NFs with tunnel pores via a simple single-needle microemulsion electrospinning method, which should pave the way for similar nanomaterials engineering with other chemistries for improved LSB performance.

Rational design and low-cost fabrication of multifunctional separators enabling high sulfur utilization in long-life lithium-sulfur batteries

The lithium-sulfur (Li-S) battery with an ultrahigh theoretical energy density has emerged as a promising rechargeable battery system. However, the practical applications of Li-S batteries are severely plagued by the sluggish reaction kinetics of sulfur species and notorious shuttling of soluble lithium polysulfides (LiPSs) intermediates that result in low sulfur utilization. The introduction of functional layers on separators has been considered as an effective strategy to improve the sulfur utilization in Li-S batteries by achieving effective regulation of LiPSs. Herein, a promising self-assembly strategy is proposed to achieve the low-cost fabrication of hollow and hierarchically porous Fe3O4 nanospheres (p-Fe3O4-NSs) assembled by numerous extremely-small primary nanocrystals as building blocks. The rationally-designed p-Fe3O4-NSs are utilized as a multifunctional layer on the separator with highly efficient trapping and conversion features toward LiPSs. Results demonstrate that the nanostructured p-Fe3O4-NSs provide chemical adsorption toward LiPSs and kinetically promote the mutual transformation between LiPSs and Li2S2/Li2S during cycling, thus inhibiting the LiPSs shuttling and boosting the redox reaction kinetics via a chemisorption-catalytic conversion mechanism. The enhanced wettability of the p-Fe3O4-NSs-based separator with the electrolyte enables fast transportation of lithium ions. Benefitting from these alluring properties, the functionalized separator with p-Fe3O4-NSs endows the battery with an admirable rate performance of 877 mAh g−1 at 2 C, an ultra-durable cycling performance of up to 2176 cycles at 1 C, and a promising areal capacity of 4.55 mAh cm−2 under high-sulfur-loading and lean-electrolyte conditions (4.29 mg cm−2, electrolyte/ratio: 8 µl mg−1). This study will offer fresh insights on the rational design and low-cost fabrication of multifunctional separator to strengthen electrochemical reaction kinetics by regulating LiPSs conversion for developing efficient and long-life Li-S batteries.

Dispersing single-layered Ti3C2TX nanosheets in hierarchically-porous membrane for high-efficiency Li+ transporting and polysulfide anchoring in Li-S batteries

Practical application of lithium-sulfur (Li-S) batteries with high areal capacity remains a challenge due to shuttle effect of soluble lithium polysulfides (LiPSs). Herein, a hierarchically porous membrane loaded with fully dispersed single-layered MXene is fabricated via a facile phase inversion method for a high-areal-capacity Li-S battery. The 3D hierarchical porous structure can strengthen Li+ and electron transporting, accommodate the volumetric expansion of sulfur, enable high sulfur loading and provide ample active sites for LiPSs anchoring. More importantly, the Ti3C2Tx nanosheets disperse uniformly in the framework prevents restacking of the MXenes layer, which makes full use of both sides of the nanosheets, thus further improves the diffusion of Li+ and enriches active sites for adsorption and catalysis of LiPSs. Benefitting from the above-multiplexed functionality, the Li-S batteries show high specific capacity and cycle stability at high sulfur loading. The proposed facile strategy sheds inspiring insights on the design of novel cathode materials for high-areal-capacity Li-S batteries.

Implanting single-atom N2-Fe-B2 catalytic sites in carbon hosts to stabilize high-loading and lean-electrolyte lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries suffer from soluble lithium polysulfide (LiPS) shuttling and sluggish redox kinetics. The rational design of carbon-supported single-atom catalysts (SACs) as both LiPS immobilizers and sulfur redox promoters is of great significance for high-loading and lean-electrolyte Li-S batteries. However, the most popular nonpolar porphyrin-like transition metal-nitrogen (M-N4) SACs cannot maximize the catalytic activity of the metal center. Herein, a B, N co-coordinated N2-Fe-B2 SAC embedded in a B, N-rich carbon matrix (denoted as Fe SAs@BCN) is disclosed for the first time to construct state-of-the-art Li-S batteries. We reveal experimentally and theoretically that the asymmetric N2-Fe-B2 configuration not only rapidly captures LiPSs through strong Lewis acid-base interactions, but also greatly catalyzes the bidirectional sulfur redox chemistry by lowering the Li2S deposition/decomposition energy barriers. As such, the well-designed SACs enable Li-S batteries to promise extraordinary durability (82% retention over 1000 cycles at 5 C) and high areal capacities even under harsh sulfur mass loadings. More encouragingly, a 359 Wh kg−1 pouch cell with an ultrahigh loading of 11.6 mg·S cm−2 and a lean electrolyte to sulfur (E/S) ratio of 3 µL mg·S−1 is further demonstrated. This work shows that N2-Fe-B2 SACs hold great promise in realizing high-energy-density Li-S batteries.

Recent Progress of Anode Protection in Li–S Batteries

Lithium‐ion batteries have gradually reached their theoretical limits. To meet the growing demand for higher energy storage technology, finding alternative battery chemistries has become the major concern. Fortunately, lithium–sulfur batteries are considered the most promising next‐generation energy storage technology due to being cost‐effective and having high theoretical energy density. However, the further commercialization of lithium–sulfur batteries is hindered due to the growth of lithium dendrites and the shuttle effect of soluble lithium polysulfides. This review provides an overview of the challenges facing lithium–sulfur batteries. Furthermore, a comprehensive overview of lithium metal protection strategies is provided including electrolyte optimization, construction of artificial solid electrolyte layers, utilization of hosting materials, and design of separators, as well as a theoretical understanding and analysis of the underlying methods. This review puts forward general conclusions and prospects for the practical application of lithium–sulfur batteries in the future and the promotion of technology development of lithium metal batteries.

A gel polymer electrolyte with Al2O3 nanofibers skeleton for lithium—sulfur batteries

As a promising secondary battery system, lithium—sulfur (Li—S) batteries have attracted extensive attention due to their high energy density. However, the development of Li—S batteries is hindered by the detrimental shuttling of soluble lithium polysulfides (LiPs) in traditional liquid electrolytes. In this work, we fabricate a functional gel polymer electrolyte for Li—S batteries. This electrolyte consists of poly(vinylidene fluoride-co-hexaflfluoropropylene) (PVDF-HFP) polymer matrix and a continuous γ-Al2O3 three-dimensional skeleton with structural and thermal stability. PVDF-HFP offers lithium-ion transport pathways and equips the electrolyte with flexibility, whereas the inorganic γ-Al2O3 skeleton as Lewis acid can suppress the shuttling of LiPs through strong Lewis acid-base interactions between γ-Al2O3 and LiPs. In addition, γ-Al2O3 has an effect on the Lewis base of bis(trifluoromethanesulphony)imide anion, facilitating the dissociation of lithium salts and leading to a high lithium-ion transference number. Moreover, γ-Al2O3 can improve the ionic conductivity by reacting with LiF to partly form the lithium-ion conductors of LiAlO2 and Li3AlF6. Benefiting from the synergistic effect of PVDF-HFP and γ-Al2O3, Li—S cells with this gel polymer electrolyte present improved cycling stability in terms of cathode capacity retention and anode morphology. This work provides a promising strategy for fabricating multifunctional gel electrolytes for high-energy Li—S batteries.

Kinetic Acceleration of Lithium Polysulfide Conversion via a Copper-Iridium Alloying Catalytic Strategy in Li-S Batteries.

To solve the shuttle effect of soluble lithium polysulfides (LiPSs), a porous N-doped carbon-supported copper-iridium alloy catalyst composite (CuIr/NC) has been synthesized and served as a modified cathode sulfur host for lithium-sulfur batteries (LSBs). The metal-organic framework-derived calcined carbon frameworks build efficient conductive channels for fast ion/electron transport. Furthermore, alloying noble metals Ir with thiophilic metal Cu provides abundant active sites to effectively capture LiPSs and accelerate the catalytic conversion process, originating from modulating the surface electronic structure of the metal Cu by introducing Ir atoms to affect the 3d-orbital distribution. All of the above are strongly supported by a range of characterization studies and density functional theory calculations. Benefiting from the above advantages, the LSBs generally show satisfactory cycling performance. Apart from exhibiting a terrific initial specific capacity of 1288 mA h g-1 at 0.2 C, they can also keep long-term cycling stability under a high current density up to 5 C together with a slow specific capacity decay ratio (0.033%) per cycle after 1000 cycles. In addition, it is worth mentioning that a high areal capacity (4.7 mA h cm-2) with a low E/S ratio (6.2 μL mg-1) could still be accomplished at higher sulfur loading (4.3 mg cm-2).

Enhancing the Catalytic Activity of Layered Double Hydroxide Supported on Graphene for Lithium–Sulfur Redox Reactions

The lithium–sulfur battery is one of the next-generation rechargeable battery candidates due to its high theoretical energy density and low cost. However, the sluggish conversion kinetics of soluble lithium polysulfides into insoluble Li2S2/Li2S leads to low sulfur utilization, retarded rate responses, and rapid capacity decay. Here, we enhance the sulfur reduction kinetics by designing and synthesizing a lamellar-structured NiFeLDH and reduced graphene oxide (rGO) composite. The assembly of a two-dimensional NiFeLDH with rGO, which has high conductivity and electrocatalytic activity, significantly enhances the electrochemical steps of sulfur reduction. The S@NiFeLDH/rGO cathode delivers an initial discharge capacity of 1014 mAh g−1 at 0.2 C and a capacity of 930 mAh g−1 after 100 cycles at 0.2 C. Even at a high current density of 1 C, the S@NiFeLDH/rGO could maintain a high capacity of 554 mAh g−1 after 400 cycles.

Unity of Opposites between Soluble and Insoluble Lithium Polysulfides in Lithium–Sulfur Batteries

Rechargeable batteries based on Li-S chemistry show promise as being possible for next-generation energy storage devices because of their ultrahigh capacities and energy densities. Research over the past decade has demonstrated that the morphology of lithium polysulfides (LPSs) in electrolytes (soluble or insoluble) plays a decisive role in battery performance. Early studies have focused mainly on inhibiting the dissolution of LPSs and invested considerable effort to realize this objective. However, in recent years, a completely different view that the dissolution of LPSs during battery discharge/charge should be promoted has emerged. At this critical juncture in the large-scale application of Li-S batteries, it is time to summarize and discuss both sides of the contradiction. Herein, an overview of these two opposite views pertaining to soluble and insoluble LPSs, including their historical environment, classical strategies, advantages, and disadvantages. Finally, the future morphology of LPSs in Li-S batteries is predicted based on a multiangle review of research studies conducted thus far, and the reasoning behind this conjecture is thoroughly discussed.

Oxygen Vacancies in Bismuth Tantalum Oxide to Anchor Polysulfide and Accelerate the Sulfur Evolution Reaction in Lithium-Sulfur Batteries.

The shuttling effect of soluble lithium polysulfides (LiPSs) and the sluggish conversion kinetics of polysulfides into insoluble Li2S2/Li2S severely hinders the practical application of Li-S batteries. Advanced catalysts can capture and accelerate the liquid–solid conversion of polysulfides. Herein, we try to make use of bismuth tantalum oxide with oxygen vacancies as an electrocatalyst to catalyze the conversion of LiPSs by reducing the sulfur reduction reaction (SRR) nucleation energy barrier. Oxygen vacancies in Bi4TaO7 nanoparticles alter the electron band structure to improve instinct electronic conductivity and catalytic activity. In addition, the defective surface could provide unsaturated bonds around the vacancies to enhance the chemisorption capability with LiPSs. Hence, a multidimensional carbon (super P/CNT/Graphene) standing sulfur cathode is prepared by coating oxygen vacancies Bi4TaO7−x nanoparticles, in which the multidimensional carbon (MC) with micropores structure can host sulfur and provide a fast electron/ion pathway, while the outer-coated oxygen vacancies with Bi4TaO7−x with improved electronic conductivity and strong affinities for polysulfides can work as an adsorptive and conductive protective layer to achieve the physical restriction and chemical immobilization of lithium polysulfides as well as speed up their catalytic conversion. Benefiting from the synergistic effects of different components, the S/C@Bi3TaO7−x coin cell cathode shows superior cycling and rate performance. Even under a high level of sulfur loading of 9.6 mg cm−2, a relatively high initial areal capacity of 10.20 mAh cm−2 and a specific energy density of 300 Wh kg−1 are achieved with a low electrolyte/sulfur ratio of 3.3 µL mg−1. Combined with experimental results and theoretical calculations, the mechanism by which the Bi4TaO7 with oxygen vacancies promotes the kinetics of polysulfide conversion reactions has been revealed. The design of the multiple confined cathode structure provides physical and chemical adsorption, fast charge transfer, and catalytic conversion for polysulfides.