Shuttling Of Lithium Polysulfides Research Articles

Addition of a Polar, Porous Phase-Inversion-PVDF Membrane to Lithium–Sulfur Cells (LSBs) Already with a Microporous Polypropylene Separator Enhances the Battery Performance

Lithium–sulfur batteries (LSBs) are widely studied as an alternative to lithium-ion batteries, this emphasis being due to their high theoretical energy density and low cost, and to the high natural abundance of sulfur. Lithium polysulfide shuttling and lithium dendrite growth have limited their commercialization. Porous polyvinylidene fluoride (PVDF) separators have shown improved performance (relative to hydrocarbon separators) in lithium-ion batteries due to faster lithium-ion migration and higher Li+ transference number. A thin polar PVDF membrane has now been fabricated via phase inversion (an immersion-precipitation method) yielding a β (polar) phase concentration of 72%. Preparation from commercial PVDF used dimethylformamide (DMF) solvent at the optimized crystallizing temperature of 70 °C, and pores in the membrane were generated by exchange of DMF with deionized water as non-solvent. The polar PVDF film produced has the advantages of being ultrathin (15 µm), lightweight (1.15 mg cm−2), of high porosity (75%) and high wettability (84%), and it shows enhanced thermal stability relative to polypropylene (PP). The porous, polar PVDF membrane was combined with a commercially available PP membrane to give a hybrid, two-layer, separator combination for LSBs. A synergy was created in the two-layer separator, providing high sulfur utilization and curbing polysulfide shuttling. The electrochemical performance with the hybrid separator (PP–β-PVDF) was evaluated in LSB cells and showed good cyclability and rate capability: those LSB cells showed a stable capacity of 750 mA h g−1 after 100 cycles at 0.1 C, much higher than that for otherwise-identical cells using a commercial PP-only separator (480 mA h g−1).

High-Temperature Lithium-Sulfur Batteries with Commercial Paper-Derived Solid-State Electrolyte

Solid-state lithium-sulfur (Li-S) battery technologies could power future electric mobility due to their potential high energy density. However, the current solid-state Li-S batteries face several challenges, such as high internal impedance at the electrode/electrolyte interfaces, shuttling of lithium polysulfides, and Li dendrite formation. Herein, we introduced a novel Li-rich cellulose-based solid-state electrolyte in combination with sulfurized polyacrylonitrile (SPAN, 36.5 wt.% S) cathode, leading to durable Li-S batteries for high-temperature applications. We utilized SPAN due to its reasonable conductivity, high reversible capacity, and stable cycling performance. The solid-state electrolyte in this study was prepared by infusing Li ions (Li+) into a copper-coordinated cellulosic paper. The infusion of Li+ was carried out by soaking the copper-treated paper in a 1 M LiTFSI in EC0.5DME0.25DOL0.25 solution (where subscripts indicate the volume fraction), followed by complete evaporation of the solvents. Three types of cellulosic paper were explored, from which the commercial copy paper resulted in the highest area-normalized conductance of 24.4 mS cm-2 and Li-ion transference number of 0.76 at 50 °C. At this temperature, the Li-SPAN cells with paper-based electrolyte delivered an initial reversible capacity of 1536 mAh gs -1 at 168 mA gs -1 (0.1C). After high-temperature cycling for 150 cycles at 0.5C, the Li-SPAN cells exhibited an exceptional capacity retention of 82.2% (from 982 to 807 mAh gs -1). The conformability of the paper-based electrolyte ensures good interfacial contact with the SPAN and Li electrodes. As a result, when this solid-state Li-S battery was subjected to fast charging/discharging (1C) at 50 °C, it delivered a reversible capacity of 670 mAh gs -1. In this talk, we will outline the results from our electron microscopy, X-ray diffraction measurements, electrochemical impedance spectroscopy, and cyclic voltammetry studies on Li-S cells to unravel the superior performance of paper-based Li-S batteries at high temperatures. Figure 1

Fe3O4-doped mesoporous carbon cathode with a plumber’s nightmare structure for high-performance Li-S batteries

Shuttling of lithium polysulfides and slow redox kinetics seriously limit the rate and cycling performance of lithium-sulfur batteries. In this study, Fe3O4-dopped carbon cubosomes with a plumber’s nightmare structure (SP-Fe3O4-C) are prepared as sulfur hosts to construct cathodes with high rate capability and long cycling life for Li-S batteries. Their three-dimensional continuous mesochannels and carbon frameworks, along with the uniformly distributed Fe3O4 particles, enable smooth mass/electron transport, strong polysulfides capture capability, and fast catalytic conversion of the sulfur species. Impressively, the SP-Fe3O4-C cathode exhibits top-level comprehensive performance, with high specific capacity (1303.4 mAh g−1 at 0.2 C), high rate capability (691.8 mAh gFe3O41 at 5 C), and long cycling life (over 1200 cycles). This study demonstrates a unique structure for high-performance Li-S batteries and opens a distinctive avenue for developing multifunctional electrode materials for next-generation energy storage devices.

A highly efficient absorptive and catalytic self-supporting Fe2O3/CC host for high performance Li-S batteries

The lithium-sulfur (Li-S) battery is a promising energy storage system because of its high energy density and low cost. However, the shuttling of lithium polysulfides (LiPSs) and low conductivity of the S cathode are barriers to its practical application. Fe2O3 nanorods were grown on a carbon cloth (Fe2O3/CC) by a solvothermal reaction and calcination to obtain a cathode for the battery. The mesoporous structure of the Fe2O3 and the CC conducting network facilitates lithium-ion and electron transport. Meanwhile, the nanorod arrangement results in the exposure of more Fe2O3 active sites, which improves the adsorption and rapid conversion of LiPSs. As a result, a Li–S cell using a Fe2O3/CC cathode has a high capacity of 1 250 mAh g−1 at 0.1 C with an excellent life of over 100 cycles with a capacity retention of 67%. It also has a 70% capacity retention after 1 000 cycles at 0.2 C. The excellent electrochemical performance of the Fe2O3/CC cathode indicates its potential applications in Li-S batteries.

Understanding synergistic catalysis on Pt–Cu diatomic sites via operando X-ray absorption spectroscopy in sulfur redox reactions

Sulfur redox reactions render lithium–sulfur (Li–S) batteries with an energy density of > 500 ​Wh ​kg−1 but suffer a low practical capacity and fast capacity fade due to sluggish sulfur redox reaction (SRR) kinetics, which lies in the complex reaction process that involves a series of reaction intermediates and proceeds via a cascade reaction. Here, we present a Pt–Cu dual-atom catalyst (Pt/Cu-NG) as an electrocatalyst for sulfur redox reactions. Pt/Cu-NG enabled the rapid conversion of soluble polysulfide intermediates into insoluble Li2S2/Li2S, and consequently, it prevented the accumulation and shuttling of lithium polysulfides, thus outperforming the corresponding single-atom catalysts (SACs) with individual Pt or Cu sites. Operando X-ray absorption spectroscopy and density functional theory calculations revealed that a synergistic effect between the paired Pt and Cu atoms modifies the electronic structure of the Pt site through d-orbital interactions, resulting in an optimal moderate interaction of the metal atom with the different sulfide species. This optimal interaction enhanced charge transfer kinetics and promoted sulfur redox reactions. Our work thus provides important insights on the atomic scale into the synergistic effects operative in dual-atom catalysts and will thus pave the way to electrocatalysts with enhanced efficiency for high-performance Li–S batteries.

Dual-Mediation pathways promote redox kinetics for High-Loading Lithium–Sulfur batteries under lean electrolyte

The high energy density (2500 Wh kg−1) makes that lithium–sulfur batteries (LSBs) have a great potential in energy storages. However, the practical application of LSBs is severely hampered by several inherent problems, including the sluggish sulfur redox kinetics, the shuttling of lithium polysulfides (LiPSs) and poor electronic conductivity. Although heterogeneous or homogeneous mediators could improve the cycling performance of LSBs to a certain extent, single mediators could not completely promote sulfur conversions, especially under high sulfur loading and lean electrolyte. Herein, dual-mediator systems consist of heterogeneous and homogeneous mediators that are introduced to address the above issues. Density functional theory (DFT) calculations and electrochemical analysis indicate that CoSe nanoparticles embedded in urchin-like nitrogen-doped porous carbon with in-situ growth of CNTs (CoSe@CNTs) as heterogeneous mediators and soluble CoCp2 as homogeneous mediators could effectively accelerate the bidirectional conversion kinetics of liquid LiPSs ↔ solid Li2S through the synergistic effect. As a consequence, the cell with dual-mediators delivers a high initial specific capacity of 1005 mAh/g with a low attenuation rate of 0.045 % per cycle at a current density of 1.0C under sulfur loading of 2.8 mg cm−2 after 800cycles. Importantly, it still maintains a high areal capacity of 6.53 mAh cm−2 under lower electrolyte/sulfur ratio (E/S, 4.2 µL mg−1) and higher sulfur loading of 7.3 mg cm−2 over 100cycles at 0.1C.

VN quantum dots anchored N-doped carbon nanosheets as bifunctional interlayer for high-performance lithium-metal and lithium-sulfur batteries

Lithium dendrite growth and shuttling of lithium polysulfides (LiPSs) seriously hinder the industrialization of lithium-sulfur (Li-S) batteries. Herein, elaborately designed VN quantum dots anchored N-doped carbon nanosheets (VN@NC) is employed as a bifunctional separator. The strong absorption and catalytic conversion of polar VN quantum dots effectively suppress the shuttling effect of LiPSs, confirmed by experimental and theoretical calculations studies; moreover, lithiophilic VN@NC acts as Li-ion redistributor to regulate and redistribute the interfacial ionic flux, thus effectively inhibit the uncontrollable growth of Li dendrites. As a result, the Li-S cell with VN@NC interlayer delivers ultralong cycle life (0.036 % per cycle at 2C over 1000 cycles) and high-rate capability (752 mAh/g at 4C). Even with sulfur loading (5.4 mg cm−2) and lean electrolyte/sulfur (E/S) usage (4.6 μL mg−1), the pouch cell can deliver an initial areal capacity of 5.16 mAh cm−2 and still retain 4.02 mAh cm−2 at 0.1C over 50 cycles. The VN@NC-based Li-Li symmetric cells demonstrate great cycling and rate performance in protecting the Li anode. This work offers a bi-functionally integrated interlayer strategy to simultaneously suppress the shuttling of LiPSs and dendrite growth of Li anode for high-performance Li-S and Li-metal batteries.

2D-2D heterostructure of ionic liquid-exfoliated MoS2/MXene as lithium polysulfide barrier for Li-S batteries

Suppressing the dissolution and shuttling of lithium polysulfides (LiPSs) in electrolytes in lithium-sulfur batteries (LSBs) is the focus of researchers. Herein, functional liquid phase exfoliated MoS2 and MXene (IL-MoS2/MX) interlayer is proposed as the separator of LSBs. The unique alternating intercalation structure of the IL-MoS2/MX interlayer provides a channel for ion transport while achieving uniform Li+ deposition on the anode side. Moreover, IL-MoS2 achieves physical and chemical anchoring to LiPSs and lowers the energy barrier for battery reactions. As a result, the separator in the coin cell delivers an initial capacity of 764.4 mAh·g−1 at 1C and high retention of 58.7 % after 700 cycles, with a decay only 0.059 % per cycle. Simultaneously, the excellent stability is also verified under varying current densities. Beyond that, ionic conductivity and lithium-ion migration number are adopted to confirm unique ion transport channels and uniform deposition of lithium. X-ray photoelectron spectroscopy, S8 and Li2S decomposition and nucleation energy barrier analysis are performed to verify the adsorption and catalytic conversion mechanisms. The convenient preparation and excellent performance of IL-MoS2/MX provide a design strategy for functionalized interlayers for LSBs, and the possibility for commercialization.

A computational study on bifunctional 1T-MnS2 with an adsorption-catalysis effect for lithium-sulfur batteries.

Lithium-sulfur (Li-S) batteries are promising rechargeable energy storage systems with a high energy density, environmental friendliness and low cost. However, the commercialization process of Li-S batteries has been seriously hindered by the shuttling of lithium polysulfides (LiPSs) and the sluggish kinetics of conversion reaction among sulfur species. In this work, the adsorption-catalysis performance of five transition metal disulfide 1T-MS2 (M = Mn, V, Ti, Zr, and Hf) surfaces is investigated by evaluating the adsorption energy of sulfur species, Li-ion diffusion energy barrier, decomposition energy barrier of Li2S, and the Gibbs free energy barrier of the sulfur reduction reaction based on first-principles calculations. Our results show that the sulfiphilicity of 1T-MS2 plays an important role in the adsorption behavior of short-chain sulfur species, in addition to lithiophilicity. Remarkably, among the five 1T-MS2 materials, our results confirm that 1T-TiS2 and 1T-VS2 show excellent adsorption-catalysis performance and it is predicted that 1T-MnS2 is an even better candidate catalyst to inhibit the shuttle effect and accelerate delithiation/lithiation kinetics. Moreover, the outstanding performance of 1T-MnS2 persists in a solvent environment and under strain modulation. Our results not only demonstrate that 1T-MnS2 is an excellent potential catalyst for high-performance Li-S batteries, but also provide great insights into the adsorption-catalysis mechanism during the cycling process.

Co‐recrystallization induced self‐catalytic Li2S cathode fully interfaced with sulfide catalyst toward a high‐performance lithium‐free sulfur battery

AbstractLithium sulfide (Li2S) is a promising cathode for a practical lithium‐sulfur battery as it can be coupled with various safe lithium‐free anodes. However, the high activation potential (>3.5 V) together with the shuttling of lithium polysulfides (LiPSs) bottleneck its practical uses. We are trying to present a catalysis solution to solve both problems simultaneously, specially with twinborn heterostructure to shoot off the trouble in interfacial contact between two solids, catalyst and Li2S. As a typical example, a Co9S8/Li2S heterostructure is reported here as a novel self‐catalytic cathode through a co‐recrystallization followed by a one‐step carbothermic conversion. Co9S8 as the catalyst effectively lowers the Li2S activation potential (<2.4 V) due to fully integrated and contacted interfaces and consistently promotes the conversion of LiPSs to suppress the shuttling. The obtained freestanding cathode of Co9S8/Li2S heterostructures encapsulated in three‐dimensional graphene shows a high capacity, reaching 92.6% of Li2S theoretical capacity, high rate performance (739 mAh g−1 at 2 C), and a low capacity fading (0.039% per cycle at 1 C over 900 cycles). Even under a high Li2S loading of 12 mg cm−2 and a low E/S ratio of , 86% of theoretical capacity can be utilized.image

Suppressing Polysulfides Shuttling and Promoting Sulfur Utilization via Transition Metal and Nitrogen Co-Doping on Graphdiyne Cathodes of Lithium-Sulfur Batteries: A First-Principles Modeling

While lithium-sulfur (Li-S) batteries are considered the next-generation energy storage devices, several issues inhibit their commercialization, including poor conductivity, shuttling of lithium polysulfides (LiPSs), and sluggish decomposition of small LiPSs. Here, we illustrate through first-principles modeling that doping graphdiyne (GDY) with transition metal (Co, Fe) and nitrogen (TM-N) effectively suppresses the shuttle effect and enhances sulfur utilization by promoting dissociation of small LiPSs. We find that the TM-N doping provides additional electrons to the substrate, which could improve the redox activity of the substrates. The additional electrons also improve charge transfer between the substrate and adsorbate that enhances the LiPS adsorption. Electronic structure analysis reveals that the strong interactions originate from the formation of TM-S bonds and electrostatic attractions between Li and N. Such strong adsorptions prevail in the interaction between the LiPSs and electrolyte molecules; hence, the doped GDY could effectively prevent the dissolution of LiPSs and inhibit the shuttle effect. Moreover, the doped GDY substrates exhibit small barriers of Li–S and Li–N bond breaking that facilitate the decomposition of small LiPSs. This implies that TM-N-doped GDY promotes kinetics of LiPS transformation, which increases sulfur utilization and diminishes capacity fading upon charge–discharge cycles. From the computational viewpoints, the TM-N-doped GDY substrates are considered promising cathodes of Li-S batteries. This work serves as a useful guide to rationally design high-performance two-dimensional (2D) carbon-based cathode materials for Li-S batteries.

Bifunctional Al2O3/polyacrylonitrile membrane to suppress the growth of lithium dendrites and shuttling of polysulfides in lithium-sulfur batteries

Interfacial engineering plays an important role in dynamically stabilizing the electrochemical performance of lithium-sulfur batteries (LSBs). Constructing a robust interface, e.g., using a multifunctional membrane, benefits not only for the suppression of lithium polysulfides (LiPSs) shuttling, but also for the inhibition of uncontrollable Li dendrite growth. Herein, a bifunctional membrane is fabricated with the Al2O3 nanoparticle-embedded polyacrylonitrile nanofibers (Al2O3/PAN) in a facile way as separator, which are found effective in blocking the growth of Li dendrite and the shuttling of LiPSs in LSBs. The exposed Al2O3 nanoparticles work in a responsible way to physiochemically capture the LiPSs and simultaneously let the Li ions shuttle through the PAN nanofiber network as the simulation indicated. The 3D cross-linked membrane can also block the oriented Li deposition and growth to make the symmetric Li||Li cell cycle over 1500 h without short circuit at 0.5 mA cm−2. Moreover, the LSB exhibits a reversible capacity of 2.08 mAh cm−2 at 500 mA g−1 under the sulfur loading of 3.6 mg cm−2. These results provide a doable and economy way to fabricate the robust membrane to deal effectively with the tough issues, which sheds new light on the design and optimization of high-energy-density sulfur prevailed rechargeable batteries.

Advances in the Development of Single-Atom Catalysts for High-Energy-Density Lithium-Sulfur Batteries.

Although lithium-sulfur (Li-S) batteries are promising next-generation energy-storage systems, their practical applications are limited by the growth of Li dendrites and lithium polysulfide shuttling. These problems can be mitigated through the use of single-atom catalysts (SACs), which exhibit the advantages of maximal atom utilization efficiency (≈100%) and unique catalytic properties, thus effectively enhancing the performance of electrode materials in energy-storage devices. This review systematically summarizes the recent progress in SACs intended for use in Li-metal anodes, S cathodes, and separators, briefly introducing the operating principles of Li-S batteries, the action mechanisms of the corresponding SACs, and the fundamentals of SACs activity, and then comprehensively describes the main strategies for SACs synthesis. Subsequently, the applications of SACs and the principles of SACs operation in reinforced Li-S batteries as well as other metal-S batteries are individually illustrated, and the major challenges of SACs usage in Li-S batteries as well as future development directions are presented.

Boosting polysulfides immobilization and conversion through CoS2 catalytic sites loaded carbon fiber for robust lithium sulfur batteries

The practical applications of lithium sulfur battery is impeded by the lithium polysulfide shuttling and sluggish redox kinetics. To address the issues, herein, a multifunctional host is developed by the combination of nitrogen, phosphorus co-doped carbon fiber (NPCF) and CoS2 towards boost the soluble polysulfides adsorption and transformation. Benefiting from the NPCF originated from biomass cattail fibers, a high conductive network is provided, and shuttle effect is reduced due to the strong chemical interaction between abundant heteroatom polar sites and lithium polysulfides. Moreover, the electrocatalytic CoS2 on the carbon skeleton facilitate lithium polysulfides conversion and lithium sulfide deposition based on the density functional theory calculations and experiments. The efficient lithium polysulfides entrapment and subsequent electrocatalytic conversion improve dynamic stability during cycling, especially for rate capability. With these advantageous features, the electrode with NPCF/CoS2 host can deliver a good rate capability (903 and 782 mAh g−1 at 1C and 2C, respectively) and stable cycling performance with an ultra-low capacity decay of 0.014% per cycle at 1C. Notably, the cell can achieve a high areal capacity of 4.96 mA h cm−2 under an elevated sulfur loading of 5.0 mg cm−2. Overall, the improvement on the electrochemical performance ascertains the validity of the design strategy based on synergy engineering, which is a highly suitable approach for energy storage and conversion application.

Engineering zwitterionic barrier by squaraine-based porous organic framework fiber for superior lithium-sulfur batteries

The lithium sulfur (Li-S) battery holds great promise in next-generation energy storage technologies. However, the lithium polysulfide (LiPS) shuttle and slow reaction kinetics still limit its commercial development. Here, a squaraine-based porous organic framework (POF) with sulfophilic and lithiophilic moieties was developed as the separator modifications for the first time. The POF coating layer on the common separator builds a strong barrier against the LiPS shuttling, resulting in a robust inhibition on the shuttle effect as well as boosted sulfur reaction kinetics. Therefore, the POF-PP separator demonstrates stable cycling performance with a low capacity attenuation rate of 0.04% over 500 cycles and high areal discharge capacity of 4.67 mAh cm−2 with a sulfur loading of 5 mg cm−2, which show high potential for high loading and practical Li-S battery.

Coordinated Adsorption and Catalytic Conversion of Polysulfides Enabled by Perovskite Bimetallic Hydroxide Nanocages for Lithium-Sulfur Batteries.

Catalysis is an effective remedy for the fast capacity decay of lithium-sulfur batteries induced by the shuttling of lithium polysulfides (LiPSs), but too strong adsorption ability of many catalysts toward LiPSs increases the risk of catalyst passivation and restricts the diffusion of LiPSs for conversion. Herein, perovskite bimetallic hydroxide (CoSn(OH)6 ) nanocages are prepared, which are further wrapped by reduced graphene oxide (rGO) as the catalytic host for sulfur. Because of the coordinated valence state of Co and Sn and the intrinsic defect of the perovskite structure, such bimetallic hydroxide delivers moderate adsorption ability and enhanced catalytic activity toward LiPS conversion. Coupled with the hollow structure and the wrapped rGO as double physical barriers, the redox reaction kinetics, and sulfur utilization are effectively improved with such a host. The assembled battery delivers a good rate performance with a high capacity of 644 mAh g-1 at 2 C and long stability with a capacity decay of 0.068% per cycle over 600 cycles at 1 C. Even with a higher sulfur loading of 3.2 mg cm-2 and a low electrolyte/sulfur ratio of 5 µL mg-1 , the battery still shows high sulfur utilization and good cycling stability.

Artificial dual solid-electrolyte interfaces based on in situ organothiol transformation in lithium sulfur battery

The interfacial instability of the lithium-metal anode and shuttling of lithium polysulfides in lithium-sulfur (Li-S) batteries hinder the commercial application. Herein, we report a bifunctional electrolyte additive, i.e., 1,3,5-benzenetrithiol (BTT), which is used to construct solid-electrolyte interfaces (SEIs) on both electrodes from in situ organothiol transformation. BTT reacts with lithium metal to form lithium 1,3,5-benzenetrithiolate depositing on the anode surface, enabling reversible lithium deposition/stripping. BTT also reacts with sulfur to form an oligomer/polymer SEI covering the cathode surface, reducing the dissolution and shuttling of lithium polysulfides. The Li–S cell with BTT delivers a specific discharge capacity of 1,239 mAh g−1 (based on sulfur), and high cycling stability of over 300 cycles at 1C rate. A Li–S pouch cell with BTT is also evaluated to prove the concept. This study constructs an ingenious interface reaction based on bond chemistry, aiming to solve the inherent problems of Li–S batteries.

Fe-cation Doping in NiSe2 as an Effective Method of Electronic Structure Modulation towards High-Performance Lithium-Sulfur Batteries.

The commercialization of Li-S batteries is hindered by the shuttling of lithium polysulfides (LiPSs), the sluggish sulfur redox kinetics as well as the low sulfur utilization during charge/discharge processes. Herein, a free-standing cathode material was developed, based on Fe-doped NiSe2 nanosheets grown on activated carbon cloth substrates (Fe-NiSe2 /ACC) for high-performance Li-S batteries. Fe-doping in NiSe2 plays a key role in the electronic structure modulation of NiSe2 , enabling improved charge transfer with the adsorbed LiPSs molecules, stronger interactions with the active sulfur species and higher electrical conductivity. Effective promotion of the sulfur redox kinetics and enhanced sulfur utilization were achieved under high areal sulfur loadings. The stronger interactions with LiPSs together with the unique 3D structure of Fe-NiSe2 /ACC also induced the transformation of Li2 S2 /Li2 S growth from conventional 2D films to 3D particles, significantly eliminating the barriers of solid nucleation and growth during the phase transition of liquid LiPSs to solid Li2 S2 /Li2 S. With a high sulfur loading of 9.9 mg cm-2 , the Fe-NiSe2 /ACC cathode enabled a high area capacity of 9.14 mAh cm-2 with a low average decay of 0.11 % per cycle over 200 cycles at 0.1 C.

Understanding effects of conductive additives in lithium-sulfur batteries

Since 2009, lithium-sulfur (Li-S) batteries have been attracting much research interest, ascribed to their high energy density and cost-effectiveness. However, their S cathodes are harassed by the poor conductivity, shuttling of lithium polysulfides (LPSs), and large volume change. In improving conductivity of S cathodes, carbon materials are widely used as conductive additives. However, there still lacks a comparative study on their geometric and structural effects in Li-S batteries. To this end, a systematic investigation is conducted on two different typical conductive additives, carbon black (CB)11CB is the abbreviation of carbon black. and nitrogen-doped graphene nanosheets (N-GNS)22N-GNS is the abbreviation of nitrogen-doped graphene nanosheets.. This work reveals that, compared to the zero-dimensional (0D) CB nanoparticles, the two-dimensional (2D) N-GNS is structurally less defective and has a larger surface area. As a result, the 2D structure of the N-GNS helps achieve higher capacity retention but inhibits Li-ion transportation. In comparison, the 0D structure of the CB facilitates the transportation of Li-ions with a higher initial capacity but exposed to a severer shuttling behavior of LPSs. It is also found that a combination of the CB and N-GNS enables better performance of Li-S batteries, in terms of sustainable capacity, Coulombic efficiency, and rate capability. This study is inspiring for designing better S cathodes for Li-S batteries.

Immobilizing Polysulfide by In Situ Topochemical Oxidation Derivative TiC@Carbon-Included TiO2 Core-Shell Sulfur Hosts for Advanced Lithium-Sulfur Batteries.

The performance of lithium-sulfur (Li-S) batteries is greatly hindered by the notorious shuttle effect of lithium polysulfides (LiPSs). To address this issue, in situ topochemical oxidation derivative TiC@carbon-included TiO2 (TiC@C-TiO2 ) core-shell composite is designed and proposed as a multifunctional sulfur host, which integrates the merits of conductive TiC core to facilitate the redox reaction kinetics of sulfur species, and porous C-TiO2 shell to suppress the dissolution and shuttling of LiPSs through chemisorption. A unique dual chemical mediation mechanism is demonstrated for the proposed TiC@C-TiO2 composite that synergistically entraps LiPSs through thiosulfate/polythionate conversion coupled with strong polar-polar interaction. The morphological characterization reveals that the TiC@C-TiO2 -based cathode can well regulate the distribution of electrode materials to retard their accumulation inside the electrode, ensuring effective contact between the active materials and electrolyte. Based on its unique function and structure, the cathode delivers an improved capacity of 1256 mAh g-1 at 0.2C, a remarkable rate capability of 643 mAh g-1 , and an ultralow capacity decay rate of 0.065% per cycle at 2C over 900 cycles. This work not only demonstrates a dual chemical mediation mechanism to immobilize LiPSs, but also provides a universal strategy to construct multifunctional sulfur hosts for advanced Li-S batteries.