Sulfur Loading Research Articles

Heterostructure Mo2C/α-MoO3/G catalyst based heterogeneous catalysis/deposition mechanism for high-performance Li-S battery

Lithium-sulfur batteries (LSBs) have been recognized as a promising energy device due to their outstanding theoretical energy density and abundant resources. However, the commercial application remains obstruction by the sluggish redox kinetics and serious shuttle effect of polysulfides. Herein, a heterostructural Mo2C/α-MoO3/graphene (Mo2C/α-MoO3/G) catalyst based on a heterogeneous catalysis/deposition mechanism is proposed to address these issues. The prepared Mo2C/α-MoO3/G catalyst is feature with high-activity facet, fast electron delocalization and build-in electric field, which drastically promotes the redox kinetics of polysulfides on the surface of crystal phase. Simultaneously, the heterostructural Mo2C/α-MoO3/G catalyst is capable of capturing polysulfides effectively and eliciting the heterogeneous deposition of Li2S on the surface of amorphous phase, of which guarantee the efficient catalytic characteristic during the charge/discharge processes. In addition, the shuttle effect is restricted with a lower shuttle factor (∼0.02). Therefore, the assembled LSBs based Mo2C/α-MoO3/G catalyst modifying separator exhibits an impressive specific capacity of 1311.4 mAh g−1 at 0.2 C and excellent rate capability of 580.3 mAh g−1 at 4 C. More importantly, it demonstrated satisfied cycling stability even at a high sulfur loading mass (4.2 mgS cm−2) and lean electrolyte conditions (9.3 μL gS-1). This work reveals a novel paradigm for optimizing the kinetics behaviors to achieve the commercialization of LSBs.

Application of Y-MOF-CNT-Derived Y2O3-C@CNT Composites in Lithium-Sulfur Battery Separators.

In order to mitigate the shuttle effect of lithium polysulfides in lithium-sulfur batteries, we propose a yttrium-metal-organic framework-carbon nanotube (Y-MOF-CNT)-derived Y2O3-C@CNT composite for modifying the separator in this study. The Y-MOFs, comprising yttrium (Y) rare earth metal and terephthalic acid, exemplify a prototypical category of metal-organic framework (MOF) materials. They manifest the advantageous attributes associated with MOFs while concurrently possessing distinctive catalytic traits ascribed to rare earth elements. In this study, Y-MOF nanoparticles were synthesized on carbon nanotube (CNT) substrates via a facile aqueous solution method, succeeded by high-temperature carbonization to yield Y2O3-C@CNT composite materials. These composites were subsequently employed as coatings on one side of polyethylene (PE) separators. The resultant Y2O3-C@CNT composite inherits the particle-like morphology and porosity from its precursor Y-MOF, alongside the inherent conductivity in carbon-based materials. This amalgamation is conducive to polysulfide capture and catalytic conversion processes within lithium-sulfur batteries. The application of the Y2O3-C@CNT-coated PE separator effectively mitigated polysulfide shuttle effects and significantly enhanced the battery electrochemical performance. At a sulfur loading level of 3 mg cm-2 under a 0.5 C rate, an initial discharge specific capacity of 900 mAh g-1 was achieved. After 400 cycles, the discharge specific capacity remained at 483.85 mAh g-1 with a capacity retention rate of 53.7%. Upon increasing sulfur loading to 5 mg cm-2, the discharge specific capacity at a lower rate (0.1 C) reached 817.8 mAh g-1; even after 100 cycles, it maintained a value of 700 mAh g-1 with a capacity retention rate of 85.6%. Notably, our modified Y2O3-C@CNT separator demonstrated exceptional cycling stability, even under conditions involving high sulfur loading.

Dynamically Regulating Polysulfide Degradation via Organic Sulfur Electrolyte Additives in Lithium‐Sulfur Batteries

AbstractLithium‐sulfur (Li‐S) batteries offer promising prospects due to their high energy density and cost‐effectiveness. However, the sluggish kinetics of lithium polysulfides (LiPSs) conversion, particularly the crucial stage from LiPSs to lithium sulfide (Li2S), hampers their development. Herein, a novel strategy for dynamically regulating LiPSs conversion by incorporating 4‐mercaptopyridine (4Mpy), as a LiPSs Redox Regulator (RR) in the electrolyte is introduced. This organic sulfur additive actively interacts with LiPSs during discharge, facilitating rapid conversion and promoting the formation of a three‐dimensional (3D) Li2S structure, thereby enhancing reaction kinetics. Both theoretical and experimental results reveal that the redox conversion mechanism with the 4Mpy additive differs from traditional electrolytes. Upon lithiation, 4Mpy forms lithium‐pyridinethiolate (Li‐pyS), which reversibly engages in the LiPSs conversion during the charging/discharging cycles, significantly improving the redox process. As a result, the Li‐S battery with 4Mpy additive demonstrates superior performances, achieving 10.05 mAh cm−2 under a high sulfur loading of 10.88 mg cm−2, surpassing industrial benchmarks. This study not only presents an approach to mitigating the shuttle effect in Li‐S batteries but also offers valuable insights into electrolyte design for other metal batteries.

Nanosized CeO2C2 with rich oxygen vacancies embedded in hollow mesoporous carbon as a multifunctional sulfur-loaded matrix for lithium-sulfur batteries

The innovative structural and compositional design of sulfur-loaded matrices is an effective strategy to improve the performance of lithium-sulfur batteries (LSBs). Herein, nanosized CeO2C2 with rich oxygen vacancies embedded in hollow mesoporous carbon composites (HMC/CeO2C2) were synthesized by hydrothermal and annealing reduction processes. This structure has several advantages: the large specific surface area and mesoporous carbon walls facilitate sulfur penetration and electron/ion transport; the abundant mesopores and hollow inner cavities provide the structural basis for sulfur storage and buffer its volume expansion; the oxygen vacancy-rich CeO2C2 nanoparticles grown in situ in HMC and in close contact with carbon form an electrically favorable CeO2C2/C heterointerface as an efficient catalyst, which is conducive to catalyzing the redox reaction of sulfur. Consequently, the retention capacity of the HMC/CeO2C2/S electrode is 728 mAh g−1 after 500 cycles at 0.5 C with a decay rate of 0.056 % per cycle, and it maintains a high reversible area capacity of 3.18 mAh cm−2 and excellent cycling performance even under a high sulfur loading of 4.7 mg cm−2. It provides an idea for the development of multifunctional sulfur-loaded materials with high sulfur loading, high conductivity, and high catalytic activity.

Hierarchical Nanowire Host Material for High‐Areal‐Capacity All‐Solid‐State S/SeS2 Batteries

AbstractAll‐solid‐state sulfur batteries (ASBs) suffer from electrical and ionic conduction problems due to the insulating sulfur. By comparing three host materials with different structural characteristics, herein, carbon nanotubes (CNTs) decorated with a conductive metal sulfide (CoMoS2@CNT) is demonstrated, designed to host sulfur and exchange both Li‐ions and electrons, effectively. In this hierarchical wire structure, porous CoMoS2 nanosheets form close interfaces with sulfur, and the CNT core directly transfers electrons to the sulfur‐impregnated CoMoS2. Simultaneously, the solid electrolyte positioned on the outer region of the nanowire material ensures facile Li‐ion conduction to the sulfur‐impregnated CoMoS2. An ASB featuring a CoMoS2@CNT host material with a sulfur loading of 3 mg cm−2 exhibits a high‐areal‐capacity of 4.5 mAh cm−2 at a current density of 2.5 mA cm−2, while retaining 79.4% of its initial capacity after 300 cycles. When sulfur is replaced with SeS2 to further reinforce the charge conduction properties, all‐solid‐state SeS2 batteries (ASeS2Bs) with an extremely high‐areal‐capacity of 16.3 mAh cm−2 retain 99.3% of their initial capacities after 60 cycles at 60 °C. This study provides guidelines for the design principles of cathode composites for the ASBs and ASeS2Bs through multiangle comparative analysis.

Developing Rapid-Charging Li-S Batteries via "Target Catalysis" of Cations and Anions Modified Electrocatalyst.

The shuttle effect and sluggish sulfur reduction reaction have resulted in significantly low efficiency and poor high current cycling stability in lithium-sulfur batteries, impeding their practical applications. To address these challenges, the introduction of Ni cations into MoS2 grown on reduced graphene oxide (MoS2/rGO) induces the formation of impurity energy levels between the conduction and valence bands of MoS2. Additionally, the introduction of anionic Se expands the interlayer spacing, enhances intrinsic conductivity, and improves ion diffusion rates. Simultaneously introducing anionic and cationic species into the MoS2/rGO causes the center of the d-band to shift upward, reducing the occupancy of electrons in antibonding orbitals. This modification leads to a rearrangement of the electronic structure of Mo, accelerating the redox reactions of lithium polysulfides. It particularly enhances the binding energy and lowers the conversion energy barrier of Li2S4. Consequently, the Li||S coin cell with the Ni-MoSSe/rGO cathode demonstrates an initial capacity of 446 mAh g-1 at 20 C, with a remarkable capacity retention of ≈96.7% after 200 cycles. Moreover, even under high sulfur loading conditions (6.45 mg cm-2) and a low electrolyte/sulfur ratio (5.4 µL mg-2), it maintains a high areal capacity of 6.42 mAh cm-2.

Synergistic promotion of reaction kinetics for LiPSs at high loadings by interfacial built-in electric field and sulfur vacancies of ternary heterostructure for high-performance Li-S batteries

The practical application of lithium-sulfur batteries is significantly impeded by the chaotic migration of lithium polysulfides, sluggish redox-reaction kinetics, and pronounced shuttle effect. Herein, a ternary heterostructure (MoS2-x/MoO2/CoP) is developed with a spontaneous built-in electric field (BIEF) and enriched sulfur vacancies. This heterostructure comprises MoS2-x, which has a high adsorption capability and work function; CoP, noted for its low work function and potent catalytic properties; and MoO2, which features a work function between that of MoS2-x and CoP and serves as a bridge with excellent electronic conductivity. An appropriate combination of the catalyst and adsorbent with sulfur vacancies controls the direction of the BIEF, realizing the “adsorption-directed migration-catalytic” reaction mechanism for sulfur species. Specifically, the synergetic effect of the BIEF and sulfur vacancies enhances electron migration from CoP to MoS2-x, which improves the lithium polysulfide (LiPSs) trapping and accelerates the directional migration of LiPSs to CoP, thereby enabling the efficient catalytic conversion of sulfur species. Consequently, batteries equipped with MoS2-x/MoO2/CoP interlayers that contain sulfur vacancies demonstrate an ultrahigh initial specific capacity of 1356.2 mA h g−1 at 0.2 C, maintaining a capacity of 708.3 mAh g−1 after 1000 cycles at 2 C. Even with sulfur loading increased to 7.13 mg cm−2, these batteries display an initial specific capacity of 7.2 mAh cm−2. This work provides a feasible approach for the rational design of vacancy-containing ternary heterostructure catalysts for commercial lithium-sulfur batteries.

In Situ Electrochemical Evolution of Amorphous Metallic Borides Enabling Long Cycling Room-/Subzero-Temperature Sodium-Sulfur Batteries.

Room temperature sodium-sulfur batteries (RT Na-S) have garnered significant attention for their high energy density and cost-effectiveness, positioning them as a promising alternative to lithium-ion batteries. However, they encounter challenges such as the dissolution of sodium polysulfides and sluggish kinetics. Introducing high-activity electrocatalysts and enhancing the density of active sites represents an efficient strategy to enhance reaction kinetics. Here, an amorphous Ni-B material that undergoes electrochemical evolution to generate the NiSx phase within an operational sodium-sulfur battery, contrasting with the crystalline NiB counterpart is fabricated. Electrochemical cycling facilitated the establishment of an interface between the amorphous Ni-B and NiSx, leading to heightened catalytic activity and improved reaction kinetics. Consequently, batteries utilizing the amorphous Ni-B showcased a notable initial specific capacity of 1487 mAh g-1 at 0.2 A g-1, exhibiting exceptional performance under high current densities of 5 A g-1, in low-temperature conditions (-10°C), with high sulfur loading, and in pouch cell configurations.

Preparation of TiO2 nanoparticles decorated porous carbon via a pseudo co-templating strategy and their application as substrates for high performance cathode of Li[sbnd]S batteries

Lithium‑sulfur batteries (LSBs) with a high theoretical specific capacity are considered as one of the most promising energy storage devices for next-generation. However, issues such as the insulation of pristine sulfur, the shuttle effect of polysulfides (LiPSs), and the volume change of sulfur cathode during cycling hinder their commercial applications. In this work, composite microspheres of TiO2@p-C consisting of porous carbon decorated with TiO2 nanoparticles, have been designed and synthesized aiming to confine and trap the polysulfides inside the porous substrates and to improve the kinetics of the electrochemical reaction therein. TiO2 particles with size of a few nanometers are prepared by a tetraethyl ammonium hydroxide assisted sol-gel method. Composite microspheres of TiO2@p-C are created through spray drying technique using chitosan as carbon source, and nanoparticles of SiO2 with TiO2 as co-template while selectively etching of the former. The confinement effects via the pores in the TiO2@p-C microspheres and the affinity between the polar TiO2 moieties and the polysulfide species work synergistically, alleviating the effusion of the polysulfides and promoting the conversion reaction of them as well. As a result, the shuttle effect of polysulfides can be inhibited obviously. Significantly, the S@TiO2@p-C-2 composite cathode exhibits excellent cyclic performance of 1263 mAh g−1 at 0.2C and maintains still a discharge capacity of 809 mAh g−1 after 100 charge and discharge cycles. At a current density of 2C, it still delivers an outstanding specific capacity of 772 mAh g−1. In the case of high sulfur load up to 90 wt%, the discharge capacity of S@TiO2@p-C-2 composite electrode could still maintain at 469.5 mAh g−1 after 100 cycles under current density of 0.2C.

Cobalt Ditelluride Meets Tellurium Vacancy: An Efficient Catalyst as a Multifunctional Polysulfide Mediator toward Robust Lithium-Sulfur Batteries.

The commercialization of lithium-sulfur batteries (LSBs) faces significant challenges due to persistent issues, such as the shuttle effect of lithium polysulfides (LiPSs) and the slow kinetics of cathodic reactions. To address these limitations, this study proposes a vacancy-engineered cobalt ditelluride catalyst (v-CoTe2) supported on nitrogen-doped carbon as a sulfur host at the cathode. Density functional theory calculations and experimental results indicate that the electron configuration modulation of v-CoTe2 enhances the chemical affinity and catalytic activity toward LiPS. Specifically, v-CoTe2 can strongly interact with PSs through multisite coordination, effectively facilitating the kinetics of the LiPS redox reaction. Furthermore, the introduction of Te vacancies generates a large number of spin-polarized electrons, further enhancing the reaction kinetics of LiPS. As a result, the v-CoTe2@S cathode demonstrates high initial capacity and excellent cyclic stability, maintaining 80.4% capacity after 500 cycles at a high current rate of 3 C. Even under a high sulfur load of 6.7 mg cm-2, a high areal capacity of 6.1 mA h cm-2 is retained after 50 cycles. These findings highlight the significant potential of Te vacancies in CoTe2 as a sulfur host material for LSBs.

Controllable assembly of polysulfides mediator induced by host-guest chemistry for upgrading energy density and longevity of lithium-sulfur batteries

Rechargeable lithium-sulfur (Li-S) batteries are deemed to one potential candidate for next-generation energy storage systems due to high theoretical energy density and environmental friendliness of sulfur. However, the sluggish redox kinetics and the inevitable shuttle effect of soluble polysulfides impede their commercialization process. Herein, the host–guest chemistry strategy has been proposed to fabricate ultrafine Co9S8/CoO nanoparticles embedded in porous carbon nanosheets (Co9S8/CoO@PC) for improving reversible conversion kinetics and adsorption ability toward polysulfides. Benefiting from bidirectional catalysis of Co9S8/CoO heterostructure and the fully exposed active sites on porous carbon nanosheets, the resultant Co9S8/CoO@PC-S electrode exhibits high specific capacity of 1549 mA h/g at 0.1C as well as outstanding cyclic stability with low average capacity decay of 0.021 % in 1000 cycles at high rate of 3C. Remarkably, the electrode delivers high specific capacities of 1209 and 756 mA h/g at 0.1C after 100 cycles with high sulfur loadings of 4.0 and 7.5 mg cm−2, respectively. This work provides new methodology for the controllable assembly of multiple dimensional composites to realize high energy density and long lifetime of Li-S batteries.

Regional Electron Delocalization Regulation Internalizes the Reduced‐Order‐Transformation of Polysulfides

AbstractThe step‐order or disproportionation conversion of lithium polysulfides (LiPSs) is still a blind box in LiS batteries (LSBs) system. The cation‐doped electrocatalyst (Fe‐CoS2@HCNF) is designed through modulating electron‐surrounding situation of the central atomic d‐band to promote regional electron‐directed LiPSs reduced‐order‐transformation (especially, Li2S4Li2S). Fe‐CoS2@HCNF satisfies the requirement of mass (electron/ion) transfer reaction, quantizing as multi‐osmosis‐connected transportation channels and an all‐encompassing interior space for sulfur reduction occurring. Based on experiments and DFT calculations, the introduced Fe presents a local electron deficiency state toward regulating regional electron delocalization between Fe and Co matrix, which induces the d‐band state of the metal site, strengthening the metal 3d orbital coupling interaction with S2−of LiPSs, further guiding the order‐transformation of intermediate LiPSs. Consequently, the Fe‐CoS2@HCNF electrode has excellent electrochemical properties, performing at 3.0 C with 0.064 % capacity decay per cycle, and even maintaining super cycle stability at a high sulfur loadings. In addition, the pouch cell assembled can also reach an initial specific capacity of 1070.3 mAh g−1 at 0.1 C, which can still show good long‐term cycle stability. This work provides a valuable prospect for analyzing SRR intermediate state by regional electron flow regulation of electrocatalyst in practical LSBs.

Construction of Heterointerfaced Nanoreactor Electrocatalyst via In Situ Evolution Toward Practical Room‐Temperature Sodium–Sulfur Batteries

AbstractSodium‐sulfur (Na─S) batteries have drawn considerable research interest owing to their high theoretical energy density and nature abundance. However, the intrinsic sluggish kinetics that has so far been scarcely explored in the conversion reaction of sodium polysulfides (NaPS) hinders its practical application. Herein, the design strategy of heterointerfaced nanoreactor is presented as sulfur reduction reaction (SRR) electrocatalyst for room temperature Na─S batteries. The synergistic incorporation of heterointerface and confined structure design can modulate the electronic structure of transitional metal active site and upshift its d‐band center, leading to enhanced NaPS adsorption and catalytic conversion toward streamlined SRR. Moreover, the spatial confinement of nanoreactor can not only stockpile nanoparticles to avoid their agglomeration and detachment, but also effectively immobilize sulfur species to inhibit shuttle effect and accommodate volume expansion over sodiation. The as‐developed electrocatalyst can achieve high discharge capacity of 1310 mAh g−1, remarkable cycling stability over 2500 cycles, and excellent performance under high sulfur loading and lean electrolyte/sulfur ratio. Ah level pouch cell can also exhibit promising performance for practical application. This strategy affords a synergistic combination of nanoreactor and heterointerface structure engineering toward fast and reliable electrochemistry, paving ways for the practical application of room temperature Na─S batteries.

Waste to Wealth: One-Step Exfoliating of Spent Graphite to Build a Low-Cost Cathode for Lithium-Sulfur Batteries.

With the booming development of Li-ion batteries (LIBs), the recycling and reusing of spent graphite (SG) from LIBs is becoming increasingly crucial. Meanwhile, developing low-cost and efficient carbon hosts for lithium-sulfur (Li-S) batteries has gained widespread attention in the past decade. Nevertheless, the processing of carbon materials as sulfur hosts is often energy-consuming and complex. Herein, a simple and environmental-friendly strategy is proposed to reuse the SG to prepare graphene/sulfur composite cathode for Li-S batteries. Due to expanded layer spacing and defects of SG, sulfur molecules can strip it into a graphene-type host via ball milling. By optimizing the S/SG ratio and ball milling time, the as-prepared graphene/sulfur composite cathode with 70 wt.% sulfur content exhibits a high capacity of 1000 mAh g-1. With a high sulfur loading of 4.68 mg cm-2, the graphene/sulfur cathode can maintain 526 mAh g-1 after 400 cycles. This work provides a novel waste-to-wealth perspective for recycling spent graphite from LIBs to reuse in Li-S batteries.

Accelerating sulfur redox kinetics by rare earth single-atom electrocatalysts toward efficient lithium–sulfur batteries

Toward practical lithium−sulfur (Li−S) batteries, there is a pressing need to improve the rate performance and longevity of cells. Herein, we report developing a cathode electrocatalyst Lu SA/NC, capable of accelerating sulfur redox kinetics with a high specific capacity of 1391.8 mAh g−1 at 0.1 C, and a low-capacity fading rate of 0.049 % per cycle over 1000 cycles even with a high sulfur loading (5.96 mg cm−2). The unparalleled cathodes are built upon the unique structure in which single-atoms of rare earth metals are doped in nitrogen-doped porous carbon (RM SAs/NC). The theoretical and experimental studies reveal that the rare earth Lu atom has an unrivaled adsorption capacity for polysulfides and can promote facile deposition and dissolution reactions in charge-discharge processes. The in-situ Raman experiments provide direct evidence for its promotion of polysulfide transformation to eliminate the shuttle effect. The theoretical calculations suggest that the presence of f-d-p hybridization enables accelerating sulfur reduction kinetics and enhancing lithium−sulfur battery performance. The strategic paradigm introduced in this study underscores significant practical potential in the exploration of rare earth single-atom catalysts for high performance Li−S batteries.

Bifunctional Mott-Schottky-type Co-Fe3N electrocatalyst as sulfur host and separator modifier to enhance the transformation kinetics of Li2S

Recently, lithium-sulfur batteries (LSBs) with ultra-high theoretical energy density attract the attention of researchers. However, the shuttle of lithium polysulfides (LPSs) seriously restrict the development of LSBs. Here, Co-Fe3N with Mott-Schottky type exhibits exceptional chemisorption and catalytic capabilities towards LPSs. The Co-Fe3N Mott-Schottky heterojunction induces charge redistribution at the heterogeneous interface, thereby increasing the rate of charge transfer, enhancing chemisorption ability, and reducing the energy barrier for S8 reduction and Li2S oxidation. The Co metal provides more catalytic and adsorption active sites for the conversion of LPSs and further improves the catalytic activity of Fe3N. Under the synergistic effect of the metal Co and Fe3N, the redox reaction of LPSs is improved, and the nucleation/decomposition energy barriers of Li2S are decreased, realizing the multifunctional coupling of adsorption-catalytic-conversion of LPSs. The LSBs with Co-Fe3N/S cathode and Co-Fe3N-PP separator exhibits a low capacity decay of 0.067 % per cycle at 1 C during 400 cycles. Even at a high sulfur loading of 3.1 mg cm−2, the LSBs delivers a reversible capacity of 1016 mA h g−1 at 0.1 C. The utilization of the Co-Fe3N with Mott-Schottky type in LSBs presents a novel approach towards designing multifunctional coupled materials with adsorption-catalysis-conversion capabilities.

Synthesis and performance evaluation of bio-derived and synthetic carbon as lithium-sulfur battery cathode

The next-generation of batteries need be both energy dense and environment friendly. Lithium sulfur batteries (LSBs) satisfy both criteria but their practical implementation is marred by the highly resistive nature of sulfur. Carbon-based cathodes play a vital role in mitigating the issue because their high conductivity allows for effective electron transfer during electrochemical cycling. Synthesis and electrochemical evaluation of carbon-based cathodes from two different sources for LSBs was carried out. Herein, two kinds of carbon, namely bio-derived carbon from coconut shells (CC500) and N-doped carbon (NC) from polyacrylonitrile fibers were synthesized and sulfur was incorporated via the melt diffusion route. The composites are characterized by PXRD and TGA, which determined 80 wt% mass loading of sulfur. The higher intensity of G-band over D-band in Raman spectroscopy indicates greater graphitic character for CC500 compared to NC. SEM images show large macro-pore like tunnels in CC500 while NC appears are irregular chunks. EDAX spectra showed 20 wt% N content in NC while CC500 is largely carbon with some minor surface oxygen. In galvanostatic charge–discharge cycling of coin cells, bare CC500/S shows better specific capacity compared to NC/S samples but the trend flips once a separator modified with 4 mg of graphene oxide (GO) is introduced (indicated as NC/S/GO4 and CC500/S/GO4). This points towards synergy between N-doped carbon and GO layer in retaining the soluble polysulfides in the catholyte region. NC/S/GO4 exhibited better capacity i.e., 1453, 1024, 866, 787, 697 mAh/g versus 1016, 779, 672, 551, 441 mAh/g offered by CC500/S/GO4 when discharged at 50, 100, 200, 300 and 500 mA/g, respectively.

Porous activated carbon integrated carbon nitride nanosheets as functionalized separators for the efficient polysulfide entrapment in Li[sbnd]S batteries

Electrification of vehicles, hybrid aircraft and the advancement of portable electronics are exacting the deployment of high energy-dense batteries. The high theoretical capacity of sulfur (1675 mAh g−1), cost-effectiveness and environmental benignity of the lithium‑sulfur batteries (LSBs) are propitious for electrochemical energy storage beyond Li-ion battery technology. In this work, we described a simple, scalable preparation and electrochemical performance of porous activated carbon (PC)-infused graphitic carbon nitride (GCN) nanosheets with various ratios (PC@GCN 11, PC@GCN 12 and PC@GCN 21) as a polysulfide anchoring functionalized separator for LSBs. The high specific area (822 m2/g), hetero porosity, conductive carbon framework, surface functionalities and enriched N-doping of the PC@GCN synergistically induce mitigation of polysulfides via chemical and physical adsorption pathways in LSBs. The PC@GCN 21 modified separator demonstrates a high initial discharge capacity of 1389 mAh g−1 at a 0.1C rate and exhibits better capacity retention over 500 cycles at a 1C rate (655 mAh g−1) with sulfur loading of 3.8 mg/cm2 accompanied by high coulombic efficiency (94 %). The assembled cell with high S-loading (5.12 mg/cm2) shows a high initial discharge capacity of 712 mAh g−1 at 0.1C rate conditions. High Li-ion transference number (0.714), stable shuttle current, minimal coulombic efficiency loss (0.84 %), low shuttle factor and negligible self-discharge behaviour support the superior performance of the PC@GCN 21 coated cells. This report demonstrates that combining the high surface area, non-polar porous carbon with polar graphitic carbon nitride is a practical approach for designing metal-free functionalized separators for energy-dense LSBs.

Nano-necklace Co/β-Mo2C hetero-nanodots encapsulating into carbon nanotubes with strong adsorption and catalytic conversion of polysulfides for lithium‑sulfur batteries separator

Due to their high theoretical capacity and high energy density, Lithium‑sulfur (LiS) batteries become the research hotspot in the field of electrochemical energy storage. However, the serious capacity loss caused by the shuttle effect and the decomposition of polysulfides is the biggest obstacle in the research process and practical application of lithium‑sulfur batteries. Herein, cobalt (Co) and molybdenum carbide (Mo2C) hetero-nanodots wrapping into nitrogen-doped carbon nanotubes (Co-Mo2C@NCNTs) are successfully prepared by direct self-catalysis annealing process. When utilized into the polypropylene (PP) separator modifier, the batteries assembled with Co-Mo2C@NCNTs//PP separator presents high capacity and outstanding rate capability. Specifically, it's worth noting that the cells display a high initial specific capacity of 1463.6mAh g−1 at 0.1C, superior rate capacity of 778.7 mAh g−1 at 3C, and excellent cycle stability with capacity decay rate of only 0.11 % per cycle for 500 cycles at 0.5C. Besides, the outstanding electrochemical performance is also demonstrated under high sulfur loading (3.5 mg cm−2). This work provides a novel guidance direction for high-performance lithium‑sulfur batteries from separator modification.

Separator modification with a high-entropy hydroxyphosphate, Co0.29Ni0.15Fe0.33Cu0.16Ca3.9(PO4)3(OH), for high-performance Li-S batteries

The shuttle effect of lithium polysulfides (LiPSs) significantly hinders the practical application of lithium-sulfur batteries (LSBs). Herein, a high-entropy hydroxyphosphate (Co0.29Ni0.15Fe0.33Cu0.16Ca3.9(PO4)3(OH), denoted as HE-CHP), was synthesized by metal cation exchange with calcium hydroxyphosphate (CHP) and then coated on polypropylene (PP) separators to suppress the shuttling of LiPSs. Density functional theory calculations indicated that the various introduced metal cations could effectively modulate the binding strength of soluble polysulfides and enhance the reaction kinetics of LiPSs conversion. As a result, LSBs using the HE-CHP@PP separator exhibited an excellent discharge capacity (1297 mAh g−1 under 0.2 C) and a slow capacity decay during long-term cycling (0.046 % per cycle at 2 C). At a sulfur loading of up to 6.5 mg cm−2, the LSB with HE-CHP@PP separator displayed a discharge capacity of 5.8 mAh cm−2. Notably, the CNT@S||Li Li-S pouch cell with HE-CHP modified separator delivered an initial energy density of 432 Wh kg−1.