Lithium Sulfur Research Articles

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.

CeVO4/KBNanoparticlesonShuttle Effect Inhibition in Lithium-Sulfur Battery Separator Modification.

Lithium-sulfur (Li-S) batteries display promise as redox-based batteries, where separators are an essential part of preventing short-circuiting of the positive and negative electrodes, while the shuttle effect is a critical issue of separators. Currently, commercial PP separators are weak in inhibiting the polysulfides shuttling, so modified separators are needed to inhibit it to improve the battery performance. This paper reports that CeVO4/KB composites act as separator materials. CeVO4/KB modified PP separators enhanced the adsorption of LiPSs, accelerated the rate of Li+ migration, and catalyzed the conversion of LiPSs. These bring about the effect that CeVO4/KB/PP batteries reach 1200.9 mAh g-1 in the first cycle with a capacity retention rate of 86.5% after 100 cycles at 0.2 C and reach 882.7 mAh g-1 of the initial cycle with a capacity decay rate of 0.063% after 1000 cycles at 3 C. This work introduces rare earth metal vanadates to modify the separator, adding new ideas for designing separators for good-performance batteries.

Physical Field Effects to Suppress Polysulfide Shuttling in Lithium-Sulfur Battery.

Lithium-sulfur batteries (LSB) with high theoretical energy density are plagued by the infamous shuttle effect of lithium polysulfide (LPS) and the sluggish sulfur reduction/evolution reaction. Extensive research is conducted on how to suppress shuttle effects, including physical structure confinement engineering, chemical adsorption strategy, and the design of sulfur redox catalysts. Recently, the rational design to mitigate shuttle effects and enhance reaction kinetics based on physical field effects has been widely studied, providing a more fundamental understanding of interactions with sulfur species. Herein, the physical field effect is focused and their methods and mechanisms of interaction are summarized systematically with LPS. Overall, the working principle of LSB system, the origin of the shuttle effect, and kinetic trouble in LSB are briefly described. Then, the mechanism and application of rational design of materials based on physical field effect concepts and the external physical field-assisted LSB are elaborated, including electrostatic force, built-in electric field, spin state regulation, strain engineering, external magnetic field, photoassisted and other physical field-assisted strategies are pivotally elaborated and discussed. Finally, the potential directions of physical field effects in enhancing the performance and weakening the shuttle effect of high-energy LSB are summarized and anticipated.

Insight into the Impact of Electrolyte on Passivation of Lithium–Sulfur Cathodes

AbstractOne of the remaining challenges for lithium–sulfur batteries toward practical application is early cathode passivation by the insulating discharge product: Li2S. To understand how to best mitigate passivation and minimize related performance loss, a kinetic Monte–Carlo model for Li2S crystal growth from solution is developed. The key mechanisms behind the strongly different natures of Li2S layer growth, structure, and morphology for salts with different (DN) are revealed. LiTFSI electrolyte in dimethyl ether leads to lateral Li2S growth on carbon and fast passivation because it increases the Li2S precipitation‐to‐dissolution probability on carbon relative to Li2S. In contrast, LiBr electrolyte has a higher DN and yields a particle‐like structure due to a significantly higher precipitation‐to‐dissolution probability on Li2S compared to carbon. The resulting large number of Li2S sites further favors particle growth, leading to low passivation. This study is able to identify the key parameters of the electrolyte and substrate material to tune Li2S morphology and growth to pave the way for optimized performance.

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.

2D Microporous Polymers/Reduced Graphene Oxide with Built-In Lithiophilic Sites for Uniform Lithium Deposition in Lithium Metal Anode.

Lithium (Li) metal is an attractive anode material for use in high-energy lithium-sulfur and lithium-air batteries. However, its practical application is severely impeded by excessive dendrite growth, huge volume changes, and severe side reactions. Herein, a novel Li metal anode composed of lithiophilic two dimensional (2D) conjugated microporous polymer (Li-CMP) and reduced graphene oxide (rGO) sandwiches (Li-CMP@rGO) for Li metal batteries (LiMBs) is reported. In the Li-CMP@rGO anode, the conductive rGO facilitates the charge transfer while the functionalized-CMP provides Li nucleation sites within the micropores, thereby preventing dendrite growth. As a result, the Li-CMP@rGO anode can be cycled smoothly at 6mA cm-2 of current density with a platting capacity of 2 mAh cm-2 for 1000h. A Coulombic efficiency of 98.4% is achieved over 350 cycles with a low overpotential of 28mV. In a full cell with LiFePO4 cathode, the Li-CMP@rGO anode also exhibited good cycling stability compared to CMP@rGO and CMP/Super-P. As expected, the simulation results reveal that Li-CMP@rGO has a strong affinity for Li ions compared to CMP@rGO. The strategies adopted in this work can open new avenues for designing hybrid porous host materials for developing safe and stable Li metal anodes.

Nitrogen and Sulfur Doped Porous Carbon Sheet with Trace Amount of Iron as Efficient Polysulfide Conversion Catalyst for High Loading Lithium-Sulfur Batteries.

The major challenges in enhancing the cycle life of lithium-sulfur (Li-S) batteries are the polysulfide (PS) shuttling and sluggish reaction kinetics (S to Li2S, Li2S to S). To alleviate the above issues use of hetero atom doped carbon as cathode host matrix is a low-cost and efficient approach as it works as a dual-functional framework for PS anchoring as well as electrocatalyst for faster redox kinetics. Here, the dual role of the Fe-containing heteroatom-doped carbon sheets (CS) in chemisorption of Li2S6 and catalyzing its faster conversion to Li2S is established through UV-Vis, XPS and CV studies. To substantiate the catalytic effect composite cathodes were prepared by encapsulating sulfur in CS which is further blended with carbon nanotubes (CNTs) to form free-standing cathode. The electrochemical performance of the three cathodes viz., S@Fe-N-CS-CNT, S@Fe-S-CS-CNT and S@Fe-NS-CS-CNT were evaluated by constructing Li-S cells. Among all, the S@Fe-NS-CS-CNT delivers a high initial discharge capacity of 1017 mAh g-1 at 0.5 C rate and sustains 751 mAh g-1 capacity after 260 cycles with a capacity retention of 73.8 %. Even at high S-loading (12 mg cm-2), it delivers an initial discharge capacity of 892 mAh g-1 and it retained 575 mAh g-1 after 200 cycles.

Anchoring ability and catalytic activity of B2C2 monolayer as the lithium-sulfur batteries cathode materials: A first principle calculation

Through first-principles calculation, the performance of B2C2 monolayer as the Li-S batteries cathode anchoring material is systematically investigated. The B2C2 monolayer exhibits excellent thermodynamic, kinetic and mechanical stability, which are helpful to resist the volume change caused by the reaction during charging and discharging process. Importantly, the adsorption energy of S8 clusters and LiPSs in the B2C2 monolayer is remarkably higher than that in the cathode electrolyte, which greatly inhibits the generation of shuttle effect. The calculations of the catalytic performance of B2C2 monolayer further suggest that the system possesses a lower the Gibbs free energy (ΔG) barrier of 0.71 eV and a fast kinetic conversion process with low diffusion barrier of 0.257 eV along hexatomic ring B2C4, implying a fast charge and discharge rate and excellent cycle performance. The B2C2 monolayer with high energy conversion efficiency and catalytic activity can be expected as an emerging sustainable clean energy source.

Emerging All-Solid-State Lithium–Sulfur Batteries: Holy Grails for Future Secondary Batteries

Emerging All-Solid-State Lithium–Sulfur Batteries: Holy Grails for Future Secondary Batteries

Regulating p‐Band Center of Sulfur in Li‐Argyrodite to Stabilize Dual Solid–Solid Interface for Robust All‐Solid‐State Lithium–Sulfur Battery

Regulating p‐Band Center of Sulfur in Li‐Argyrodite to Stabilize Dual Solid–Solid Interface for Robust All‐Solid‐State Lithium–Sulfur Battery

Exploration of experimentally feasible α-AsP as promising sulfur host material with superior electrochemic features for lithium-sulfur battery

Lithium-sulfur (Li-S) battery has become an ideal energy storage system due to high energy density and theoretical specific capacity. For the application of such a technique, a key is to find out a suitable sulfur host material. In this work, we, via examinations of 372 possible polysulfide@α-AsP configurations based on density functional theory (DFT), evaluated the potential of experimentally synthesized two-dimensional (2D) α-AsP structure as a promising sulfur host material of Li-S battery. Interestingly, we, revealed that polysulfides, that are caught on α-AsP substrate, can well maintain geometrical characteristics of isolated ones. Furthermore, some enthralling electrochemic features were revealed: (a) Adsorption energies of soluble polysulfides on α-AsP are lower than those on 1,2-dimethoxyethane (DME) and 1,3-dioxolane (DOL), which enables α-AsP to exhibit a good anchoring ability for the suppression of shuttle effect; (b) In particular, low rate-limiting barrier of 0.50 eV of sulfur reduction reaction (SRR) and low Li2S decomposition barrier of 0.70 eV were demonstrated, which renders α-AsP to be a bifunctional catalyst for high conversion efficiencies; (c) In addition, we also observed that α-AsP can provide a platform for rapid Li ion diffusion with a low energy barrier of 0.15 eV, which further facilitates charging/discharging processes of Li-S battery. Our findings disclose a feasible sulfur host material with superior electrochemic features for high-performance Li-S battery.

Unique flake-shaped sulfur morphology favored by the binder-free electrophoretically deposited TiO2 layer as a promising cathode structure for Li-S batteries

Metal oxides have been extensively studied as catalyst additives in Li-S batteries due to their high affinity for soluble lithium polysulfides (LiPSs). The present study developed a novel carbon nanomaterials- and binder-free 3D sulfur host by electrophoretic deposition (EPD) of TiO2 nanoparticles on carbon fiber paper (CFP). Benefiting from the unique well-connected TiO2 porous layer formed by EPD, the initial discharge capacity of Li-S battery was increased from 1160 mAh g−1 in conventional cast TiO2/binder/S cathode (Cast:CFP/PVDF/TiO2/S) to 1310 mAh g−1 in the EPD:CFP/TiO2/S cathode, along with an overpotential drop of 16 %. Electron microscopic studies at 100% state-of-charge (SoC) revealed that while notorious sulfur particulates were formed on Cast:CFP/PVDF/TiO2/S, the surface of EPD:CFP/TiO2/S was covered with flake-shaped sulfur precipitates. The formation of sulfur flakes effectively suppressed pulverization in EPD:CFP/TiO2/S, leading to superior electrochemical performance and cycle life. Microstructural studies and real-time EIS investigations revealed that sulfur flakes nucleated across the Li2S matrix at the initial stages of charge and grew vertically from the sulfur/TiO2 interface. The preferential growth mechanism of sulfur flakes was attributed to the superior surface conductance of the EPD-TiO2 film enabled by the ordered clusters formed during EPD, enhancing the kinetics of electrocatalytic reactions of polysulfides at the TiO2/sulfur interface. Our results show that developing novel methods to modify the morphology of secondary sulfur upon cycling is critical for enhancing charge-discharge performance in Li-S batteries.

Single-Step PECVD Synthesis of Graphene@Carbon Nanotubes Electrocatalyst.

Graphene (Gr) and carbon nanotubes (CNTs), the two intriguing carbon nanomaterials, have presented great potential in serving as high-performance electrocatalysts in lithium-sulfur (Li-S) chemistry. The concurrent management of both materials would achieve a promoted synergistic effect. Nevertheless, there still remains a lack of an effective material synthesis route. Herein, a single-step plasma-enhanced chemical vapor deposition (PECVD) strategy is devised to prepare Gr@CNTs heterostructures with strong bonded connections. In the PECVD system, the damaged sidewalls generated in CNT tubes can serve as appropriate nucleation sites for further Gr growth. The formation mechanisms are thoroughly explored in aspects of both experimental characterizations and theoretical calculations. To confirm the validity of this approach, thus-constructed Gr@CNTs architectures are employed as the sulfur host, enabling boosted redox kinetics of polysulfides. This project provides fundamental insight into the mechanism exploration for single-step PECVD growth of Gr@CNTs heterostructure, hence promoting the practical application prospect of carbon nanomaterials toward Li-S systems.

Breaking the Passivation Effect for MnO2 Catalysts in Li-S Batteries by Anion-Cation Doping.

Transition metal oxides (TMOs) are recognized as high-efficiency electrocatalyst systems for restraining the shuttle effect in lithium-sulfur (Li-S) batteries, owing to their robust adsorption capabilities for polysulfides. However, the sluggish catalytic conversion of Li2S redox and severe passivation effect of TMOs exacerbate polysulfide shuttling and reduce the cyclability of Li-S batteries, which significantly hinders the development of TMOs electrocatalysts. Here, through the anion-cation doping approach, dual incorporation of phosphorus and molybdenum into MnO2 (P,Mo-MnO2) was engineered, demonstrating effective mitigation of the passivation effect and allowing for the simultaneous immobilization of polysulfides and rapid redox kinetics of Li2S. Both experimental and theoretical investigations reveal the pivotal role of dopants in fine-tuning the d-band center and optimizing the electronic structure of MnO2. Furthermore, this well-designed configuration processes catalytic selectivity. Specifically, P-doping expedites rapid Li2S nucleation kinetics by minimizing reaction-free energy, while Mo-doping facilitates robust Li2S dissolution kinetics by mitigating decomposition barriers. This dual-doping approach equips P,Mo-MnO2 with robust bi-directional catalytic activity, effectively overcoming passivation effect and suppressing the notorious shuttle effect. Consequently, Li-S batteries incorporating P,Mo-MnO2-based separators demonstrate favorable performance than pristine TMOs. This design offers rational viewpoint for the development of catalytic materials with superior bi-directional sulfur electrocatalytic in Li-S batteries.

Bimetallic NiCo@C with a Hollow Sea Urchin Structure Enables Li-S Batteries to Hasten the Reaction Kinetics and Effectively Inhibit the Shuttling of Polysulfides.

The "shuttle effect" and several issues related to it are seen as "obstacles" to the study and development of lithium-sulfur batteries (LSBs). This work aims at finding how to fully expose bimetallic sites and quicken the battery reaction kinetics. Here, a bimetallic NiCo-MOF and its derivative NiCo@C with a hollow sea urchin structure are produced. The obtained NiCo@C possesses a micromesoporous structure and fully disclosed bimetallic active sites because of its distinctive structure. The experimental findings demonstrate that fully exposed bimetallic active sites take on chemical adsorbents and collaborate with micromesopores as physical constraints to effectively suppress the "shuttle effect". Furthermore, the hollow sea urchin structure of NiCo@C enables a highly conductive grid, which provides channels to facilitate the movement of solvated Li+. Thanks to these advantages, the NiCo@C-based sulfur cathode offers a high initial discharge specific capacity of 924.41 mAh g-1 at 0.1 C and sustains 390.35 mAh g-1 discharge specific capacity after 100 cycles. The quick transfer of solvated lithium ions (DLi+ = 1.81 × 10-8 cm2 s-1) enables the battery to still contribute a discharge specific capacity of 367.54 mAh g-1 at 1 C. This work provides a new understanding for the structural design of positive electrodes in LSBs.

Single-Atom Cobalt Catalyst with Boron and Nitrogen Codoped Graphene (Co-BN-G) Enables Adsorption and Catalytic Conversion of Polysulfides for High-Performance Lithium-Sulfur Batteries.

In lithium-sulfur batteries, the shuttling effect and sluggish redox conversion of soluble polysulfides lead to unsatisfactory sulfur utilization and capacity retention. In this research, we used a one-pot hydrothermal method to prepare graphene with single-atom Co and B, N codoped as a sulfur host in Li-S batteries, thereby suppressing the shuttling effect and facilitating the redox conversion of lithium polysulfides (LiPSs). A series of characterizations demonstrated that dual doping of B and N introduces more lattice defects and structural deformations in graphene oxide, thus enhancing its adsorption of polysulfides. Simultaneously, single-atom cobalt can also polarize adsorption and accelerate the conversion reaction of LiPSs. The Li-S cell with the as-prepared Co-BN-G sulfur host materials exhibited an excellent capacity of 1034 mAh g-1 at 0.5 C and satisfactory cycle performance (retention of 69% over 500 cycles). Even at a rate of 2 C, a discharge capacity of 851 mAh g-1 is achieved. The results show that the Co-BN-G configuration efficiently captures LiPSs and enhances their rate conversion kinetics in redox reactions, demonstrating significant practical potential.

Understanding the improved performances of Lithium–Sulfur batteries containing oxidized microporous carbon with an affinity-controlled interphase as a sulfur host

Li–S batteries (LSBs) based on the solid-phase conversion reaction that contain microporous carbon (MC) materials as their S hosts exhibit high cycling stabilities. Oxidized MC with O-containing functional groups increases the capacity of LSBs and lowers their internal resistance. Although these polar functional groups should improve the electrolyte affinities of electrode materials, their effects on the MC–S cathode/electrolyte interface have not yet been clarified. Herein, we report the affinity between the MC–S cathode and electrolyte. Contrary to conventional wisdom, the O-containing functional groups form affinity-controlled interphases on the MC–S cathodes, alleviating electrolyte decomposition and the formation of a cathode–electrolyte interphase during LSB cycling. This lowers the internal resistance of the LSB by facilitating unhindered Li-ion conduction, which stabilizes cycling at a low electrolyte [μL]/S [mg] ratio of 2.0, with an improved capacity (from 6.58 to 309.4 mAh g−1) in the second cycle. Thus, the use of an affinity-controlled interphase should improve the energy densities of LSBs and other energy storage devices.

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.

Engineering rare earth metal Ce-N coordination as catalyst for high redox kinetics in lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries are a key area of research in energy storage due to their high theoretical energy density, low cost, and environmental friendliness. However, the shuttle effect caused by lithium polysulfides (LiPSs) intermediates often results in poor cycling stability. Therefore, constructing rational cathode structures to achieve fast reaction kinetics in adsorbing and catalyzing LiPSs is the key to obtain high-performance Li-S batteries. Metallic single-atom catalysts (SACs), known for their 100 % atomic utilization rate and low cost, have demonstrated excellent catalytic activity and selectivity in the redox reactions of Li-S batteries, positioning them as one of the most promising catalysts in this field. Rare earth metallic SACs with versatile oxidation states, diverse coordination chemistry and environmentally friendly are rarely investigated in Li-S system. Herein, we fabricate a rare earth metal-based single-atom catalyst (CeSAs) supported on a three-dimensional porous N-doped carbon (3DCeSA-N-WS), and systematically study its performance in Li-S batteries. Benefitting from the atomic dispersion and versatile oxidation states (Ce3+/Ce4+), the 3DCeSA-N-WS demonstrates excellent performance in anchoring and catalyzing LiPSs, significantly enhancing the redox reaction kinetics. Consequently, the prepared sulfur cathode exhibits exceptional electrochemical performance, with a high initial specific discharge capacity of 1225 mAh g−1 at 0.2 C and a capacity retention of 76.1 % after 160 cycles. The assembled 100 mAh-level pouch cellmaintains a high specific discharge capacity of 877 mAh g−1 after 50 cycles at 0.5 C. This work provides new insights into the design of sulfur cathode catalysts, thereby contributing to the realization of 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.