Redox Reaction Of Lithium Polysulfides Research Articles

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.

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.

Carbon-coated mesoporous Fe3O4 nanospindles with interconnected porosities as polysulfide mediator for lithium–sulfur batteries

Lithium-sulfur batteries are plagued by the shuttle effect and sluggish kinetics in the redox reaction of lithium polysulfides (LiPSs) to Li2S, resulting in a limited capacity and shortened lifetime. To address these issues, it is crucial to develop an efficient catalytic sulfur host by creating active sites that can both confine LiPSs and accelerate their conversion. Herein, we developed carbon-coated mesoporous Fe3O4 (C@M−Fe3O4) nanospindles and applied them as sulfur host material to improve the electrochemical performance of Li–S batteries. Besides, the conductive C@M−Fe3O4 particles with rich sites of electrolyte/Fe3O4/carbon ‘‘triple-phase’’ can also accelerate the conversion of LiPSs and promote the nucleation and growth of Li2S. With these merits, our C@M-Fe3O4/S electrode shows good cycling stability with a remaining capacity of 1064.3 mAh/g at 0.2 C after 100 cycles and delivers an initial capacity of 712.0 mAh/g at 2 C. The proposed synthetic method could pave the way for designing similar porous transition metal-based compounds with different precursors (e.g. carbonates, hydroxides, oxalates) for other electrochemical applications.

Cobalt-Carbon nanotubes supported on V2O3 nanorods as sulfur hosts for High-performance Lithium-Sulfur batteries

Exploring advanced sulfur cathode materials with high catalytic activity to accelerate the slow redox reactions of lithium polysulfides (LiPSs) is of great significance for lithium-sulfur batteries (LSBs). In this study, a coral-like hybrid composed of cobalt nanoparticle-embedded N-doped carbon nanotubes supported by Vanadium (III) oxide (V2O3) nanorods (Co-CNTs/C @V2O3) was designed as an efficient sulfur host using a simple annealing process. Characterization combined with electrochemical analysis confirmed that the V2O3 nanorods exhibited enhanced LiPSs adsorption capacity, and the in situ grown short-length Co-CNTs improved electron/mass transport and enhanced the catalytic activity for conversion to LiPSs. Owing to these merits, the S@Co-CNTs/C@V2O3 cathode exhibits effective capacity and cycle lifetime. Its initial capacity was 864 mAh g−1 at 1.0C and remained at 594 mAh g−1 after 800cycles with a decay rate of 0.039%. Furthermore, even at a high sulfur loading (4.5 mg cm−2), S@Co-CNTs/C@V2O3 also shows acceptable initial capacity of 880 mAh g−1 at 0.5C. This study provides new ideas for preparing long-cycle S-hosting cathodes for LSBs.

CeO2 nanoparticles decorated CMK-3 as high-performance sulfur host for Li-S batteries

The development of Li-S batteries is hindered by some inherent drawbacks such as the shuttle effect of lithium polysulfides and the volume expansion of sulfur. Herein, 3–6 nm CeO2 nanoparticles decorated CMK-3 (CMK-3 @CeO2) is prepared and used as the sulfur host for Li-S batteries. As a conductive carbon support, CMK-3 can improve the electrical conductivity of sulfur-based electrode, and its mesopores provide the space required for the volume expansion of sulfur. Meanwhile, the decorative CeO2 nanoparticles can not only change the non-polar carbon surface into the polar CeO2 surface for capturing lithium polysulfides, but also accelerate the redox reaction of lithium polysulfides, which effectively inhibits the shuttle effect of lithium polysulfides. Therefore, compared to pure CMK-3 supported sulfur (CMK-3 @S), CMK-3 @CeO2 supported sulfur (CMK-3 @CeO2 @S) exhibits better electrochemical performance, such as a discharge capacity of 686 mA h g−1 after 800 cycles at 1 C. Besides, the size effect of CeO2 nanoparticles on the electrochemical performance of CMK-3 @CeO2 @S is also studied. This work provides a simple method for improving the electrochemical performance of CMK-3 as the sulfur host, and this strategy can be extended to the other metal oxides decorated sulfur host materials.

Metal Ion Cutting-Assisted Synthesis of Defect-Rich MoS2 Nanosheets for High-Rate and Ultrastable Li2S Catalytic Deposition.

Active metal ions often show a strong cutting effect on the chemical bonds during high-temperature thermal processes. Herein, a one-pot metal ion cutting-assisted method was adopted to design defect-rich MoS2-x nanosheet (NS)/ZnS nanoparticle (NP) heterojunction composites on carbon nanofiber skeletons (CNF@MoS2-x/ZnS) via a simple Ar-ambience annealing. Results show that Zn2+ ions capture S2- ions from MoS2 and form into ZnS NPs, and the MoS2 NSs lose S2- ions and become MoS2-x ones. As sulfur hosts for lithium-sulfur batteries (LSBs), the CNF@MoS2-x/ZnS-S cathodes deliver a high reversible capacity of 1233 mA h g-1 at 0.1 C and keep 944 mA h g-1 at 3 C. Moreover, the cathodes also show an extremely low decay rate of 0.012% for 900 cycles at 2 C. Series of analysis indicate that the MoS2-x NSs significantly improve the chemisorption and catalyze the kinetic process of redox reactions of lithium polysulfides, and the heterojunctions between MoS2-x NSs and ZnS NPs further accelerate the transport of electrons and the diffusion of Li+ ions. Besides, the CNF@MoS2-x/ZnS-S LSBs also show an ultralow self-discharge rate of 1.1% in voltage. This research would give some new insights for the design of defect-rich electrode materials for high-performance energy storage devices.

Graphene-supported polyoxometalate entrapped in a MIL-88A network with highly efficient conversion of polysulfides in Li-S batteries.

It has been demonstrated that polyoxometalates (POMs) have strong anchoring abilities with efficient catalysis of lithium polysulfides (LiPSs). However, the severe aggregation that buries the effective active sites of POMs along with poor electrical conductivity limits the practical application of POMs in lithium sulfur batteries (LSBs). In our strategy, we utilized reduced graphene oxide (rGO) to support a POM catalyst entrapped in a MIL-88A(FeCo) network with a hollow shell skeleton as the sulfur host material. H4PW11VO40 (PW11V) with optimal vanadium atom implantation ensures the ruggedness and integrity of the hollow structure, which is conducive to achieving high sulfur loading as well as accommodating the volume change of the sulfur cathode during the charging and discharging process. Importantly, PW11V can capture polysulfides through firm chemical adsorption and accelerate redox reactions of LiPS conversion by effective electrochemical catalysis. Furthermore, the satisfactory electrical conductivity of rGO provides access for electrons to reach the interface of PW11V and polysulfides and trigger Li-S conversion reactions. Thus, the constructed PW11V-based sulfur cathode exhibited a superior specific capacity of 905 mA h g-1 after 100 cycles under 0.2 C and long cycling life with a capacity recession rate of 0.046% for each cycle upon 500 cycles under 3 C. This research reveals the effect of vanadium atom substitution of POMs on the cycling performance of a sulfur cathode and affords insight for developing high-performance LSBs.

Manganese–nickel bimetallic oxide electrocatalyzing redox reactions of lithium polysulfides in lithium–sulfur batteries

MnOx–NiOx/C composite bidirectionally catalyzes LiPS reduction and Li2S oxidation via constructing a thiosulfate-mediating reaction path beyond the common route. These intensified Li2Sx (x ≤ 4) redox reactions promote long-term cycling.

Nano-confined synthesis of multi yolk-shell Co-NC@N-HCSs hybrid as sulfur host for high performance lithium-sulfur batteries

Lithium-sulfur (Li-S) battery has been considered as one promising rechargeable battery with ultrahigh theoretical energy density. However, its practical application is mainly hindered by volume expansion during cycling and irreversible shuttle effect of soluble lithium polysulfides (LiPSs). Herein, we reported a rational design and fabrication of multi yolk-shell Co-NC@ nitrogen doped hollow carbon spheres (Co-NC@N-HCSs) as sulfur host for high performance Li-S batteries via a nano-confined synthesis strategy. The growth mechanism of multi yolk-shell ZIF-67s@N-HCSs nanostructure was studied and the ZIF-67 yolks were tunable by changing the reactant concentration. Regarding to multi yolk-shell Co-NC@N-HCSs hybrid, the nitrogen doped carbon shell provides effective physical confinement, abundant sulfur loading space and volume expansion alleviation, while the multi polar Co-NC yolks can enhance the internal electron conductivity inside the cavity and offer stronger chemisorption capability for LiPSs as well as catalytic effects on the redox reaction of LiPSs. Benefiting from the unique multi yolk-shell design, the S/Co-NC@N-HCSs electrode with sulfur content of 80.82 wt%, exhibits high discharge capacity of 1173 mAh g−1 at 0.1C and 995.8 mAh g−1 at 1C. It also shows long cycle life up to 450 cycles with a slow capacity decay rate of 0.13% per cycle. The electrochemical performance of S/Co-NC@N-HCSs is obviously promoted compared with S/N-HCSs, suggesting its potential to develop high performance lithium sulfur batteries.

CoFe2O4 nanoparticles loaded N-doped carbon nanofibers networks as electrocatalyst for enhancing redox kinetics in Li-S batteries

Lithium sulfur (Li-S) batteries have been paid more attention to meet the demand of high capacity energy storage. However, most substrates applied to electrodes, which have both high conductivity and full coverage of adsorption-catalysis synergies, are difficult to achieve. Herein, the combination of electrospinning and hydrothermal method is developed to fabricate the composite membrane of ferri-based spinel CoFe2O4 (CFO) loaded nitrogen doped carbon nanofibers (CFONC) applied to positive current collector with Li2S6 catholyte and binder-free of Li-S batteries. Benefiting from the improved catalytic performances in redox reaction of lithium polysulfides due to the abundant active sites which originate from CFO, the CFONC composite with S loading of 4.74 mg exhibits an initial specific discharge capacity of 1096 mAh g−1 at 0.2 C and a high specific discharge capacity of 681 mAh g−1 after 500 cycles with a capacity decay as small as 0.076% per cycle. Even with S loading of 7.11 mg, the cell of CFONC delivers a high initial capacity of 6.1 mAh and maintains 4.8 mAh after 300 cycles. The results show that the efficient chemical anchoring polysulfides and catalyzing redox reaction by multifunctional CFONC composites is a feasible strategy for the large-scale application of lithium sulfur batteries with high performance in the future.

Improved Redox Reaction of Lithium Polysulfides on the Interfacial Boundary of Polar CoC2 O4 as a Polysulfide Catenator for a High-Capacity Lithium-Sulfur Battery.

Invited for this month's cover is the group of Jaeyoung Lee at the Gwangju Institute of Science and Technology. The cover shows how the cobalt oxalates faced on the conductive carbon can act as an electrocatalyst to facilitate the redox reaction of lithium polysulfide at the cathode interface in lithium-sulfur batteries. The facilitated electrochemical redox reaction of lithium polysulfides was proved by a series of catenation reactions formed on the interfacial boundary area. The electrochemical performance was enhanced in terms of the specific capacity and long-term cycle performance from the facilitated electrochemical activity. The Full Paper itself is available at 10.1002/cssc.202002140.

Front Cover: Improved Redox Reaction of Lithium Polysulfides on the Interfacial Boundary of Polar CoC2O4 as a Polysulfide Catenator for a High‐Capacity Lithium‐Sulfur Battery (ChemSusChem 3/2021)

Front Cover: Improved Redox Reaction of Lithium Polysulfides on the Interfacial Boundary of Polar CoC₂O₄ as a Polysulfide Catenator for a High‐Capacity Lithium‐Sulfur Battery (ChemSusChem 3/2021)

Improved Redox Reaction of Lithium Polysulfides on the Interfacial Boundary of Polar CoC2 O4 as a Polysulfide Catenator for a High-Capacity Lithium-Sulfur Battery.

The performance of cobalt oxalate as an electrocatalyst in a lithium-sulfur battery (LSB) is improved owing to the suitable adsorbent properties of sulfur. The adsorption mechanism is elucidated by UV/Vis spectroscopy and surface analysis through X-ray photoelectron spectroscopy. Li2 S6 is converted into thiosulfate and polythionate by a catenation reaction on the interfacial boundary of CoC2 O4 contacted with carbon. Following this, the active polythionate and short-chained liquid lithium polysulfides (LiPS) bound to the cobalt surface are further reduced as CoC2 O4 reduces the overpotential to facilitate the LiPS redox reaction, leading to high specific capacity, lower self-discharge rate, and stable long-term cycling performance.

A Class of Catalysts of BiOX (X = Cl, Br, I) for Anchoring Polysulfides and Accelerating Redox Reaction in Lithium Sulfur Batteries.

The lithium-sulfur battery system contains a complex reaction process of sulfur involving multielectron reactions and phase conversions. Moreover, the diffusion of intermediate polysulfides during reduction and sluggish kinetic conversion of polysulfides into insoluble Li2S still plague the use of Li-S batteries. Herein, BiOX was employed as sulfur host material in Li-S batteries, which could integrate suppression of the shuttle effect and promote kinetics redox reactions of lithium polysulfides. The polar BiOX displays a robust chemical adsorption ability with polysulfides, and the electrocatalytic activity of BiOX would accelerate the fragmentation of polysulfides into shorter chains. The results indicate that the good polysulfide reactivity not only ensures the effective reduction of polarization but also performs high discharge capacity and stable cycle performance. The battery with a BiOCl/G-S cathode reveals a high capacity of 1414 mA h/g at a current of 0.1 C and a low capacity decay rate of 0.007% during 2000 cycles at a current of 2 C. This work proposes the prospect of application of the BiOX materials in lithium sulfur batteries.