Performance Of Lithium-sulfur Batteries Research Articles

Synergistic improvements on capacity and Coulombic efficiency of lithium-sulfur batteries with NiSe-Ni2P/C modification on PP separators

Lithium-sulfur batteries (LSBs) emerge as promising energy storage devices due to their high theoretical energy density. So far, there are constrained issues that need to be urgently addressed, such as the shuttle effect of lithium polysulfides (LiPS) and the sluggish kinetics of redox reactions. Herein, NiSe-Ni2P/C composite was synthesized and casted on the cathode side of polypropylene (PP) separator. This investigation reveals that the adsorption-catalysis synergistic effect of NiSe-Ni2P/C composite, accelerates the reduction of LiPS to lithium sulfide (Li2S) as well as the oxidation of Li2S. The synergistic effect effectively mitigates the shuttle effect of LiPS, reduces concentration polarization, and improves Coulombic efficiency (CE) throughout the entire lifespan. At a current density of 0.05 C, LSBs with NiSe-Ni2P/C modified PP separators exhibit a remarkable high initial CE of 97.0% and a substantial discharge specific capacity of 1205.4 mAh gs−1. Even under conditions of a high sulfur loading (4.3 mg cm−2) and a limited electrolyte dosage (10 μL mgs−1), the LSBs maintained a reversible specific capacity of 804 mAh gs−1, a CE of 94%, and an energy density of 1232.1 Wh kgs−1 after 720 h of continuous cycling at 0.05 C. This work provides a solution for achieving long-time, high-capacity, and high-CE electrochemical performance in LSBs with a high sulfur loading and a limited electrolyte dosage.

Synergistic Effect of CNT-TiO2 Catalyst and 3D Electrode Architecture for Electrochemical Performance in Lithium-Sulfur Batteries

Lithium-sulfur batteries (LSBs) are a potential electrochemical storage system for the future with high capacity (1675 mAh g−1) and energy density (∼2600 Wh kg−1). The poor conductivity of sulfur, polysulfide shuttle effect, and volume expansion of the sulfur cathode are the main hurdles to their commercialization. To mitigate these issues, this work represents a rational composite of hybrid multiwalled carbon nanotubes (MWCNT) -TiO2 high surface area carbon-sulfur composite (CTHS) onto a 3D carbon fiber (CF) based free-standing electrode (CTHS@CF) architecture. TiO2 can effectively anchor the polysulfides by chemical bonding and improve cyclability. MWCNTs and CFs are the effective electron transport materials that accelerate the redox kinetics of polysulfides. The electrochemistry of CTHS@CF reveals an excellent discharge capacity of 910 mAh g−1 (1st cycle) at 100 mA g−1 compared to the conventional aluminum-coated (CTHS@Al) of 532 mAh g−1. The CTHS@CF (at 300 mA g−1) displays 514 mAh g−1 (initial discharge) capacity with 83% capacity retention up to 100 cycles, whereas CTHS@Al shows 394 mAh g−1 with 44% capacity retention. Combining 3D electrode architecture with the metal oxide (TiO2) plays a vital role in the electrochemistry of LSBs by improving the stability of the battery’s cycle life and overall energy density.

Revisiting the unified principle for the single-atom electrocatalysts in sulfur reduction reaction: from liquid to solid-state electrolytes

The conversion of lithium-polysulfides (LPSs) through the sulfur reduction reaction (SRR) is a crucial process for improving the electrochemical performance of lithium-sulfur (Li-S) batteries. However, the microscopic mechanism of SRR...

Discharge characteristic analysis of lithium-sulfur batteries considering the discontinuous deposit and transport-limited effects

The modeling research plays a crucial role in grasping the reaction mechanisms and forecasting the performance of lithium-sulfur (Li–S) batteries. A transient Li–S battery model including continuity, transportation, and reaction kinetics by simultaneously considering the discontinuous deposit of discharge product Li2S and the transport limitation in the concentrated electrolyte, is developed to reveal the discharge phenomena. The effects of operating conditions and electrolyte and electrode properties on the discharge behaviors including voltage-capacity curve, energy density, profiles of solid product (ɛLi2S) and porosity (ɛ) at the cathode are quantitatively studied. It is found that low discharge rate is beneficial to the discharge capacity and utilization of cathode sulfur. Enhancing precipitate (S8) solubility Ksp, S8 and ionic diffusivity Di improves voltage plateau and specific energy to varying degrees; the promotion of voltage plateau will be inconspicuous as electrode conductivity σ is enlarged over 0.1 S/m. With the rise of ɛ from 0.5 to 0.9, the specific capacity and the specific energy are expanded by around 5 times. When lengthening Lca from 20 μm to 60 μm, the specific capacity ascends from 944.5 to 991.5 mAh/g-S, whereas the growth rate of specific capacity and specific energy decreases gradually; the practical total energy almost increases linearly with thickness, yielding a 218.75% enhancement. With a certain period of relaxation, the recovered cell capacity after the high discharge rate is higher than that after the low discharge rate. This work may guide in designing electrodes and electrolytes and provide performance regulation strategies for Li–S batteries.

Theoretical investigation of synergistically boosting the anchoring and electrochemical performance of lithiophilic/sulfiphilic transition metal carbides for lithium-sulfur batteries.

Lithium-sulfur (Li-S) battery is one of the most promising next-generation energy-storage systems with a high energy density and low cost. However, their commercial applications face several challenges, such as the shuttle effect caused by the soluble lithium polysulfide (LiPSs) intermediates and the sluggish sulfur redox reaction. In this article, we systematically investigated the anchoring and electrochemical performance of a series of transition metal carbides (TMCs: TiC, VC, ZrC, NbC, HfC, TaC) as cathode materials for Li-S batteries by theoretical calculations. The lithiophilic/sulfiphilic non-polar (001) surfaces of TMCs can offer moderate binding strength with LiPS intermediates, ensuring good performance of sulfur immobilization. These TMCs can also facilitate lithium diffusion, indicating the good rate performance of Li-S batteries. We also demonstrated that the studied TMCs can be classified into two classes according to their catalytic activity for Li2S decomposition which originated from their different electronic structural features. Furthermore, TiC, ZrC, and HfC exhibited excellent bifunctional electrochemical activity through reducing the Gibbs free energy for sulfur reduction reactions (SRRs) and lowering the barrier for Li2S decomposition which facilitates accelerating electrode kinetics and elevating utilization of sulfur. Our results offer a systematic approach to designing and screening non-polar materials for high-performance Li-S batteries, based on the rational electronic structure and lattice match strategy.

APPLICATION OF SULFUR RADICAL ANIONS IN ORGANIC SYNTHESIS. DETERMINATION OF FORMS OF SULFUR

The study of reactions involving sulfur anion radicals in organic synthesis has become an area of active research in the last few years. The role of polysulfide radicals in the electrochemical processes of lithium-sulfur (Li-S) batteries has been particularly discussed. Understanding the pathways of the electrochemical reactions is crucial for improving the performance of Li-S batteries. In order to summarize and analyze the most relevant literature data, the review presents information on the application and study of sulfur anion radicals in organic synthesis and methods for the determination of sulfur forms. We have classified and discussed in detail the spectra of various forms of sulfur in the ultraviolet and visible ranges. The article describes the choice of solvent, the correlation between the properties of solvents, the influence of the nature of the solvent on the absorption band shift of sulfur particles and on the stability of the anion radical, the identification of sulfur forms in the ultraviolet and visible spectrum regions, and the possibility of stabilizing anion radicals by complexation with crown ethers. The absorption bands for S22-, S32-, S52-, S72- strongly overlap with other particles while having lower intensities, leading to different conclusions regarding the distribution of polysulfides and different forms of sulfur in aqueous media. The data presented in the review have an applied meaning, contribute to the understanding of the application of sulfur anion radicals in organic synthesis and can be used for the choice of method for the determination of sulfur forms and solvent. This review article may be of interest to specialists in the field and will help to plan studies on the study of sulfur forms and the interpretation of spectra of different sulfur forms.

Theoretical study of highly efficient VS2-based single-atom catalysts for lithium-sulfur batteries.

Lithium-sulfur (Li-S) batteries have become a research hotspot due to their high energy density. However, they also have certain disadvantages and limitations. To enhance the performance of Li-S batteries, this study focuses on the utilization of transition metal (TM)-embedded vanadium disulfide (VS2) materials as cathode catalysts. Using density functional theory (DFT), comprehensive calculations and atomic-level screening of ten TM atoms were conducted to understand the underlying mechanisms and explore the potential of TM@VS2 catalysts for enhancing battery performance. The computational results indicate that five selected catalysts possess sufficient bonding strength towards high-order lithium polysulfide intermediates by the formation of a significant covalent bond between S atoms in Li2Sn and TM atoms, thereby effectively suppressing the shuttle effect. The Ni@VS2 catalyst can effectively decrease the decomposition energy barrier of Li2S in the charge reaction and can have an optimal Gibbs free energy at the rate-determining step among TM@VS2 catalysts for the discharge reaction. This study elucidates the mechanism of VS2-based transition-metal single-atom catalysts and provides an effective reference for the anchoring of TM atoms on other materials.

Sulfonic groups modified carbon nanotubes: the decorative strategy for enhancing the performance of lithium-sulfur batteries

Porous carbon nanotubes can not only provide a large surface area for anchoring sulfur and restraining polysulfides, but also provide continuous conductive networks to facilitate ion transport in lithium-sulfur batteries...

A zinc coordination supramolecular network synergized manganese dioxide achieves high-rate lithium-sulfur batteries

Lithium-sulfur batteries (LSBs) have attracted large attention due to their high capacity and energy density, however, the electrochemical performance of LSBs limited by the difficult conversion of lithium polysulfides (LiPSs)....

CoFe2O4 nanoparticles modified amidation of N-doped carbon nanofibers hybrid catalysts to accelerate electrochemical kinetics of Li-S batteries with high sulfur loading

Lithium-sulfur battery have been considered as promising energy storage devices because of its superiority in energy density. However, the low active material utilization, low sulfur loading, shuttle effect and torpid kinetics of polysulfides, and poor cycling stability limit its commercial applications. Herein, the functionalized nitrogen doped carbon nanofibers containing amide groups were designed by electrospun and polyamidoamine dendrimer (PAMAM) solution impregnation techniques. The obtained amide groups modified nitrogen-doped carbon nanofibers (ANF) were combined with spinel CoFe2O4 (CFO) nanoparticles (CFOANF) via hydrothermal method to design as membrane electrode containing Li2S6 catholyte for lithium-sulfur batteries. The introduction of nitrogen doped and amide groups modified ANF can increase fibers polarity, which have chemical adsorption capability toward lithium polysulfides. CFO nanoparticles can further absorb the soluble polysulfides by strong chemical interaction due to its intrinsic polarity and also serve as a catalyst to promote the redox kinetics of polysulfides conversion. Benefiting from the synergism of the physical confinement, polar chemical adsorption, and catalytic conversion, the as-prepared CFOANF delivers excellent electrochemical performances at high sulfur loading. The as-prepared CFOANF membrane with 6.3 mg cm−2 sulfur loading delivers a high initial capacity of 940 mAh g−1 and excellent long-term cycling stability up to 450 cycles with a low decay rate 0.059 % per cycle at 0.2C. Remarkably, even at 12.6 mg cm−2 and 16.4 mg cm−2 sulfur loading, the CFOANF membrane electrodes show high capacity of 9.7 mAh cm−2 and 11.8 mAh cm−2, respectively. The results show that the chemically anchoring polysulfides and catalyzing redox reaction by multifunctional CFOANF hybrid composite is promising for assembling with a high sulfur loading electrode, which exhibits a superior electrochemical performance in lithium-sulfur batteries.

Highly Concentrated Electrolytes for Lithium Sulfur Batteries – the Role of the Anion(s)

Lithium-sulfur batteries (Li-S) have attracted a lot of attention as a alternative/complement to lithium-ion batteries (LIBs) – due to both high energy density, availability, and inexpensive materials used.[1]Yet, dissolution of sulfur from the C/S cathode and subsequent shuttling of lithium polysulfides (LiPS) to the anode as well as the instability of the Li metal anode itself are true scientific and technological challenges. Advancing in the field of electrolytes is one promising way to overcome both issues.Switching from the standard 1 M electrolyte design of LIBs to highly concentrated electrolytes (HCEs) may both prevent the dissolution of LiPSs and hinder dendrite formation at the lithium metal anode.[2]Here we combine experimental methods and computational approaches to investigate several HCEs based on various Li-salts in several standard organic solvents. Experimentally we targeted electrochemical properties, local electrolyte structure, and physico-chemical properties, with focus on the role(s) of the Li-salt anions. Furthermore, to predict the solubility of sulfur the conductor like screening model for real solvents (COSMO-RS), a computational fluid phase thermodynamic approach, was used.[3] Overall, the challenges and opportunities associated with the use of HCEs in Li-S batteries will be addressed, also highlighting potential areas for future research and development.References Peng et al., "Drastic effect of salt concentration in ionic liquid on performance of lithium sulfur battery." Journal of the Electrochemical Society 169.5 (2022): 050515.Suo et al., "A new class of solvent-in-salt electrolyte for high-energy rechargeable metallic lithium batteries." Nature communications 4.1 (2013): 1481.Jeschke and P. Johansson, "Predicting the Solubility of Sulfur: A COSMO‐RS‐Based Approach to Investigate Electrolytes for Li–S Batteries." Chemistry–A European Journal 23.38 (2017): 9130-9136.

Effect of Oxygen Functionalities inside Carbon Micropore on Lithium-Sulfur Battery Performance

Introduction Lithium-sulfur batteries (LSB) using a sulfur cathode with a high specific capacity (1672 mAh g-1) have been regarded as one of the most promising candidates for large-scale energy storage systems, while the sulfur cathode's drawback hinders the commercial application of LSB. Soluble Li2Sx (x = 4 – 8) generated during a charge-discharge process dissolves into electrolytes, which induces LSB's self-discharge and capacity decay. The main efforts to overcome this issue have been on physical confinement of sulfur in the pores of porous carbons [1,2]; however, carbon materials, being non-polar in nature, interact weakly with the polar Li2Sx, which still leads to low cycle stability of LSB. Hence, the surface modification to porous carbon, which provides polar-polar interaction between the carbon surface and Li2Sx, has been performed, suppressing the Li2Sx dissolution and improving LSB's performance [1,3].On the other hand, we reported that polar-oxygen functionalities on microporous carbon (MC), which are generated with oxidants, significantly improve the discharge capacity of LSB [4]. The formation of Li2Sx (x = 4 – 8) is inhibited in micropores (pore diameter < 2 nm) [5]; therefore, the oxygen functional groups probably improve the discharge capacity of LSB assembled with a MC-sulfur composite cathode due to factors other than the suppression effect of Li2Sx dissolution. Our previous study revealed that oxygen functionalities on the MC surface contribute to the enhanced electrochemical performance of the LSB by preventing electrolyte decomposition and thus decreasing the resistance of the cathode electrolyte interface (Rcei) [6]. However, the ratio of Rcei to the total resistance of the LSB is small; the oxygen functional groups would improve the performance of LSB by affecting other resistance. Herein, we investigate the effect of surface oxygen functionalities on charge transfer resistance (Rct) and Li+ diffusion of LSB. Our report would provide deep insight into the surface modification of carbon materials as LSB’s cathode. Method 2.1. Preparation of Oxidized MC-Sulfur composite MC was added into 69 wt.% HNO3 and refluxed at 120ºC for 2 h (Ox MC). Washed and dried Ox MC was mixed with sulfur at a weight ratio of 48: 52. The mixture was heated at 155ºC for 5 h (Ox MC-S). 2.2. Assembling of Cells To obtain the Ox MC-S cathode, the slurry prepared by mixing the Ox MC-S, acetylene black, carboxymethyl cellulose, and styrene butadiene rubber at a weight ratio of 89: 5: 3: 3 was coated on an Al foil. The cells with the Ox MC-S cathode and Li metal anode were assembled in a glove box. Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI): tetraglyme (G4): 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropylether (HFE) = 10: 8: 40 (by mol) was used as the electrolyte. 2.3. Activation Energy Measurement with Electrochemical Impedance Spectroscopy (EIS) To elucidate the effect of oxidation treatment on the Rct and Warburg impedance (Rw) of Li-S batteries, activation energy measurement was carried out at 2.5 V in the 50th charging process. The temperature range was 0 – 25°C, and the alternating current voltage amplitude was 10 mV. Rw was investigated with the calculation of the Warburg coefficient (σ). Major results and conclusion The activation energy of Rct (Ect) and σ were determined to investigate the effects of oxygen functional groups formed at MC surfaces on charge transfer processes and Li+ diffusion. While Ect increased from 0.65 to 0.72 eV by oxidation treatment, the frequency factor increased from 17.7 to 20.9; this indicates that the oxygen functional groups improve the number of reaction sites where three substances (carbon, active material, and electrolyte) come into contact with each other. The σ of MC-S and Ox MC-S were 281.2 and 178.9 Ω s-1/2, respectively. Therefore, a decrease in Rw due to oxygen functional groups was suggested.The charge transfer process and Li+ diffusion occur inside the microporous carbon particles where the confined sulfur is present. We processed the Ox MC-S particle from the cathode after the 50th charging using focused ion beam (FIB) milling to obtain a cross-section and observed it with STEM-EELS. This result will also be reported in our presentation.This work was supported by “Advanced Low Carbon Technology Research and Development Program, Specially Promoted Research for Innovative Next Generation Batteries (ALCA-SPRING [JPMJAL1301])” from JST.[1] X. Ji et al., Nat. Mater., 8 (2009) 500.[2] T. Takahashi et al., Prog. Nat. Sci., 25 (2015) 612.[3] L. Yoshida et al., Electrochim. Acta, 429 (2022) 141000.[4] S. Okabe et al., Electrochemistry, 85 (2017) 671.[5] Y. Xiao et al., RSC Adv., 10 (2020) 39875.[6] L. Yoshida et al., 242nd ECS Meeting s, Z01-2299 (2022).

Factors Improving Lithium Sulfur Battery Performance with Mesoporous Carbon-Sulfur Cathode by Mixing Vinylene Carbonate Electrolyte with Fluoroethylene Carbonate

1. IntroductionLithium-ion batteries (LIB) are used in a variety of applications, including portable devices such as smartphones. More recently, the development of rechargeable batteries is expected for applications such as next-generation electric mobility, requiring energy storage devices with higher energy density than conventional LIB, and lithium-sulfur (Li-S) batteries are attracting attention among these applications. To realize Li-S batteries with high energy density and safety, we have focused on mesoporous carbon-sulfur cathodes and carbonate-based electrolytes. In previous studies, we have reported that Li-S batteries using vinylene carbonate (VC) and fluoroethylene carbonate (FEC) as electrolyte solvents exhibit superior rate characteristics than using only VC solvent 1). This study investigates the factors that contribute to the improved performance when using a FEC-VC mixed electrolyte.2. Experimental method(1) We assembled the cells using 1.0 M lithium bis(trifluoromethanesulfonyl)imide / VC (Only VC electrolyte) or 1.0 M lithium bis(trifluoromethanesulfonyl)imide / FEC: VC (FEC-VC electrolyte). The cell was pre-cycled at 0.1C in the voltage range of 1 - 3 V, and then discharged at 10 C or 0.1 C and charged at 0.1 C for three cycles. After discharging and charging, each cell and electrode were evaluated using electrochemical impedance spectroscopy (EIS) or XPS. (2) Radical polymerization of VC with 2,2'-azobis(isobutyronitrile) (AIBN) was made by mixing VC and AIBN (VC radical polymer). Anionic polymerization of VC with lithium ethoxide (LiOEt) was also obtained by mixing VC and LiOEt (VC anionic polymer). These polymers were analyzed using XPS and MALDI-TOFMS. (3) The cathode materials after discharging and charging were stripped from the current collector. The powder was analyzed by APCI-TOFMS. (4) The cathode after 10 cycles was analyzed by STEM-EELS.3. Results and discussionWe conducted EIS on Li-S batteries charged and discharged with Only VC electrolyte or FEC-VC electrolyte at 10 C or 0.1 C, respectively. As a result, in the case of Only VC electrolyte, the interfacial resistance increased significantly after charge-discharge at 10 C when compared to that after charge-discharge at 0.1 C. On the other hand, when using FEC-VC electrolyte, the increase in interfacial resistance was suppressed. In addition, XPS investigation of the electrodes after discharging and charging showed that the SEI film thickness increased significantly after discharging and charging at 10 C when using Only VC electrolyte, whereas the increase in SEI film thickness was suppressed when using FEC-VC electrolyte. These suggest that when using FEC-VC electrolyte, a good SEI that suppresses electrolyte decomposition more is formed, and thin and low-resistance SEI is maintained even after rapid discharge, thereby improving rate performance. In addition, the XPS C1s spectra observed on the electrode film showed similar profiles to those of the VC radical polymer when using Only VC electrolyte, and to those of the VC anionic polymer when using FEC-VC electrolyte. Therefore, these polymers were used as models for the assumed SEI organic components when using respective electrolytes and were investigated by MALDI-TOFMS. As a result, the molecular weight of the monomer unit of the polymer was 250 for the VC radical polymer, while it was 60 for the VC anionic polymer. The results of the APCI-TOFMS investigation on the cathode materials after discharging and charging showed that the components with higher molecular weight decreased as using the electrolyte solvent with a higher mixing ratio of FEC to VC. Therefore, we considered that the mixing of FEC makes the SEI organic components less bulky and denser, which suppresses the continuous formation of SEI kinetically and reduces the interfacial resistance. We conducted further investigation about SEI that could suppress electrolyte degradation more when using FEC-VC electrolyte. STEM-EELS investigation of the cathode after 10 cycles of charge-discharge showed that the SEI layer is divided into two layers when using FEC-VC electrolyte, and the SEI inner layer is mainly composed of S, F and Li. The XPS results also revealed the presence of LiF and Li2Sx (x=2-8) inside the SEI. Therefore, it is suggested that when using FEC-VC electrolyte, the formation of a layer that mainly composed of LiF and Li2Sx (x=2-8) inside the SEI acts as a barrier between the electrode and the electrolyte, which can suppress excessive decomposition of the electrolyte.AcknowledgementsThis research was partly performed as a subcontract (JPNP15005) from the New Energy and Industrial Technology Development Organization (NEDO) (contractor: GS Yuasa Corporation; subcontractor: Kansai University).Reference1) K. Kishida et al., The 60th Battery Symposium in Japan, The Committee of Battery Technology, The Electrochemical Society of Japan, p. 2D04 (2019).

Enhanced polysulfides conversion with hybrid bipolar membrane composed of CoSe2 and amide-functionalized CNTs composites for lithium sulfur batteries

Lithium sulfur battery has been considered as promising energy storage devices because of its superiority in energy density. However, the sulfur loading, low active material utilization, shuttle effect and torpid kinetic of polysulfides, and poor cycling stability limit its commercial applications. Herein, a hybrid bipolar membrane composed cobalt diselenide nanoparticles and amide-functionalized CNTs (CoSe2@A-CNTs) composites has been fabricated by the combination of hydrothermal and vacuum filtration technology, and contained Li2S6 catholyte for lithium sulfur batteries. The introduction of amidation functional groups enhance the polarity of the mesoporous CNTs surface and promote adsorption capability toward lithium polysulfides. The intrinsic polarity of CoSe2 nanoparticles can further adsorb the soluble polysulfides and serve as catalysts to promote the redox kinetics of polysulfides conversion. Benefiting from the synergism of physical confinement, polar chemical adsorption, and catalytic conversion, the as-prepared CoSe2@A-CNTs delivers excellent electrochemical performances at high sulfur loading. The lithium sulfur cell with CoSe2@A-CNTs membrane with 4.8 mg cm−2 sulfur loading exhibits a high initial capacity of 1009.7 mAh g−1 and excellent long-term cycling stability up to 300 cycles with a low decay rat 0.07 % per cycle at 0.2C. Remarkably, even at 9.6 mg cm−2 sulfur loading, the CoSe2@A-CNTs membrane displays high area capacity of 7.5 mAh cm−2 and maintains 6 mAh cm−2 over 100 cycles. The results show that the efficient chemical anchoring polysulfides and catalyzing redox reaction by multifunctional CoSe2@A-CNTs hybrid composites is promising for assembling with a high sulfur loading electrode, which exhibits a superior electrochemical performance in lithium sulfur batteries.

Mo2C-MoP heterostructure regulate the adsorption energy of electrocatalysts in high-performance Li-S batteries

The cathodic polysulfides electrocatalyst, such as Mo2C, offers a promising approach to mitigate the shuttling effect by providing strong polysulfide adsorption and catalyst abilities to improve the electrochemical performance of Lithium-sulfur (Li-S) batteries. However, according to the Sabatier principle, excessive adsorption of Mo2C undermines the conversion of polysulfides. This undesirable effect can be mitigated by forming the heterostructure of Mo2C-MoP. Even more importantly, the introduction of MoP can prevent the surface gelation of Mo2C and expose more active sites. Consequently, the Li-S batteries with the Mo2C-MoP sulfur host exhibit outstanding long-term cycling stability, showcasing a mere 0.035% capacity decay per cycle over 800 cycles at 1 C. This work on the balance between adsorption capacity and catalytic active of cathodic polysulfides electrocatalyst provides a new vision for realizing a high-performance Li-S batteries.

Enhancing Lithium-Sulfur Battery Performance by MXene, Graphene, and Ionic Liquids: A DFT Investigation.

The efficacy of lithium-sulfur (Li-S) batteries crucially hinges on the sulfur immobilization process, representing a pivotal avenue for bolstering their operational efficiency and durability. This dissertation primarily tackles the formidable challenge posed by the high solubility of polysulfides in electrolyte solutions. Quantum chemical computations were leveraged to scrutinize the interactions of MXene materials, graphene (Gr) oxide, and ionic liquids with polysulfides, yielding pivotal binding energy metrics. Comparative assessments were conducted with the objective of pinpointing MXene materials, with a specific focus on d-Ti3C2 materials, evincing augmented binding energies with polysulfides and ionic liquids demonstrating diminished binding energies. Moreover, a diverse array of Gr oxide materials was evaluated for their adsorption capabilities. Scrutiny of the computational outcomes unveiled an augmentation in the solubility of selectively screened d-Ti3C2 MXene and ionic liquids-vis à vis one or more of the five polysulfides. Therefore, the analysis encompasses an in-depth comparative assessment of the stability of polysulfide adsorption by d-Ti3C2 MXene materials, Gr oxide materials, and ionic liquids across diverse ranges.

Ketjen Black@Ce-MOF derived KB@CeO2-C as separator coating for lithium sulfur batteries

Lithium‑sulfur batteries (LSBs) have received wide attention because of their advantages of high theoretical specific capacity. However, shuttle effect of lithium polysulfides need to be solved urgently, which makes the commercial application of LSBs difficult. To solve these problems, Ce-MOF and conductive carbon material Ketjen Black (KB) are used to compound to obtain a composite precursor, and then further calcined at a high temperature to obtain KB@CeO2-C derivative. After applying KB@CeO2-C to commercial separators, the performance of LSBs is improved because of its excellent adsorption and catalytic capability. Through experimental analysis, when the sulfur areal density on the cathode electrode is 2.8 mg cm−1, the discharge specific capacity of the KB@CeO2-C separator battery in the first cycle at 0.5C is 835 mAh g−1, and after 900 cycles, the discharge specific capacity can still maintain 400.1 mAhg−1. When the sulfur loading of the electrode is added to 5 mg cm−1, the initial specific capacity at 0.1C can reach 1090.3 mAh g−1, and it can be stabilized for 120 cycles, which demonstrates its application potential.

Long-term stability of lithium–sulfur batteries via synergistic integration of nitrogen-doped graphitic carbon-coated cobalt selenide nanocrystals within porous three-dimensional graphene-carbon nanotube microspheres

Three-dimensional porous microspheres consist of highly conductive reduced graphene oxide-carbon nanotube (rGO‒CNT) framework with well-embedded cobalt selenide (CoSe2) nanocrystals coated with N-doped graphitic carbon (NGC) were synthesized (referred as “P–CoSe2@NGC/rGO‒CNT” microspheres) and utilized as an electrocatalytic interlayer to enhance the performance of lithium-sulfur (Li–S) batteries. The incorporation of the NGC layer and rGO‒CNT framework not only enhances the electronic conductivity significantly but also offers numerous conductive pathways (primary and secondary) for efficient electron transport. Macropores (φ = 100 nm) formed by the decomposition of PS nanobeads (φ = 200 nm) guarantee effective electrolyte penetration and short diffusion pathways. Moreover, the CoSe2 nanocrystals offer a multitude of polar active sites that effectively anchor polysulfide intermediates, reducing the loss of active material. Benefiting from the nanostructure merits, Li–S cells featuring a P–CoSe2@NGC/rGO‒CNT-coated separator and a conventional sulfur electrode demonstrated outstanding rate capability (up to 2.0 C) and remarkable cycling stability (1000 cycles at 2.0 C). Even under more demanding cell conditions, such as high sulfur content (71 %), high sulfur loading (4.6 mg cm−2), and low E/S (5.6 μL mg−1) ratio, the cell exhibits impressive cycling stability with 420 cycles at 0.1 C, along with feasible rate performance up to 0.3 C.

Graphene supported In2S3 nanostructure as electrode material for lithium sulfur batteries and supercapacitors

A facile one-pot fabrication of reduced graphene oxide (rGO) supported In2S3-rGO is presented here with improved electrochemical performance in lithium-sulfur (Li–S) batteries and supercapacitors (SCs). Increasing the concentration of rGO in the nanostructures successfully mitigated the conversation kinetics, polysulfide shuttle effect and improved the overall cyclability in Li–S batteries. A battery made from In2S3-rGO30 electrode loses only 8 % of its discharge capacity after 250 continuous charge-discharge cycles, compared to a 36 % loss from a bare In2S3 electrode. It presented a high discharge capacity of 947.3 mA h g−1 at 1C, superb rate performance of 821.65 mA h g−1 at 5C, excellent capacity retention and Columbic efficiency of ⁓100 % over 250 cycles are achieved. The In2S3-rGO30 electrode provides a specific capacitance of 645.2 F g−1 at a current density of 2 A g−1 for SC application. The electrode retains 96 % of its capacity after 1000 continuous discharge cycles at a higher current density of 5 A g−1, performing well and staying ahead of other nanocomposites. This study successfully demonstrates the integration of In2S3 with a two-dimensional conductive substrate as a multifunctional and cost-effective host for designing high-performance cathode for Li–S batteries and battery-type electrode material for SC application.

Rational Design of TiO2@g-C3N4/CNT Composite Separator for High Performance Lithium-Sulfur Batteries to Promote the Redox Kinetics of Polysulfide.

Lithium-sulfur batteries (LSB) show excellent potential as future energy storage devices with high energy density, but their slow redox kinetics and the shuttle effect seriously hinder their commercial application. Herein, a 0D@2D composite was obtained by anchoring polar nano-TiO2 onto a 2D layered g-C3N4 surface in situ, and a functional separator was prepared using multi-walled carbon nanotubes as a conductive substrate. Due to their long-range conductivity, multi-walled carbon nanotubes make up for the low conductivity of TiO2@g-C3N4 to some extent. A lithium-sulfur battery prepared with a modified separator exhibited excellent long-term cycle performance, a good lithium ion diffusion rate, and rapid redox kinetics. The initial specific discharge capacity of the composite was 1316 mAh g-1 at 1 C, and a high specific discharge capacity of 569.9 mAh g-1 was maintained after 800 cycles (the capacity decay rate per cycle was only 0.07%). Even at the high current density of 5 C, a specific capacity of 784 mAh g-1 was achieved. After 60 cycles at 0.5 C, the modified separator retained the discharge capacity of 718 mAh g-1 under a sulfur load of 2.58 mg cm-2. In summary, the construction of a heterojunction significantly improved the overall cycle stability of the battery and the utilization rate of active substances. Therefore, this study provides a simple and effective strategy for further improving the overall performance and commercial application of lithium-sulfur batteries.