Long-chain Lithium Polysulfides Research Articles

Mirror Plane Effect of Magnetoplumbite-Type Oxide Restraining Long-Chain Polysulfides Disproportionation for High Loading Lithium Sulfur Batteries.

A facile solid-state approach is employed to synthesize a novel magnetoplumbite-type oxide of NdMgAl11O19, which integrates spinel-stacking layers (MgAl2O4) with Nd-O6 mirror plane structures. The resulting NdMgAl11O19 exhibits remarkable catalytic activity and conversion efficiency during the sulfur reduction reaction (SRR) in lithium-sulfur batteries. By employing the 2D projection mapping technique of in situ confocal Raman spectroscopy and electrochemical technique, it is discovered that the exposed mirror plane structure of Nd-O6 can effectively suppress the undesiring disproportionation reaction (S8 2-→S6 2-+1/4 S8) of long-chain lithium polysulfides at the initial stages of sulfur reduction, thereby promoting the positive process of sulfur to lithium sulfide. This not only mitigates the issue of sulfur shuttle loss but also significantly improve the kinetics of the conversion process. Leveraging these advantages, the NdMgAl11O19/S cathode delivered an impressive initial capacity of up to 1398 mAh g-1 at an electrolyte/sulfur (E/S) ratio of 5.1µL mg-1 and a sulfur loading of 2.3mg cm-2. Even when the sulfur loading is increased to 10.02mg cm-2, the cathode retained a reversible areal capacity of 10.01 mAh cm-2 after 200 cycles. This mirror engineering strategy provides valuable and universal insights into enhancing the efficiency of cathodes in Li-S battery.

Effect of the anionic composition of sulfolane based electrolytes on the performances of lithium-sulfur batteries

In lithium-sulfur batteries, cell design, specifically electrolyte design, has a key impact on the battery performance. The effect of lithium salt anion donor number (DN) (DN[PF6]− = 2.5, DN[N(SO2CF3)2]− = 5.4, DN[ClO4]− = 8.4, DN[SO3CF3]− = 16.9, and DN[NO3]− = 21.1) on the patterns of lithium-sulfur batteries and lithium metal electrode performances with sulfolane-based electrolytes is investigated. An increase in DN of lithium salt anions leads to an increase in the depth and rate of electrochemical reduction of sulfur and long-chain lithium polysulfides and to a decrease in those for medium- and short-chain lithium polysulfides. DN of lithium salt anions has weak effect on the discharge capacity of lithium-sulfur batteries and the Coulomb efficiency during cycling, with the exception of LiSO3CF3 and LiNO3. An increase in DN of lithium salt anions leads to an increase in the cycling duration of lithium metal anodes and to a decrease in the presence of lithium polysulfides. In sulfolane solutions of LiNO3 and LiSO3CF3, lithium polysulfides do not affect the cycling duration of lithium metal anodes.

Suppression of long-chain lithium polysulfide formation through a selenium-doped linear sulfur copolymer cathode for high-performance lithium–organosulfur batteries

A novel organosulfur cathode material for practical Li–S batteries was developed, featuring a selenium-doped linear sulfur chain bonded to a trithiocyanuric acid copolymer (SexS-TTCA).

Nafion-Based Quasi-Solid-State Polymer Electrolyte for Lithium-Sulfur Batteries

Lithium-sulfur batteries are considered a strong contender for next-generation high-energy battery systems given their high gravimetric energy density. However, this battery chemistry is still facing challenges such as the polysulfide shuttle effect caused by the high solubility of long-chain lithium polysulfides (Li2Sn) resulting in active material loss and compromised cycle life. Solid-state polymer electrolytes (SPEs) represent a promising pathway to address this issue by preventing the formation and transport of these undesirable polysulfide intermediates.1,2 Moreover, the application of flexible polymer electrolytes promotes safe high energy batteries for smart textiles.In this study, single lithium-ion conducting solid polymer electrolytes (SLIC-SPEs) based on lithiated Nafion membrane have been investigated, utilizing the chemical and thermal stability of this kind of ionomers. Among others, a mixture of ethylene carbonate (EC) and propylene carbonate (PC) was tested as organic aprotic swelling solvent offering advantageous characteristics such as great chemical stability and high ion mobility while avoiding phase separation issues and undesired leaching.Sulfur-infiltrated ultramicroporous carbon composite cathodes were utilized in combination with the investigated SLIC-SPEs, facilitating a quasi-solid-state lithium-sulfur full cell with carbonate-solvent compatibility and high active material utilization.3 Electrochemical performance of the full cell was investigated elaborately and compared with a reference system using solely the liquid EC:PC solvent. While rapid capacity fading can be observed for the liquid electrolyte cell, an enduring high capacity is found in the lithiated-Nafion system. For better understanding of these effects, cycling analysis was accompanied by implementing impedance spectroscopy upon galvanostatic cycling. The electrochemical characterization indicates the formation of a stable film and high degree of reversibility during cycling of the lithiated-Nafion cell whereas an increased film resistance due to sulfur cross-over and electrolyte decomposition was observed within the liquid electrolyte system.(1) Z. Li, W. Lu, N. Zhang, Q. Pan, Y. Chen, G. Xu, D. Zeng, Y. Zhang, W. Cai, M. Yang, J. Mater. Chem. A 2018, 6 (29), 14330-14338.(2) X. Hao, H. Wenren, X. Wang, X. Xia, J. Tu, J. Colloid Interface sci. 2020, 558, 145-154,(3) M. Nojabaee, B. Sievert, M. Schwan, J. Schettler, F. Warth, N. Wagner, B. Milow, K. A. Friedrich, J. Mater. Chem. A 2021, 9 (10), 6508-6519,

(Digital Presentation) Electrocatalytic and Conductive Vanadium Oxide on Carbonized Bacterial Cellulose Aerogel for the Sulfur Cathode in Li-S Batteries

Li-S chemistry is regarded as promising next-generation battery technology. However, its complex redox process and long-chain lithium polysulfides shuttling are hindering the development of practical Li-S battery technology. To address these problems, many transition-metal-oxide-based catalysts have been investigated to chemically bind soluble lithium polysulfides and accelerate their redox kinetics. However, the intrinsic poor electrical conductivities of these oxides restrict their catalytic performance, consequently limiting the sulfur utilization and the rate performance of Li-S batteries. Herein, we report a freestanding electrocatalytic sulfur host consisting of hydrogen-treated VO2 nanoparticles (H-VO2) anchored on nitrogen-doped carbonized bacterial cellulose aerogels (N-CBC). The hydrogen treatment enables the formation and stabilization of the rutile VO2(R) phase with metallic conductivity at room temperature, significantly enhancing its catalytic capability compared to the as-synthesized insulative VO2(M) phase. We characterized the electrocatalytic performance of this unique H-VO2@N-CBC structure using several methods and found that the activation energy between S8 and polysulfides and the one between polysulfides and Li2S are largely reduced by 28.2 and 43.3 kJ/mol, respectively. Accordingly, the Li-S battery performance is greatly improved, with a high initial specific capacity of 1347 mAh g−1 at 0.1 C and remarkable cycling stability with a capacity of 758 mAh g-1 after 300 cycles at 1 C. This work provides an effective strategy for designing and fabricating conductive oxide catalysts to promote the electrochemical performance of Li-S batteries.

Highly electrocatalytic active amorphous Al2O3 in porous carbon assembled on carbon cloth as an independent multifunctional interlayer for advanced lithium-sulfur batteries

To realize practical applications of lithium-sulfur batteries, rational strategies have to be applied to overcome obstacles such as the shuttle effect and sluggish reaction kinetics of soluble long-chain lithium polysulfides (LPS). In this work, highly electrocatalytic active amorphous Al2O3 uniformly dispersed in porous carbon (Al2O3/C) anchored on carbon cloth (CC) was successfully fabricated. The resultant flexible Al2O3/C@CC was used as an independent interlayer for Li-S batteries, demonstrating strong physical confinement and chemical binding ability for LPS, as well as high catalytic activity for LPS conversion kinetics due to a synergistic effect of 3D conductive network, amorphous nature of Al2O3/C, porous structure and abundant active sites. The cells with such interlayer exhibit high specific capacity, superior cycling stability and rate capability, 903 mAh/g at 0.2C after 100 cycles and 810 mAh/g at 1.0C after 300 cycles can be achieved, moreover, 741 mAh/g can still be retained at a high rate of up to 5.0C. By contrast, Al-MOF grown on carbon cloth (Al-MOF@CC) exhibits limited performance improvement due to poor electrical conductivity, low structure stability, as well as limited ion diffusion rate and weak Lewis acid-base interactions due to lack of open channels.

Desolvation Synergy of Multiple H/Li-Bonds on an Iron-Dextran-Based Catalyst Stimulates Lithium-Sulfur Cascade Catalysis.

Traditional lithium-sulfur battery catalysts are still facing substantial challenges in solving sulfur redox reactions, which involve multistep electron transfer and multiphase transformations. Here, inspired by the combination of iron dextran (INFeD) and ascorbic acid (VC) as a blood tonic for the treatment of anemia, a highly efficient VC@INFeD catalyst is developed in the sulfur cathode, accomplishing the desolvation and enrichment of high-concentration solvated lithium polysulfides at the cathode/electrolyte interface with the assistance of multiple H/Li-bonds and resolving subsequent sulfur transformations through gradient catalysis sites where the INFeD promotes long-chain lithium polysulfide conversions and VC accelerates short-chain lithium polysulfide conversions. Comprehensive characterizations reveal that the VC@INFeD can substantially reduce the energy barrier of each sulfur redox step, inhibit shuttle effects, and endow the lithium-sulfur battery with high sulfur utilization and superior cycling stability even under a high sulfur loading (5.2mg cm-2 ) and lean electrolyte (electrolyte/sulfur ratio, ≈7µL mg-1 ) condition.

Carbonized Bacterial Cellulose Decorated with ZIF-8 Derived Iron Single-Atom Catalyst Nanocages As a Cathode Host for Lithium-Sulfur Batteries

Li-S chemistry is regarded as promising next-generation battery technology. However, its complex redox process and long-chain lithium polysulfides shuttling are hindering the development of practical Li-S battery technology. Various electrocatalysts are being investigated to address the problem by expediting reaction kinetics. Here we report Fe single metal atom catalyst (Fe-SAC) used in the sulfur cathode of Li-S batteries.Fe-SAC is synthesized using a modified metal-organic framework (MOF)-based approach, in which the low vapor pressure Fe element substitutes Zn during pyrolysis of ZIF-8 to attain Fe-N4 moieties by being coordinated with four substitutional nitrogen atoms in the graphene lattice. A freestanding 3D structure with Fe-SAC-functionalized carbon nanocages linked by a carbon nanofiber network is applied as the sulfur cathode scaffold. Here the nanocages are derived from Fe-doped ZIF with Fe-N4 SAC moieties embedded on the inside and outside surfaces. The carbon nanofiber network is derived from the carbonization of bacterial cellulose.We report several methods for assessing Fe-SAC catalytic function on sulfide redox reactions for the prepared electrode in cells with lithium polysulfides electrolytes. Electrochemical studies compare the performance of the nanostructured electrodes with or without Fe-SAC to confirm the catalytic effects in improving the Li-S battery performance. Accordingly, the prepared composite cathode delivers a high initial capacity of 1338 mAh/g at 0.1C and excellent rate capability at 2C with a reversible capacity of 840 mAh/g.

Polysulfide Speciation in Li–S Battery Electrolyte via In-Operando Optical Imaging and Ex-Situ UV-vis Spectra Analysis

Lithium sulfur (Li–S) batteries have received significant attention as one of the energy storage systems with excellent prospects for emerging applications due to their high energy density and low-cost. However, there are fundamental challenges impeding the commercialization of Li–S batteries. Notorious among those challenges is the “polysulfide shuttle” consisting of the dissolution into the electrolyte solvent and subsequent crossover to the anode of long-chain lithium polysulfides. Sparingly solvating electrolytes have been exploited as an approach to reduce the dissolution of polysulfides and thereby the shuttle effect. Using an optical in operando lithium-sulfur cell and ex situ UV–vis spectroscopy, we elucidate the speciation of polysulfides in fully and sparingly solvating electrolytes for Li–S batteries. Extensive literature meta-analysis reveals that the most unambiguous effect of sparingly solvating solvent is in improving the coulombic efficiency of sulfur-cells. Experimental optical imaging and UV–vis characterization elucidate a shift towards shorter-chain polysulfides in electrolytes with increasing lithium-salt concentration (more sparingly solvating). The shift to shorter-chain polysulfides corresponds to a reduction of polysulfide species participating in shuttling which corroborate the increased coulombic efficiency in sparingly-solvating electrolytes.

Oxygen heteroatom enhanced sulfur-rich polymers synthesized by inverse vulcanization for high-performance lithium-sulfur batteries

Sulfur-rich polymers, synthesized through inverse vulcanization, with tunable heteroatom containing crosslinkers were investigated as the S-containing cathode active material within Li–S cells. The polymers possess up to 73% active sulfur while, importantly, not containing any unreacted, crystalline sulfur. Li–S-polymer cells achieve specific capacities of 1206 mAh gs−1 for an active material polymer containing 80 wt% sulfur, with 10 wt% of a structural crosslinker (dicyclopentadiene), and 10 wt% of an oxygen-containing crosslinker (ethylene glycol dimethacrylate). The high capacity achieved within this composition is associated with of this sample, in a higher average sulfur rank within the polymer structure. Furthermore, S-polymers with heteroatomic crosslinkers exhibited lower capacity fade (0.093% per cycle) compared with polymers without functionalized heteroatomic crosslinkers (0.165% per cycle) and elemental sulfur (0.312% per cycle). X-ray photoelectron spectroscopy showed the inherent binding between the ester group carbonyl oxygen within the crosslinker to the long-chain lithium polysulfides, which may inhibit dissolution of these intermediates.

Uniformly distributed 1T/2H-MoS2 nanosheets integrated by melamine foam-templated 3D graphene aerogels as efficient polysulfides trappers and catalysts in lithium-sulfur batteries

• MF-GA-MoS 2 composite acts as a new separator-modified material. • 1T/2H-MoS 2 nanosheets were integrated onto the 3D graphene aerogel using melamine foam as template. • GA framework acts a conductive network and physical barrier of LiPSs. • 1T/2H-MoS 2 nanosheets can produce strong chemossorption to LiPSs and promote their conversion to Li 2 S 2 /Li 2 S. Lithium-sulfur (Li-S) batteries are regarded as one of the next-generation batteries because of their low cost and higher energy density than Li-ion batteries. However, the rapid capacity fading due to the shuttling effect of long-chain lithium polysulfides (LiPSs) between electrodes and sluggish redox kinetics remain a big hindrance in practical applications. Herein, three-dimensional nitrogen-doped graphene aerogel (GA) with uniformly distributed and defect-rich 1T/2H-MoS 2 nanosheets has been developed by adding melamine foam (MF) as the hard template. The resultant MF-GA-MoS 2 composites have strong electron transfer capabilities and rich catalytic activity sites that can adsorb and catalyze the conversion of LiPSs to Li 2 S 2 /Li 2 S, thus reducing the shuttle effect to improve the performance of Li-S batteries. Li-S batteries with the defect-rich MF-GA-MoS 2 composites modified separator exhibit amazing initial discharge capacity of 1323 mAh g −1 at 0.2C, high ratio capacity of 718 mAh g −1 at 1C after 400 cycles, and low decay rate of 0.0485% per lap after 800 cycles at 3C. This work provides a novel strategy for the development of separator modified materials with high adsorption and catalytic properties in Li-S batteries.

Simultaneously Regulating the Band Gap and Catalytic Activity of TiO2 via Embedded MoO2 Based on Interlaced CNT Carrier for Li-S Battery to Achieve Efficient Adsorption

To tackle the issues of lithium sulfur battery (Li-S), a strategy of simultaneous regulating the band gap and catalytic activity of TiO2 via embedded MoO2 based on interlaced carbon nanotubes carrier as substrate material to achieve efficient adsorption has been proposed. This substrate material is controlled to be nanosized with abundant catalytically active sites and widely-distributed pore through the cross-linked porous conductive skeleton, further promoting the electrolyte penetration and charge transfer. In addition, the introduction of MoO2 tailors the Ti electronic states, so the substrate material renders high adsorption energy of −1.47 eV for Li2S6 by theoretical calculation. Furthermore, the cathode exhibits high conversion efficiency from long-chain lithium polysulfide to Li2S (Qlow/Qhigh (the conversion capacity of Li2S) is 2.91 at 0.1C) and excellent sulfur utilization and fast sulfur reaction kinetics. The cathode also exhibits a low-capacity fade and excellent cycling performance.

Effect of surface bonding PEI with electrospun carbon nanofiber on the dissolution of polysulfide intermediates for lithium-sulfur batteries

It is essential to examine the behavior of the dissolution and migration of long-chain lithium polysulfide (LiPS) intermediates (Li2Sx, 4 ≤ x ≤ 8) in the sulfur cathode to promote the performance of Li-S batteries. In this work, PEI functionalized electrospun carbon nanofibers (CNFs-PEI) were prepared to host sulfur to form carbon nanofibers polyethylenimine/sulfur (CNFs-PEI/S) composites for high performance Li-S batteries. The as-prepared CNFs-PEI/S cathode with a sulfur content of 67% delivers an initial discharge capacity of 1279 mAh g−1 at 0.1 C and retains a cycling stability for 80 cycles with a low capacity fading rate of 0.26% per cycle. Further, compared with CNFs/S, the CNFs-PEI/S revealed an enhanced rate capability and cyclic stability primarily attributed to the formation of the electrostatic interaction between amino groups in the PEI chains and LiPS intermediates, leading to suppression of LiPS dissolution and restraint of the shuttle effect during the charge-discharge cycling process. An in situ rotating ring-disk electrode (RRDE) collection experiment is designed to further examine the LiPS dissolution extent from a sulfur electrode during cycling. A maximum slope of ring current change with time (voltage) occurred at the major LiPS intermediate dissolution step over a voltage range between 2.4 and 2.0 V during disk negative scan (reduction). The CNFs-PEI/S showed a lower maximum slope value, which can be attributed to a lower dissolution of LiPS intermediates from the sulfur electrode. The present study also demonstrated the proposed simple RRDE experiment is a useful method to evaluate the dissolution properties of LiPS intermediates from various sulfur electrode materials.

Mn2O3 Incorporated Carbonized Bacterial Cellulose As Sulfur Host for Lithium-Sulfur Batteries

Early development and commercialization of lithium-ion batteries (LIBs) have enabled the portable electronic devices and powered the world. However, the ever-increasing demand for higher energy batteries have led to the quest for further improvement. Lithium-sulfur batteries (LSBs), with lithium anode and sulfur-based composite as cathode, have high theoretical specific energy of 2600 W h kg-1 (around 10 folds higher than LIBs system). Moreover, sulfur is produced as a by-product from petroleum refineries making research in LSBs more lucrative. However, there are a few critical challenges which restrict the commercialization of LSBs. First, insulating nature of sulfur (5 × 10-30 S cm-1) and lithium sulfide (Li2S, 10-13 S cm-1) impedes the electronic conductivity which results in low utilization of active sulfur. Secondly, the dissolution and diffusion of long-chain lithium polysulfides in electrolyte to lithium anode under concentration gradient causes series of severe issues such as loss of active sulfur, pulverization of lithium anode. Thirdly, the volume change during lithiation (up to 80%) results in degradation of cathode.To tackle aforementioned issues, we have utilized Mn2O3 incorporated carbonized bacterial cellulose (Mn2O3@CBC) as sulfur host for LSB. A facile melt-diffusion approach was adopted to encapsulate sulfur into Mn2O3@CBC matrix. The material was characterized using various physicochemical techniques - X-ray diffraction spectroscopy, Raman spectroscopy, Thermal gravimetric analysis, and Surface area analyzer. The Mn2O3@CBC system developed in this work offers the following benefits: (a) interconnected carbon nanofiber assembly which helps in fast diffusion of Li-ion and electrons; (b) porous morphology to accommodate volume change and to act as a reservoir for long-chain lithium polysulfides accumulation; (c) Mn2O3 as long-chain lithium polysulfide binding site and catalyst for conversion of long-chain lithium polysulfides to short-chain lithium polysulfides.To investigate the electrochemical property of the material, the performance is compared to bare sulfur and sulfur incorporated carbonized bacterial cellulose (S-CBC). Various electrochemical characterization such as cyclic voltammograms, galvanostatic charge-discharge, rate capability, long-term cycling was performed to investigate the performance of the materials. The material (S-Mn2O3@CBC) exhibited initial reversible capacity of 1150 mA h g-1 at 0.1C and retained 254.4 mA h g-1 at the extremely high current rate of 15C which is far ahead than the bare sulfur and S-CBC. Furthermore, the cycle life of LSB with low and high-sulfur loading was performed to further establish the advantage of using Mn2O3 as electro catalyst. Moreover, first-principles calculation was carried out to understand the functional mechanism for interaction of Mn2O3@CBC and intermediate lithium polysulfides. The excellent electrochemical performance substantiates that the S-Mn2O3@CBC is a good choice for cathode for LSBs. Figure 1

Liquid Metal as a Self-Healing and Polysulfide Trapping Binder for Lithium Sulfur Battery

Lithium sulfur battery (LSB) is one of the promising candidates as next generation energy storage technology due to its high energy density, low cost and environmental friendliness surpassing that of current lithium ion batteries (LIBS). However, LSBs still have some issues that need to be overcome before they can be used commercially. The major obstacle that limits their performance is the dissolution of long-chain lithium polysulfides into the electrolyte which leads to the loss of active material and the capacity decay during the charge/discharge cycles. In this work, we developed an innovative cathode design for LSB by mixing liquid metal (LM) nanoparticles with sulfur and a carbon cloth as a current collector. Because of its liquid nature, LM provides a strong encapsulation of the sulfur particles and prevents the detachment from the current collector albeit the large volume changes and cracking of the sulfur during lithiation and delithiation. Here, electrically conductive LM maintains an electron conduction path and mitigates the loss of active materials. In addition, it acts as a lithium polysulfide entrapment to prevent the shuttle effect and improves the Coulombic efficiency and extends the cycle lifetime. This combination of LM nanoparticles and carbon cloth results in good electrochemical performance and excellent capacity retention by providing high surface area, flexibility, ability to accommodate volume changes, and high electrical conductivity. Our results demonstrate an opportunity of the novel LSB electrode composite using multi-functional LM binder to improve the LSB performance and set a new direction towards the implementation to practical applications.

Decoration of carbon nanofibers with bimetal sulfides as interlayer for high performance lithium-sulfur battery

In order to obtain high-performance lithium-sulfur (Li-S) batteries, the rapid capacity loss caused by the notorious polysulfide shuttle effect is an urgent challenge to be solved. It is widely reported that polysulfides are trapped in electrolytes due to the strong chemisorption of polar materials in Li-S batteries. Here, a free-standing NiCo2S4 nanoparticles decorated carbon nanofibers (NiCo2S4-CNFs) interlayer is prepared via electrospinning and simple hydrothermal method for the application in Li-S batteries. Three-dimensional carbon fibers (CNFs) skeleton builds a highly conductive carbon network, which provides a large quantities of transmission paths for electrons and ions. Uniformly distributed NiCo2S4 nanoparticles act as an absorbent of the long-chain lithium polysulfides (LiPSs) and a catalyst to accelerate the conversion of sulfur species. Meticulous designed NiCo2S4-CNFs interlayer significantly improves the capacity retention rate and cycle stability of Li-S batteries. It supplies an initial specific capacity of 1421 mAh g−1 at 0.1 C, and its capacity remains at 918 mAh g−1 after 200 cycles at 0.2 C. Even at a high current density of 1 C, it still possesses a reversible specific capacity of 515 mAh g−1 after 500 cycles and extremely low capacity decay of 0.06% per cycle. More importantly, the NiCo2S4-CNFs interlayer still delivers excellent electrochemical performance with a higher sulfur loading of 4.5 mg cm−2, which verifies its huge commercial application potential.

In-situ fabrication of few-layered MoS2 wrapped on TiO2-decorated MXene as anode material for durable lithium-ion storage

Rational construction of hybrid materials integrating the collective virtues of individual building blocks has spurred significant interest in electrode materials for energy storage. Herein, a smart hybrid was fabricated via in-situ assembling of the few-layered MoS2 (f-MoS2) coated on the multi-layered Ti3C2 MXene decorated with the TiO2 nanoparticles by the scalable hydrothermal and annealing approaches. In the unique architecture, the multi-layered Ti3C2 with the expanded interspaces as the conductive backbone can facilitate the electron transport, provide adequate space to facilitate the infiltration of organic electrolyte into the interior of electrode, and inhibit the aggregation of MoS2 nanosheets, while the f-MoS2 with enlarged interlayer can be beneficial for the lithium-ion diffusion and prevent the multi-layered Ti3C2from restacking. Moreover, the TiO2 decorated on the Ti3C2 can effectively inhibit the instability of long-chain lithium polysulfides dissolved in organic electrolyte to improve the cycling stability. Thanks to the synergistic effect of the building blocks, the Ti3C2/TiO2@f-MoS2 hybrid employed as lithium storage anode delivers an extraordinary endurable ability with a high storage capacity of 403.1 mA h g−1 after 1200 cycles at 2 A g−1. Importantly, the smart hybridization strategy in this work paves an efficient way to explore the high-performance MXene-based hybrid materials in energy storage fields.

Non-Confinement Approach Towards Employing Carbonate-Based Electrolytes in Li-S Battery

Rechargeable lithium-sulfur (Li-S) batteries have received increasing attention due to the high theoretical capacity of sulfur cathodes (1675 mAh.g-1), abundance, environmental friendliness, low toxicity and low cost of elemental sulfur. The commercialization of this technology, however, relies heavily on tackling yet unsolved operational issues that hinder the practical energy density delivered by Li-S batteries, such as (i) low electrical conductivity of sulfur and lithium sulfide (Li2S), (ii) severe capacity fade due to shuttling of long-chain lithium polysulfides, and (iii) lithium dendrite growth. In addition, another major obstacle towards commercialization is use of ether-based electrolytes owing towards its high flammability slightly above room temperature.Carbonate-based electrolytes demonstrate safe and stable electrochemical performance in lithium ion batteries. Literature reports have demonstrated that sulfur can trigger substantial electrolyte decomposition due to formation of polysulfides to exhibit sudden battery failure. However, few types of cathodes with confinement of sulfur and cross-linking with polymer can be employed. However, higher sulfur loading, and improved conductivity of cathode still remains a prominent challenge in carbonate-based electrolyte. In this work, we have developed free-standing carbon nanofiber/S cathodes for achieving long-term cycling in Li-S batteries. The as-prepared CNF/S (1 – 5 mg.cm-2, ~50 wt% S) cathodes were used directly in 2032 type coin cells. The electrochemical tests were performed in EC:DEC based electrolyte against Li/Li+anode. The cyclic voltammetry and charge discharge results showed a single potential for conversion of sulfur to Li2S. The CNF/S cathodes delivered capacity of ~1300 mAh.g-1 during the first cycle with ~93% coulombic efficiency. The capacity of Li-S cells was stabilized at ~800 mAh.g-1 after Ist cycle and sustained up to 4000 cycles with only ~.01% decay rate per cycle. The postmortem XRD results confirmed the conversion of sulfur to Li2S and vice versa. Further, postmortem XPS analysis was conducted to understand the underlaying conversion mechanism. The preliminary results showed that the observed single plateau and long-term cycling of Li-S cells were the convoluted effect of deposited sulfur and digression from typical polysulfide formation route.

Implanting Cobalt Atom Clusters within Nitrogen-Doped Carbon Network as Highly Stable Cathode for Lithium-Sulfur Batteries.

Realization of highly efficient sulfur electrochemistry, as well as the high capacity of lithium-sulfur (Li-S) batteries, can be achieved by the scientific construction of electrode host materials. In this study, using molten NaCl, a 3D porous nitrogen-doped carbon with uniformly embedded Co atom clusters (Co/PNC) is developed by pyrolyzing the precursors with NaCl at high temperatures. In the composite structure, a network carbon skeleton containing hierarchical pores acts as an advanced matrix for sulfur electrodes, and the doping of N and Co is subject to inhibit the shuttle of long-chain lithium polysulfides through chemical adsorption. The Co/PNC, with the optimized amount of Co, delivers an initial specific capacity of 1105.4 mAh g-1 at 0.2 C with a capacity drop of only 0.064% after the cell is charged and discharged for 300 cycles at 1 C, revealing its potential in promoting the large-scale application of Li-S batteries.

The Failure Mechanism of Lithium-Sulfur Batteries under Lean-Ether-Electrolyte Conditions

With a superb ability to dissolve the long-chain lithium polysulfides (Li2S4−8, LPSs) intermediates and promote the conversion between sulfur (S) and lithium sulfide (Li2S), ether-based electrolytes have been widely employed in lithium-sulfur (Li-S) batteries. While for ether-based Li-S batteries, the low reaction barrier is only overserved under superfluous electrolyte conditions. Aiming to figure out how Li-S batteries work and fail under lean-ether-electrolyte conditions, herein, we carefully simulated the internal electrolyte environment and investigated the electrochemical behavior of the ether-based Li-S batteries under the different E/S ratios (1, 2, 3, 4, 6, and 10 μL mg−1). The physicochemical and electrochemical characterizations reveal that the dissolution of the long-chain LPSs intermediates in lean ether electrolytes significantly reduces the wettability and conductivity of the electrolytes, and consequently results in the increased internal contact and charge-transfer resistance of the cells, which are responsible for the failure of the Li-S batteries under lean-ether-electrolyte conditions. We also demonstrate that by replacing the ether electrolytes with a sparingly solvating electrolyte, the electrochemical performance of the lean-electrolyte Li-S batteries could be markedly improved, which directs the future development of the high-energy Li-S batteries.