Dissolution Of Polysulfides Research Articles

Wood-Based Cathodes for High-Performance Lithium-Sulfur Batteries

Lithium-ion batteries (LIBs) are dominant electrochemical energy storage systems in rapidly growing electronic markets. However, the conventional anode and cathode materials have limited specific capacity and quickly approach their theoretical limit. Hence, alternate battery chemistry beyond LIBs is required. Lithium-sulfur (Li-S) batteries are noteworthy energy storage systems due to their high theoretical capacity (1672 mAh/g), high theoretical energy density (2600 Wh/kg), and low cost of raw materials. Unfortunately, commercialization of Li-S batteries is hindered by the low electronic conductivity of sulfur and intermediate polysulfides, polysulfide dissolution and shuttle effect, volume expansion of elemental sulfur during the charge/discharge process, and lithium dendrite growth at the anode side. To address these challenges, various strategies such as modification of sulfur hosts, electrolyte optimization, and separator modifications have been employed. Initially, researchers encapsulated sulfur in various carbonaceous materials to mitigate the polysulfide shuttle. Later, a new active material, called sulfurized polyacrylonitrile (SPAN), was developed to mitigate the polysulfide shuttle and extend the life cycle of Li-S batteries. The main advantage of the SPAN over elemental sulfur is that it is more effective in mitigating polysulfide dissolution and shuttling due to the presence of the C−S bonds, consequently preventing the loss of active material. On the other hand, due to the limited number of binding sites in the SPAN structure, the sulfur content of SPAN materials is limited to 40 – 44 wt.%. To compete with the state-of-the-art LIBs, the Li-S batteries should provide an areal capacity of >5 mAh/cm2, corresponding to a sulfur loading of >5 mg/cm2. Realizing such a high S loading using 2D planar current collectors (e.g., aluminum foil) without compromising specific capacity and cycling stability is practically unrealistic. Using synthetic materials (e.g., graphene foam, graphene aerogel, metal-organic framework), three-dimensional (3D) electrode architectures with high SPAN loading and efficient electron and ion conductive pathways have been constructed. However, preparing these 3D electrodes mainly involves synthetic raw materials, harsh chemicals, and costly fabrication processes. Porous carbon frameworks derived from biomass, which are plant-based materials derived from nature, are alternative candidates. Biomass structures with interconnected channels over multiple length scales can provide a natural 3D template for electrochemical energy storage systems.In this study, we took advantage of the inherent porous structure of natural wood and engineered 3D frameworks using a delignification/low-temperature pyrolysis approach. A block of Balsa wood was sliced into thin sheets parallel to the tree growth direction. To facilitate the permeation of active material into the cellular structure, we first subjected the wood to a facile chemical treatment to remove lignin and hemicellulose. The delignified wood (DW) was then converted to an ultra-lightweight carbonized DW (CDW) scaffold using a low-temperature pyrolysis approach. To prepare CDW scaffolds, the DW sheets were pyrolyzed at 500, 600, 700, and 1000 °C. Continuous electron transport through the CDW conductive network and ion transport along the highly porous cellular body makes intrinsic and effective charge transfer through the CDW scaffold. SPAN active material was synthesized by pyrolyzing a mixture of elemental S and polyacrylonitrile under nitrogen flow and then using it to prepare an aqueous slurry of SPAN, CMC, and carbon black with a mass ratio of 70:15:15. To prepare the cathodes, CDWs were cut into squares with an area of 1.00 ± 0.05 cm2, dipped into a beaker of SPAN slurry, and kept under a vacuum. SPAN-impregnated free-standing electrodes (SPAN@CDW) were dried and utilized for electrochemical studies. The unique design of the SPAN@CDW electrode, wherein the interconnected pathways run in three-dimension, ensured effective electron and ion transport within the cathode. Thus, SPAN@CDW cathodes exhibited an excellent rate capability, with discharge capacities >1000 mAh/gs at 1C (1672 mA/g). The electrode with CDW pyrolyzed at 600 °C, and S loading of ~2 mg/cm2 exhibited a high specific capacity of ~1350 mAh/gs after 500 cycles at 0.1C, indicating good cycling stability. We also demonstrated the fabrication of SPAN@CDW electrodes with a high S loading of ~12.3 mg/cm2, which could deliver a high areal capacity of ~15.1 mAh/cm2 at 0.1C.

(Invited) Garnet Solid Electrolytes for Advanced All-Solid-State Li Metal Batteries

These days, Li metal anode-based battery has been arisen as one of the key energy storage technologies due to its high theoretical energy density compared to conventional lithium and sodium ion-based batteries. The present Li-S batteries suffer due to Li dendrite formation and capacity decay due to polysulfide dissolution effect, because of organic electrolytes used in the current research. Solid state (ceramic) electrolytes are promising to prevent Li dendrite growth and polysulfide dissolution. Among different ceramic electrolytes garnet-type structure solid inorganic electrolytes are very promising because of its high lithium-ion conductivity and stability with elemental Li. However, the high interfacial resistance with the electrode is the major bottleneck for the practical use of ceramic electrolyte. Polymer and ceramic hybrid electrolytes exhibit low interfacial resistance. In this talk, we will present development of electrolytes for all-solid-state Li metal batteries.

(Invited) Lithium – Sulfur Batteries

These days, Li-S battery has been arisen as one of the key energy storage technologies due to its high theoretical energy density compared to conventional lithium and sodium ion-based batteries. The present Li-S batteries suffer due to Li dendrite formation and capacity decay due to polysulfide dissolution effect, due to organic electrolytes used in the current research. Solid state (ceramic) electrolytes are promising to prevent Li dendrite growth and polysulfide dissolution. Among different ceramic electrolytes garnet-type structure solid inorganic electrolytes are very promising because of its high lithium-ion conductivity and stability with elemental Li. However, the high interfacial resistance with the electrode is the major bottleneck for the practical use of ceramic electrolyte. Polymer and ceramic hybrid electrolytes exhibit low interfacial resistance. In this talk, we will present development of novel hybrid electrolytes for all-solid-state Li-S batteries, along with new methods to produce S cathodes with minimal polysulfide shuttle effect.

Organosulfur Cathodes with High Compatibility in Carbonate Ester Electrolytes for Long Cycle Lithium–Sulfur Batteries

Lithium-sulfur batteries (LSBs) are potential candidates for high energy storage technologies due to their theoretical gravimetric energy density of ∼2600 Wh kg-1 and lightweight electrodes. In LSBs, ether electrolytes are frequently utilized because sulfur cathodes and the polysulfide redox intermediate species are chemically stable. However, LSBs in ether electrolytes suffer from the dissolution of higher-order polysulfides, and migration of the soluble polysulfides into electrolytes causes the polysulfide shuttle effect. The shuttle polysulfides react with the lithium anode and give rise to the irreversible deposition of lithium sulfides, deteriorate the morphology of the anode, and cause rapid capacity fading. Moreover, ether electrolytes are highly flammable and trigger safety issues. As an alternative, carbonate ester electrolytes are promising choices to substitute ether electrolytes in LSBs. Organic carbonate electrolytes used in LSBs result in irreversible reactions with long-chain polysulfide anions that cause the cell to shut down. Therefore, carbonate ester electrolytes compatible sulfur cathodes design needs special attention. Sulfurized polyacrylonitrile (SPAN) and short-chain sulfur cathodes are compatible with organic carbonate electrolytes. However, the sulfur contents in these cathodes are mostly below 50 wt% which hamper the practical application of the LSBs. Here, we designed an organosulfur cathode with a high chemical bonded sulfur content of ~58 wt% in the cathode composite. The prepared organosulfur cathode showed excellent compatibility with carbonate ester electrolytes. The organosulfur cathode exhibits a high initial discharge capacity of 1301 mAh g-1 and long cycle stability for 400 cycles with nearly 99.99% coulombic efficiency.

Synthesis of hollow S/FeS2@carbon nanotubes microspheres and their long-term cycling performances as cathode material for lithium-sulfur batteries

• The dissolution of lithium polysulfides is effectively alleviated. • CNTs improve the conductivity of S/FeS 2 @CNTs composites. • Low capacity decay rate of 0.024% per cycle for over 500 cycles is obtained. The lithium-sulfur batteries as a promising next-generation rechargeable battery are practically limited by their poor long-term cycling performance originating from the dissolution of lithium polysulfides. Combining physical and chemical interactions to trap lithium polysulfides is an effective way to improve the long-term cycling performance. Herein we have synthesized the hollow S/FeS 2 @Carbon nanotubes (S/FeS 2 @CNTs) microspheres by loading sulfur into FeS 2 @CNTs microspheres with carbon nanotubes entangling hollow FeS 2 microspheres. The hollow S/FeS 2 @CNTs microspheres working as cathode for lithium-sulfur batteries have delivered initial discharge capacity of 1245 mA h g −1 at 0.2 C. Particularly, the long-term cycling performance has been achieved that the capacity beyond 440.2 mA h g -1 can maintain for 500 cycles at 1 C, with a low capacity decay rate of 0.024 % per cycle. The significantly improved cycling performance of S/FeS 2 @CNTs can be attributed to the synergistic effects that the dissolution of lithium polysulfides diminishes by combining the physical interaction of CNTs with chemical absorption of FeS 2 , as well as the volume expansion of the cathode can be alleviated by the internal void space.

Enhanced High-Rate Capability and Long Cycle Stability of FeS@NCG Nanofibers for Sodium-Ion Battery Anodes.

The development of advanced hierarchical anode materials has recently become essential to achieving high-performance sodium-ion batteries. Herein, we developed a facile and cost-effective scheme for synthesizing graphene-wrapped, nitrogen-rich carbon-coated iron sulfide nanofibers (FeS@NCG) as an anode for SIBs. The designed FeS@NCG can provide a significant reversible capacity of 748.5 mAh g-1 at 0.3 A g-1 for 50 cycles and approximately 3.9-fold higher electrochemical performance than its oxide analog (Fe2O3@NCG, 192.7 mAh g-1 at 0.3 A g-1 for 50 cycles). The sulfur- and nitrogen-rich multilayer package structure facilitates efficient suppression of the porous FeS volume expansion during the sodiation process, enabling a long cycle life. The intimate contact between graphene and porous carbon-coated FeS nanofibers offers strong structural barriers associated with charge-transfer pathways during sodium insertion/extraction. It also reduces the dissolution of polysulfides, enabling efficient sodium storage with superior stable kinetics. Furthermore, outstanding capacity retention of 535 mAh g-1 at 5 A g-1 is achieved over 1010 cycles. The FeS@NCG also exhibited a specific capacity of 640 mAh g-1 with a Coulombic efficiency of above 99.8% at 5 A g-1 at 80 °C, indicating its development prospects in high-performance SIB applications.

A multifunctional separator based on dilithium tetraaminophthalocyanine self-assembled on rGO with improved cathode and anode performance in Li–S batteries

Li–S batteries are strong candidates for next-generation energy-storage applications. However, practical cells face critical challenges including the dissolution and shuttling of polysulfides on the cathode as well as the uncontrolled dendrite growth and degradation of the anode. Herein, we demonstrate a multifunctional separator based on dilithium tetraaminophthalocyanine (Li2TaPc) self-assembled on rGO that exhibits a comprehensive regulation effect on important ion transport properties to address the above issues in one configuration. Li2TaPc presents strong sulfiphilic/lithiophilic binding sites for the confinement of polysulfides within the cathode region to improve sulfur utilization. Charge transfers from the central cavity of the TaPc ligand to the rGO promotes the dissociation of Li+ cations to produce additional charge carriers. The negatively-charged TaPc ligand exhibits strong electrostatic repulsions to the salt anions and hinders their migration across the separator. The apparently increased Li+ transference number (0.41–0.89) suppresses dendrite formation and improves the reversibility of the Li anode. Meanwhile, the strong coordination effects of Li+ with Li2TaPc enable a high retention of Li + conductivity. The comprehensive functionalities of the separator result in significantly improved electrochemical performance of Li–S full cells. Pouch cells with a high areal sulfur loading and limited electrolyte addition are also demonstrated.

Simple and scalable gelatin-mediated synthesis of a novel iron sulfide/graphitic carbon nanoarchitecture for sustainable sodium-ion storage

Transition metal sulfide (TMS)-based sodium-ion batteries (SIBs) are inherently different from traditional intercalation-based ones because of their ability to store more than one Na+ per transition metal ion via conversion reaction. Iron sulfide (FeS) is an attractive conversion electrode material with a high theoretical capacity. Apart from the extensive availability and cost-effectiveness, many issues deter the development of iron sulfide-based SIBs. Huge volume changes accompanied by polysulfide generation and dissolution with long-term electrochemical cycling of FeS result in tremendous deterioration in capacity. To resolve these complex concerns, we herein present the strategic design of a porous, three-dimensional (3D) interconnected network of carbon nanosheets consisting of well-confined FeS nanoparticles via a simple and scalable gelatin-mediated sol-gel method utilizing the coordination capability of carboxylic and amino acid groups in biomass precursor gelatin with Fe3+. While the in-situ generated nano FeS shortens the Na+ diffusion pathway, the heteroatom (N, S) doped graphitic carbon network improves the ion/electron transport, buffers the volume change in FeS, and simultaneously immobilizes the polysulfide species dissolved in ether electrolyte. The as-synthesized novel composite delivers a high specific capacity of 303.4 mAh g−1 after 1200 cycles at a high current rate of 10 A g−1, with a low capacity-decay rate of 0.029% per cycle, delivering stable, long-term sodium-ion storage. Additionally, a full sodium-ion battery assembled with Na3V2(PO4)3 cathode and this composite achieve a stable specific capacity of 347.9 mAh g−1 after 100 cycles at 0.5 A g−1 with a capacity retention of ∼86.5% demonstrating the competence for practical applications.

High‐Energy and Long‐Lifespan Potassium–Sulfur Batteries Enabled by Concentrated Electrolyte

AbstractPotassium–sulfur (K–S) batteries are emerging as low‐cost and high‐capacity energy‐storage technology. However, conventional K–S batteries suffer from two critical issues that have not yet been successfully resolved: the dissolution of potassium polysulfides (KPS) into the liquid electrolyte and the formation of K dendrites on the K metal anode, which lead to inadequate cycling efficiencies with a low reversible capacity. Herein, a high‐capacity and long cycle‐life K–S battery consisting of a highly concentrated electrolyte (HCE) (4.34 mol kg−1 potassium bis(fluorosulfonyl)imide in a 1,2‐Dimethoxyethane) and a sulfurized polyacrylonitrile (SPAN) cathode is presented The application of a HCE efficiently suppresses the dendritic growth of K, as evidenced by operando optical imaging and phase field modeling, owing to the reduced K‐ion depletion on the electrode surface and a uniform Faradaic current density over the K metal anode surface. Additionally, because S is covalently bonded to the C backbone of PAN in the SPAN structure, the SPAN cathode inhibits the dissolution of KPS. These features generate synergy that the proposed K–S battery can provide a practical areal capacity of 2.5 mAh cm−2 and unprecedented lifetimes with high Coulombic efficiencies over 700 cycles.

Hierarchically porous carbon nanofiber binder-free electrode for high-performance lithium–sulfur batteries

It is still a challenge for lithium–sulfur (Li-S) batteries to possess high sulfur utilization and excellent electrochemical performances due to the low electrical conductivity and dissolution of polysulfides. To resolve these issues, a free-standing sulfur host composed of hierarchically porous carbon nanofibers (HPCNFs) has been synthesized via electrospinning technology. The HPCNFs with an interconnected and porous structure can facilitate electron transfer and electrolyte penetration. The mesopores in HPCNFs can provide high levels of sulfur loading, and the micropores can inhibit shuttle effects of the sulfur cathode during discharge and charge processes. After encapsulating a high mass of sulfur (76.4 wt%, HPCNFs@S), the electrode was directly applied as a cathode for the Li-S battery, which exhibited a high specific discharge capacity of 1,145 mA h g−1 at 0.1 C (1 C = 1,675 mA g−1) and maintained 787 mA h g−1 after 150 charge/discharge cycles. This work provides a new insight into optimizing the electrochemical performance of Li-S batteries.

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.

Wide-Temperature-Range Li-S Batteries Enabled by Thiodimolybdate [Mo2S12]2- as a Dual-Function Molecular Catalyst for Polysulfide Redox and Lithium Intercalation.

In lithium-sulfur batteries, a serious obstacle is the dissolution and diffusion of long-chain polysulfides, resulting in rapid capacity decay and low Coulombic efficiency. At present, a common practice is designing cathode materials to solve this problem, but this gives rise to reduced gravimetric and volumetric energy densities. Herein, we present a thiodimolybdate [Mo2S12]2- cluster as sulfur host material that can effectively confine the shuttling of polysulfides and contribute its own capacity in Li-S cells. Moreover, the [Mo2S12]2- cluster as a "bidirectional catalyst" can effectively catalyze polysulfide reduction and lithium sulfide oxidation. We further investigate the catalytic mechanism of [Mo2S12]2- clusters by theoretical calculations, in situ spectroscopic techniques, and electrochemical studies. The (NH4)2Mo2S12/S cathodes show good electrochemical performance under a wide range of temperatures. In addition, a pouch cell fabricated with (NH4)2Mo2S12/S cathodes maintains a stable output for more than 50 cycles.

Bioconfined SnS2N-doped carbon fibers with multiwall robust structure for boosting sodium storage

The development of biosynthetic materials is a front research area that offers significant possibility to design electrode materials with improved performance for energy storage. Here, we demonstrate a dual-carbon layer strategy for constructing SnS2 composite electrode material, where nitrogen doped carbon fibers derived from fungus and PDA carbon layer function as confined template and reinforced layer, respectively (C@SnS2@NCFs). When used as the anode material for the sodium ion battery, the C@SnS2@NCFs electrode exhibits good cycle stability of 382 mAh g-1 after 100 cycles at 0.1 A g-1 and rate performance of 158 mAh g-1 at 10 A g-1. Such good performances are benefited from the dual-carbon structure, which greatly restricts the expansion of the SnS2 crystal and the dissolution of polysulfide during the cycle and ensures the stability of the electrode structure.

Graphene oxide/Cu(OH)2 composites as efficient multifunctional hosts for lithium-sulfur batteries

Lithium-sulfur batteries are advanced energy storage system with high theoretical specific capacity and low cost but suffer from poor cyclic performance. To overcome the shortcomings, this study synthesized graphene oxide (GO)/Cu(OH)2 composites using the modified Hummers method and electrostatic self-assembly process. The sulfur was anchored in the GO/Cu(OH)2 composites using the melting method. The oxygen-containing function groups of GO are helpful for achieving good ion/electron accessibility, and the interlayers of GO have many active sites for polysulfide conversion. The polar hydrophilic hydroxyl group of Cu(OH)2 particles have strong chemisorption for polysulfides during the electrochemical process. Therefore, the synergistic effect of GO and Cu(OH)2 in the composites as sulfur hosts can inhibit the dissolution and shuttling of polysulfides. The lithium-sulfur batteries with GO/Cu(OH)2 composites as hosts have high capacity of 1427 mAh g−1 at 0.1 C, 1222 mAh g−1 at 0.5 C, and excellent cyclic performance for 250 cycles with a retained capacity of 929 mAh g−1 (0.5 C).

Visualization of polysulfide dissolution in lithium-sulfur batteries using in-situ NMR microimaging

Lithium-sulfur batteries offer the highest theoretical energy density among enclosed rechargeable batteries. However, there are various issues that need to be addressed before their practical adoption, such as the dissolution of intermediate lithium polysulfides (Li2Sn) into the electrolyte solution, which causes rapid degradation of the battery. Herein, we used nuclear magnetic resonance (NMR) and in-situmagnetic resonance imaging (MRI) to visualize the dissolution of the intermediate species formed during the discharge–charge process in Li-S batteries. A strong enhancement in the MRI signal was observed when the cell was first discharged, which is associated with the dissolution of intermediate polysulfides. To determine the origin of this signal enhancement, 1H NMR spectra, T1 relaxation time, and electron spin resonance (ESR) measurements were performed on electrolyte containing polysulfides. The origin of the strong enhancement of the MRI signal by the dissoluted polysulfides is mainly attributed to the paramagnetic interaction due to the formation of S3*- and S4*- radicals in the dissoluted polysulfides. The results demonstrate that 1H MRI is an indirect and effective way to study and visualize the intermediate species formed during Li-S battery operation.

Changes in structure and stability of lithium polysulfides encapsulated in carbon nanotubes: A DFT study

• Carbon nanotubes (CNTs) can act as possible anchoring channels to immobilize soluble lithium polysulfides. • The interior of CNTs can accommodate lithium polysulfides and suppress the shuttling effect. • Electrostatic interactions between CNTs and lithium polysulfides are responsible for the stability of these complexes. • Confinement of lithium polysulfides inside CNT weakens the bonding between Li and S. • Incarceration inside CNT destabilizes the Li 2 S molecule and helps in the conversion kinetics. Lithium-sulfur (Li S) batteries are emanating as the next generation alternatives for rechargeable batteries. However, the loss of capacity and self-discharge due to the dissolution of lithium polysulfides hinders their practical applications. In this study, we performed density functional theory simulations to explore the importance of carbon nanotubes (CNTs) as possible anchoring channels to immobilize soluble lithium polysulfides (Li 2 S 2n , where n = 2,3, and 4). We quantitatively investigated the interplay between confinement effects and interaction energy of Li 2 S 2n species with CNT to address the shuttling effect. Our results demonstrate that the interaction between CNTs and lithium polysulfides is governed by electrostatic interactions. Based on the interaction energies, Charge transfer analysis, and density of states, we found that CNTs facilitate the immobilization of Li 2 S 2n . Results obtained from this study will provide useful guidelines to improve the performance of Li S batteries.

Fabrication of Cubic and Porous Carbon Cages with In-Situ-Grown Carbon Nanotube Networks and Cobalt Phosphide for High-Capacity and Stable Lithium–Sulfur Batteries

Lithium–sulfur (Li–S) batteries have attracted considerable attention due to their high specific capacity, low cost, and eco-friendly raw material. However, the insulating property of sulfur and dissolution of lithium polysulfides (LiPSs) lead to rapid capacity decay and low Coulombic efficiency. In this work, we smartly synthesized a composite material as the host material of active S by a facile one-step pyrolysis method. It was composed of in-situ-grown carbon nanotubes (CNTs) and CoP particles inside the porous carbon cages (denoted as CoP-CNT@C). The CNT networks in porous carbon cages can improve the conductivity of the cathode, while the CoP particles are capable of enhancing the adsorption of LiPSs, thereby effectively mitigating the “shuttle effect”. Moreover, the porous structure of the carbon cages could effectively store the elemental sulfur. As a matter of fact, the Li–S battery based on the CoP-CNT@C/S cathode exhibited an ultrahigh initial specific capacity of 1456.8 mAh g–1 at 0.1C and superior performance (663.3 mAh g–1) at a high current rate of 3C. It is worth mentioning that a capacity of 473.9 mAh g–1 has been retained after 750 cycles tested at 0.5C, indicating the outstanding stability of the Li–S battery based on the CoP-CNT@C/S cathode. Overall, the CoP-CNT@C composite prepared is promising for the application of Li–S batteries as the host material.

Synergistic Restriction to Polysulfides by a Carbon Nanotube/Manganese Sulfide-Decorated Separator for Advanced Lithium–Sulfur Batteries

Polysulfide dissolution and shuttling limit the capacity output and cycle life of lithium–sulfur batteries to a great extent. Separator modification using polar materials exploiting the ability to entrap polysulfides has been demonstrated as an effective approach to deal with the conundrum of polysulfide shuttling. Herein, a carbon nanotube/manganese sulfide nanocomposite is designed as a separator modifier in lithium–sulfur batteries for the first time. Furthermore, the carbon nanotube network provides a continuous network for rapid electronic conduction, imparts structural stability, and acts as a secondary barrier for polysulfides. Consequently, the cell displays an initial discharge capacity of 876 mAh g–1 at 0.5 C and sustains excellent stability with a retained capacity of 76% after 500 cycles. The self-discharge of the cell is also conspicuously reduced, maintaining a constant voltage for 100 h under open-circuit conditions. The electrochemical results represent an effective strategy to realize better performing Li–S batteries.

V2O5 plates anchored in CNTS composite materials with a network structure as polysulfide capture for lithium–sulfur battery

Lithium-sulfur batteries (Li–S) are one of the future battery systems due to environmental friendliness and high theoretical specific capacity. However, the commercial development of Li–S battery faces numerous challenges, including the back-and-forth shuttle of long-chain polysulfides and the insulating properties of sulfur. To address these difficulties, we here prepared a carbon nanotubes/V2O5 plates/S (CNTs/V2O5/S) material as the host material. The CNTs can serve as a conductive network that speeds up the sulfur reaction rate. In addition, the polar V2O5 plates can effectively hinder the dissolution of polysulfides. The specific capacity of the CNTs/V2O5/S electrode was 709.9 mAh/g−1 at 0.1C, and the capacity retention rate was 72.6% over 100 cycles. After 500 cycles, the capacity retention efficiency is 71.7% and the decay rate is 0.056% at 1C. As-prepared CNTs/V2O5 composites, on the one hand, CNTs can enhance electron transport. On the other hand, the polar V2O5 plates block polysulfide diffusion. This provides a novel route for manufacturing Li–S batteries.

FeS2 Nanoparticles Encapsulated in S/N Co-Doped Carbon Nanofibers With a Three-Dimensional Multi-Channel Structure for Lithium-Ion Batteries.

Pyrite (FeS2) is one of the potential candidates for advanced rechargeable Li-ion batteries (LIBs) owing to its inherent capacity (849 mAh g-1), environmental friendliness, and abundant natural resources. However, the volume expansion of FeS2 and the dissolution of polysulfide in the electrochemical reaction severely limit its application in the field of energy conversion and storage. Herein, FeS2 nanoparticles are encapsulated in S/N co-doped three-dimensional multi-channel structural carbon nanofibers (FeS2@CNFs) through the electrospinning method. As a cathode material for LIBs, FeS2@CNFs demonstrated excellent rate property and cyclic stability. The 3FeS2@CNFs (weight ratio of FeS2 is 30%) present the initial capacity of 1,336.7mAh g-1 and the remaining 856.5 mAh g-1 at 0.02Ag-1 after 100 circles. The favorable electrochemical properties have confirmed that carbon nanofibers can enhance the electroconductivity of electrodes, reduce the volume collapse of FeS2, and remit the dissolution of polysulfide during the Li+ ions insertion/de-insertion process. In addition, co-doped S/N can supply abundant active sites for electrochemical reactions, providing enough space for Li+ ion storage. The results indicate that 3FeS2@CNFs is a cathode with a developmental prospect for LIBs.