Improving the Performance of Lithium-Sulfur Batteries by Employing Polyimide Particles as Hosting Matrixes

Viologen-based ionic conjugated mesoporous polymer as the electron conveyer for efficient polysulfide trapping and conversion

The commercialization of lithium-sulfur (Li-S) batteries has been hindered by the shuttle effect and sluggish redox kinetics of lithium polysulfides (LiPSs). Herein, we reported a viologen-based ionic conjugated mesoporous polymer (TpV-Cl), which acts as the cathode host for modifying Li-S batteries. The viologen component serves as a reversible electron conveyer, leading to a comprehensive enhancement in the adsorption of polysulfides and improved conversion rate of polysulfides during the electrochemical process. As a result, the S@TpV-PS cathode exhibits outstanding cycling performance, achieving 300 cycles at 2.0 C (1 C = 1675 mA g-1) with low decay rate of 0.032% per cycle. Even at a high sulfur loading of 4.0 mg cm-2, S@TpV-PS shows excellent cycling stability with a Coulombic efficiency of up to 98%. These results highlight the significant potential of S@TpV-PS in developing high-performance Li-S batteries.

Phenyl Tellurosulfides as Cathode Materials for Rechargeable Lithium Batteries

Phenyl ditelluride (PDTe) as a cathode material for rechargeable batteries has a low specific capacity (130.9 mAh g-1) due to limited active sites (two). To increase its capacity, additional active species need to be added to the structure of PDTe, like sulfur. Here, phenyl tellurosulfide (PDTeS) and phenyl tellurodisulfide (PDTeS2) can be formed via addition reactions and have specific capacities of 242.8 and 339.6 mAh g-1, respectively. The products are characterized by mass spectrometry and Raman spectroscopy. The Li/PDTeSn (n = 1-2) cells exhibit high material utilization (>85%) and unique redox mechanism. They can be cycled stably for more than 1000 cycles at an areal mass loading of 1.1 mg cm-2 and maintain capacity retentions of >72% after 100 cycles with PDTeSn loading of ∼6 mg cm-2. Moreover, the Li/PDTeS2 cell achieves a specific energy of up to 695 Wh kg-1 even when the electrolyte/PDTeS2 ratio is as low as 2.5 μL mg-1. The successful synthesis and application of PDTeSn prove that they are promising cathode materials for rechargeable lithium batteries.

Multichalcogen-Integrated Cathodes for Novel Lithium-Chalcogenide Batteries in Ether and Ester Electrolytes

Lithium-sulfur (Li-S) batteries and lithium-selenium (Li-Se) batteries that contain only one single active element have unique advantages and disadvantages. Inspired by ternary lithium batteries, multielement chalcogenide compounds with integrated advantages may improve upon the performance of lithium-chalcogenide batteries at the source. In this work, activated carbon (AC) with an Al₂O₃@SiO₂ heterojunction is used as the carrier, and the performances and mechanisms of elemental substances (X/AC, X = S, Se, and Te) are studied in ether and ester electrolytes as the basis for preparing multielement chalcogenide composites (SST/AC, SST: S-Se-Te compound). In the ester electrolyte system, SST811/AC (where S/Se/Te = 8:1:1, molar ratio) exhibited the best cycling performance, and the capacity remained at 1024.9 mA h g^-1 after 300 cycles. The characterization results revealed the mechanisms and sequences of the gradual liquid-phase reactions of SST/AC in ether electrolytes and the direct solid-phase reactions in ester electrolytes. The active elements in SST/AC fully demonstrated their own functions, enabling the effective construction of new lithium-chalcogenide battery systems. This work provides inspiration for the subsequent research of multielement lithium-chalcogenide batteries and paves the way for their application.

Polymers in Lithium-Sulfur Batteries

Lithium-sulfur batteries (LSBs) hold great promise as one of the next-generation power supplies for portable electronics and electric vehicles due to their ultrahigh energy density, cost effectiveness, and environmental benignity. However, their practical application has been impeded owing to the electronic insulation of sulfur and its intermediates, serious shuttle effect, large volume variation, and uncontrollable formation of lithium dendrites. Over the past decades, many pioneering strategies have been developed to address these issues via improving electrodes, electrolytes, separators and binders. Remarkably, polymers can be readily applied to all these aspects due to their structural designability, functional versatility, superior chemical stability and processability. Moreover, their lightweight and rich resource characteristics enable the production of LSBs with high-volume energy density at low cost. Surprisingly, there have been few reviews on development of polymers in LSBs. Herein, breakthroughs and future perspectives of emerging polymers in LSBs are scrutinized. Significant attention is centered on recent implementation of polymers in each component of LSBs with an emphasis on intrinsic mechanisms underlying their specific functions. The review offers a comprehensive overview of state-of-the-art polymers for LSBs, provides in-depth insights into addressing key challenges, and affords important resources for researchers working on electrochemical energy systems.

The Electrostatic Attraction and Catalytic Effect Enabled by Ionic-Covalent Organic Nanosheets on MXene for Separator Modification of Lithium-Sulfur Batteries

It is of great significance to mediate the redox kinetics and shuttle effect of polysulfides in pursuit of high-energy-density and long-life lithium-sulfur (Li-S) batteries. Herein, a new strategy is proposed based on the electrostatic attraction and catalytic effect of polysulfides for the modification of the polypropylene (PP) separator. Guanidinium-based ionic-covalent organic nanosheets (iCON) on the surface of Ti₃ C₂ is presented as a coating layer for the PP separator. The synergetic effects of Ti₃ C₂ and iCON provide new platforms to suppress the shuttle effect of polysulfides, expedite the redox kinetics of sulfur species, and promote efficient conversion of the intercepted polysulfides. The functional separator endows carbon nanotube/sulfur cathodes with excellent electrochemical performance. The average capacity decay per cycle within 2000 cycles at 2 C is as low as 0.006%. The separator is even effective in the case of sulfur content of 90 wt% and sulfur loading of 7.6 mg cm^-2 ; the reversible capacity, areal capacity, and volumetric capacity at 0.1 C are as high as 1186 mA h g^-1 , 9.01 mA h cm^-2 , and 1201 mA h cm^-3 , respectively. This work provides a promising approach toward separator modification for the development of high-performance Li-S batteries.

Recent advances in cathode engineering to enable reversible room-temperature aluminium-sulfur batteries

The rigorous requirements, such as high abundance, cost-effectiveness, and increased storage capacities, pose severe challenges to the existing Li-ion batteries' long-term sustainability. Room-temperature aluminum-sulfur (Al-S) chemistry, in particular, is gaining importance due to its high theoretical energy density (1700 W h kg^-1). Al-S battery technology is one of the emerging metal-sulfur candidates that can surpass current Li-ion chemistries. When coupled with sulfur, aluminum metal brings a cheap and energy-rich option to existing battery technologies. Owing to the unique virtues of the Al-S battery, it has garnered increasing interest among scientific communities. Al-S chemistry has been investigated for quite some time, yet the cell performance remained in its infancy, which poses a challenge to this technology's viability. Besides stabilizing the Al metal anode, the most important challenge in the practical development of Al-S batteries is the development of a suitable sulfur cathode material. Owing to the complexity of this multivalent system, numerous factors have been taken into account, but the best sulfur cathode is yet to be identified. A detailed exploration of sulfur cathodes and their implications on the battery performance are discussed in this mini-review article. We present a detailed picture of cathode materials that may serve as the reference guide for developing more practical cathode materials. Also, fundamental principles and challenges encountered in the development of the sulfur cathodes are highlighted. Through the knowledge disseminated in this mini-review, the development in the multivalent post-Li-ion battery can be accelerated. A glimpse of the future outlook on the Al-S battery system with different potential solutions is also discussed.

Anodized Aluminum Oxide Separators with Aligned Channels for High-Performance Li-S Batteries

Lithium-sulfur (Li-S) batteries are promising to enable high-energy-density storage systems; however, their commercialization is hampered by several technical challenges such as polysulfide shuttle and safety issues related to the lithium metal anode. Herein, we use anodized aluminum oxide (AAO) membranes as separators in Li-S batteries for the first time. AAO membranes are rigid and nonflammable, which is helpful for improving battery safety. The aligned and uniform channels within AAO membranes provide fast pathways for lithium ion transport, leading to low areal specific resistance due to the electroosmotic flow of lithium ions in nanoscaled channels. In addition, the AAO separator leads to low overpotential during lithium deposition/stripping in lithium symmetric cells. The Li-S cells with AAO separators show better cycling performance than those with Celgard ones, in particular, at high C rates. At the 2 C rate, the cell shows a battery performance of 480 cycles with a capacity degradation rate of 0.105%, which is much better than that when the Celgard separator is used. This work demonstrates that AAO membranes are promising separators with unique properties for improving the performance of Li-S batteries.

Graphdiyne-Modified Polyimide Separator: A Polysulfide-Immobilizing Net Hinders the Shuttling of Polysulfides in Lithium-Sulfur Battery

Graphdiyne (GDY), a new type of carbon material with an electron-rich conjugated structure, has been investigated as a separator coating layer to enhance the electrochemical performance of lithium-sulfur (Li-S) battery. Acetylenic bond (-C≡C-C≡C-) and benzene ring in the GDY coating layer are experimentally verified to reversibly attract the soluble lithium polysulfides by chemical adsorption during cycling. Meanwhile, the shuttle effect of soluble polysulfides is further physically restricted by the GDY coating layer due to the evenly distributed pores (5.42 Å) and a consistent interlayer spacing (3.65 Å) of GDY. Moreover, GDY is a conducting carbon skeleton with high Li⁺ mobility that can improve the rate performance. Hence, Li-S battery with an as-prepared GDY coating layer shows excellent electrochemical performances including superior specific capacity, excellent rate performance, and low capacity attenuation rate. The high initial discharge capacity of 1648.5 mA h g^-1 at 0.1C and 819.5 mA h g^-1 even at a high rate of 2C is achieved by this novel separator. The initial capacity of 1112.9 mA h g^-1 at 0.5C is retained to 816.7 mA h g^-1 after 200 cycles with a low attenuation rate of 0.13% per cycle. Compared with other coated separators, these results show that the GDY coating layer endows the separator with superior electrochemical performances for Li-S battery.

Electrochemical Performance of Sb4O5Cl2 as a New Anode Material in Aqueous Chloride-Ion Battery

Chloride-ion battery is considered as the promising electrochemical system due to its high energy density in theory. However, aqueous chloride-ion redox materials are limitedly reported owing to their instability or dissolution in aqueous electrolyte. Here, we synthetize a new electrochemical chloride-ion material, Sb₄O₅Cl₂, investigate its electrochemical performance in aqueous NaCl electrolyte, and assemble into aqueous chloride-ion battery with silver as cathode. During the battery charge process, Sb₄O₅Cl₂ anode electrochemically releases chloride ions, which are captured by Ag cathode with the formation of silver chloride while the discharging reverses the process. The battery demonstrates favorable electrochemical performance. With current density of 600 mA g^-1, the battery discharge capacity of 34.6 mAh g^-1 can be maintained for 50 cycles. This work is greatly significant for the development of anion electrochemical energy storage.

Sulfur in Hyper-cross-linked Porous Polymer as Cathode in Lithium-Sulfur Batteries with Enhanced Electrochemical Properties

Sulfur was impregnated into hyper-cross-linked porous polymer (HCP) with a high specific area and unique porous structure. Compared to its inorganic or carbon counterparts, the HCP has a relatively high specific surface area of 1980 m² g^-1 with a total pore volume of 2.61 cm³ g^-1, resulting in sulfur content in HCP/S of as high as 80 wt %. As a benefit of the unique HCP structure, the HCP/S composite exhibits a high initial discharge specific capacity (1333 mA h g^-1 at 0.2 C), high-rate property, and good cycling stability (658 mA h g^-1 after 120 cycles at 0.5 C and 604 mA h g^-1 after 80 cycles at 1 C). Furthermore, the capacity of cells loses less than 1% after the first 20 charge/discharge cycles, while the HCP/S cathode can be cycled with an excellent Coulombic efficiency of above 94% after 120 cycles. Compared with pristine sulfur, the superior electrochemical performance of HCP/S composite is related to the cross-linked porous framework. Such structure could provide short ionic/electronic conduction pathways and suppress the polysulfide shuttle during the discharge process.

Electrostatic Polysulfides Confinement to Inhibit Redox Shuttle Process in the Lithium Sulfur Batteries

Cationic polymer can capture polysulfide ions and inhibit polysulfide shuttle effect in lithium sulfur (Li-S) rechargeable batteries, enhancing the Li-S battery cycling performance. The cationic poly[bis(2-chloroethyl) ether-alt-1,3-bis[3-(dimethylamino) propyl]urea] quaternized (PQ) with a high density quaternary ammonium cations can trap the lithium polysulfide through the electrostatic attraction between positively charged quaternary ammonium (R₄N⁺) and negatively charged polysulfide (S_x^2-). PQ binder based sulfur electrodes deliver much higher capacity and provide better stability than traditional polyvinylidene fluoride (PVDF) binder based electrodes in Li-S cells. A high sulfur loading of 7.5 mg/cm² is achieved, which delivers a high initial areal capacity of 9.0 mAh/cm² and stable cycling capacity at around 7.0 mAh/cm² in the following cycles.

Microporous Carbon Polyhedrons Encapsulated Polyacrylonitrile Nanofibers as Sulfur Immobilizer for Lithium-Sulfur Battery

Microporous carbon polyhedrons (MCPs) are encapsulated into polyacrylonitrile (PAN) nanofibers by electrospinning the mixture of MCPs and PAN. Subsequently, the as-prepared MCPs-PAN nanofibers are employed as sulfur immobilizer for lithium-sulfur battery. Here, the S/MCPs-PAN multicomposites integrate the advantage of sulfur/microporous carbon and sulfurized PAN. Specifically, with large pore volume, MCPs inside PAN nanofibers provide a sufficient sulfur loading. While PAN-based nanofibers offer a conductive path and matrix. Therefore, the electrochemical performance is significantly improved for the S/MCPs-PAN multicomposite with a suitable sulfur content in carbonate-based electrolyte. At the current density of 160 mA g^-1_sulfur, the S/MPCPs-PAN composite delivers a large discharge capacity of 789.7 mAh g^-1_composite, high Coulombic efficiency of about 100% except in the first cycle, and good capacity retention after 200 cycles. In particular, even at 4 C rate, the S/MCPs-PAN composite can still release the discharge capacity of 370 mAh g^-1_composite. On the contrary, the formation of the thick SEI layer on the surface of nanofibers with a high sulfur content are observed, which is responsible for the quick capacity deterioration of the sulfur-based composite in carbonate-based electrolyte. This design of the S/MCPs-PAN multicomposite is helpful for the fabrication of stable Li-S battery.

A review of recent developments in rechargeable lithium-sulfur batteries

The research and development of advanced energy-storage systems must meet a large number of requirements, including high energy density, natural abundance of the raw material, low cost and environmental friendliness, and particularly reasonable safety. As the demands of high-performance batteries are continuously increasing, with large-scale energy storage systems and electric mobility equipment, lithium-sulfur batteries have become an attractive candidate for the new generation of high-performance batteries due to their high theoretical capacity (1675 mA h g^-1) and energy density (2600 Wh kg^-1). However, rapid capacity attenuation with poor cycle and rate performances make the batteries far from ideal with respect to real commercial applications. Outstanding breakthroughs and achievements have been made to alleviate these problems in the past ten years. This paper presents an overview of recent advances in lithium-sulfur battery research. We cover the research and development to date on various components of lithium-sulfur batteries, including cathodes, binders, separators, electrolytes, anodes, collectors, and some novel cell configurations. The current trends in materials selection for batteries are reviewed and various choices of cathode, binder, electrolyte, separator, anode, and collector materials are discussed. The current challenges associated with the use of batteries and their materials selection are listed and future perspectives for this class of battery are also discussed.

Novel Conjugated Ladder-Structured Oligomer Anode with High Lithium Storage and Long Cycling Capability

Herein we report the development of nanostructured poly(1,4-dihydro-11H-pyrazino[2',3':3,4]cyclopenta[1,2-b]quinoxalin-11-one) (PPCQ), a novel conjugated ladderlike oligomer with the presence of a rich amount of heteroatoms, as the anode material. Beyond its remarkable lithium storage of 972 mAh g(-1) after 120 cycles, the superior cycle life and stable capacity performance of 489 mAh g(-1) revealed by ultralong testing of 1000 cycles (with an average Coulombic efficiency 99.8%) at a high current density of 2.5 A g(-1) indicate its excellent electrochemical stability to be promisingly applied for high-performance lithium-ion batteries (LIBs).

Synergistically Enhanced Polysulfide Chemisorption Using a Flexible Hybrid Separator with N and S Dual-Doped Mesoporous Carbon Coating for Advanced Lithium-Sulfur Batteries

Because of the outstanding high theoretical specific energy density of 2600 Wh kg(-1), the lithium-sulfur (Li-S) battery is regarded as a promising candidate for post lithium-ion battery systems eligible to meet the forthcoming market requirements. However, its commercialization on large scale is thwarted by fast capacity fading caused by the Achilles' heel of Li-S systems: the polysulfide shuttle. Here, we merge the physical features of carbon-coated separators and the unique chemical properties of N and S codoped mesoporous carbon to create a functional hybrid separator with superior polysulfide affinity and electrochemical benefits. DFT calculations revealed that carbon materials with N and S codoping possess a strong binding energy to high-order polysulfide species, which is essential to keep the active material in the cathode side. As a result of the synergistic effect of N, S dual-doping, an advanced Li-S cell with high specific capacity and ultralow capacity degradation of 0.041% per cycle is achieved. Pushing our simple-designed and scalable cathode to a highly increased sulfur loading of 5.4 mg cm(-2), the Li-S cell with the functional hybrid separator can deliver a remarkable areal capacity of 5.9 mAh cm(-2), which is highly favorable for practical applications.

Development of a γ-polyglutamic acid binder for cathodes with high mass fraction of sulfur

PGA binder, with a high density of electron-rich functional groups on the molecule, could suppress diffusion of polysulfides.