Review of Carbon Materials for Lithium-Sulfur Batteries

Impact of the Sulfurized Polyacrylonitrile Cathode Microstructure on the Electrochemical Performance of Lithium-Sulfur Batteries

The growing demand for advanced energy storage systems requires the development of next-generation battery technologies with superior energy density and cycle stability, with lithium-sulfur (Li-S) batteries representing a promising solution. Sulfur-containing polyacrylonitrile cathodes (SPAN) for Li-S batteries are a significant advancement for this next-generation battery chemistry, addressing the major issue of limited cycle life encountered in conventional carbon/sulfur composite cathodes. In the presented study, the influence of available ionic and electronic conduction pathways within the cathode on the electrochemical performance of SPAN-based Li-S batteries is studied in details. To this end, a series of SPAN cathodes with different microstructures is prepared by adapting the compression degree of calendering. Mechanical and morphological characterizations confirm a pronounced springback effect due to a characteristic elastic deformation behavior of SPAN. Electrochemical impedance spectroscopy (EIS) shows increased cathode impedance values with multiple overlapping processes in the high- to mid-frequency region in highly compressed SPAN cathodes. Moreover, while the (first) discharge capacity is unaffected, the subsequent charge capacity decreases substantially for highly compressed cathodes. The electrochemical experiments and electrochemical continuum simulations confirm that this phenomenon is mainly due to the disturbance of the electronic percolation pathways caused by the springback behavior during calendering.

The Interaction of Ether-Based Functionalized Ionic Liquids in Lithium-Sulfur Batteries: A First-Principles Study

Ionic liquids (ILs) as electrolytes in lithium-sulfur (Li-S) batteries effectively mitigate the shuttle effect. Solvated cationic ether-based ILs, comprising [Li(G1)2]+, [Li(G2)2]+, [LiG3]+, [LiG4]+, or [LiG6]+ paired with bis(trifluoromethyllsulfonyl)imide ([TFSA]-) anions, are evaluated for their ability to suppress short-chain lithium polysulfide (LiPS: Li2S1, Li2S2, Li2S4) adsorption on lithium metal. The chelating capacity of solvated cations governs interactions with LiPSs and anions. Solvation via Li+ chelation prevents free Li+ fusion with LiPSs, reducing shuttle effects. Remarkably, the cyclic [LiG6]+ cation exhibits superior Li+ chelation, stability, and minimized LiPS adsorption compared to linear cations. Ab initio molecular dynamics simulations confirm ether-based ILs stabilize anions and lower LiPS-lithium surface reactivity. These findings highlight solvated cation ILs as tailored electrolytes to control interfacial LiPS behavior, advancing high-performance LiS battery design.

Single-Atom Cobalt Catalyst with Boron and Nitrogen Codoped Graphene (Co-BN-G) Enables Adsorption and Catalytic Conversion of Polysulfides for High-Performance Lithium-Sulfur Batteries

In lithium-sulfur batteries, the shuttling effect and sluggish redox conversion of soluble polysulfides lead to unsatisfactory sulfur utilization and capacity retention. In this research, we used a one-pot hydrothermal method to prepare graphene with single-atom Co and B, N codoped as a sulfur host in Li-S batteries, thereby suppressing the shuttling effect and facilitating the redox conversion of lithium polysulfides (LiPSs). A series of characterizations demonstrated that dual doping of B and N introduces more lattice defects and structural deformations in graphene oxide, thus enhancing its adsorption of polysulfides. Simultaneously, single-atom cobalt can also polarize adsorption and accelerate the conversion reaction of LiPSs. The Li-S cell with the as-prepared Co-BN-G sulfur host materials exhibited an excellent capacity of 1034 mAh g-1 at 0.5 C and satisfactory cycle performance (retention of 69% over 500 cycles). Even at a rate of 2 C, a discharge capacity of 851 mAh g-1 is achieved. The results show that the Co-BN-G configuration efficiently captures LiPSs and enhances their rate conversion kinetics in redox reactions, demonstrating significant practical potential.

Attenuating the Polysulfide Shuttle Mechanism by Separator Coating

Lithium-sulfur batteries have a high energy density but lack cycle stability to reach market maturity. This is mainly due to the polysulfide shuttle mechanism, i. e., the leaching of active material from the cathode into the electrolyte and subsequent side reactions. We demonstrate how to attenuate the polysulfide shuttle by magnetron sputtering molybdenum oxysulfide, manganese oxide, and chromium oxide onto microporous polypropylene separators. The morphology of the amorphous coatings was analyzed by SEM and XRD. Electrochemical cyclization quantified how these coatings improved Coulombic efficiency and cycle stability. These tests were conducted in half cells. We compare the different performances of the different coatings with the known chemical and adsorption properties of the respective coating materials.

Transition metal nitrides embedded in N-doped porous graphitic Carbon: Applications as electrocatalytic sulfur host materials

While transition metal nitrides (TMNs) are promising electrocatalysts, their widespread use is challenged by the complex synthetic methodology and a limited understanding of the underlying electrocatalytic mechanisms. Herein, we describe a novel synthesis of TMNs (including Mo2N, NbN, and ZrN) and explore their potential as electrocatalysts to affect sulfur cathode reactions. The TMNs were prepared in-situ using a process that simultaneously infuses nitrogen-doped porous graphitic carbon (designated as TMN@N-PGC). The methodology avoids the use of ammonia, which poses safety risks due to its flammability and toxicity. Analysis of the d-p hybridized orbitals formed between the transition metal ions and sulfur species revealed that the antibonding orbitals are empty. Thus, TMNs with more negative d-band centers exhibit stronger affinities towards polysulfides. NbN facilitated polysulfide conversion as well as Li2S detachment, and thus featured a high electrocatalytic capability for promoting cathode kinetics. Lithium-sulfur (Li-S) batteries containing NbN@N-PGC exhibited the highest performance metrics in terms of specific capacity (1488 mA h g-1 at 0.1 C), rate capacity (521 mA h g-1 at 6 C), and cycling stability (603 mA h g-1 at 0.5 C after 1300 cycles, corresponding a capacity decay of 0.030% per cycle). Li-S cells with high sulfur loadings also exhibit outstanding performance.

First-row transition metal carbide nanosheets as high-performance cathode materials for lithium-sulfur batteries

Despite the prodigious potential of lithium-sulfur (Li-S) batteries as future rechargeable electrochemical systems, their commercial implementation is hindered by several vital issues, including the shuttle effect and sluggish migration of lithium-polysulfides leading to rapid capacity fading. Here, we systematically investigate the potential of first-row two-dimensional transition metal carbides (TMCs) as sulfur cathodes for Li-S batteries. The adsorption strength of lithium-polysulfides on TMCs is induced by the amount of charge transfer from the former to the latter and the proposed periodic relationship between sulfur in Li2S and 3d-transition metals. Our findings show that the VC nanosheet possesses immense anchoring potential and exhibits a comparatively low migration energy barrier for lithium-ion and Li2S molecules. Additionally, we report ab initio molecular dynamics simulations for lithiated polysulfide species anchored on a TMC-based model with a liquid-electrolyte medium. The microscopic reaction mechanism, revealed by the evolution of the reaction voltage during lithiation, demonstrates that the dissolution of high-order lithium-polysulfides in the electrolytes can be prevented due to their robust interaction with TMC-based cathode materials. These appealing features suggest that TMCs present colossal performance improvements for anchoring lithium-polysulfides, stimulating the active design of sulfur cathodes for practical Li-S batteries.

Stable High-Capacity Elemental Sulfur Cathodes with Simple Process for Lithium Sulfur Batteries

Lithium sulfur batteries are suitable for drones due to their high gravimetric energy density (2600 Wh/kg of sulfur). However, on the cathode side, high specific capacity with high sulfur loading (high areal capacity) is challenging due to the poor conductivity of sulfur. Shuttling of Li-sulfide species between the sulfur cathode and lithium anode also limits specific capacity. Sulfur-carbon composite active materials with encapsulated sulfur address both issues but require expensive processing and have low sulfur content with limited areal capacity. Proper encapsulation of sulfur in carbonaceous structures along with active additives in solution may largely mitigate shuttling, resulting in cells with improved energy density at relatively low cost. Here, composite current collectors, selected binders, and carbonaceous matrices impregnated with an active mass were used to award stable sulfur cathodes with high areal specific capacity. All three components are necessary to reach a high sulfur loading of 3.8 mg/cm² with a specific/areal capacity of 805 mAh/g/2.2 mAh/cm². Good adhesion between the carbon-coated Al foil current collectors and the composite sulfur impregnated carbon matrices is mandatory for stable electrodes. Swelling of the binders influenced cycling retention as electroconductivity dominated the cycling performance of the Li-S cells comprising cathodes with high sulfur loading. Composite electrodes based on carbonaceous matrices in which sulfur is impregnated at high specific loading and non-swelling binders that maintain the integrated structure of the composite electrodes are important for strong performance. This basic design can be mass produced and optimized to yield practical devices.

High-entropy oxychloride increasing the stability of Li-sulfur batteries

A novel lithiated high-entropy oxychloride Li0.5(Zn0.25Mg0.25Co0.25Cu0.25)0.5Fe2O3.5Cl0.5 (LiHEOFeCl) with spinel structure belonging to the cubic Fd3̄m space group is synthesized by a mechanochemical-thermal route. Cyclic voltammetry measurement of the pristine LiHEOFeCl sample confirms its excellent electrochemical stability and the initial charge capacity of 648 mA h g-1. The reduction of LiHEOFeCl starts at ca. 1.5 V vs. Li+/Li, which is outside the electrochemical window of the Li-S batteries (1.7/2.9 V). The addition of the LiHEOFeCl material to the composite of carbon with sulfur results in improved long-term electrochemical cycling stability and increased charge capacity of this cathode material in Li-S batteries. The carbon/LiHEOFeCl/sulfur cathode provides a charge capacity of 530 mA h g-1 after 100 galvanostatic cycles, which represents ca. 33% increase as compared to the charge capacity of the blank carbon/sulfur composite cathode after 100 cycles. This considerable effect of the LiHEOFeCl material is assigned to its excellent structural and electrochemical stability within the potential window of 1.7 V/2.9 V vs. Li+/Li. In this potential region, our LiHEOFeCl has no inherent electrochemical activity. Hence, it acts solely as an electrocatalyst accelerating the redox reactions of polysulfides. This can be beneficial for the performance of Li-S batteries, as evidenced by reference experiments with TiO2 (P90).

Insights into the electrochemical properties of Li2FeS2 after FeS2 discharging

All-solid-state lithium-sulfur batteries (ASSLSBs) have high reversible characteristics owing to the high redox potential, high theoretical capacity, high electronic conductivity, and low Li⁺ diffusion energy barrier in the cathode. Monte Carlo simulations with cluster expansion, based on the first-principles high-throughput calculations, predicted a phase structure change from Li₂FeS₂ (P3̄M1) to FeS₂ (PA3̄) during the charging process. LiFeS₂ is the most stable phase structure. The structure of Li₂FeS₂ after charging was FeS₂ (P3̄M1). By applying the first-principles calculations, we explored the electrochemical properties of Li₂FeS₂ after charging. The redox reaction potential of Li₂FeS₂ was 1.64 to 2.90 V, implying a high output voltage of ASSLSBs. Flatter voltage step plateaus are important for improving the electrochemical performance of the cathode. The charge voltage plateau was the highest from Li_0.25FeS₂ to FeS₂ and followed from Li_0.375FeS₂ to Li_0.25FeS₂. The electrical properties of Li_xFeS₂ remained metallic during the Li₂FeS₂ charging process. The intrinsic Li Frenkel defect of Li₂FeS₂ was more conducive to Li⁺ diffusion than that of the Li₂S Schottky defect and had the largest Li⁺ diffusion coefficient. The good electronic conductivity and Li⁺ diffusion coefficient of the cathode implied a better charging/discharging rate performance of ASSLSBs. This work theoretically verified the FeS₂ structure after Li₂FeS₂ charging and explored the electrochemical properties of Li₂FeS₂.

Double Heteroatom Reconfigured Polar Catalytic Surface Powers High-Performance Lithium-Sulfur Batteries

The modification of apolar carbon materials by heteroatom doping is an effective method that can effectively improve the surface polarity of carbon materials. In the main body of the lithium-sulfur battery cathode, the structural properties of the carbon material itself with porous structure and large specific surface area provide sufficient space for sulfur accommodation and mitigate the bulk effect of the sulfur cathode (79%). The polarized surface of the reconstructed carbon material possesses strong adsorption effect on LiPs, which mitigates the notorious "shuttle effect." In this paper, the surface structure of the Ketjen black cathode body was reconstructed by B and N double heteroatoms to polarize it. The modified polarized Ketjen black improves the adsorption and anchoring ability of LiPs during the reaction and accelerates their kinetic conversion, while its own uniformly distributed small mesopores and oversized BET structural properties are beneficial to mitigate the bulk effect of sulfur cathodes. Lithium-sulfur batteries using B and N modified cathodes have an initial discharge capacity of 1344.49 mAh/g at 0.1 C and excellent cycling stability at 0.5 C (381.4 mAh/g after 100 cycles).

Module-Designed Carbon-Coated Separators for High-Loading, High-Sulfur-Utilization Cathodes in Lithium-Sulfur Batteries

Lithium–sulfur batteries have great potential as next-generation energy-storage devices because of their high theoretical charge-storage capacity and the low cost of the sulfur cathode. To accelerate the development of lithium–sulfur technology, it is necessary to address the intrinsic material and extrinsic technological challenges brought about by the insulating active solid-state materials and the soluble active liquid-state materials. Herein, we report a systematic investigation of module-designed carbon-coated separators, where the carbon coating layer on the polypropylene membrane decreases the irreversible loss of dissolved polysulfides and increases the reaction kinetics of the high-loading sulfur cathode. Eight different conductive carbon coatings were considered to investigate how the materials’ characteristics contribute to the lithium–sulfur cell’s cathode performance. The cell with a nonporous-carbon-coated separator delivered an optimized peak capacity of 1112 mA∙h g⁻¹ at a cycling rate of C/10 and retained a high reversible capacity of 710 mA∙h g⁻¹ after 200 cycles under lean-electrolyte conditions. Moreover, we demonstrate the practical high specific capacity of the cathode and its commercial potential, achieving high sulfur loading and content of 4.0 mg cm⁻² and 70 wt%, respectively, and attaining high areal and gravimetric capacities of 4.45 mA∙h cm⁻² and 778 mA∙h g⁻¹, respectively.

Carbonaceous Hosts for Sulfur Cathode in Alkali-Metal/S (Alkali Metal = Lithium, Sodium, Potassium) Batteries

Alkali-metal/sulfur batteries hold great promise for offering relatively high energy density compared to conventional lithium-ion batteries. By providing viable sulfur composites that can be effectively used, carbonaceous hosts as a key component play critical roles in overcoming the preliminary challenges associated with the insulating sulfur and its relatively soluble polysulfides. Herein, a comprehensive overview and recent progress on carbonaceous hosts for advanced next-generation alkali-metal/sulfur batteries are presented. In order to encapsulate the highly active sulfur mass and fully limit polysulfide dissolution, strategies for tailoring the design and synthesis of carbonaceous hosts are summarized in this work. The sticking points that remain for sulfur cathodes in current alkali-metal/sulfur systems and the future remedies that can be provided by carbonaceous hosts are also indicated, which can lead to long cycling lifetimes and highly reversible capacities under repeated sulfur reduction reactions in alkali-metal/sulfur during cycling.

The Dual Functions of Defect-Rich Carbon Nanotubes as Both Conductive Matrix and Efficient Mediator for LiS Batteries

LiS batteries are considered a promising energy storage system owing to the great abundance of sulfur and its high specific capacity. Polysulfide shuttling and sluggish reaction kinetics in sulfur cathodes significantly degrade the cycle life of LiS batteries. A modified method is employed to create defects in carbon nanotubes (CNTs), anchoring polysulfides, and accelerating electrochemical reactions. The defect-rich CNTs (D-CNT) enable dramatic improvement in both cycling and rate performance. A specific capacity of 600 mAh g^-1 with a current density of 0.5 C is achieved after 400 cycles, and even at a very high current density (5.0 C), a specific capacity of 434 mAh g^-1 is observed. Cycling stability up to 1000 cycles is also achieved under the conditions of high sulfur loading and lean electrolyte. Theoretical calculations revealed that the improvement is mainly attributable to the electronic structure of defect-rich carbon, which has higher binding energy with polysulfides because of the upshift of the p-band center. Furthermore, rotating disk electrode measurements demonstrate that the defect-rich carbon can accelerate the polysulfide conversion process. It is anticipated that this new design strategy can be the starting point for mediator-like carbon materials with good conductivity and high catalytic activity for LiS batteries.

Multiscale Understanding of Covalently Fixed Sulfur-Polyacrylonitrile Composite as Advanced Cathode for Metal-Sulfur Batteries

Metal-sulfur batteries (MSBs) provide high specific capacity due to the reversible redox mechanism based on conversion reaction that makes this battery a more promising candidate for next-generation energy storage systems. Recently, along with elemental sulfur (S8 ), sulfurized polyacrylonitrile (SPAN), in which active sulfur moieties are covalently bounded to carbon backbone, has received significant attention as an electrode material. Importantly, SPAN can serve as a universal cathode with minimized metal-polysulfide dissolution because sulfur is immobilized through covalent bonding at the carbon backbone. Considering these unique structural features, SPAN represents a new approach beyond elemental S8 for MSBs. However, the development of SPAN electrodes is in its infancy stage compared to conventional S8 cathodes because several issues such as chemical structure, attached sulfur chain lengths, and over-capacity in the first cycle remain unresolved. In addition, physical, chemical, or specific treatments are required for tuning intrinsic properties such as sulfur loading, porosity, and conductivity, which have a pivotal role in improving battery performance. This review discusses the fundamental and technological discussions on SPAN synthesis, physicochemical properties, and electrochemical performance in MSBs. Further, the essential guidance will provide research directions on SPAN electrodes for potential and industrial applications of MSBs.

Advanced Current Collectors with Carbon Nanofoams for Electrochemically Stable Lithium-Sulfur Cells

An inexpensive sulfur cathode with the highest possible charge storage capacity is attractive for the design of lithium-ion batteries with a high energy density and low cost. To promote existing lithium–sulfur battery technologies in the current energy storage market, it is critical to increase the electrochemical stability of the conversion-type sulfur cathode. Here, we present the adoption of a carbon nanofoam as an advanced current collector for the lithium–sulfur battery cathode. The carbon nanofoam has a conductive and tortuous network, which improves the conductivity of the sulfur cathode and reduces the loss of active material. The carbon nanofoam cathode thus enables the development of a high-loading sulfur cathode (4.8 mg cm⁻²) with a high discharge capacity that approaches 500 mA·h g⁻¹ at the C/10 rate and an excellent cycle stability that achieves 90% capacity retention over 100 cycles. After adopting such an optimal cathode configuration, we superficially coat the carbon nanofoam with graphene and molybdenum disulfide (MoS₂) to amplify the fast charge transfer and strong polysulfide-trapping capabilities, respectively. The highest charge storage capacity realized by the graphene-coated carbon nanofoam is 672 mA·h g⁻¹ at the C/10 rate. The MoS₂-coated carbon nanofoam features high electrochemical utilization attaining the high discharge capacity of 633 mA·h g⁻¹ at the C/10 rate and stable cyclability featuring a capacity retention approaching 90%.

Nanoporosity of Carbon-Sulfur Nanocomposites toward the Lithium-Sulfur Battery Electrochemistry

An ideal high-loading carbon–sulfur nanocomposite would enable high-energy-density lithium–sulfur batteries to show high electrochemical utilization, stability, and rate capability. Therefore, in this paper, we investigate the effects of the nanoporosity of various porous conductive carbon substrates (e.g., nonporous, microporous, micro/mesoporous, and macroporous carbons) on the electrochemical characteristics and cell performances of the resulting high-loading carbon–sulfur composite cathodes. The comparison analysis of this work demonstrates the importance of having high microporosity in the sulfur cathode substrate. The high-loading microporous carbon–sulfur cathode attains a high sulfur loading of 4 mg cm⁻² and sulfur content of 80 wt% at a low electrolyte-to-sulfur ratio of 10 µL mg⁻¹. The lithium–sulfur cell with the microporous carbon–sulfur cathode demonstrates excellent electrochemical performances, attaining a high discharge capacity approaching 1100 mA∙h g⁻¹, a high-capacity retention of 75% after 100 cycles, and superior high-rate capability of C/20–C/3 with excellent reversibility.

Porous N-doped carbon nanofibers assembled with nickel ferrite nanoparticles as efficient chemical anchors and polysulfide conversion catalyst for lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries are deemed to have great prospects in the next generation advanced energy storage systems and have been considered in recent years. However, the majority of substrates with both high electronic conductivity and full coverage of adsorption-catalysis synergy are difficult to achieve. Herein, nitrogen functionalized porous carbon nanofibers assembled with nickel ferrite nanoparticles (NFO/NCFs) are successfully prepared by electrospinning combined with hydrothermal treatment, which were applied to current collector containing Li₂S₆ catholyte and binder-free for Li-S batteries. With its abundant active sites, the NFO/NCFs have a vital role in the adsorption and catalysis of the polysulfides, which further accelerate the redox kinetics. Consequently, Li₂S₆ catholyte impregnated NFO/NCFs electrode (sulfur loading: 5.09 mg cm^-2) exhibits the first discharge capacity of 997 mAh g^-1 and maintains at 637 mAh g^-1 after 350 cycles at 0.2C, which is superior cycling performance than NCFs. Even at 10.2 mg cm^-2 sulfur loading, the composite electrode shows a high area capacity of 8.35 mAh cm^-2 at 0.1C and retains 6.01 mAh cm^-2 after 150 cycles. The results suggest the multifunction NFO/NCFs that anchor effectively and catalysis are beneficial to realize the goal of the large-scale application for Li-S batteries.

Applications of Carbon in Rechargeable Electrochemical Power Sources: A Review

Rechargeable power sources are an essential element of large-scale energy systems based on renewable energy sources. One of the major challenges in rechargeable battery research is the development of electrode materials with good performance and low cost. Carbon-based materials have a wide range of properties, high electrical conductivity, and overall stability during cycling, making them suitable materials for batteries, including stationary and large-scale systems. This review summarizes the latest progress on materials based on elemental carbon for modern rechargeable electrochemical power sources, such as commonly used lead–acid and lithium-ion batteries. Use of carbon in promising technologies (lithium–sulfur, sodium-ion batteries, and supercapacitors) is also described. Carbon is a key element leading to more efficient energy storage in these power sources. The applications, modifications, possible bio-sources, and basic properties of carbon materials, as well as recent developments, are described in detail. Carbon materials presented in the review include nanomaterials (e.g., nanotubes, graphene) and composite materials with metals and their compounds.

Binder-free and high-loading sulfurized polyacrylonitrile cathode for lithium/sulfur batteries

Sulfurized polyacrylonitrile (SPAN) is a promising active material for Li/S batteries owing to its high sulfur utilization and long-term cyclability. However, because SPAN electrodes are synthesized using powder, they require large amounts of electrolyte, conducting agents, and binder, which reduces the practical energy density. Herein, to improve the practical energy density, we fabricated bulk-type SPAN disk cathodes from pressed sulfur and polyacrylonitrile powders using a simple heating process. The SPAN disks could be used directly as cathode materials because their π–π structures provide molecular-level electrical connectivity. In addition, the electrodes had interconnected pores, which improved the mobility of Li⁺ ions by allowing homogeneous adsorption of the electrolyte. The specific capacity of the optimal electrode was very high (517 mA h g_electrode⁻¹). Furthermore, considering the weights of the anode, separator, cathode, and electrolyte, the Li/S cell exhibited a high practical energy density of 250 W h kg⁻¹. The areal capacity was also high (8.5 mA h cm⁻²) owing to the high SPAN loading of 16.37 mg cm⁻². After the introduction of 10 wt% multi-walled carbon nanotubes as a conducting agent, the SPAN disk electrode exhibited excellent cyclability while maintaining a high energy density. This strategy offers a potential candidate for Li/S batteries with high practical energy densities.

A simple synthesis procedure to prepare bulk-type SPAN electrodes toward the realization of Li/S batteries with enhanced practical energy densities.

Li2 S-Based Li-Ion Sulfur Batteries: Progress and Prospects

The great demand for high-energy-density batteries has driven intensive research on the Li-S battery due to its high theoretical energy density. Consequently, considerable progress in Li-S batteries is achieved, although the lithium anode material is still challenging in terms of lithium dendrites and its unstable interface with electrolyte, impeding the practical application of the Li-S battery. Li₂ S-based Li-ion sulfur batteries (LISBs), which employ lithium-metal-free anodes, are a convenient and effective way to avoid the use of lithium metal for the realization of practical Li-S batteries. Over the past decade, studies on LISBs are carried out to optimize their performance. Herein, the research progress and challenges of LISBs are reviewed. Several important aspects of LISBs, including their working principle, the physicochemical properties of Li₂ S, Li₂ S cathode material composites, LISBs full batteries, and electrolyte for Li₂ S cathode, are extensively discussed. In particular, the activation barrier in the initial charge process is fundamentally analyzed and the mechanism is discussed in detail, based on previous reports. Finally, perspectives on the future direction of the research of LISBs are proposed.

A Novel Synthesizing Strategy of 3D Cose2 Porous Hollow Flowers for High Performance Lithium–Sulfur Batteries

Redox kinetics of lithium polysulfides (LiPSs) conversion and poor electrical conductivity of sulfur during the charge-discharge process greatly inhibit the commercialization of high-performance lithium–sulfur (Li–S) batteries. Herein, we synthesized CoSe2 porous hollow flowers (CoSe2-PHF) by etching and further selenizing layered double hydroxide, which combined the high catalytic activity of transition metal compound and high electrical conductivity of selenium. The obtained CoSe2-PHF can efficiently accelerate the catalytic conversion of LiPSs, expedite the electron transport, and improve utilization of active sulfur during the charge-discharge process. As a result, with CoSe2-PHF/S-based cathodes, the Li–S batteries exhibited a reversible specific capacity of 955.8 mAh g−1 at 0.1 C and 766.0 mAh g−1 at 0.5 C, along with a relatively small capacity decay rate of 0.070% per cycle within 400 cycles at 1 C. Even at the high rate of 3 C, the specific capacity of 542.9 mAh g−1can be maintained. This work enriches the way to prepare porous composites with high catalytic activity and electrical conductivity as sulfur hosts for high-rate, long-cycle rechargeable Li–S batteries.

Simple and Sustainable Preparation of Nonactivated Porous Carbon from Brewing Waste for High-Performance Lithium-Sulfur Batteries

The development of renewable energy sources requires the parallel development of sustainable energy storage systems because of its noncontinuous production. Even the most-used battery on the planet, the lithium-ion battery, is reaching its technological limit. In light of this, lithium-sulfur batteries have emerged as one of the most promising technologies to address this problem. The use of biomass to produce cathodes for these batteries addresses not only the aforementioned problem, but it also reduces the carbon footprint and gives added value to something normally considered waste. Here, the production, by simple and nonactivating pyrolysis, of a carbon material using the abundant "after-boiling waste" derived from beer brewing is reported. After adding a high sulfur loading (70 %) to this biowaste-derived carbon by the "melt diffusion" method, the sulfur-carbon composite is used as an effective cathode in Li-S batteries. The cathode shows excellent performance, reaching high capacity values with long-term cyclability at high current-847 mAh g^-1 at 1 C, 586 mAh g^-1 at 2 C, and even 498 mAh g^-1 at 5 C after 400 cycles-drastically reducing capacity loss to values approaching 0.01 % per cycle. This work demonstrates the possibility of obtaining low-cost, highly sustainable cathodic materials for the design of advanced energy storage systems.

Development of a Synergistic Activation Strategy for the Pilot-Scale Construction of Hierarchical Porous Graphitic Carbon for Energy Storage Applications

Pursuing scalable production of porous carbon with facile and environmentally friendly synthesis methodology is a global goal. Herein, a unique hierarchical porous graphitic carbon (HPGC) with outstanding textural characteristics is achieved by a special synergistic activation mechanism, in which the low-temperature molten state of polymorphisms can induce a high-rate liquid phase porous activation. HPGC with high specific surface area (SSA, ∼2571 m² g^-1) and large pore volume (PV, ∼2.21 cm³ g^-1) can be achieved, which also possesses the capability to tune textural characteristics (i.e., SSA, PV, pore size distribution, etc.) within a wide range. Furthermore, the pilot-scale production of HPGC is accomplished, which shows similar textural characteristics to the lab-scale HPGC. Due to the unique structure of HPGC and the capability of the textural control, it can be applicable in a variety of energy storage, energy conversion, and catalysis applications. The applications of pilot-scale HPGC products in supercapacitors and lithium sulfur batteries are highlighted in this work. Furthermore, the synergistic activation strategy can be promoted to other alkali-based carbon activation routes, which can open up new possibilities for the activated carbon production and lead to more widespread industrialized applications of HPGC.

A Collaboratively Polar Conductive Interface for Accelerating Polysulfide Redox Conversion

In order to alleviate the inferior cycle stability of the sulfur cathode, a self-assembled SnO₂-doped manganese silicate nanobubble (SMN) is designed as a sulfur/polysulfide host to immobilize the intermediate Li₂S _x, and nitrogen-doped carbon (N-C) is coated on SMN (SMN@C). The exquisite N-C conductive network not only provides sufficient free space for the volume expansion during the phase transition of solid sulfur into lithium sulfide but also reduces R_ct of SMN. During cycling, the soluble polysulfide could be fastened by the silicate with an oxygen-rich functional group and heteronitrogen atoms through chemical bonding, enabling a confined shuttle effect. The synergistic effect between N-C and SMN could also effectively facilitate the interconversion between lithium polysulfides and Li₂S, reducing the potential barrier and accelerating the redox kinetics. With an areal sulfur loading of 2 mg/cm², the S-SMN@C cathodes demonstrate a high initial capacity of 1204 mA·h/g at 0.1 C, and an outstanding cycle stability with a capacity fading rate of 0.0277%, ranging from the 2nd cycle to the 1000th cycle at 2 C.

Ultradispersed titanium dioxide nanoparticles embedded in a three-dimensional graphene aerogel for high performance sulfur cathodes

Lithium-sulfur (Li-S) batteries are regarded as one of the most promising energy storage technologies, however, their practical application is greatly limited by a series of sulfur cathode challenges such as the notorious "shuttle effect", low conductivity and large volume change. Here, we develop a facile hydrothermal method for the large scale synthesis of sulfur hosts consisting of three-dimensional graphene aerogel with tiny TiO₂ nanoparticles (5-10 nm) uniformly dispersed on the graphene sheet (GA-TiO₂). The obtained GA-TiO₂ composites have a high surface area of ∼360 m² g^-1 and a hierarchical porous structure, which facilitates the encapsulation of sulfur in the carbon matrix. The resultant GA-TiO₂/S composites exhibit a high initial discharge capacity of 810 mA h g^-1 with an ultralow capacity fading of 0.054% per cycle over 700 cycles at 2C, and a high rate (5C) performance (396 mA h g^-1). Such architecture design paves a new way to synthesize well-defined sulfur hosts to tackle the challenges for high performance Li-S batteries.

Almond Shell as a Microporous Carbon Source for Sustainable Cathodes in Lithium⁻Sulfur Batteries

A microporous carbon derived from biomass (almond shells) and activated with phosphoric acid was analysed as a cathodic matrix in Li⁻S batteries. By studying the parameters of the carbonization process of this biomass residue, certain conditions were determined to obtain a high surface area of carbon (967 m² g^-1) and high porosity (0.49 cm³ g^-1). This carbon was capable of accommodating up to 60% by weight of sulfur, infiltrated by the disulphide method. The C⁻S composite released an initial specific capacity of 915 mAh g^-1 in the Li⁻S cell at a current density of 100 mA g^-1 with a high retention capacity of 760 mAh g^-1 after 100 cycles and a coulombic efficiency close to 100%. The good performance of the composite was also observed under higher current rates (up to 1000 mA g^-1). The overall electrochemical behaviour of this microporous carbon acting as a sulfur host reinforces the possibility of using biomass residues as sustainable sources of materials for energy storage.