Sulfur Encapsulated in Graphitic Carbon Nanocages for High-Rate and Long-Cycle Lithium-Sulfur Batteries

Carbon Nanofiber-Based Sandwich Free-Standing Cathode for High-Performance Lithium-Sulfur Batteries

Challenges including rapid capacity degradation and reduced Coulombic efficiency due to the shuttle effect have hindered the commercial viability of lithium-sulfur (Li-S) batteries. A novel sandwich-structured electrode with an optimized electrode structure and current collector interface design was presented as a free-standing positive electrode for Li-S batteries. Fabricated via a simple slurry coating process, the electrode embedded multiwalled carbon nanotubes within carbon nanofiber composite films (PCNF/T). Owing to the superior conductivity and reduced weight in comparison to both carbon nanofibers (PCNF) and the conventional aluminum foil current collector (Al), the PCNF/T electrode exhibited diminished polarization and accelerated redox reaction kinetics. Thus, it delivers an initial discharge capacity of 990.23 mA h g-1 at 0.5 C. Even after 400 cycles, while retains a reversible capacity of 707.45 mA h g-1, corresponding to a minimal capacity degradation rate of merely 0.07% per cycle. Notably, the electrode exhibits a capacity retention of 619.81 mA h g-1 after 400 cycles at 1 C, with a capacity decay rate of only 0.08% per cycle. This study presents an innovative approach to developing a new free-standing cathode for high-performance Li-S batteries.

Bimetallic metal-organic framework-derived bamboo-like N-doped carbon nanotube-encapsulated Ni-doped MoC nanoparticles for water oxidation

Molybdenum carbide materials with unique electronic structures have received special attention as water-splitting catalysts, but their structural stability in the alkaline water electrolysis process is not satisfactory. This study reports an in situ pyrolysis method for preparing NiMo-based metal-organic framework (MOF)-derived chain-mail oxygen evolution reaction (OER) electrocatalysts and bamboo-like N-doped carbon nanotube (NCNT)-encapsulated Ni-doped MoC nanoparticles (NiMoC-NCNTs). The NCNTs can provide chain mail shells to protect the inner highly reactive Ni-doped MoC cores from electrochemical corrosion by the alkaline electrolyte and regulate their catalytic properties through charge redistribution. Benefiting from high N-doping with abundant pyridinic moieties and abundant active sites of the periodic bamboo-like nodes, the as-prepared NiMoC-NCNTs display an outstanding activity for the OER with an overpotential of 310 mV at 10 mA cm-2 and a superior long-term stability of 50 h. Density functional theory calculations reveal that the excellent electrocatalytic activity of NiMoC-NCNTs comes from the electron transfer from NiMoC nanoparticles to NCNTs, resulting in a decrease in the local work function at the carbon surface and optimized free efficiencies of OER intermediates on C sites. This work provides an effective approach to improve the structural stability of fragile catalysts by equipping them with carbon-based chain.

MoSe2 @rGO as Highly Efficient Host and Catalyst for Li-Organosulfide Battery

Organosulfides are promising high-capacity cathode materials for rechargeable lithium batteries. However, sluggish kinetics and inferior utilization impede its practical application in batteries. Rationally designing redox mediators and identifying their active moieties remain formidable challenges. Currently, as a rising star of transition metal dichalcogenides, few-layered MoSe2 decorated reduced graphene oxide (rGO) (MoSe2 @rGO) with high electronic conductivity and narrow energy band is used to manipulate electrocatalytic redox kinetics of organosulfides, thereby enhancing the battery performance. Here, an exotic MoSe2 @rGO is reported with Se defects material obtained from 2D MoSe2 growing on rGO for Li-dipentamethylenethiuram tetrasulfide (Li-PMTT) batteries. MoSe2 @rGO with Se defects has a large specific surface area, and sufficient pores, as well as exce llent catalytic ability for organosulfides conversion reactions. Therefore, the PMTT@MoSe2 @rGO cathode delivers a high reversible capacity of 405 mAh g-1 in the first cycle at 0.5 C and can maintain 238.3 mAh g-1 specific capacity after 300 cycles. This work offers an understanding of organosulfides electrochemistry toward fast and durable performance, holding great promise for developing practically feasible lithium-organosulfides battery material designs.

Highly stable lithium sulfur batteries enhanced by flocculation and solidification of soluble polysulfides in routine ether electrolyte

Lithium-sulfur batteries (LSBs) are among the most promising next-generation high energy density energy-storage systems. However, practical application has been hindered by fundamental problems, especially shuttling by the higher-order polysulfides (PSs) and slow redox kinetics. Herein, a novel electrolyte-based strategy is proposed by adding an ultrasmall amount of the low-cost and commercially available cationic antistatic agent octadecyl dimethyl hydroxyethyl quaternary ammonium nitrate (SN) into a routine ether electrolyte. Due to the strong cation-anion interaction and bridge-bonding with SN, rapid flocculation of the soluble polysulfide intermediates into solid-state polysulfide-SN sediments is found, which significantly inhibited the adverse shuttling effect. Moreover, a catalytic effect was also demonstrated for conversion of the polysulfide-SN intermediates, which enhanced the redox kinetics of Li-S batteries. Encouragingly, for cells with only 0.1 % added SN, an initial specific capacity of 783.6 mAh/g and a retained specific capacity of 565.7 mAh/g were found at 2C after 200 cycles, which corresponded to an ultralow capacity decay rate of only 0.014 % per cycle. This work may provide a simple and promising regulation strategy for preparing highly stable Li-S batteries.

Functional Carbon from Nature: Biomass-Derived Carbon Materials and the Recent Progress of Their Applications

Biomass is considered as a promising source to fabricate functional carbon materials for its sustainability, low cost, and high carbon content. Biomass-derived-carbon materials (BCMs) have been a thriving research field. Novel structures, diverse synthesis methods, and versatile applications of BCMs have been reported. However, there has been no recent review of the numerous studies of different aspects of BCMs-related research. Therefore, this paper presents a comprehensive review that summarizes the progress of BCMs related research. Herein, typical types of biomass used to prepare BCMs are introduced. Variable structures of BCMs are summarized as the performance and properties of BCMs are closely related to their structures. Representative synthesis strategies, including both their merits and drawbacks are reviewed comprehensively. Moreover, the influence of synthetic conditions on the structure of as-prepared carbon products is discussed, providing important information for the rational design of the fabrication process of BCMs. Recent progress in versatile applications of BCMs based on their morphologies and physicochemical properties is reported. Finally, the remaining challenges of BCMs, are highlighted. Overall, this review provides a valuable overview of current knowledge and recent progress of BCMs, and it outlines directions for future research development of BCMs.

Synergy between highly dispersed Ni nanocrystals and graphitized carbon derived from a single source as a strategy for high performance Lithium-Sulfur batteries

Due to their higher energy density, lower prices, and more environmentally friendly active components, Li-S batteries will soon compete with the current Li-ion batteries. However, issues persist that hinder this implementation, such as the poor conductivity of S and sluggish kinetics due to the polysulfide shuttle, among others. Herein, Ni nanocrystals encapsulated in a C matrix are obtained by a novel strategy based on the thermal decomposition of a Ni oleate-oleic acid complex at low-to-moderate temperatures: 500 and 700 °C. The two C/Ni composites were employed as hosts in Li-S batteries. Although the C matrix is amorphous at 500 °C, it is highly graphitized at 700 °C. At this moderate temperature, the simultaneous generation of Ni nanocrystals and the carbon matrix enhances the catalytic activity of Ni toward the graphitization process, which is negligible if starting from a mixture of a Ni salt and carbon source, even when calcined at temperatures as high as 1000 °C. The electrode made from the C/Ni composite obtained at 700 °C exhibits a high reversible capacity and an enhanced rate capability, much better not only than the C/Ni composite obtained at 500 °C but than others based on amorphous C calcined at very high temperatures, around 1000 °C. These properties are attributed to an increase in the electrical conductivity parallel to the ordering of the layers. We believe this work provides a new strategy to design C-based composites capable of combining the formation of nanocrystalline phases and the control of the C structure with superior electrochemical properties for Li-S batteries.

Recent Progress of Hollow Carbon Nanocages: General Design Fundamentals and Diversified Electrochemical Applications

Hollow carbon nanocages (HCNCs) consisting of sp2  carbon shells featured by a hollow interior cavity with defective microchannels (or customized mesopores) across the carbon shells, high specific surface area, and tunable electronic structure, are quilt different from the other nanocarbons such as carbon nanotubes and graphene. These structural and morphological characteristics make HCNCs a new platform for advanced electrochemical energy storage and conversion. This review focuses on the controllable preparation, structural regulation, and modification of HCNCs, as well as their electrochemical functions and applications as energy storage materials and electrocatalytic conversion materials. The metal single atoms-functionalized structures and electrochemical properties of HCNCs are summarized systematically and deeply. The research challenges and trends are also envisaged for deepening and extending the study and application of this hollow carbon material. The development of multifunctional carbon-based composite nanocages provides a new idea and method for improving the energy density, power density, and volume performance of electrochemical energy storage and conversion devices.

Electronic Modulation and Structural Engineering of Carbon-Based Anodes for Low-Temperature Lithium-Ion Batteries: A Review

Lithium-ion batteries (LIBs) have become the preferred battery system for portable electronic devices and transportation equipment due to their high specific energy, good cycling performance, low self-discharge, and absence of memory effect. However, excessively low ambient temperatures will seriously affect the performance of LIBs, which are almost incapable of discharging at -40~-60 °C. There are many factors affecting the low-temperature performance of LIBs, and one of the most important is the electrode material. Therefore, there is an urgent need to develop electrode materials or modify existing materials in order to obtain excellent low-temperature LIB performance. A carbon-based anode is one candidate for use in LIBs. In recent years, it has been found that the diffusion coefficient of lithium ion in graphite anodes decreases more obviously at low temperatures, which is an important factor limiting its low-temperature performance. However, the structure of amorphous carbon materials is complex; they have good ionic diffusion properties, and their grain size, specific surface area, layer spacing, structural defects, surface functional groups, and doping elements may have a greater impact on their low-temperature performance. In this work, the low-temperature performance of LIBs was achieved by modifying the carbon-based material from the perspectives of electronic modulation and structural engineering.

The Multi-Functional Effects of CuS as Modifier to Fabricate Efficient Interlayer for Li-S Batteries

The shuttle effect of lithium polysulfides in lithium-sulfur batteries (LSBs) has a detrimental impact on their electrochemical performance. To effectively mitigate the shuttle effect, in this study, the coral-like CuS is introduced to modify the carbon nanotube (CNTs), which is coated on commercial separator and served as the S cathode interlayer (PE@CuS/CNTs). The CuS/CNTs interlayer possesses efficient physical impediment and chemisorption to polysulfide anions. When achieving maximum adsorption to polysulfide anions, a "polysulfide-phobic" surface would be formed as a shield to restrain the polysulfide anions in the cathode region. Simultaneously, the CuS/CNTs interlayer can improve the lithium ion diffusion and guarantee desirable electrochemical reaction kinetics. Consequently, the LSBs with PE@CuS/CNTs show an initial discharge capacity of 1242.4 mAh g^-1 at 0.5 C (1 C = 1675 mA g^-1 ) and retain a long-term cycling stability (568.5 mAh g^-1 after 1000 cycles, 2 C), corresponding to an ultra-low capacity fading rate of only 0.05% per cycle. Also, the LSBs with PE@CuS/CNTs exhibit high resistance to self-discharge and favorable performance under high S loading (4.5 mg cm^-2 ) and lean electrolyte (9.4 mL_Electrolyte  g _S ^-1 ).

Poly(ionic liquid) Nanovesicle-Templated Carbon Nanocapsules Functionalized with Uniform Iron Nitride Nanoparticles as Catalytic Sulfur Host for Li-S Batteries

Poly(ionic liquid)s (PIL) are common precursors for heteroatom-doped carbon materials. Despite a relatively higher carbonization yield, the PIL-to-carbon conversion process faces challenges in preserving morphological and structural motifs on the nanoscale. Assisted by a thin polydopamine coating route and ion exchange, imidazolium-based PIL nanovesicles were successfully applied in morphology-maintaining carbonization to prepare carbon composite nanocapsules. Extending this strategy further to their composites, we demonstrate the synthesis of carbon composite nanocapsules functionalized with iron nitride nanoparticles of an ultrafine, uniform size of 3-5 nm (termed "Fe_xN@C"). Due to its unique nanostructure, the sulfur-loaded Fe_xN@C electrode was tested to efficiently mitigate the notorious shuttle effect of lithium polysulfides (LiPSs) in Li-S batteries. The cavity of the carbon nanocapsules was spotted to better the loading content of sulfur. The well-dispersed iron nitride nanoparticles effectively catalyze the conversion of LiPSs to Li₂S, owing to their high electronic conductivity and strong binding power to LiPSs. Benefiting from this well-crafted composite nanostructure, the constructed Fe_xN@C/S cathode demonstrated a fairly high discharge capacity of 1085 mAh g^-1 at 0.5 C initially, and a remaining value of 930 mAh g^-1 after 200 cycles. In addition, it exhibits an excellent rate capability with a high initial discharge capacity of 889.8 mAh g^-1 at 2 C. This facile PIL-to-nanocarbon synthetic approach is applicable for the exquisite design of complex hybrid carbon nanostructures with potential use in electrochemical energy storage and conversion.

Polysulfide Regulation by Hypervalent Iodine Compounds for Durable and Sustainable Lithium-Sulfur Battery

Herein, a type of hypervalent iodine compound-iodosobenzene (PhIO)-is proposed to regulate the LiPSs electrochemistry and enhance the performance of Li-S battery. PhIO owns the practical advantages of low-cost, commercial availability, environmental friendliness and chemical stability. The lone pair electrons of oxygen atoms in PhIO play a critical role in forming a strong Lewis acid-base interaction with terminal Li in LiPSs. Moreover, the commercial PhIO can be easily converted to nanoparticles (≈20 nm) and uniformly loaded on a carbon nanotube (CNT) scaffold, ensuring sufficient chemisorption for LiPSs. The integrated functional PhIO@CNT interlayer affords a LiPSs-concentrated shield that not only strongly obstructs the LiPSs penetration but also significantly enhances the electrolyte wettability and Li⁺ conduction. The PhIO@CNT interlayer also serves as a "vice current collector" to accommodate various LiPSs and render smooth LiPSs transformation, which suppresses insulating Li₂ S₂ /Li₂ S layer formation and facilitates Li⁺ diffusion. The Li-S battery based on PhIO@CNT interlayer (6 wt% PhIO) exhibits stable cycling over 1000 cycles (0.033% capacity decay per cycle) and excellent rate performance (686.6 mAh g^-1 at 3 C). This work demonstrates the great potential of PhIO in regulating LiPSs and provides a new avenue towards the low-cost and sustainable application of Li-S batteries.

A Solid-Phase Conversion Sulfur Cathode with Full Capacity Utilization and Superior Cycle Stability for Lithium-Sulfur Batteries

Solid phase conversion sulfur cathode is an effective strategy for eliminating soluble polysulfide intermediates (LiPSs) and improving cyclability of Li-S batteries. However, realizing such a sulfur cathode with high sulfur loading and high capacity utilization is very challenging due to the insulating nature of sulfur. In this work, a strategy is proposed for fabricating solid phase conversion sulfur cathode by encapsulating sulfur in the mesoporous channels of CMK-3 carbon to form a coaxially assembled sulfur/carbon (CA-S/C) composite. Vinyl carbonate (VC) is simultaneously utilized as the electrolyte cosolvent to in-situ form a dense solid electrolyte interface (SEI) on the CA-S/C composite surface through its nucleophilic reaction with the freshly generated polysulfides at the beginning of initial discharge, thus separating the direct contact of interior sulfur with the outer electrolyte. As expected, such a CA-S/C cathode can operate in a solid phase conversion manner in the VC-ether cosolvent electrolyte to exhibit a full capacity utilization (1667 mA h g^-1 , ≈100%), a high rate capability of 2.0 A g^-1 and excellent long-term cyclability over 500 cycles even at a high sulfur loading (75%, based on the weight of CA-S/C composite), demonstrating great promise for constructing high-energy-density and cycle-stable Li-S batteries.

A Comparative Study of Cobalt Chalcogenides as the Electrode Materials on Lithium-Sulfur Battery Performance

Lithium-sulfur batteries, as viable options for energy storage, have gained popularity because of their high energy density. However, the poor conductivity of sulfur and Li₂ S, as well as the shuttling effect of lithium polysulfides, seriously limits their commercialization. Herein, cobalt chalcogenides (Co₃ O₄ , CoS, and Co₃ Se₄ ) supported by reduced graphene oxide are synthesized as the electrode materials, which feature high conductivity, rapid kinetic conversion, and catalytic effect. Based on complementary experimental outputs and advanced computation, it is revealed that the change in anion results in distinctive performance. Among them, the cathode material based on Co₃ Se₄ /reduced graphene oxide is the best. The reasons can be ascribed to the conductive and catalytic improvement. This comparative study provides guidelines in the design of lithium-sulfur batteries via the meticulous regulation of the anions.

An integrated flexible film as cathode for High-Performance Lithium-Sulfur battery

Poor cycling stability and low volumetric capacity of sulfur cathode prevents practical application of Lithium-sulfur (Li-S) batteries. Herein, we demonstrate a strategy to address the two drawbacks of sulfur cathode by synthesizing a compact and flexible film cathode with bilayer structure using a two-step vacuum filtration method. Two layers make up the sulfur cathode, active layer (sulfur-acethlene black (SC) spheres) and barrier layer (three dimensional MnO₂-graphene oxide-multi-walled carbon nanotubes (MnO₂-GO-CNTs) composites), which are integrated together by reduced graphene oxide (rGO) through self-binding. The rGO sheets provide an electrical conductive framework and a stable architecture to accommodate volume changes of sulfur. SC spheres stacked orderly between the rGO layers facilitate fast Li⁺ storage and energy release. Polar MnO₂-GO-CNTs composites with large specific surface area have not only afforded efficient sites for chemically binding polysulfides, but also provided fast electron transfer for accelerating polysulfides redox reaction. Consequently, the integrated film cathode exhibits an unprecedented cycling stability of ~0.0279% capacity decay per cycle over more than 600 cycles at 1C and high volumetric capacity of 1021.9 Ah L^-1 at 2C. Meanwhile, a foldable Li-S battery based on this flexible cathode is fabricated and shows excellent mechanical and electrochemical properties. The integrated flexible sulfur cathode of this study sheds light on the design strategies for application in flexible high volumetric capacity system.

Hollow urchin-like Mn3O4 microspheres as an advanced sulfur host for enabling Li-S batteries with high gravimetric energy density

Lithium-sulfur (Li-S) batteries are considered to be promising candidates for next-generation storage systems. However, the practical applications are still hindered by the severe capacity decay, mainly caused by the large volume change, polysulfide shuttle and sluggish sulfur conversion kinetics. Herein, hollow urchin-like Mn₃O₄ (HU-Mn₃O₄) microspheres as sulfur hosts have been synthesized by the hydrothermal method and calcination treatment, aiming to prevent the polysulfide dissolution (benefiting from the strong polysulfide anchoring effect of Mn₃O₄) and alleviate the volume expansion of sulfur (benefiting from the special hollow structure). Meanwhile, the urchin-like thorny surface also facilitates the rapid ion/electron transfer and the abundant active sites for the fast sulfur redox kinetics. When used as the sulfur host in Li-S batteries, the S@HU-Mn₃O₄ cathode delivers a high initial capacity of 1137.4 mAh g^-1 with a slow capacity decay of 0.042% after 200 cycles at 0.2 C. Even under the conditions of lean electrolyte (E/S = 7 mL g^-1) and low N/P ratio (N/P = 2.1), the S@HU-Mn₃O₄ cathode still enables a stable cycling performance with a high gravimetric energy density (202 Wh kg cell^-1), demonstrating its great potential in the development of future practical Li-S battery materials.

Biomass-Derived Carbon/Sulfur Composite Cathodes with Multiwalled Carbon Nanotube Coatings for Li-S Batteries

Lithium sulfur (Li-S) batteries stand out among many new batteries for their high energy density. However, the intermediate charge–discharge product dissolves easily into the electrolyte to produce a shuttle effect, which is a key factor limiting the rapid development of Li-S batteries. Among the various materials used to solve the challenges related to pure sulfur cathodes, biomass derived carbon materials are getting wider research attention. In this work, we report on the fabrication of cathode materials for Li-S batteries based on composites of sulfur and biomass-derived porous ramie carbon (RC), which are coated with multiwalled carbon nanotubes (MWCNTs). RC can not only adsorb polysulfide in its pores, but also provide conductive channels. At the same time, the MWCNTs coating further reduces the dissolution of polysulfides into the electrolyte and weakens the shuttle effect. The sulfur loading rate of RC is 66.3 wt.%. As a result, the initial discharge capacity of the battery is 1325.6 mAh·g−1 at 0.1 C long cycle, and it can still maintain 812.5 mAh·g−1 after 500 cycles. This work proposes an effective double protection strategy for the development of advanced Li-S batteries.

Towards High Performance Li-S Batteries via Sulfonate-Rich COF-Modified Separator

Lithium-sulfur (Li-S) batteries are held great promise for next-generation high-energy-density devices; however, polysulfide shuttle and Li-dendrite growth severely hinders their commercial production. Herein, a sulfonate-rich COF (SCOF-2) is designed, synthesized, and used to modify the separator of Li-S batteries, providing a solution for the above challenges. It is found that the SCOF-2 features stronger electronegativity and larger interlayer spacing than that of none/monosulfonate COFs, which can facilitate the Li⁺ migration and alleviate the formation of Li-dendrites. Density functional theory (DFT) calculations and in situ Raman analysis demonstrate that the SCOF-2 possesses a narrow bandgap and strong interaction on sulfur species, thereby suppressing self-discharge behavior. As a result, the modified batteries deliver an ultralow attenuation rate of 0.047% per cycle over 800 cycles at 1 C, and excellent anti-self-discharge performance by a low-capacity attenuation of 6.0% over one week. Additionally, even with the high-sulfur-loading cathode (3.2-8.2 mg_s cm^-2 ) and lean electrolyte (5 µL mg_s ^-1 ), the batteries still exhibit ≈80% capacity retention over 100 cycles, showing great potential for practical application.

Constructing Heterogeneous Structure in Metal-Organic Framework-Derived Hierarchical Sulfur Hosts for Capturing Polysulfides and Promoting Conversion Kinetics

Lithium-sulfur batteries (LSBs) are still severely blocked by the shuttle of polysulfides (LiPSs), resulting in low sulfur utilization and decreased lifetime. The optimal design of hosts with tailored porous structures and catalytic sites is expected to address this issue. Herein, a Bi/Bi₂O₃ heterostructure within the metal-organic framework (MOF)-derived sulfur host with a hierarchical structure was elaborated for both serving as sulfur hosts and promoting the redox reaction kinetics of LiPSs. The shuttle effects of LiPSs can be mitigated by the dual functional Bi/Bi₂O₃ heterostructure enriched in the outer layer of CAU-17-derived carbonic rods, i.e., the effective redox conversion of LiPSs can be realized at the Bi/Bi₂O₃ heterointerface by the adsorption of LiPSs over Bi₂O₃ and subsequently catalytic conversion over Bi. Benefiting from these merits, the fabricated LSBs realized a significantly optimized performance, including a high discharge capacity of 740.8 mAh g^-1 after 1000 cycles with an ultralow decay rate of 0.022% per cycle at 1 C, a high areal capacity of 6.6 mAh cm^-2 after 100 cycles with a sulfur loading of 8.1 mg cm^-2, and good performance in pouch cells as well.

Recent Advances and Perspectives in Lithium-Sulfur Pouch Cells

Lithium–sulfur batteries (LSBs) are considered one of the most promising candidates for next-generation energy storage owing to their large energy capacity. Tremendous effort has been devoted to overcoming the inherent problems of LSBs to facilitate their commercialization, such as polysulfide shuttling and dendritic lithium growth. Pouch cells present additional challenges for LSBs as they require greater electrode active material utilization, a lower electrolyte–sulfur ratio, and more mechanically robust electrode architectures to ensure long-term cycling stability. In this review, the critical challenges facing practical Li–S pouch cells that dictate their energy density and long-term cyclability are summarized. Strategies and perspectives for every major pouch cell component—cathode/anode active materials and electrode construction, separator design, and electrolyte—are discussed with emphasis placed on approaches aimed at improving the reversible electrochemical conversion of sulfur and lithium anode protection for high-energy Li–S pouch cells.

Uniform Magnesium Electrodeposition via Synergistic Coupling of Current Homogenization, Geometric Confinement, and Chemisorption Effect

Unevenly distributed magnesium (Mg) electrodeposits have emerged as a major obstacle for Mg-metal batteries. A comprehensive design matrix is reported for 3D magnesiophilic hosts, which regulate the uniform Mg electrodeposition through a synergistic coupling of homogenizing current distribution, geometric confinement, and chemisorptive interaction. Vertically aligned nitrogen- and oxygen-doped carbon nanofiber arrays on carbon cloth (denoted as "VNCA@C") are developed as a proof of concept. The evenly arranged short nanoarray architecture helps to homogenize the surface current density and the microchannels built in this 3D host allow the preferential nucleation of Mg due to their geometrical confinement effect. Besides, the nitrogen-/oxygen-doped carbon species exhibit strong chemisorptive interaction toward Mg atoms, providing preferential nucleation sites as demonstrated by first-principle calculation results. Electrochemical analysis reveals a peculiar yet highly reversible microchannel-filling growth behavior of Mg metals, which empowers the delicately designed VNCA@C host with the ability to deliver a reduced nucleation overpotential of 429 mV at 10.0 mA cm^-2 and an elongated Mg plating/stripping cycle life (110 cycles) under high current density of 10.0 mA cm^-2 . The proposed design matrix can be extended to other metal anodes (such as lithium and zinc) for high-energy-density batteries.

Hierarchical Porous Graphene Bubbles as Host Materials for Advanced Lithium Sulfur Battery Cathode

The serious shuttle effect, low conductivity, and large volume expansion have been regarded as persistent obstacles for lithium sulfur (Li-S) batteries in its practical application. Carbon materials, such as graphene, are considered as promising cathode hosts to alleviate those critical defects and be possibly coupled with other reinforcement methods to further improve the battery performance. However, the open structure of graphene and the weak interaction with sulfur species restrict its further development for hosting sulfur. Herein, a rational geometrical design of hierarchical porous graphene-like bubbles (PGBs) as a cathode host of the Li-S system was prepared by employing magnesium oxide (MgO) nanoparticles as templates for carbonization, potassium hydroxide (KOH) as activation agent, and car tal pitch as a carbon source. The synthesized PGBs owns a very thin carbon layer around 5 nm that can be comparable to graphite nanosheets. Its high content of mesoporous and interconnected curved structure can effectively entrap sulfur species and impose restrictions on their diffusion and shuttle effect, leading to a much stable electrochemical performance. The reversible capacity of PGBs@S 0.3 C still can be maintained at 831 mAh g⁻¹ after 100 cycles and 512 mAh g⁻¹ after 500 cycles.

ZIF-Derived Carbon Nanoframes as a Polysulfide Anchor and Conversion Mediator for High-Performance Lithium-Sulfur Cells

Improving the redox kinetics of sulfur species, while suppressing the "shuttle effects" to achieve stable cycling under high sulfur loading is an inevitable problem for lithium-sulfur (Li-S) cells to commercialization. Herein, the three-dimensional Zn, Co, and N codoped carbon nanoframe (3DZCN-C) was successfully synthesized by calcining precursor which protected by mesoporous SiO₂ and was used as cathode host for the first time to improve the performance of Li-S cells. Combining the merits of strong lithium polysulfides (LiPSs) anchoring and accelerating the conversion kinetics of sulfur species, 3DZCN-C effectively inhibit the shuttling of LiPSs and achieves excellent cyclability with capacity fading rate of 0.03% per cycle over 1000 cycles. Furthermore, the Li-S pouch cell has been assembled and has been shown to operate reliably with high energy density (>300 Wh kg^-1) even under a high sulfur loading of 10 mg cm^-2. This work provides a simple and effective way for the promotion and commercial application of Li-S cells.

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.

In situ Construction of Robust Biphasic Surface Layers on Lithium Metal for Lithium-Sulfide Batteries with Long Cycle Life

Lithium-sulfur (Li-S) batteries have potential in high energy density battery systems. However, intermediates of lithium polysulfides (LiPSs) can easily shuttle to the Li anode and react with Li metal to deplete the active materials and cause rapid failure of the battery. A facile solution pretreatment method for Li anodes involving a solution of metal fluorides/dimethylsulfoxide was developed to construct robust biphasic surface layers (BSLs) in situ. The BSLs consist of lithiophilic alloy (Li_x M) and LiF phases on Li metal, which inhibit the shuttle effect and increase the cycle life of Li-S batteries. The BSLs allow Li⁺ transport and they inhibit dendrite growth and shield the Li anodes from corrosive reaction with LiPSs. Li-S batteries containing BSLs-Li anodes demonstrate excellent cycling over 1000 cycles at 1 C and simultaneously maintain a high coulombic efficiency of 98.2 %. Based on our experimental and theoretical results, we propose a strategy for inhibition of the shuttle effect that produces high stability Li-S batteries.

A high-energy and long-cycling lithium-sulfur pouch cell via a macroporous catalytic cathode with double-end binding sites

Lithium-sulfur batteries are attractive alternatives to lithium-ion batteries because of their high theoretical specific energy and natural abundance of sulfur. However, the practical specific energy and cycle life of Li-S pouch cells are significantly limited by the use of thin sulfur electrodes, flooded electrolytes and Li metal degradation. Here we propose a cathode design concept to achieve good Li-S pouch cell performances. The cathode is composed of uniformly embedded ZnS nanoparticles and Co-N-C single-atom catalyst to form double-end binding sites inside a highly oriented macroporous host, which can effectively immobilize and catalytically convert polysulfide intermediates during cycling, thus eliminating the shuttle effect and lithium metal corrosion. The ordered macropores enhance ionic transport under high sulfur loading by forming sufficient triple-phase boundaries between catalyst, conductive support and electrolyte. This design prevents the formation of inactive sulfur (dead sulfur). Our cathode structure shows improved performances in a pouch cell configuration under high sulfur loading and lean electrolyte operation. A 1-A-h-level pouch cell with only 100% lithium excess can deliver a cell specific energy of >300 W h kg^-1 with a Coulombic efficiency >95% for 80 cycles.

Fast conversion of lithium (poly)sulfides in lithium–sulfur batteries using three-dimensional porous carbon

A three-dimensional porous carbon was prepared as a sulfur host. It effectively restrains dissolution of polysulfides by improving the conversion kinetics between polysulfides, thereby enhancing the electrochemical cycling stability.

Novel Bifunctional Separator with a Self-Assembled FeOOH/Coated g-C3N4/KB Bilayer in Lithium-Sulfur Batteries

Separator modification with metal oxide and carbon composite recently has become a potential and competitive way to confine polysulfide diffusion and mitigate the shuttling effect. However, other modification methods also have an impact on the stability of the modified layer and the enhancement of electrochemical performance. Herein, we first design a novel bifunctional separator combined with one self-assembled FeOOH layer via a chemical way and one conductive g-C₃N₄/KB layer by physical coating. Different from directly coating the metal oxide and carbon composite on the separator, the self-assembled FeOOH layer is firmly formed on the PP separator, which enables the chemical capture of the soluble polysulfide and prohibit the shuttling effect. Then, the coated g-C₃N₄/KB layer is further introduced to greatly enhance the transportation of lithium ions and physically confine the migration of intermediates. As a result, the battery with this bifunctional separator (G-SFO) achieves outstanding rate capacities (1000, 901, and 802 mA h/g at 0.5, 1, and 2 C). After 900 cycles at 1 C, it also shows excellent long cycle performance, with relatively low fading (0.055%). This original fabrication will present a new and feasible strategy for fabricating a bifunctional separator with metal oxide and carbon material.

Carbon Nanocage/Fe3O4/DNA-Based Magnetically Targeted Intracellular Imaging of Telomerase via Catalyzed Hairpin Assembly and Photodynamic-Photothermal Combination Therapy of Tumor Cells

Human telomerase has been identified as a potential tumor biomarker for early cancer diagnosis and cancer progression monitoring. We construct a novel magnetic targeting carbon nanocage/Fe₃O₄/DNA (CNC/Fe₃O₄/DNA) nanoprobe for intracellular imaging of telomerase via the signal amplification strategy catalyzed hairpin assembly (CHA) and for photodynamic-photothermal therapy of tumor cells. Telomerase primer DNA, trigger DNA, hairpin DNA1 (H1), and hairpin DNA2 (H2) were adsorbed to the surface of CNC/Fe₃O₄ nanoparticles (CNC/Fe₃O₄ NPs), and the fluorescence of (chlorin e6) Ce6 was quenched by CNC/Fe₃O₄ NPs. After entering the living cell through magnetic targeting, the telomerase primer DNA can be extended in the presence of highly activated telomerase, leading to the issue of trigger DNA, which can initiate the CHA cycling process followed by the amplification of the fluorescence intensity. The in vitro detection results justified that the proposed nanoprobe showed good sensitivity and selectivity for telomerase. Confocal microscopy studies indicated that such a nanoprobe can be used to detect the activity of telomerase in living cells and the fluorescence signal was stronger under the guidance of a magnetic field. We successfully employed this nanoprobe to monitor the dynamic activity of telomerase in various types of tumor cells and normal cells and to damage tumor cells by photodynamic-photothermal combination therapy, which evidenced that this is a promising biological method for early cancer diagnosis and tumor cell therapy.

New High Donor Electrolyte for Lithium-Sulfur Batteries

The unparalleled theoretical specific energy of lithium-sulfur (Li-S) batteries has attracted considerable research interest from within the battery community. However, most of the long cycling results attained thus far relies on using a large amount of electrolyte in the cell, which adversely affects the specific energy of Li-S batteries. This shortcoming originates from the low solubility of polysulfides in the electrolyte. Here, 1,3-dimethyl-2-imidazolidinone (DMI) is reported as a new high donor electrolyte for Li-S batteries. The high solubility of polysulfides in DMI and its activation of a new reaction route, which engages the sulfur radical (S₃ ^•- ), enables the efficient utilization of sulfur as reflected in the specific capacity of 1595 mAh g^-1 under lean electrolyte conditions of 5 μL_electrolyte mg_sulfur ^-1 . Moreover, the addition of LiNO₃ stabilizes the lithium metal interface, thereby elevating the cycling performance to one of the highest known for high donor electrolytes in Li-S cells. These engineered high donor electrolytes are expected to advance Li-S batteries to cover a wide range of practical applications, particularly by incorporating established strategies to realize the reversibility of lithium metal electrodes.

Immobilizing Polysulfide by In Situ Topochemical Oxidation Derivative TiC@Carbon-Included TiO2 Core-Shell Sulfur Hosts for Advanced Lithium-Sulfur Batteries

The performance of lithium-sulfur (Li-S) batteries is greatly hindered by the notorious shuttle effect of lithium polysulfides (LiPSs). To address this issue, in situ topochemical oxidation derivative TiC@carbon-included TiO₂ (TiC@C-TiO₂ ) core-shell composite is designed and proposed as a multifunctional sulfur host, which integrates the merits of conductive TiC core to facilitate the redox reaction kinetics of sulfur species, and porous C-TiO₂ shell to suppress the dissolution and shuttling of LiPSs through chemisorption. A unique dual chemical mediation mechanism is demonstrated for the proposed TiC@C-TiO₂ composite that synergistically entraps LiPSs through thiosulfate/polythionate conversion coupled with strong polar-polar interaction. The morphological characterization reveals that the TiC@C-TiO₂ -based cathode can well regulate the distribution of electrode materials to retard their accumulation inside the electrode, ensuring effective contact between the active materials and electrolyte. Based on its unique function and structure, the cathode delivers an improved capacity of 1256 mAh g^-1 at 0.2C, a remarkable rate capability of 643 mAh g^-1 , and an ultralow capacity decay rate of 0.065% per cycle at 2C over 900 cycles. This work not only demonstrates a dual chemical mediation mechanism to immobilize LiPSs, but also provides a universal strategy to construct multifunctional sulfur hosts for advanced Li-S batteries.

Metal-organic frameworks (MOFs) derived carbon-coated NiS nanoparticles anchored on graphene layers for high-performance Li-S cathode material

Due to its high capacity (1675 mAh g^-1), Li-S batteries have been considered as one of the ideal energy storage systems. The grand challenges of lithium-sulfur batteries are sulfur immobilization and improving electrical conductivity of cathode composite. The carbon-sulfur (C-S) composites and the polar materials (Ni(OH)₂, TiO₂, MnO₂, TiS₂, Co₉S₈, etc) integration have been proven to be two of the most effective routes to achieving good Li-S battery performance. However, each strategy has drawbacks: the C-S composites have low volume density and the polar materials are often lack of electrical conductivity. Therefore, the hybridization of carbon and polar materials shall provide synergistic effects achieving ideal sulfur cathode. Herein, a hybrid material with carbon-coated NiS nanoparticles grown on graphene sheets was synthesized through a hydrothermal reaction followed by two steps of annealing. The obtained composite has a well-balanced ratio between graphene and NiS. An optimized energy density was demonstrated in lithium-sulfur cells.

A separator based on natural illite/smectite clay for highly stable lithium-sulfur batteries

In spite of high theoretical specific capacity and specific energy of lithium-sulfur (Li-S) batteries, the poor cycle stability caused by polysulfides shuttle severely hinders their real-world applications. Here, a natural clay mineral (illite/smectite, ISC) and carbon black (C) coated Celgard^@2400 (ISC/C@Celgard) separator is reported. The separator shows super-electrolyte-philicity and good mechanical stability. The low-cost and eco-friendly ISC with abundant -OH groups can quickly trap a lot of polysulfides by Li-O and Li-S bonding with polysulfides. The ISC/C layer with uniform nanopores can also inhibit polysulfides shuttle by physical shield. Moreover, good electrical conductivity of the ISC/C layer can reactivate the adsorbed polysulfides and thus enhance S utilization. So, the separator endows the Li-S battery with very high initial reversible capacity (1322 mA h g^-1) at 0.1 C and excellent cycle stability with low capacity decay rate (0.054% per cycle) during 500 cycles at 1.0 C. Furthermore, a very high areal capacity (5.9 mAh cm^-2) is achieved for the battery composed of the separator and the self-supporting high S loading (8.9 mg cm^-2) CNT/S cathode at 0.32 mA cm^-2. This study opens the possibility of developing advanced separators using natural clay minerals for highly stable Li-S batteries.

Superhierarchical Conductive Framework Implanted with Nickel/Graphitic Carbon Nanocages as Sulfur/Lithium Metal Dual-Role Hosts for Li-S Batteries

High-energy-density Li-S batteries (LSBs) are considered as a promising next-generation energy-storage system. However, the sluggish redox kinetics and severe polysulfide shuttle effect in elemental sulfur cathodes, along with uncontrollable dendrite propagation in lithium metal anodes, inevitably depress the electrochemical performance of LSBs and impede their practical implementation. Motivated by a unique hierarchical geometry, specific chemical affinity, and nitrogen-enriched collagen component of natural skin fibers (SFs), here we proposed an effective structural engineering strategy for crafting an SF-derived superhierarchical N-doped porous carbon framework in situ implanted with nickel/graphitic carbon nanocages as a dual-role host to simultaneously address the challenges faced on the sulfur cathode and lithium anode in LSBs. The experimental results and theoretical calculation disclose that the implanted Ni nanoparticles and highly graphitic sp² carbon nanocages together with doped N heteroatoms not only provide a synergetic trapping-catalytic-conversion effect for regulating soluble polysulfides with promoted redox kinetics in the cathode at both room and elevated (55 °C) temperatures but also yield Ni-enhanced lithiophilic N-heteroatom active sites in the host framework to control Li deposition and suppress Li dendrite growth in anodes. Combining the cathodic and anodic improvements further achieves a superb rate and cycling performance in full LSB cells with stable Coulombic efficiency, showing great potential in developing reliable LSBs.

Carbon-Based Nanocages: A New Platform for Advanced Energy Storage and Conversion

Energy storage and conversion play a crucial role in modern energy systems, and the exploration of advanced electrode materials is vital but challenging. Carbon-based nanocages consisting of sp² carbon shells feature a hollow interior cavity with sub-nanometer microchannels across the shells, high specific surface area with a defective outer surface, and tunable electronic structure, much different from the intensively studied nanocarbons such as carbon nanotubes and graphene. These structural and morphological characteristics make carbon-based nanocages a new platform for advanced energy storage and conversion. Up-to-date synthetic strategies of carbon-based nanocages, the utilization of their unique porous structure and morphology for the construction of composites with foreign active species, and their significant applications to the advanced energy storage and conversion are reviewed. Structure-performance correlations are discussed in depth to highlight the contribution of carbon-based nanocages. The research challenges and trends are also envisaged for deepening and extending the study and application of this multifunctional material.

Toward Commercially Viable Li-S Batteries: Overall Performance Improvements Enabled by a Multipurpose Interlayer of Hyperbranched Polymer-Grafted Carbon Nanotubes

Shuttle effect and the low utilization of dissolved lithium polysulfides (LiPSs) are two prevailing concerns in Li-S battery (LSB) research. Energy efficiency on the other hand is often overlooked but vital to the commercial deployment of battery technology. In this work, a composite of hyperbranched poly(amidoamine)-modified multiwalled carbon nanotubes (PAMAM-CNTs) is successfully prepared by chemical grafting and employed as an interlayer material in LSBs. The high content and highly dispersed polar functional groups of PAMAM can efficiently adsorb and enhance the redox reaction of LiPSs. The CNTs function as a scaffold and current collector that reduces the internal polarization. The assembled LSB displays a high energy efficiency of 86% and a low capacity fading rate of 0.037% per cycle over 1200 cycles at 2 C. The cell also shows excellent cycle performance, high sulfur utilization, and improved stability at a high areal capacity of 9 mAh cm^-2 (achieved at a sulfur loading of 8.7 mg cm^-2) and low electrolyte/sulfur ratio of 6.1 mL g^-1. This thin (12 μm) and lightweight (0.34 mg cm^-2) interlayer has a negligible impact on the overall cell energy density.

A Rational Reconfiguration of Electrolyte for High-Energy and Long-Life Lithium-Chalcogen Batteries

Lithium-chalcogen batteries are an appealing choice for high-energy-storage technology. However, the traditional battery that employs liquid electrolytes suffers irreversible loss and shuttle of the soluble intermediates. New batteries that adopt Li⁺ -conductive polymer electrolytes to mitigate the shuttle problem are hindered by incomplete discharge of sulfur/selenium. To address the trade-off between energy and cycle life, a new electrolyte is proposed that reconciles the merits of liquid and polymer electrolytes while resolving each of their inferiorities. An in situ interfacial polymerization strategy is developed to create a liquid/polymer hybrid electrolyte between a LiPF₆ -coated separator and the cathode. A polymer-gel electrolyte in situ formed on the separator shows high Li⁺ transfer number to serve as a chemical barrier against the shuttle effect. Between the gel electrolyte and the cathode surface is a thin gradient solidification layer that enables transformation from gel to liquid so that the liquid electrolyte is maintained inside the cathode for rapid Li⁺ transport and high utilization of active materials. By addressing the dilemma between the shuttle chemistry and incomplete discharge of S/Se, the new electrolyte configuration demonstrates its feasibility to trigger higher capacity retention of the cathodes. As a result, Li-S and Li-Se cells with high energy and long cycle lives are realized, showing promise for practical use.

Enhanced Multiple Anchoring and Catalytic Conversion of Polysulfides by Amorphous MoS3 Nanoboxes for High-Performance Li-S Batteries

The practical implementation of lithium-sulfur batteries is obstructed by poor conductivity, sluggish redox kinetics, the shuttle effect, large volume variation, and low areal loading of sulfur electrodes. Now, amorphous N-doped carbon/MoS₃ (NC/MoS₃ ) nanoboxes with hollow porous architectures have been meticulously designed as an advanced sulfur host. Benefiting from the enhanced conductivity by the N-doped carbon, reduced shuttle effect by the strong chemical interaction between unsaturated Mo and lithium polysulfides, improved redox reaction kinetics by the catalytic effect of MoS₃ , great tolerance of volume variation and high sulfur loading arising from flexible amorphous materials with hollow-porous structures, the amorphous NC/MoS₃ nanoboxes enabled sulfur electrodes to deliver a high areal capacity with superior rate capacity and decent cycling stability. The synthetic strategy can be generalized to fabricate other amorphous metal sulfide nanoboxes.