Compactly Coupled Nitrogen‐Doped Carbon Nanosheets/Molybdenum Phosphide Nanocrystal Hollow Nanospheres as Polysulfide Reservoirs for High‐Performance Lithium–Sulfur Chemistry

Lithium–sulfur (Li–S) batteries have been disclosed as one of the most promising energy storage systems. However, the low utilization of sulfur, the detrimental shuttling behavior of polysulfides, and the sluggish kinetics in electrochemical processes, severely impede their application. Herein, 3D hierarchical nitrogen‐doped carbon nanosheets/molybdenum phosphide nanocrystal hollow nanospheres (MoP@C/N HCSs) are introduced to Li–S batteries via decorating commercial separators to inhibit polysulfides diffusion. It acts not only as a polysulfides immobilizer to provide strong physical trapping and chemical anchoring toward polysulfides, but also as an electrocatalyst to accelerate the kinetics of the polysulfides redox reaction, and to lower the Li₂S nucleation/dissolution interfacial energy barrier and self‐discharge capacity loss in working Li–S batteries, simultaneously. As a result, the Li–S batteries with MoP@C/N HCS‐modified separators show superior rate capability (920 mAh g^?1 at 2 C) and stable cycling life with only 0.04% capacity decay per cycle over 500 cycles at 1 C with nearly 100% Coulombic efficiency. Furthermore, the Li–S battery can achieve a high area capacity of 5.1 mAh cm^?2 with satisfied capacity retention when the cathode loading reaches 5.5 mg cm^?2. This work offers a brand new guidance for rational separator design into the energy chemistry of high‐stable Li–S batteries.     

Designing a Multifunctional Separator for High‐Performance Li–S Batteries at Elevated Temperature

The practical applications of lithium–sulfur (Li–S) batteries are seriously limited by the undesirable polysulfide shuttling and lithium dendrite growth. Herein, a multifunctional membrane is designed and prepared by coating a lithiated Nafion (Li@Nafion) layer and an Al₂O₃ layer on the two sides of a routine polymer membrane (polypropylene/polyethylene/polypropylene, PEP). The Li@Nafion layer faced to the sulfur cathode builds a “polysulfide‐phobic” surface to restrain the shuttle effect via Coulomb repulsion, while the Al₂O₃ layer with a uniform porous structure aids in regulating homogeneous Li⁺ fluxes to achieve stable Li electrodeposition. As a result, the Li//Li symmetric cell with a Li@Nafion/PEP/Al₂O₃ (LNPA) separator realizes stable Li plating/striping even after 1000 h at a high current density (5 mA cm^?2). Moreover, the Li–S batteries incorporating LNPA separators not only can achieve excellent outstanding cyclic stability at an ultrahigh sulfur loading (7.6 mg cm^?2), but also exhibit impressive electrochemical performance at an elevated temperature (60 °C). The rational design of the LNPA separator presents new insights to develop high‐performance Li–S batteries.     

MoS2/Celgard Separator as Efficient Polysulfide Barrier for Long‐Life Lithium–Sulfur Batteries

A high lithium conductive MoS₂/Celgard composite separator is reported as efficient polysulfides barrier in Li–S batteries. Significantly, thanks to the high density of lithium ions on MoS₂ surface, this composite separator shows high lithium conductivity, fast lithium diffusion, and facile lithium transference. When used in Li–S batteries, the separator is proven to be highly efficient for depressing polysulfides shuttle, leading to high and long cycle stability. With 65% of sulfur loading, the device with MoS₂/Celgard separator delivers an initial capacity of 808 mAh g^?1 and a substantial capacity of 401 mAh g^?1 after 600 cycles, corresponding to only 0.083% of capacity decay per cycle that is comparable to the best reported result so far. In addition, the Coulombic efficiency remains more than 99.5% during all 600 cycles, disclosing an efficient ionic sieve preventing polysulfides migration to the anode while having negligible influence on Li⁺ ions transfer across the separator. The strategy demonstrated in this work will open the door toward developing efficient separators with flexible 2D materials beyond graphene for energy‐storage devices.     

Promoting Reversible Redox Kinetics by Separator Architectures Based on CoS2/HPGC Interlayer as Efficient Polysulfide‐Trapping Shield for Li–S Batteries

Main obstacles from the shuttle effect and slow conversion rate of soluble polysulfide compromise the sulfur utilization and cycling life for lithium sulfur (Li–S) batteries. In pursuit of a practically viable high performance Li–S battery, a separator configuration (CoS₂/HPGC/interlayer) as efficient polysulfide trapping barrier is reported. This configuration endows great advantages, particularly enhanced conductivity, promoted polysulfide trapping capability, accelerated sulfur electrochemistry, when using the functional interlayer for Li–S cells. Attributed to the above merits, such cell shows excellent cyclability, with a capacity of 846 mAh g^?1 after 250 cycles corresponding to a high capacity retention of 80.2% at 0.2 C, and 519 mAh g^?1 after 500 cycles at 1C (1C = 1675 mA g^?1). In addition, the optimized separator exhibits a high initial areal capacity of 4.293 mAh cm^?2 at 0.1C. Moreover, with CoS₂/HPGC/interlayer, the sulfur cell enables a low self‐discharge rate with a very high capacity retention of 97.1%. This work presents a structural engineering of the separator toward suppressing the dissolution of soluble Li₂Sn moieties and simultaneously promoting the sulfur conversion kinetics, thus achieving durable and high capacity Li–S batteries.     

Robust,Ultra‐Tough Flexible Cathodes for High‐Energy Li–S Batteries

Sulfur cathodes have become appealing for rechargeable batteries because of their high theoretical capacity (1675 mA h g^?1). However, the conventional cathode configuration borrowed from lithium‐ion batteries may not allow the pure sulfur cathode to put its unique materials chemistry to good use. The solid_(sulfur)–liquid_{(polysulfides)}–solid_(sulfides) phase transitions generate polysulfide intermediates that are soluble in the commonly used organic solvents in Li–S cells. The resulting severe polysulfide diffusion and the irreversible active‐material loss have been hampering the development of Li–S batteries for years. The present study presents a robust, ultra‐tough, flexible cathode with the active‐material fillings encapsulated between two buckypapers (B), designated as buckypaper/sulfur/buckypaper (B/S/B) cathodes, that suppresses the irreversible polysulfide diffusion to the anode and offers excellent electrochemical reversibility with a low capacity fade rate of 0.06% per cycle after 400 cycles. Engineering enhancements demonstrate that the B/S/B cathodes represent a facile approach for the development of high‐performance sulfur electrodes with a high areal capacity of 5.1 mA h cm^?2, which increases further to approach 7 mA h cm^?2 on coupling with carbon‐coated separators.     

Integration of Binary Active Sites: Co3V2O8 as Polysulfide Traps and Catalysts for Lithium‐Sulfur Battery with Superior Cycling Stability

Lithium‐sulfur (Li‐S) batteries as a promising energy storage candidate have attracted attention due to their high energy density (2600 Wh kg^?1). However, the serious shuttle effect caused by the dissolution of the lithium polysulfides (LiPS) in electrolyte significantly degrades their cycling life and rate performance. Herein, the “binary active sites” concept in a Li‐S battery system via the design of a cobalt vanadium oxide (CVO) modified multifunctional separator is designed. In the case of CVO, active vanadium sites simultaneously anchor the LiPS through the chemical affinity and active cobalt sites can dominate a rapid kinetic conversion. Such a synergistic effect contributes to improving the utilization of sulfur in the electrochemical process for the enhanced electrochemical performance. As a result, the Li‐S battery with the CVO modified separator possesses a high reversible capacity of 1585.5 mAh g^?1 at 0.1 C and superior cycling stability with 0.012% capacity decay cycle^?1 after 3000 cycles. More impressively, the assembled soft‐packaged Li‐S devices can exhibit the excellent stability under bending states. This binary active sites strategy provides a route to design the functional materials for modifying separators of Li‐S batteries to improve the performance.     

Stabilizing Lithium–Sulfur Batteries through Control of Sulfur Aggregation and Polysulfide Dissolution

Lithium–sulfur (Li–S) batteries are investigated intensively as a promising large‐scale energy storage system owing to their high theoretical energy density. However, the application of Li–S batteries is prevented by a series of primary problems, including low electronic conductivity, volumetric fluctuation, poor loading of sulfur, and shuttle effect caused by soluble lithium polysulfides. Here, a novel composite structure of sulfur nanoparticles attached to porous‐carbon nanotube (p‐CNT) encapsulated by hollow MnO₂ nanoflakes film to form p‐CNT@Void@MnO₂/S composite structures is reported. Benefiting from p‐CNTs and sponge‐like MnO₂ nanoflake film, p‐CNT@Void@MnO₂/S provides highly efficient pathways for the fast electron/ion transfer, fixes sulfur and Li₂S aggregation efficiently, and prevents polysulfide dissolution during cycling. Besides, the additional void inside p‐CNT@Void@MnO₂/S composite structure provides sufficient free space for the expansion of encapsulated sulfur nanoparticles. The special material composition and structural design of p‐CNT@Void@MnO₂/S composite structure with a high sulfur content endow the composite high capacity, high Coulombic efficiency, and an excellent cycling stability. The capacity of p‐CNT@Void@MnO₂/S electrode is ≈599.1 mA h g^?1 for the fourth cycle and ≈526.1 mA h g^?1 after 100 cycles, corresponding to a capacity retention of ≈87.8% at a high current density of 1.0 C.     

Highly Safe Electrolyte Enabled via Controllable Polysulfide Release and Efficient Conversion for Advanced Lithium–Sulfur Batteries

Conventional lithium–sulfur batteries often suffer from fatal problems such as high flammability, polysulfide shuttling, and lithium dendrites growth. Here, highly‐safe lithium–sulfur batteries based on flame‐retardant electrolyte (dimethoxyether/1,1,2,2‐tetrafluoroethyl 2,2,3,3‐tetrafluoropropyl ether) coupled with functional separator (nanoconductive carbon‐coated cellulose nonwoven) to resolve aforementioned bottle‐neck issues are demonstrated. It is found that this flame‐retardant electrolyte exhibits excellent flame retardancy and low solubility of polysulfide. In addition, Li/Li symmetrical cells using such flame‐retardant electrolyte deliver extraordinary long‐term cycling stability (less than 10 mV overpotential) for over 2500 h at 1.0 mA cm^?2 and 1.0 mAh cm^?2. Moreover, bare sulfur cathode–based lithium–sulfur batteries using this flame retardant electrolyte coupled with nanoconductive carbon‐coated cellulose separator can retain 83.6% discharge capacity after 200 cycles at 0.5 C. Under high charge/discharge rate (4 C), lithium–sulfur cells still show high charge/discharge capacity of ≈350 mAh g^?1. Even at an elevated temperature of 60 °C, discharge capacity of 870 mAh g^?1 can be retained. More importantly, high‐loading bare sulfur cathode (4 mg cm^?2)–based lithium–sulfur batteries can also deliver high charge/discharge capacity over 806 mAh g^?1 after 56 cycles. Undoubtedly, the strategy of flame retardant electrolyte coupled with carbon‐coated separator enlightens highly safe lithium–sulfur batteries at a wide range of temperature.     

Yolk–Shelled C@Fe3O4 Nanoboxes as Efficient Sulfur Hosts for High‐Performance Lithium–Sulfur Batteries

Owing to the high theoretical specific capacity (1675 mA h g^?1) and low cost, lithium–sulfur (Li–S) batteries offer advantages for next‐generation energy storage. However, the polysulfide dissolution and low electronic conductivity of sulfur cathodes limit the practical application of Li–S batteries. To address such issues, well‐designed yolk–shelled carbon@Fe₃O₄ (YSC@Fe₃O₄) nanoboxes as highly efficient sulfur hosts for Li–S batteries are reported here. With both physical entrapment by carbon shells and strong chemical interaction with Fe₃O₄ cores, this unique architecture immobilizes the active material and inhibits diffusion of the polysulfide intermediates. Moreover, due to their high conductivity, the carbon shells and the polar Fe₃O₄ cores facilitate fast electron/ion transport and promote continuous reactivation of the active material during the charge/discharge process, resulting in improved electrochemical utilization and reversibility. With these merits, the S/YSC@Fe₃O₄ cathodes support high sulfur content (80 wt%) and loading (5.5 mg cm^?2) and deliver high specific capacity, excellent rate capacity, and long cycling stability. This work provides a new perspective to design a carbon/metal‐oxide‐based yolk–shelled framework as a high sulfur‐loading host for advanced Li–S batteries with superior electrochemical properties.     

Graphene Oxide Sieving Membrane for Improved Cycle Life in High‐Efficiency Redox‐Mediated Li–O2 batteries

As soluble catalysts, redox‐mediators (RMs) endow mobility to catalysts for unconstrained access to tethered solid discharge products, lowering the energy barrier for Li₂O₂ formation/decomposition; however, this desired mobility is accompanied by the undesirable side effect of RM migration to the Li metal anode. The reaction between RMs and Li metal degrades both the Li metal and the RMs, leading to cell deterioration within a few cycles. To extend the cycle life of redox‐mediated Li–O₂ batteries, herein graphene oxide (GO) membranes are reported as RM‐blocking separators. It is revealed that the size of GO nanochannels is narrow enough to reject 5,10‐dihydro‐5,10‐dimethylphenazine (DMPZ) while selectively allowing the transport of smaller Li⁺ ions. The negative surface charges of GO further repel negative ions via Donnan exclusion, greatly improving the lithium ion transference number. The Li–O₂ cells with GO membranes efficiently harness the redox‐mediation activity of DMPZ for improved performance, achieving energy efficiency of above 80% for more than 25 cycles, and 90% for 78 cycles when the capacity limits were 0.75 and 0.5 mAh cm^‐2, respectively. Considering the facile preparation of GO membranes, RM‐sieving GO membranes can be cost‐effective and processable functional separators in Li–O₂ batteries.     

Single Nickel Atoms on Nitrogen‐Doped Graphene Enabling Enhanced Kinetics of Lithium–Sulfur Batteries

Lithium–sulfur (Li–S) batteries have arousing interest because of their high theoretical energy density. However, they often suffer from sluggish conversion of lithium polysulfides (LiPS) during the charge/discharge process. Single nickel (Ni) atoms on nitrogen‐doped graphene (Ni@NG) with Ni–N₄ structure are prepared and introduced to modify the separators of Li–S batteries. The oxidized Ni sites of the Ni–N₄ structure act as polysulfide traps, efficiently accommodating polysulfide ion electrons by forming strong S_x ^2????Ni? N bonding. Additionally, charge transfer between the LiPS and oxidized Ni sites endows the LiPS on Ni@NG with low free energy and decomposition energy barrier in an electrochemical process, accelerating the kinetic conversion of LiPS during the charge/discharge process. Furthermore, the large binding energy of LiPS on Ni@NG also shows its ability to immobilize the LiPS and further suppresses the undesirable shuttle effect. Therefore, a Li–S battery based on a Ni@NG modified separator exhibits excellent rate performance and stable cycling life with only 0.06% capacity decay per cycle. It affords fresh insights for developing single‐atom catalysts to accelerate the kinetic conversion of LiPS for highly stable Li–S batteries.     

Rational design of graphene @ nitrogen and phosphorous dual-doped porous carbon sandwich-type layer for advanced lithium–sulfur batteries

Lithium sulfur (Li–S) batteries show great prospect as a next generation high energy density rechargeable battery systems. However, the practical utilization of Li–S batteries is still obstructed by the shuttle effects which inducing the fast capacity fading and the loss of active sulfur. Herein, a special graphene @ nitrogen and phosphorous dual-doped porous carbon (N–P–PC/G) is presented to modify a commercial separator for an advanced Li–S battery. The N–P–PC/G nanosheet employs graphene layer as an excellent conductive framework covered with uniform layers of N, P dual-doped porous carbon on both sides which possessing massive interconnected meso-/micropores. It is demonstrated that the N–P–PC/G-modified separator can suppress the shuttle effects by coupling interactions including physical absorption, chemical adsorption and interfacial interaction. With the aid of the N–P–PC/G-modified separator, the pure sulfur cathode with high-sulfur loading of 3 mg cm^?2 offers a high initial discharge capacity of 1207 mA h g^?1 at 0.5 C (1 C = 1675 mA h g^?1), and a maintained capacity of 635 mA h g^?1 (fading rate of only 0.095% per cycle), after 500 cycles. This work suggests that combining hybrid nanocarbon with multi-heteroatom doping to modify the commercial separator is an effective approach to obtain high electrochemical performance Li–S batteries.     

Promoting the Transformation of Li2S2 to Li2S: Significantly Increasing Utilization of Active Materials for High‐Sulfur‐Loading Li–S Batteries

Lithium–sulfur (Li–S) batteries with high sulfur loading are urgently required in order to take advantage of their high theoretical energy density. Ether‐based Li–S batteries involve sophisticated multistep solid–liquid–solid–solid electrochemical reaction mechanisms. Recently, studies on Li–S batteries have widely focused on the initial solid (sulfur)–liquid (soluble polysulfide)–solid (Li₂S₂) conversion reactions, which contribute to the first 50% of the theoretical capacity of the Li–S batteries. Nonetheless, the sluggish kinetics of the solid–solid conversion from solid‐state intermediate product Li₂S₂ to the final discharge product Li₂S (corresponding to the last 50% of the theoretical capacity) leads to the premature end of discharge, resulting in low discharge capacity output and low sulfur utilization. To tackle the aforementioned issue, a catalyst of amorphous cobalt sulfide (CoS₃) is proposed to decrease the dissociation energy of Li₂S₂ and propel the electrochemical transformation of Li₂S₂ to Li₂S. The CoS₃ catalyst plays a critical role in improving the sulfur utilization, especially in high‐loading sulfur cathodes (3–10 mg cm^?2). Accordingly, the Li₂S/Li₂S₂ ratio in the discharge products increased to 5.60/1 from 1/1.63 with CoS₃ catalyst, resulting in a sulfur utilization increase of 20% (335 mAh g^?1) compared to the counterpart sulfur electrode without CoS₃.     

A Highly Conductive MOF of Graphene Analogue Ni3(HITP)2 as a Sulfur Host for High‐Performance Lithium–Sulfur Batteries

Lithium–sulfur (Li–S) batteries have been considered as one of the most promising energy storage systems owing to their high theoretical capacity and energy density. However, their commercial applications are obstructed by sluggish reaction kinetics and rapid capacity degradation mainly caused by polysulfide shuttling. Herein, the first attempt to utilize a highly conductive metal–organic framework (MOF) of Ni₃(HITP)₂ graphene analogue as the sulfur host material to trap and transform polysulfides for high‐performance Li–S batteries is made. Besides, the traditional conductive additive acetylene black is replaced by carbon nanotubes to construct matrix conduction networks for triggering the rate and cycling performance of the active cathode. As a result, the S@Ni₃(HITP)₂ with sulfur content of 65.5 wt% shows excellent sulfur utilization, rate performance, and cyclic durability. It delivers a high initial capacity of 1302.9 mAh g^?1 and good capacity retention of 848.9 mAh g^?1 after 100 cycles at 0.2 C. Highly reversible discharge capacities of 807.4 and 629.6 mAh g^?1 are obtained at 0.5 and 1 C for 150 and 300 cycles, respectively. Such kinds of pristine MOFs with high conductivity and abundant polar sites reveal broad promising prospect for application in the field of high‐performance Li–S batteries.     

A High‐Capacity O2‐Type Li‐Rich Cathode Material with a Single‐Layer Li2MnO3 Superstructure

A high capacity cathode is the key to the realization of high‐energy‐density lithium‐ion batteries. The anionic oxygen redox induced by activation of the Li₂MnO₃ domain has previously afforded an O3‐type layered Li‐rich material used as the cathode for lithium‐ion batteries with a notably high capacity of 250–300 mAh g^?1. However, its practical application in lithium‐ion batteries has been limited due to electrodes made from this material suffering severe voltage fading and capacity decay during cycling. Here, it is shown that an O2‐type Li‐rich material with a single‐layer Li₂MnO₃ superstructure can deliver an extraordinary reversible capacity of 400 mAh g^?1 (energy density: ≈1360 Wh kg^?1). The activation of a single‐layer Li₂MnO₃ enables stable anionic oxygen redox reactions and leads to a highly reversible charge–discharge cycle. Understanding the high performance will further the development of high‐capacity cathode materials that utilize anionic oxygen redox processes.     

A Delicately Designed Sulfide Graphdiyne Compatible Cathode for High‐Performance Lithium/Magnesium–Sulfur Batteries

Novel sulfur cathodes hold the key to the development of metal–sulfur batteries, the promising candidate of next‐generation high‐energy‐storage systems. Herein, a fascinating sulfur cathode based on sulfide graphdiyne (SGDY) is designed with a unique structure, which is composed of a conducting carbon skeleton with high Li⁺ mobility and short sulfur energy‐storing unites. The SGDY cathode can essentially avoid polysulfide dissolution and be compatible with commercially available carbonate‐based electrolytes and Grignard reagent‐based electrolytes (all phenyl complex (APC) type electrolytes). Both the assembled Li–S and Mg–S batteries exhibit excellent electrochemical performances including large capacity, superior rate capability, high capacity retention, and high Coulombic efficiency. More importantly, this is the first implementation case of a reliable Mg–S system based on nucleophilic APC electrolytes.     

Engineering Oxygen Vacancies in a Polysulfide-Blocking Layer with Enhanced Catalytic Ability

The practical application of the lithium–sulfur (Li–S) battery is seriously restricted by its shuttle effect, low conductivity, and low sulfur loading. Herein, first-principles calculations are conducted to verify that the introduction of oxygen vacancies in TiO₂ not only enhances polysulfide adsorption but also greatly improves the catalytic ability and both the ion and electron conductivities. A commercial polypropylene (PP) separator decorated with TiO₂ nanosheets with oxygen vacancies (OVs-TiO₂@PP) is fabricated as a strong polysulfide barrier for the Li–S battery. The thickness of the OVs-TiO₂ modification layer is only 500 nm with a low areal mass of around 0.12 mg cm⁻², which enhances the fast lithium-ion penetration and the high energy density of the whole cell. As a result, the cell with the OVs-TiO₂@PP separator exhibits a stable electrochemical behavior at 2.0 C over 500 cycles, even under a high sulfur loading of 7.1 mg cm⁻², and an areal capacity of 5.83 mAh cm⁻² remains after 100 cycles. The proposed strategy of engineering oxygen vacancies is expected to have wide applications in Li–S batteries.     

Defect-Rich Single Atom Catalyst Enhanced Polysulfide Conversion Kinetics to Upgrade Performance of Li–S Batteries

Lithium–sulfur (Li–S) batteries have attracted considerable attention owing to their extremely high energy densities. However, the application of Li–S batteries has been limited by low sulfur utilization, poor cycle stability, and low rate capability. Accelerating the rapid transformation of polysulfides is an effective approach for addressing these obstacles. In this study, a defect-rich single-atom catalytic material (Fe-N4/DCS) is designed. The abundantly defective environment is favorable for the uniform dispersion and stable existence of single-atom Fe, which not only improves the utilization of single-atom Fe but also efficiently adsorbs polysulfides and catalyzes the rapid transformation of polysulfides. To fully exploit the catalytic activity, catalytic materials are used to modify the routine separator (Fe-N₄/DCS/PP). Density functional theory and in situ Raman spectroscopy are used to demonstrate that Fe-N₄/DCS can effectively inhibit the shuttling of polysulfides and accelerate the redox reaction. Consequently, the Li–S battery with the modified separator achieves an ultralong cycle life (a capacity decay rate of only 0.03% per cycle at a current of 2 C after 800 cycles), and an excellent rate capability (894 mAh g⁻¹ at 3 C). Even at a high sulfur loading of 5.51 mg cm⁻² at 0.2 C, the reversible areal capacity still reaches 5.4 mAh cm⁻².     

Long‐Life Lithium–Sulfur Batteries with a Bifunctional Cathode Substrate Configured with Boron Carbide Nanowires

Developing high‐energy‐density lithium–sulfur (Li–S) batteries relies on the design of electrode substrates that can host a high sulfur loading and still attain high electrochemical utilization. Herein, a new bifunctional cathode substrate configured with boron‐carbide nanowires in situ grown on carbon nanofibers (B₄C@CNF) is established through a facile catalyst‐assisted process. The B₄C nanowires acting as chemical‐anchoring centers provide strong polysulfide adsorptivity, as validated by experimental data and first‐principle calculations. Meanwhile, the catalytic effect of B₄C also accelerates the redox kinetics of polysulfide conversion, contributing to enhanced rate capability. As a result, a remarkable capacity retention of 80% after 500 cycles as well as stable cyclability at 4C rate is accomplished with the cells employing B₄C@CNF as a cathode substrate for sulfur. Moreover, the B₄C@CNF substrate enables the cathode to achieve both high sulfur content (70 wt%) and sulfur loading (10.3 mg cm^?2), delivering a superb areal capacity of 9 mAh cm^?2. Additionally, Li–S pouch cells fabricated with the B₄C@CNF substrate are able to host a high sulfur mass of 200 mg per cathode and deliver a high discharge capacity of 125 mAh after 50 cycles.     

Direct Visualization of the Reversible O2−/O− Redox Process in Li‐Rich Cathode Materials

Conventional cathodes of Li‐ion batteries mainly operate through an insertion–extraction process involving transition metal redox. These cathodes will not be able to meet the increasing requirements until lithium‐rich layered oxides emerge with beyond‐capacity performance. Nevertheless, in‐depth understanding of the evolution of crystal and excess capacity delivered by Li‐rich layered oxides is insufficient. Herein, various in situ technologies such as X‐ray diffraction and Raman spectroscopy are employed for a typical material Li_1.2Ni_0.2Mn_0.6O₂, directly visualizing O^?? O^? (peroxo oxygen dimers) bonding mostly along the c‐axis and demonstrating the reversible O^2?/O^? redox process. Additionally, the formation of the peroxo O? O bond is calculated via density functional theory, and the corresponding O? O bond length of ≈1.3 Å matches well with the in situ Raman results. These findings enrich the oxygen chemistry in layered oxides and open opportunities to design high‐performance positive electrodes for lithium‐ion batteries.