Conductive Porous Laminated Vanadium Nitride as Carbon-Free Hosts for High-Loading Sulfur Cathodes in Lithium-Sulfur Batteries

Novel Zn0.079V2O5·0.53H2O/Graphene aerogel as high-rate and long-life cathode materials of aqueous zinc-ion batteries

Aqueous zinc-ion batteries (ZIBs) have attracted more and more attention due to their advantages of low cost, high safety and environmental protection. Unfortunately, the unsatisfactory capacity at high current density and long-term cycling performance of cathode materials hinder the development of ZIBs. Here, a novel Zn0.079V2O5·0.53H2O/graphene (ZVOH@rGO) hybrid aerogel composed of ultrathin Zn0.079V2O5·0.53H2O (ZVOH) nanoribbons and 3D continuous graphene conductive network was successfully prepared and used as cathode of ZIBs. Taking advantage of the synergistic effects associated with ion doping, morphology control and unique aerogel structure, the ZVOH@rGO electrode demonstrated ultrafast charge/discharge capability and remarkable cycling stability: A high reversible capacity of 286.7 mAh g-1 was achieved at a current density as large as 30 A g-1, and an impressive capacity retention ratio of 75.6 % was realized over 9800 ultra-long cycles at 12 A g-1. This work is of great significance for the synthesis modification of vanadium oxides and the development of high performance ultrafast charge-discharge ZIBs.

Rechargeable Metal-Sulfur Batteries: Key Materials to Mechanisms

Rechargeable metal-sulfur batteries are considered promising candidates for energy storage due to their high energy density along with high natural abundance and low cost of raw materials. However, they could not yet be practically implemented due to several key challenges: (i) poor conductivity of sulfur and the discharge product metal sulfide, causing sluggish redox kinetics, (ii) polysulfide shuttling, and (iii) parasitic side reactions between the electrolyte and the metal anode. To overcome these obstacles, numerous strategies have been explored, including modifications to the cathode, anode, electrolyte, and binder. In this review, the fundamental principles and challenges of metal-sulfur batteries are first discussed. Second, the latest research on metal-sulfur batteries is presented and discussed, covering their material design, synthesis methods, and electrochemical performances. Third, emerging advanced characterization techniques that reveal the working mechanisms of metal-sulfur batteries are highlighted. Finally, the possible future research directions for the practical applications of metal-sulfur batteries are discussed. This comprehensive review aims to provide experimental strategies and theoretical guidance for designing and understanding the intricacies of metal-sulfur batteries; thus, it can illuminate promising pathways for progressing high-energy-density metal-sulfur battery systems.

Regulating Electron Filling and Orbital Occupancy of Anti-Bonding States of Transition Metal Nitride Heterojunction for High Areal Capacity Lithium-Sulfur Full Batteries

The commercialization of lithium-sulfur (Li-S) battery is seriously hindered by the shuttle behavior of lithium (Li) polysulfide, slow conversion kinetics, and Li dendrite growth. Herein, a novel hierarchical p-type iron nitride and n-type vanadium nitride (p-Fe2 N/n-VN) heterostructure with optimal electronic structure, confined in vesicle-like N-doped nanofibers (p-Fe2 N/n-VN⊂PNCF), is meticulously constructed to work as "one stone two birds" dual-functional hosts for both the sulfur cathode and Li anode. As demonstrated, the d-band center of high-spin Fe atom captures more electrons from V atom to realize more π* and moderate σ* bond electron filling and orbital occupation; thus, allowing moderate adsorption intensity for polysulfides and more effective d-p orbital hybridization to improve reaction kinetics. Meanwhile, this unique structure can dynamically balance the deposition and transport of Li on the anode; thereby, more effectively inhibiting Li dendrite growth and promoting the formation of a uniform solid electrolyte interface. The as-assembled Li-S full batteries exhibit the conspicuous capacities and ultralong cycling lifespan over 2000 cycles at 5.0 C. Even at a higher S loading (20 mg cm-2 ) and lean electrolyte (2.5 µL mg-1 ), the full cells can still achieve an ultrahigh areal capacity of 16.1 mAh cm-2 after 500 cycles at 0.1 C.

Coupling Engineering of NH4 + Pre-Intercalation and Rich Oxygen Vacancies in Tunnel WO3 Toward Fast and Stable Rocking Chair Zinc-Ion Battery

Herein, for the first time, a pre-intercalated non-metal ion (NH₄ ⁺ ) with rich oxygen vacancies stabilized tunnel WO₃ is proposed as a new intercalation anode to construct Zn-metal-free rocking-chair ZIBs. With the ethylene glycol additive in the aqueous electrolyte, the Zn²⁺ solvation structure can be regulated and the side reaction of hydrogen evolution can also be suppressed. Owing to the integrated synergetic modification, a high-rate and ultra-stable aqueous Zn-(NH₄ )_x WO₃ battery can be constructed, which exhibits an improved specific capacity (153 mAh g^-1 at 0.1 A g^-1 ), excellent rate performance (when the current density increases to 3 A g^-1 , the specific capacitance is still 86 mAh g^-1 ), and a high cycle stability with 100% capacity retention after 2,200 cycles under 5 A g^-1 . Ex situ X-ray diffraction and XPS reveal the reversible insertion/extraction of Zn²⁺ in (NH₄ )_x WO₃ . The assembled (NH₄ )_x WO₃ //MnO₂ rocking-chair ZIBs delivers excellent capacity of 82 mAh g^-1 at 0.1 A g^-1 , impressive cyclic stability. Additionally, the flexible (NH₄ )_x WO₃ //MnO₂ ZIBs can power the electrochromic device-based PANI/WO₃ with high color contrast and fast response time. This study provides new insight for developing high-performance rechargeable aqueous ZIBs.

Progressive activation of porous vanadium nitride microspheres with intercalation-conversion reactions toward high performance over a wide temperature range for zinc-ion batteries

Rechargeable aqueous zinc-ion batteries have great promise for becoming next-generation storage systems, although the irreversible intercalation of Zn²⁺ and sluggish reaction kinetics impede their wide application. Therefore, it is urgent to develop highly reversible zinc-ion batteries. In this work, we modulate the morphology of vanadium nitride (VN) with different molar amounts of cetyltrimethylammonium bromide (CTAB). The optimal electrode has porous architecture and excellent electrical conductivity, which can alleviate volume expansion/contraction and allow for fast ion transmission during the Zn²⁺ storage process. Furthermore, the CTAB-modified VN cathode undergoes a phase transition that provides a better framework for vanadium oxide (VO_x). With the same mass of VN and VO_x, VN provides more active material after phase conversion due to the molar mass of the N atom being less than that of the O atom, thus increasing the capacity. As expected, the cathode displays an excellent electrochemical performance of 272 mAh g^-1 at 5 A g^-1, high cycling stability up to 7000 cycles, and excellent performance over a wide temperature range. This discovery creates new possibilities for the development of high-performance multivalent ion aqueous cathodes with rapid reaction mechanisms.

Proton-Induced Defect-Rich Vanadium Oxides as Reversible Polysulfide Conversion Sites for High-Performance Lithium Sulfur Batteries

Lithium-sulfur (Li-S) batteries have attracted attention due to their high theoretical energy density, natural abundance, and low cost. However, the diffusion of polysulfides decreases the utilization and further degrades the battery's life. We have successfully fabricated a defect-rich layered sodium vanadium oxide with proton doping (HNVO) nanobelt and used it as the functional interface layer on the separator in Li-S batteries. Benefiting from the abundant defects of NVO and the catalytic activity of metal vanadium in the electrochemical process, the shuttle of polysulfides was greatly decreased by reversible chemical adsorption. Moreover, the extra graphene layer contributes to accelerating the charge carrier at high current densities. Therefore, a Li-S battery with G@HNVO delivers a high capacity of 1494.8 mAh g^-1 at 0.2 C and a superior cycling stability over 700 cycles at 1 C. This work provides an effective strategy for designing the electrode/separator interface layer to achieve high-performance Li-S batteries.

Unraveling Polysulfide's Adsorption and Electrocatalytic Conversion on Metal Oxides for Li-S Batteries

Lithium sulfur (LiS) batteries possess high theoretical capacity and energy density, holding great promise for next generation electronics and electrical vehicles. However, the LiS batteries development is hindered by the shuttle effect and sluggish conversion kinetics of lithium polysulfides (LiPSs). Designing highly polar materials such as metal oxides (MOs) with moderate adsorption and effective catalytic activity is essential to overcome the above issues. To design efficient MOs catalysts, it is critical and necessary to understand the adsorption mechanism and associated catalytic processes of LiPSs. However, most reviews still lack a comprehensive investigation of the basic mechanism and always ignore their in-depth relationship. In this review, a systematic analysis toward understanding the underlying adsorption and catalytic mechanism in LiS chemistry as well as discussion of the typical works concerning MOs electrocatalysts are provided. Moreover, to improve the sluggish "adsorption-diffusion-conversion" process caused by the low conductive nature of MOs, oxygen vacancies and heterostructure engineering are elucidated as the two most effective strategies. The challenges and prospects of MOs electrocatalysts are also provided in the last section. The authors hope this review will provide instructive guidance to design effective catalyst materials and explore practical possibilities for the commercialization of LiS batteries.

Cathode materials for lithium-sulfur battery: a review

Lithium-sulfur batteries (LSBs) are considered to be one of the most promising candidates for becoming the post-lithium-ion battery technology, which would require a high level of energy density across a variety of applications. An increasing amount of research has been conducted on LSBs over the past decade to develop fundamental understanding, modelling, and application-based control. In this study, the advantages and disadvantages of LSB technology are discussed from a fundamental perspective. Then, the focus shifts to intermediate lithium polysulfide adsorption capacity and the challenges involved in improving LSBs by using alternative materials besides carbon for cathode construction. Attempted alternative materials include metal oxides, metal carbides, metal nitrides, MXenes, graphene, quantum dots, and metal organic frameworks. One critical issue is that polar material should be more favorable than non-polar carbonaceous materials in the aspect of intermediate lithium polysulfide species adsorption and suppress shuttle effect. It will be also presented that by preparing cathode with suitable materials and morphological structure, high-performance LSB can be obtained.

Graphical abstract

Self-Assembled Networks for Regulating Lithium Polysulfides in Lithium-Sulfur Batteries

Inhibiting the shuttle effect caused by soluble lithium polysulfides (LiPSs) is of importance for lithium-sulfur (Li-S) batteries. Here, a strategy was developed to construct protective layers by self-assembly networks to regulate the LiPSs. 2,5-Dichloropyridine (25DCP) holds two kinds of functional groups. Among them, the two C-Cl bonds were nucleophilic substituted by S in LiPSs to form long chains. The pyridine N interacted with Li in other LiPSs via Li bonds to form a short chain. As a result, the long chains were cross-linked by the short chain to form an insoluble network. The as-prepared network covered the sulfur electrode interface to suppress the shuttle effect of the subsequently generated LiPSs. Furthermore, 25DCP improved the redox dynamics by changing the energy level and electronic structure of the sulfur species. Therefore, the Li-S batteries with 25DCP exhibited good electrochemical performance. This work provides a feasible strategy for regulating the LiPSs.

A cerium vanadate/S heterostructure for a long-life zinc-ion battery: efficient electron transfer by the anchored sulfur

Ce_0.25V₂O₅(H₂O)·H₂O (CeVO) or Ce_0.3V₂O₅(H₂O)·H₂O/S (CeVS) was synthesized based on a facile one-step hydrothermal reaction of Ce(SO₄)₂ and V₂O₅ or VS₂. Rietveld refinement of CeVO unveils the intercalation of Ce ions into layered V₂O₅ with a large (001) lattice spacing of 12.1 Å. CeVS is a CeVO/S heterostructure, which originates from the hydrothermal transformation of VS₂ → V₂O₅ + S₈ and the simultaneous intercalation of Ce ions. The pre-intercalation of Ce ions leads to a Zn²⁺ migration barrier of 1.32 eV in CeVO, and CeVO shows a capacity of 376 mA h g^-1 at 0.1 A g^-1. However, CeVS exhibits a higher capacity (438 mA h g^-1) and an ultralong lifespan with a capacity retention of 100% over 10 500 cycles at 5 A g^-1. The conversion between S⁰ and vanadium sulfide (yS⁰ + 2e^- ↔ S_y^2-) in CeVS during the discharge and charge process can not only provide extra capacity, but also maintain the crystallinity and stability of CeVO, in which S transfers electrons like an electron shuttle to avoid the structural collapse and fast capacity fading of CeVO.

Flower-Shaped Hollow VOOH Spheres Wrapped by Carbon Nanotubes as the Cathode Electrocatalyst Enable Ultrafast and Long-Lasting Li-S Batteries

Lithium-sulfur batteries (LSBs) have been considered promising candidates for next-generation energy storage devices owing to their high energy density, low price, and environment-friendly characteristics. However, their commercialization has been hindered by the "shuttle effect", which occurs during the charge/discharge cycles and leads to poor cycling performance and low coulombic efficiency. Here, we synthesized flower-shaped hollow VOOH spheres on the carbon nanotube (CNT) network, which were used as the multifunctional sulfur host materials for the first time in LSBs. These VOOH spheres can chemically and physically confine polysulfides as well as catalyze their redox conversion; additionally, their hollow structure can effectively accommodate the volume change during cycling. Moreover, the CNTs among spheres can improve the conductivity of the host material and increase the number of active sites for interfacial reactions. Accordingly, when used as a cathode material, VOOH@CNTs/S composites exhibited a large specific discharge capacity of 1414.63 mAh/g at 0.1 C and excellent cycling stability. At a low current density of 0.5 C, VOOH@CNTs/S exhibited a capacity decay of 0.044% per cycle after 100 cycles. Importantly, at an ultrahigh current density of 5 C, a specific capacity as high as 455.09 mAh/g could be still be delivered after 1000 cycles, corresponding to a superior capacity retention of 90.46% and an ultralow capacity decay of 0.009% per cycle. These findings open up a new material for the practical application of LSBs with ultrafast charge/discharge property and long-lasting cyclic stability.

Selective Nitridation Crafted a High-Density, Carbon-Free Heterostructure Host with Built-In Electric Field for Enhanced Energy Density Li-S Batteries

To achieve both high gravimetric and volumetric energy densities of lithium-sulfur (Li-S) batteries, it is essential yet challenging to develop low-porosity dense electrodes along with diminishment of the electrolyte and other lightweight inactive components. Herein, a compact TiO₂ @VN heterostructure with high true density (5.01 g cm^-3 ) is proposed crafted by ingenious selective nitridation, serving as carbon-free dual-capable hosts for both sulfur and lithium. As a heavy S host, the interface-engineered heterostructure integrates adsorptive TiO₂ with high conductive VN and concurrently yields a built-in electric field for charge-redistribution at the TiO₂ /VN interfaces with enlarged active locations for trapping-migration-conversion of polysulfides. Thus-fabricated TiO₂ @VN-S composite harnessing high tap-density favors constructing dense cathodes (≈1.7 g cm^-3 ) with low porosity (<30 vol%), exhibiting dual-boosted cathode-level peak volumetric-/gravimetric-energy-densities nearly 1700 Wh L^-1 _cathode /1000 Wh kg^-1 _cathode at sulfur loading of 4.2 mg cm^-2 and prominent areal capacity (6.7 mAh cm^-2 ) at 7.6 mg cm^-2 with reduced electrolyte (<10 µL mg^-1 _sulfur ). Particular lithiophilicity of the TiO₂ @VN is demonstrated as Li host to uniformly tune Li nucleation with restrained dendrite growth, consequently bestowing the assembled full-cell with high electrode-level volumetric/gravimetric-energy-density beyond 950 Wh L^-1 _{cathode+anode} /560 Wh kg^-1 _{cathode+anode} at 3.6 mg cm^-2 sulfur loading alongside limited lithium excess (≈50%).

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.

VN and SeS2 embedded porous carbon-nanofiber film as a free-standing electrode for improved Li-SeS2 batteries

We design a vanadium nitride (VN) modified porous carbon nanofiber film as the host to load SeS₂ as the cathode (SeS₂@VN/CNFs) for improving Li storage capacity. The conductive porous carbon nanofibers can accommodate active SeS₂ and release the volume change. The introduced VN nanoparticles can chemically anchor the intermediate species and improve the utilization of SeS₂. As a result, the SeS₂@VN/CNFs cathode displays a superior electrochemical performance including a high reversible capacity of 806 mAh g^-1 at 0.2 C and good long-term cycling stability in Li-SeS₂ batteries.

A graphene oxide scaffold-encapsulated microcapsule for polysulfide-immobilized long life lithium-sulfur batteries

Engineering high-performance cathodes for high energy-density lithium-sulfur (Li-S) batteries is quite significant to achieve commercialization. Here, we develop a graphene oxide scaffold/sulfur composite-encapsulated microcapsule (GSM) for high-performance Li-S batteries, which is prepared through the co-flow focusing (CFF) approach. The GSM-based cathode displays a high capacity of 1004 mA h g^-1 at 0.2C after cycling 200 times, a long-term cycling stability after 1000 cycles at 2C, and a good rate-performance. At temperatures of -5 °C and 45 °C, the electrochemical performance is also excellent. The computational calculations based on density functional theory (DFT) verify the high adsorption energies of the microcapsules towards polysulfides, suppressing the shuttle effect efficiently. It is expected that the GSM system developed based on the CFF method here and its high electrochemical performance will enable it to be applicable for preparing many other emerging energy-storage materials and secondary batteries.

Using sp2 N atom anchoring effect to prepare ultrafine vanadium nitride particles on porous nitrogen-doped carbon as cathode for lithium-sulfur battery

Porous carbon-supported transition metals and their compounds have attracted much attention as sulfur host materials for cathodes of lithium-sulfur batteries, due to their high chemisorption capacity and ability to catalyze the conversion of polysulfides. However, actual activity of these materials is not very high because of low specific surface areas of transition metal compounds synthesized at high temperatures. In this study, ultra-fine vanadium nitride particles with an average particle size of ca. 4 nm (VN/M/NC) are successfully grown on the surface of nitrogen-doped three-dimensional carbon using sp² nitrogen atoms, resulting from melamine pyrolysis in the presence of ammonium metavanadate, as anchor points to lock vanadium atoms in the VN/M/NC material. When used as a cathode for lithium-sulfur battery, VN/M/NC demonstrates initial discharge specific capacity of 1080 mAh g^-1 at 0.2 C, and retains a discharge capacity of 475 mAh g^-1 at a high rate of 2 C. With capacity attenuation of only 0.037% per cycle after 500 cycles at 1 C, the newly obtained VN/M/NC can be a promising cathode material for lithium-sulfur batteries.

A conductive framework embedded with cobalt-doped vanadium nitride as an efficient polysulfide adsorber and convertor for advanced lithium-sulfur batteries

The industrialization and commercialization of Li-S batteries are greatly hindered by several defects such as the sluggish reaction kinetics, polysulfide shuttling and large volume expansion. Herein, we propose a heteroatom doping method to optimize the electronic structure for enhancing the adsorption and catalytic activity of VN that is in situ embedded into a spongy N-doped conductive framework, thus obtaining a Co-VN/NC multifunctional catalyst as an ideal sulfur host. The synthesized composite has both the unique structural advantages and the synergistic effect of cobalt, VN, and nitrogen-doped carbon (NC), which not only improve the polysulfide anchoring of the sulfur cathode but also boost the kinetics of polysulfide conversion. The density functional theory (DFT) calculations revealed that Co doping could enrich the d orbit electrons of VN for elevating the d band center, which improves its interaction with lithium polysulfides (LiPSs) and accelerates the interfacial electron transfer, simultaneously. As a result, the batteries present a high initial discharge capacity of 1521 mA h g^-1 at 0.1 C, good rate performance, and excellent cycling performances (∼876 mA h g^-1 at 0.5 C after 300 cycles and ∼490 mA h g^-1 at 2 C after 1000 cycles, respectively), even with a high areal sulfur loading of 4.83 mg cm^-2 (∼4.70 mA h cm^-2 at 0.2 C after 100 cycles). This well-designed work provides a good strategy to develop effective polysulfide catalysis and further obtain high-performance host materials for Li-S batteries.

Combining Organic Plastic Salts with a Bicontinuous Electrospun PVDF-HFP/Li7La3Zr2O12 Membrane: LiF-Rich Solid-Electrolyte Interphase Enabling Stable Solid-State Lithium Metal Batteries

Solid-state electrolytes can guarantee the safe operation of high-energy density lithium metal batteries (LMBs). However, major challenges still persist with LMBs due to the use of solid electrolytes, that is, poor ionic conductivity and poor compatibility at the electrolyte/electrode interface, which reduces the operational stability of solid-state LMBs. Herein, a novel fiber-network-reinforced composite polymer electrolyte (CPE) was designed by combining an organic plastic salt (OPS) with a bicontinuous electrospun polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP)/Li₇La₃Zr₂O₁₂ (LLZO) membrane. The presence of LLZO in the composite helps to promote the dissociation of FSI^- from OPSs. Subsequently, the dissociated FSI^- is then involved in the formation of a LiF-rich solid electrolyte interphase (SEI) layer on the lithium anode via a reductive decomposition reaction, which was affirmed by theoretical calculations and experimental results. Due to the LiF-rich SEI layer, the Li/Li symmetric cell was able to demonstrate a long cyclic life of over 2600 h at a current density of 0.1 mA cm^-2. More importantly, the as-prepared CPE achieved a high ionic conductivity of 2.8 × 10^-4 S cm^-1 at 25 °C, and the Li/LiFePO₄ cell based on the CPE exhibited a high discharge capacity and 83.3% capacity retention after 500 cycles at 1.0 C. Thus, the strategy proposed in this work can inspire the future development of highly conductive solid electrolytes and compatible interface designs toward high-energy density solid-state LMBs.

Confined Co9S8 nanocrystals into N/S-Co-doped carbon nanofibers as a chainmail-like electrocatalyst for high-performance lithium-sulfur batteries with high sulfur loading

Accelerating phase transposition efficiency of lithium polysulfides (LiPSs) to L₂S and hampering the solution of LiPSs are the keys to stabilizing lithium-sulfur (Li-S) batteries. Hence, the sulfiphilic ultrafine Co₉S₈ nanoparticles embedded lithiophilic N, S co-doping carbon nanofibers (Co₉S₈/NSCNF) are prepared via the dual-template method, which are then used as sulfur host in Li-S batteries. Particularly, the double active sites (Co₉S₈ and N, S) in Co₉S₈/NSCNF are prone to form "Co-S", "Li-O" or "Li-N" bonds, and then simultaneously improving the chemisorption and interface transposition capability of LiPSs. In case of the S@ Co₉S₈/NSCNF composites with high sulfur loading of 89% are employed as cathode, the cell possesses optimized "sulfiphilicity" and "lithiophilicity", which achieves remarkable sulfur electrochemistry, including outstanding reversibility of 816.8mAhg^-1 over 500 cycles at 1.0C, excellent rate property of 742.2mAhg^-1at 5.0C, and long-term cycling with a low attenuation of 0.011% per cycle over 1800 cycles at 3.0C. Impressively, a remarkable areal capacity of 11.51mAhcm^-2 is retained under the sulfur loading of 15.3 mg cm^-2 for 50 cycles. This research will deepen the understanding of the complex LiPSs interface transposition procedure and provide new ideas for the design of new host materials.

Rational construction of a CNTs@VO2 nanosheets modified separator for enhancing the performance of lithium-sulfur batteries

Although lithium-sulfur (Li-S) batteries possess great potential to become the next generation of energy storage technology due to their fivefold higher energy density than commercial lithium-ion batteries, their practical application is still hindered by their poor cycling stability, especially resulting from the disturbing shuttle effect of soluble intermediates. In this study, vanadium dioxide (VO₂) nanosheets were successfully grown onto CNTs to form CNTs@VO₂ through hydrothermal and calcining processes. The hollow structure of the high conductive CNTs offers internal space and mesopores to accommodate the electrolyte combined with the polar metal oxide VO₂ nanosheets providing the chemical anchoring. The hollow binary core-shell host acting as the nanoreactor that serves as the modifier of the separator results in the intensive physical and chemical dual adsorption of lithium polysulfide species (LiPSs), promoting the conversion of long-chain LiPSs to alleviate the shuttle effect significantly and boosting the performance. In addition, the CNTs enhance the electronic conductivity and the electrolyte infiltration of the separator. Notably, the modified separator demonstrates a high initial discharge capacity of 1397 mA h g^-1 at 0.2C and retains a stable cycling ability with a reversible capacity of 965 mA h g^-1 over 200 cycles at 1C. Even for the high sulfur loading of 7.4 mg cm^-2, it can deliver a high areal capacity of 5.4 mA h cm^-2 at 0.5C.

Hollow heterostructure design enables self-cleaning surface for enhanced polysulfides conversion in advanced lithium-sulfur batteries

Constructing interpenetrating heterointerface with reasonable interface energy barriers to improve electron/ion transport and accelerate the deposition/decomposition of lithium sulfide (Li₂S) is an effective method to improve the electrochemical performance of lithium-sulfur (Li-S) batteries. Herein, NiCoO₂/NiCoP heterostructures with hollow nanocage morphology are prepared for efficient multifunctional Li-S batteries. The hollow nanocage structure exposes abundant active sites, traps lithium polysulfides and inhibits the shuttle effect. The NiCoO₂/NiCoP heterostructure, combing strong adsorption capacity of NiCoO₂ and excellent catalytic ability of NiCoP, facilitates the process of anchoring-diffusion-transformation of polysulfides. The successful construction of heterostructures reduces the reaction barrier, accelerating the lithium ion (Li⁺) diffusion rate and thus effectively enhancing the redox reaction kinetics. More importantly, NiCoO₂/NiCoP heterostructure plays a role in self-cleaning that minimizes solid sulfur species accumulation to maintain surface clean during long cycling for a continuously catalysis of the polysulfides conversion reactions. With the merit of these features, the NiCoO₂/NiCoP modified separator exhibits excellent cycling stability with a low capacity decay of 0.043% per cycle up to 1000 cycles at 2 C. The design of NiCoO₂/NiCoP hollow nanocage heterostructures offers a new option for high-performance electrochemical energy storage devices.

Integrated Porous Cu Host Induced High-Stable Bidirectional Li Plating/Stripping Behavior for Practical Li Metal Batteries

The double-sided electrodes with active materials are widely used for commercial lithium (Li) ion batteries with a higher energy density. Accordingly, developing an anode current collector that can accommodate the stable and homogeneous Li plating/stripping on both sides will be highly desired for practical Li metal batteries (LMBs). Herein, an integrated bidirectional porous Cu (IBP-Cu) film with a through-pore structure is fabricated as Li metal hosts using the powder sintering method. The resultant IBP-Cu current collector with tunable pore volume and size exhibits high mechanical flexibility and stability. The bidirectional and through-pore structure enables the IBP-Cu host to achieve homogeneous Li deposition and effectively suppresses the dendritic Li growth. Impressively, the as-fabricated Li/IBP-Cu anode exhibits a remarkable capacity of up to 7.0 mAh cm^-2 for deep plating/stripping, outstanding rate performance, and ultralong cycling ability with high Coulombic efficiency of ≈100% for 1000 cycles. More practicably, a designed pouch cell coupled with one Li/IBP-Cu anode and two LiFePO₄ cathodes exhibits a highly elevated energy density (≈187.5%) compared with a pouch cell with one anode and one cathode. Such design of a bidirectional porous Cu current collector with stable Li plating/stripping behaviors suggests its promising practical applications for next-generation Li metal batteries.

InOOH as an efficient bidirectional catalyst for accelerated polysulfides conversion to enable high-performance lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries with the prominent advantages are greatly expected to be the attractive alternatives in the next-generation energy-storage systems. However, the practical success of Li-S batteries suffers from the shuttle effect and depressed redox kinetics of polysulfides. Herein, for the first time, InOOH nanoparticles are employed as a potent catalytic additive in sulfur electrode to overcome these issues. As demonstrated by the theoretical and experimental results, the strong interactions between the InOOH nanoparticles and sulfur species enable the effective adsorption of polysulfides. More significantly, InOOH nanoparticles not only effectively expedite the reduction of sulfur during the discharge process, but also dramatically accelerate the oxidation of Li₂S during the charge process, presenting the marvelous bidirectional catalytic effects. Benefited from these distinctive superiorities, the cells with InOOH nanoparticles harvest an excellent capacity retention of 69.5% over 500 cycles at 2C and a commendable discharge capacity of 891 mAh g^-1 under a high-sulfur loading of 5.0 mg cm^-2. The detailed investigations in this work provide a novel insight to ameliorate the Li-S electrochemistry by the bidirectional catalyst for high-performance Li-S batteries.

Rational Design of the Lotus-Like N-Co2 VO4 -Co Heterostructures with Well-Defined Interfaces in Suppressing the Shuttle Effect and Dendrite Growth in Lithium-Sulfur Batteries

The shuttle effect caused by soluble lithium polysulfides (LiPSs) and intrinsic slow electrochemical transformation from LiPSs to Li₂ S/Li₂ S₂ will induce undesirable cycling performance, which is the primary obstruct limiting the practical applications of lithium-sulfur (Li-S) batteries. Here a convenient method is designed to fabricate the 2D louts-like N-Co₂ VO₄ -Co heterostructures with well-abundant interfaces and oxygen vacancies (V_o ), endowing the materials with both "sulfiphilic" and "lithiophilic" features. When employed as the modification layer coated on commercial Celgard 2400 separator, the as-prepared N-Co₂ VO₄ -Co/PP with synergistic adsorption-electrocatalysis effects achieves desirable sulfur electrochemistry, thus showing a high initial discharge capacity of 1466.4 mAh g^-1 at 0.1 C and stable cycle life with a fade rate of 0.03% per cycle over 1000 cycle at 3.0 C. Moreover, a superior areal capacity of 12.84 mAh cm^-2 is preserved under high sulfur loading of 14.3 mg cm^-2 .

New Covalent Triazine Framework Rich in Nitrogen and Oxygen as a Host Material for Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries have been widely considered as the next-generation energy storage system but hindered by the soluble polysulfide intermediate-induced shuttle effect. Doping heteroatoms was confirmed to enhance the affinity of polysulfide and the carbon host, release the shuttle effect, and improve the battery performance. To enhance the Lewis acidity and reinforce the interaction between polysulfide and the carbon skeleton, a novel covalent triazine framework (CTFO) was designed and fabricated by copolymerizing 2,4,6-triphenoxy-s-triazine and 2,4,6-trichloro-1,3,5-triazine through Friedel-Crafts alkylation. Polymerization led to triazine substitution on the para-position of the phenoxy groups of 2,4,6-triphenoxy-triazine and produced two-dimensional three-connected honeycomb nanosheets. These nanosheets were confirmed to exhibit packing in the AB style through the intralayer π-π interaction to form a three-dimensional layered network with micropores of 0.5 nm. The practical and simulated results manifested the enhanced polysulfide capture capability due to the abundant N and O heteroatoms in CTFO. The unique porous polar network endowed CTFO with improved Li-S battery performance with high Coulombic efficiency, rate capability, and cycling stability. The S@CTFO cathode delivered an initial discharge capacity of 791 mAh g^-1 at 1C and retained a residual capacity of 512 mAh g^-1 after 300 charge-discharge cycles with an attenuation rate of 0.117%. The present results confirmed that multiple heteroatom doping enhances the interaction between the porous polar CTF skeleton and polysulfide intermediates to improve the Li-S battery performance.

Understanding the modulation effect and surface chemistry in a heteroatom incorporated graphene-like matrix toward high-rate lithium-sulfur batteries

The underlying interface effects of sulfur hosts/polysulfides at the molecular level are of great significance to achieve advanced lithium-sulfur batteries. Herein, we systematically study the polysulfide-binding ability and the decomposition energy barrier of Li₂S enabled by different kinds of nitrogen (pyridinic N, pyrrolic N and graphitic N) and phosphorus (P-O, PO and graphitic P) doping and decipher their inherent modulation effect. The doping process helps in forming a graphene-like structure and increases the micropores/mesopores, which can expose more active sites to come into contact with polysulfides. First-principles calculations reveal that the PO possesses the highest binding energies with polysulfides due to the weakening of the chemical bonds. Besides, PO as a promoter is beneficial for the free diffusion of lithium ions, and the pyridinic N and pyrrolic N can greatly reduce the kinetic barrier and catalyze the polysulfide conversion. The synergetic effects of nitrogen and phosphorus as bifunctional active centers help in achieving an in situ adsorption-diffusion-conversion process of polysulfides. Benefiting from these features, the graphene-like network achieves superior rate capability (a high reversible capacity of 954 mA h g^-1 at 2C) and long-term stability (an ultralow degradation rate of 0.009% around 800 cycles at 5C). Even at a high sulfur loading of 5.6 mg cm^-2, the cell can deliver an areal capacity of 4.6 mA h cm^-2 at 0.2C.

Three-Dimensional Engineering of Sulfur/MnO2 Composites for High-Rate Lithium-Sulfur Batteries

Herein, a three-dimensional interconnected sulfur (3DIS) system is used to construct a cathode of the lithium-sulfur battery. Compared with the traditional methods of encapsulating sulfur, the 3DIS system serves as a framework to grow MnO₂, which ensures a high sulfur content of 91.5 wt % (the ratio of sulfur/host was 10.8) and a uniform distribution of sulfur. Due to the synergistic effect of the 3D interconnected architecture and the uniform coating layer of polar MnO₂, 3DIS@MnO₂ (3DISMO) delivers a capacity of 891 mA h g^-1 after 900 cycles at 1 C. Even at a rate of 10 C, a capacity decay rate of 0.061% per cycle is achieved.

Self-branched Nb2O5 nanoarrays as “electron-ion reservoirs” to enhance the conversion of polysulfides in flexible Li–S batteries

A novel sulfur matrix integrating self-branched Nb2O5 nanoarrays and flexible carbon cloth (NBCC) is designed. Intriguingly, the selected Nb2O5 nanoarrays can work as “electron-ion reservoirs” to accelerate the conversion reaction of LiPSs.