Phosphorene as a Polysulfide Immobilizer and Catalyst in High-Performance Lithium-Sulfur Batteries

Leveraging doping strategies and interface engineering to enhance catalytic transformation of lithium polysulfides for high-performance lithium-sulfur batteries

The commercialization of lithium-sulfur (Li-S) batteries has faced challenges due to the shuttle effect of soluble intermediate polysulfides and the sluggish kinetics of sulfur redox reactions. In this study, a synergistic catalyst medium was developed as a high-performance sulfur cathode material for Li-S batteries. Termed A/R-TiO2@ Ni-N-MXene, this sulfur cathode material features an in-situ derived anatase-rutile homojunction of TiO2 nanoparticles on Ni-N dual-atom-doped MXene nanosheets. Using in-situ transmission electron microscopy (TEM) technique, we observed the growth process of the homojunction for the first time confirming that homojunctions facilitated charge transfer, while dual-atom doping offered abundant active sites for anchoring and converting soluble polysulfides. Theoretical calculations and experiments showed that these synergistic effects effectively mitigated the shuttle effect, leading to improved cycling performance of Li-S batteries. After 500 cycles at a 1C rate, Li-S batteries using A/R-TiO2@Ni-N-MXene as cathode materials exhibited stable and highly reversible capacity with a capacity decay of only 0.056 % per cycle. Even after 150 cycles at a 0.1C rate, a high-capacity retention rate of 62.8 % was achieved. Additionally, efficient sulfur utilization was observed, with 1280.76 mA h/g at 0.1C, 694.24 mA h/g at 1C, alongside a sulfur loading of 1.5-2 mg/cm2. The effective strategy based on homojunctions showcases promise for designing high-performance Li-S batteries.

The Impact of Oxygen Content in O-Doped MoS2 on the Kinetics of Polysulfide Conversion in Li-S Batteries

Polysulfide shuttle and sluggish sulfur redox kinetics remain key challenges in lithium-sulfur batteries. Previous researches have shown that introducing oxygen into transition metal sulfides helps to capture polysulfides and enhance their conversion kinetics. Based on this, further investigations are conducted to explore the impact of oxygen doping levels on the physical-chemical properties and electrocatalytic performance of MoS2. The findings reveal that MoS2 doped with high-content oxygen exhibits enhanced conductivity and polysulfides conversion kinetics compared to MoS2 with low-content oxygen doping, which can be attributed to the alteration of crystal structure from 2H-phase to the 1T-phase, the introduction of increased Li-O interactions, and the effect of defects resulting from high-oxygen doping. Consequently, the lithium-sulfur batteries using high-oxygen doped MoS2 as a catalyst deliver a high discharge capacity of 1015 mAh g-1 at 0.25C and maintain 78.5% capacity after 300 more cycles. Specifically, lithium-sulfur batteries employing paper-based electrodedemonstrate an areal capacity of 3.91 mAh cm-2 at 0.15C, even with sulfur loading of 4.1 mg cm-2 and electrolyte of 6.7 µL mg-1. These results indicate that oxygen doping levels can modify the properties of MoS2, and high-oxygen doped MoS2 shows promise as an efficient catalyst for lithium-sulfur batteries.

Heterostructured WOx/W2C Nanocatalyst for Li2S Oxidation in Lithium-Sulfur Batteries with High-Areal-Capacity

Lithium-sulfur (Li-S) batteries show extraordinary promise as a next-generation battery technology due to their high theoretical energy density and the cost efficiency of sulfur. However, the sluggish reaction kinetics, uncontrolled growth of lithium sulfide (Li2S), and substantial Li2S oxidation barrier cause low sulfur utilization and limited cycle life. Moreover, these drawbacks get exacerbated at high current densities and high sulfur loadings. Here, a heterostructured WOx/W2C nanocatalyst synthesized via ultrafast Joule heating is reported, and the resulting heterointerfaces contribute to enhance electrocatalytic activity for Li2S oxidation, as well as controlled Li2S deposition. The densely distributed nanoparticles provide abundant binding sites for uniform deposition of Li2S. The continuous heterointerfaces favor efficient adsorption and promote charge transfer, thereby reducing the activation barrier for the delithiation of Li2S. These attributes enable Li-S cells to deliver high-rate performance and high areal capacity. This study provides insights into efficient catalyst design for Li2S oxidation under practical cell conditions.

A computational study on bifunctional 1T-MnS2 with an adsorption-catalysis effect for lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries are promising rechargeable energy storage systems with a high energy density, environmental friendliness and low cost. However, the commercialization process of Li-S batteries has been seriously hindered by the shuttling of lithium polysulfides (LiPSs) and the sluggish kinetics of conversion reaction among sulfur species. In this work, the adsorption-catalysis performance of five transition metal disulfide 1T-MS₂ (M = Mn, V, Ti, Zr, and Hf) surfaces is investigated by evaluating the adsorption energy of sulfur species, Li-ion diffusion energy barrier, decomposition energy barrier of Li₂S, and the Gibbs free energy barrier of the sulfur reduction reaction based on first-principles calculations. Our results show that the sulfiphilicity of 1T-MS₂ plays an important role in the adsorption behavior of short-chain sulfur species, in addition to lithiophilicity. Remarkably, among the five 1T-MS₂ materials, our results confirm that 1T-TiS₂ and 1T-VS₂ show excellent adsorption-catalysis performance and it is predicted that 1T-MnS₂ is an even better candidate catalyst to inhibit the shuttle effect and accelerate delithiation/lithiation kinetics. Moreover, the outstanding performance of 1T-MnS₂ persists in a solvent environment and under strain modulation. Our results not only demonstrate that 1T-MnS₂ is an excellent potential catalyst for high-performance Li-S batteries, but also provide great insights into the adsorption-catalysis mechanism during the cycling process.

Application of Inorganic Quantum Dots in Advanced Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries have emerged as one of the most attractive alternatives for post-lithium-ion battery energy storage systems, owing to their ultrahigh theoretical energy density. However, the large-scale application of Li-S batteries remains enormously problematic because of the poor cycling life and safety problems, induced by the low conductivity , severe shuttling effect, poor reaction kinetics, and lithium dendrite formation. In recent studies, catalytic techniques are reported to promote the commercial application of Li-S batteries. Compared with the conventional catalytic sites on host materials, quantum dots (QDs) with ultrafine particle size (<10 nm) can provide large accessible surface area and strong polarity to restrict the shuttling effect, excellent catalytic effect to enhance the kinetics of redox reactions, as well as abundant lithiophilic nucleation sites to regulate Li deposition. In this review, the intrinsic hurdles of S conversion and Li stripping/plating reactions are first summarized. More importantly, a comprehensive overview is provided of inorganic QDs, in improving the efficiency and stability of Li-S batteries, with the strategies including composition optimization, defect and morphological engineering, design of heterostructures, and so forth. Finally, the prospects and challenges of QDs in Li-S batteries are discussed.

Black phosphorus quantum dots induce autophagy and apoptosis of human bronchial epithelial cells via endoplasmic reticulum stress

PURPOSE

The board application of black phosphorus quantum dots (BP-QDs) increases the risk of inhalation exposure in the manufacturing process. The aim of this study is to explore the toxic effect of BP-QDs on human bronchial epithelial cells (Beas-2B) and lung tissue of Balb/c mice.

METHODS

The BP-QDs were characterized using transmission electron microscopy (TEM) and a Malvern laser particle size analyzer. Cell Counting Kit-8 (CCK-8) and TEM were used to detect cytotoxicity and organelle injury. Damage to the endoplasmic reticulum (ER) was detected by using the ER-Tracker molecular probe. Rates of apoptosis were detected by AnnexinV/PI staining. Phagocytic acid vesicles were detected using AO staining. Western blotting and immunohistochemistry were used to examine the molecular mechanisms.

RESULTS

After treatment with different concentrations of BP-QDs for 24 h, the cell viability decreased, as well as activation of the ER stress and autophagy. Furthermore, the rate of apoptosis was increased. Inhibition of ER stress caused by 4-phenyl butyric acid (4-PBA) was shown to significantly inhibit both apoptosis and autophagy, suggesting that ER stress could be an upstream mediator of both autophagy and apoptosis. BP-QD-induced autophagy can also inhibit the occurrence of apoptosis using molecules related to autophagy including rapamycin (Rapa), 3-methyladenine (3-MA), and bafilomycin A1 (Bafi A1). In general, BP-QDs activate ER stress in Beas-2B cells, which further induces autophagy and apoptosis, and autophagy may be activated as a factor that protects against apoptosis. We also observed strong staining of related proteins of ER stress, autophagy, and apoptosis proteins in mouse lung tissue following intracheal instillation over the course of a week.

CONCLUSION

BP-QD-induced ER stress facilitates autophagy and apoptosis in Beas-2B cells and autophagy may be activated as a protective factor against apoptosis. Under conditions of ER stress induced by BP-QDs, The interplay between autophagy and apoptosis determines cell fate.

Coordinating Interface Polymerization with Micelle Mediated Assembly Towards Two-Dimensional Mesoporous Carbon/CoNi for Advanced Lithium-Sulfur Battery

Lithium-sulfur battery has attracted significant attention by virtues of their high theoretical energy density, natural abundance, and environmental friendliness. However, the notorious shuttle effect of polysulfides intermediates severely hinders its practical application. Herein, a novel 2D mesoporous N-doped carbon nanosheet with confined bimetallic CoNi nanoparticles sandwiched graphene (mNC-CoNi@rGO) is successfully fabricated through a coordinating interface polymerization and micelle mediated co-assembly strategy. mNC-CoNi@rGO serves as a robust host material that endows lithium-sulfur batteries with a high reversible capacity of 1115 mAh g^-1 at 0.2 C after 100 cycles, superior rate capability, and excellent cycling stability with 679.2 mAh g^-1 capacity retention over 700 cycles at 1 C. With sulfur contents of up to 5.0 mg cm^-2 , the area capacity remains to be 5.1 mAh cm^-2 after 100 cycles at 0.2 C. The remarkable performance is further resolved via a series of experimental characterizations combined with density functional theory calculations. These results reveal that the ordered mesoporous N-doped carbon-encapsulated graphene framework acts as the ion/electron transport highway with excellent electrical conductivity, while bimetallic CoNi nanoparticles enhance the polysulfides adsorption and catalytic conversion that simultaneously accelerate the multiphase sulfur/polysulfides/sulfides conversion and inhibit the polysulfides shuttle.

2D Layers of Group VA Semiconductors: Fundamental Properties and Potential Applications

Members of the 2D group VA semiconductors (phosphorene, arsenene, antimonene, and bismuthine) present a new class of 2D materials, which are recently gaining a lot of research interest. These materials possess layered morphology, tunable direct bandgap, high charge carrier mobility, high stability, unique in-plane anisotropy, and negative Poisson's ratio. They prepare the ground for novel and multifunctional applications in electronics, optoelectronics, and batteries. The most recent analytical and empirical developments in the fundamental characteristics, fabrication techniques, and potential implementation of 2D group VA materials in this review, along with presenting insights and concerns for the field's future are analyzed.

Ni3Sn2/nitrogen-doped graphene composite with chemisorption and electrocatalysis as advanced separator modifying material for lithium sulfur batteries

Lithium-sulfur batteries have been widely studied because of their advantages of abundant reserves, environmental friendliness, low cost andhighspecific capacity. However, the volume expansionand the low electrical conductivity of sulfur, and the shuttle effect of polysulfides limit their application. Herein,wesynthesizea two-dimensional layered Ni₃Sn₂/nitrogen-doped graphene (NG) composite asseparator modifying material for lithium-sulfur batteries. The Ni₃Sn₂formed by dual metal salts Ni(NO₃)₂·6H₂O and SnCl₂·2H₂O can adsorb polysulfide and catalyze its transformation to improve the electrochemical reaction kinetics. Moreover, the layered NG can not only disperse the Ni₃Sn₂particles, but alsoensure rapid electron transfer. Therefore, the lithium-sulfur battery with the Ni₃Sn₂/NG modified separator shows excellent electrochemical performance. At a current rate of 1 C, the lithium-sulfur battery with the Ni₃Sn₂/NG modified separator can provide a high initial discharge capacity of 1022.1 mAh g^-1and maintain a reversible specific capacity of 758.3 mAh g^-1after 400 cycles.

High-Density Oxygen Doping of Conductive Metal Sulfides for Better Polysulfide Trapping and Li2 S-S8 Redox Kinetics in High Areal Capacity Lithium-Sulfur Batteries

Exploring new materials and methods to achieve high utilization of sulfur with lean electrolyte is still a common concern in lithium-sulfur batteries. Here, high-density oxygen doping chemistry is introduced for making highly conducting, chemically stable sulfides with a much higher affinity to lithium polysulfides. It is found that doping large amounts of oxygen into NiCo2 S4 is feasible and can make it outperform the pristine oxides and natively oxidized sulfides. Taking the advantages of high conductivity, chemical stability, the introduced large Li-O interactions, and activated Co (Ni) facets for catalyzing Sn 2- , the NiCo2 (O-S)4 is able to accelerate the Li2 S-S8 redox kinetics. Specifically, lithium-sulfur batteries using free-standing NiCo2 (O-S)4 paper and interlayer exhibit the highest capacity of 8.68 mAh cm-2 at 1.0 mA cm-2 even with a sulfur loading of 8.75 mg cm-2 and lean electrolyte of 3.8 µL g-1 . The high-density oxygen doping chemistry can be also applied to other metal compounds, suggesting a potential way for developing more powerful catalysts towards high performance of Li-S batteries.

Understanding the interactions between lithium polysulfides and anchoring materials in advanced lithium-sulfur batteries using density functional theory

Lithium-sulfur batteries (LSBs) are promising energy storage devices because of their high theoretical capacity and energy density. However, the "shuttle" effect in lithium polysulfides (LiPSs) is an unresolved issue that can hinder their practical commercial application. Research on LSBs has focused on finding appropriate materials that suppress this effect by efficiently anchoring the LiPSs intermediates. Quantum chemical computations are a useful tool for understanding the mechanistic details of chemical interaction involving LiPSs, and they can also offer strategies for the rational design of LiPSs anchoring materials. In this perspective, we highlight computational and theoretical work performed on this topic. This includes elucidating and characterizing the adsorption mechanisms, and the dominant types of interactions, and summarizing the binding energies of LiPSs on anchoring materials. We also give examples and discuss the potential of descriptors and machine learning approaches to predict the adsorption strength and reactivity of materials. We believe that both approaches will become indispensable in modelling future LSBs.

Design Rules of a Sulfur Redox Electrocatalyst for Lithium-Sulfur Batteries

Seeking an electrochemical catalyst to accelerate the liquid-to-solid conversion of soluble lithium polysulfides to insoluble products is crucial to inhibit the shuttle effect in lithium-sulfur (Li-S) batteries and thus increase their practical energy density. Mn-based mullite (SmMn₂ O₅ ) is used as a model catalyst for the sulfur redox reaction to show how the design rules involving lattice matching and 3d-orbital selection improve catalyst performance. Theoretical simulation shows that the positions of Mn and O active sites on the (001) surface are a good match with those of Li and S atoms in polysulfides, resulting in their tight anchoring to each other. Fundamentally, dz² and dx² -y² around the Fermi level are found to be crucial for strongly coupling with the p-orbitals of the polysulfides and thus decreasing the redox overpotential. Following the theoretical calculation, SmMn₂ O₅ catalyst is synthesized and used as an interlayer in a Li-S battery. The resulted battery has a high cycling stability over 1500 cycles at 0.5 C and more promisingly a high areal capacity of 7.5 mAh cm^-2 is achieved with a sulfur loading of ≈5.6 mg cm^-2 under the condition of a low electrolyte/sulfur (E/S) value ≈4.6 µL mg^-1 .

Customized Structure Design and Functional Mechanism Analysis of Carbon Spheres for Advanced Lithium-Sulfur Batteries

Lithium-sulfur batteries (LSBs) are attracting much attention due to their high theoretical energy density and are considered to be the predominant competitors for next-generation energy storage systems. The practical commercial application of LSBs is mainly hindered by the severe "shuttle effect" of the lithium polysulfides (LiPSs) and the serious damage of lithium dendrites. Various carbon materials with different characteristics have played an important role in overcoming the above-mentioned problems. Carbon spheres (CSs) are extensively explored to enhance the performance of LSBs owing to their superior structures. The review presents the state-of-the-art advances of CSs for advanced high-energy LSBs, including their preparation strategies and applications in inhibiting the "shuttle effect" of the LiPSs and protecting lithium anodes. The unique restriction effect of CSs on LiPSs is explained from three working mechanisms: physical confinement, chemical interaction, and catalytic conversion. From the perspective of interfacial engineering and 3D structure designing, the protective effect of CSs on the lithium anode is also analyzed. Not only does this review article contain a summary of CSs in LSBs, but also future directions and prospects are discussed. The systematic discussions and suggested directions can enlighten thoughts in the reasonable design of CSs for LSBs in near future.

Two-dimensional N-doped Pd/carbon for highly efficient heterogeneous catalysis

A novel two-dimensional ZIF-derived Pd@CN material prepared via one-step calcination exhibits outstanding catalytic activity in heterogeneous hydrogenation. Its well-developed porous structure, low dimensions and low density make active sites more accessible. This facile and effective strategy can guide the synthesis of highly active and durable Pd@CN catalysts with specific morphologies.

"First-Cycle Effect" of Trace Li2S in a High-Performance Sulfur Cathode

Lithium-sulfur battery is one of the most promising choices for next-generation batteries due to its high theoretical energy density and natural abundance. However, the sulfur cathode undergoes a stepwise reduction process and generates multiple soluble polysulfide intermediates; for the further conversion from the dissolved intermediates to the final solid product (Li₂S), the surface nucleation barrier limits the speed of the electrochemical precipitation, resulting in serious polysulfide diffusion loss and low sulfur utilization. Herein, the trace Li₂S (tLi₂S) is modified on the carbon fiber (CF) skeleton as preloaded crystal nuclei to boost the electrokinetics of Li₂S deposition in the initial cycle. The trace Li₂S decreases the nucleation barrier on the modified electrode (tLi₂S@CF), resulting in a high initial capacity of 1423 mAh g^-1 for the Li₂S₆ catholyte (0.2 C), which corresponds to a nearly 100% utilization of Li₂S₆. Furthermore, the trace Li₂S nuclei induce a uniform distribution of the redeposited active materials, and the uniform distribution persists in the following cycles, which benefits the cycle life significantly. The sulfur cathode based on the tLi₂S@CF matrix maintains a capacity of 1106 mAh g^-1 at 1 C rate after 100 cycles. The strategy can provide a new avenue for the rational design of the sulfur cathode.

Polysulfide Catalytic Materials for Fast-Kinetic Metal-Sulfur Batteries: Principles and Active Centers

Benefiting from the merits of low cost, ultrahigh-energy densities, and environmentally friendliness, metal-sulfur batteries (M-S batteries) have drawn massive attention recently. However, their practical utilization is impeded by the shuttle effect and slow redox process of polysulfide. To solve these problems, enormous creative approaches have been employed to engineer new electrocatalytic materials to relieve the shuttle effect and promote the catalytic kinetics of polysulfides. In this review, recent advances on designing principles and active centers for polysulfide catalytic materials are systematically summarized. At first, the currently reported chemistries and mechanisms for the catalytic conversion of polysulfides are presented in detail. Subsequently, the rational design of polysulfide catalytic materials from catalytic polymers and frameworks to active sites loaded carbons for polysulfide catalysis to accelerate the reaction kinetics is comprehensively discussed. Current breakthroughs are highlighted and directions to guide future primary challenges, perspectives, and innovations are identified. Computational methods serve an ever-increasing part in pushing forward the active center design. In summary, a cutting-edge understanding to engineer different polysulfide catalysts is provided, and both experimental and theoretical guidance for optimizing future M-S batteries and many related battery systems are offered.

Two-Dimensional Conductive Metal-Organic Frameworks as Highly Efficient Electrocatalysts for Lithium-Sulfur Batteries

Lithium-sulfur batteries (LiSBs) which are expected to fulfill the increasing demands of high-density energy storage have been under intensive investigation. However, the development of LiSBs is facing many obstacles, such as the poor electronic conductivity of sulfur, shuttling effects of lithium polysulfides (LiPSs), sluggish Li₂S decomposition, and low discharging/charging efficiency. Suitable electrocatalysts that can solve the above problems are promising in the development of LiSBs. Herein, 13 two-dimensional (2D) metal-organic frameworks (MOFs) of nitrogen-, sulfur-, and oxygen-coordinated transition-metal (TM) atoms (Co, Ni, Cu, and Zn) are selected and constructed to reveal the structure-activity relationship of 2D MOFs in terms of the electrocatalytic performance. Among all the 2D MOFs investigated, Cu₃(HITP)₂, Zn₃(HITP)₂, and Cu₃(C₁₈H₉O₃N₃)₂ offer moderate binding strength to LiPSs, which effectively suppresses Li₂S_n dissolution and shuttling. Cu₃(HITP)₂ exhibits good electrical conductivity, a low Gibbs free energy barrier, effective electrocatalytic ability for Li₂S decomposition, and a high sulfur loading amount. A descriptor φ is proposed to correlate the binding energies of the 2D MOFs to the coordination environment and the electronegativity of the TM atoms in the LiPSs via an implicit volcano plot. These findings are helpful for understanding the electrocatalytic effect of 2D MOFs in LiSBs and represent a promising approach for the development of future LiSBs.

Two-dimensional square metal organic framework as promising cathode material for lithium-sulfur battery with high theoretical energy density

Lithium-sulfur (Li-S) batteries are considered as new generation of energy storage which offer cost-effectiveness and high energy density. However, their commercialization is restricted due to a host of challenges associated with the cathode material which usually contains sulfur with several drawbacks, including a low electronic conductivity of sulfur, the 'shuttle effect', and a large volume expansion during discharge. Herein, a novel two-dimensional porphyrin-like square metal organic framework (MOF) was explored as a promising cathode material using first principles density function theory (DFT) assisted by genetic global search. The DFT results show that, among 7 kinds of transition-metal organic framework (TM-MOF), only V-MOF and Ru-MOF is found to possess considerable chemical interactions with S₈ and lithium polysulfides (LiPSs) in both vacuum and in electrolytic solvents, demonstrating distinguishable anchoring performance. The genetic global search and further DFT calculations indicate that the lithiation process on V-MOF exhibited a nearly constant open-circuit voltage of about 1.92 V to 1.95 V, and the theoretical energy density could reach up to 1469 Wh kg^-1 when lithiation of S₈ is considered on both sides of the substrate. The volume expansion of V-MOF during discharge is found to be about 34%, much smaller than 80% for solid sulfur. The band structure and density of states of V-MOF suggest metallic properties or a small band gap for bare surface or during the lithiation process. These results indicate that two-dimensional (2D) V-MOFs can serve as high-performance cathode material with distinguished anchoring performance to block polysulfide dissolution and thereby reduce the 'shuttle effect', and help attain ultra-high energy density. Our work points the way for designing and providing experimental realization of 2D layered materials applied in cathode with high energy density and stability.

CoFe Alloy-Decorated Interlayer with a Synergistic Catalytic Effect Improves the Electrochemical Kinetics of Polysulfide Conversion

Good electrical conductivity, strong catalytic activity, high interaction with lithium polysulfides (LIPSs), simple method, and low cost should be considered for the design and preparation of high-performance electrochemical catalysts that catalyze the conversion of LIPSs. In this work, we designed a bimetallic alloyed multifunctional interlayer with multiple adsorption/catalysis sites. The interwoven carbon fibers derived from bacterial cellulose (BC) not only contribute to reducing metal ions to metals but also confine the growth of Co-Fe alloys formed in situ. The metal supported on carbon is very effective for the conversion of LIPSs due to its high adsorption and catalytic sites. In addition, the synergistic effect between Fe and Co species leads to excellent bifunctional catalytic activity. Through detailed electrochemical analysis and theoretical calculations, we revealed that CoFe@CNFs has superior electrocatalytic activity, and the lithium-sulfur (Li-S) batteries with a catalytic interlayer can deliver satisfactory rate and cycle performance. At a high current density of 2C, the discharge capacity can still reach 627 mAh g^-1. At a current density of 1C, the Coulombic efficiency is maintained at a level close to 100% during the whole cycle process and a satisfying low capacity decay of 0.08% per cycle. More importantly, even if the ambient temperature drops to 0 °C, the Li-S battery using the interlayer can still be charged and discharged normally and shows acceptable discharge capacity, which shows that it has good rate kinetics.

Scalable Production of Freestanding Few-Layer β12-Borophene Single Crystalline Sheets as Efficient Electrocatalysts for Lithium-Sulfur Batteries

Two-dimensional (2D) borophene has attracted tremendous interest due to its fascinating properties, which have potential applications in catalysts, energy storage devices, and high-speed transistors. In the past few years, borophene was theoretically predicted as an ideal electrode material for lithium-sulfur (Li-S) batteries because of its low-density, metallic conductivity, high Li-ion surface mobility, and strong interface bonding energy to polysulfide. But until now, borophene-based Li-S batteries have not yet been achieved in experiments due to the absence of a large-scale synthetic method of freestanding borophene nanostructures with a high enough structural stability, conductivity, and uniformity. Herein, we developed a low-temperature liquid exfoliation (LTLE) method to synthesize freestanding few-layer β₁₂-borophene single-crystalline sheets with a P6¯m2 symmetry in tens of milligrams. The as-synthesized 2D sheets were used as the polysulfide immobilizers and electrocatalysts of Li-S batteries. The resulting borophene-based Li-S battery delivered an extralarge areal capacity of 5.2 mAh cm^-2 at a high sulfur loading of 7.8 mg cm^-2, an excellent rate performance of 8 C (@721 mAh g^-1), and an ultralow capacity fading rate of 0.039% in 1000 cycles, outperforming commercial Li-ion batteries and many other 2D material-based Li-S batteries. Based on the density functional theory model, the excellent electrochemical performances of the borophene-based Li-S batteries should originate from the enormous enhancement of β₁₂-borophene sheets for both the surface migration of the Li-ions and the adsorption energy of Li₂S_n clusters. Our results thus demonstrate a great potential for scalable production of freestanding β₁₂-borophene single-crystalline sheets in future high-performance Li-S batteries.

Ultrafast stimulated resonance Raman signatures of lithium polysulfides for shuttling effect characterization: An ab initio study

The shuttling effect is a crucial obstacle to the practical deployment of lithium sulfur batteries (LSBs). This can be ascribed to the generation of lithium polysulfide (LiPS) redox intermediates that are soluble in the electrolyte. The detailed mechanism of the shuttling, including the chemical structures responsible for the loss of effective mass and the dynamics/kinetics of the redox reactions, are not clear so far. To obtain this microscopic information, characterization techniques with high spatial and temporal resolutions are required. Here, we propose that resonance Raman spectroscopy combined with ultrafast broadband pulses is a powerful tool to reveal the mechanism of the shuttling effect. By combining the chemical bond level spatial resolution of resonance Raman and the femtosecond scale temporal resolution of the ultrafast pulses, this novel technique holds the potential of capturing the spectroscopic fingerprints of the LiPS intermediates during the working stages of LSBs. Using ab initio simulations, we show that, in addition to the excitation energy selective enhancement, resonance Raman signals of different LiPS intermediates are also characteristic and distinguishable. These results will facilitate the real-time in situ monitoring of LiPS species and reveal the underlying mechanism of the shuttling effect.

Array-Structured Double-Ion Cooperative Adsorption Sites as Multifunctional Sulfur Hosts for Lithium-Sulfur Batteries with Low Electrolyte/Sulfur Ratio

Low electrolyte/sulfur ratio (E/S) is a crucial factor that promotes the development of lithium-sulfur batteries (LSBs) with desired energy density. However, it causes multiple problems, including a strong "shuttle effect" during both the cycle and storage process, and limited sulfur utilization. Herein, we develop a Na₂Ti₆O₁₃ (NTO) nanowire array as a multifunctional sulfur host to simultaneously tackle both the above problems. The synergistic coordination between Na and Ti cations in NTO can accelerate the conversion of soluble polysulfides (PSs) to insoluble sulfides and significantly enhance their adsorption. Therefore, accumulation of PSs, which is the primary cause of the "shuttle effect", can be avoided in two ways. One is fast conversion kinetics during cycles; another is strong PS adsorption, which can suppress the disproportionation of PSs during storage. The as-prepared array represents an easy-to-infiltrate structure with efficient electron transport that allows good wetting ability of the conductive surface toward the electrolyte. Therefore, it helps improve sulfur utilization that is mainly limited by the presence of unwetted conductive surface. Consequently, NTO/sulfur array cathodes exhibit high sulfur utilization and extended cycle- and shelf-lives at a low E/S (5:1). Our work suggests that array materials featuring cooperative multi-ion adsorption sites are promising hosts for LSBs.

Confined Polysulfides in N-Doped 3D-CNTs Network for High Performance Lithium-Sulfur Batteries

Improving the utilization efficiency of active materials and suppressing the dissolution of lithium polysulfides into the electrolyte are very critical for development of high-performance lithium-sulfur batteries. Herein, a novel strategy is proposed to construct a three-dimensional (3D) N-doped carbon nanotubes (CNTs) networks to support lithium polysulfides (3D-NCNT-Li₂S₆) as a binder-free cathode for high-performance lithium-sulfur batteries. The 3D N-doped CNTs networks not only provide a conductive porous 3D architecture for facilitating fast ion and electron transport but also create void spaces and porous channels for accommodating active sulfur. In addition, lithium polysulfides can be effectively confined among the networks through the chemical bond between Li and N. Owing to the synergetic effect of the physical and chemical confinement for the polysulfides dissolution, the 3D-NCNT-Li₂S₆ cathodes exhibit enhanced charge capacity and cyclic stability with lower polarization and faster redox reaction kinetics. With an initial discharge capacity of 924.8 mAh g^-1 at 1 C, the discharge capacity can still maintain 525.1 mAh g^-1 after 200 cycles, which is better than that of its counterparts.

Emerging beyond-graphene elemental 2D materials for energy and catalysis applications

Elemental two-dimensional (2D) materials have emerged as promising candidates for energy and catalysis applications due to their unique physical, chemical, and electronic properties. These materials are advantageous in offering massive surface-to-volume ratios, favorable transport properties, intriguing physicochemical properties, and confinement effects resulting from the 2D ultrathin structure. In this review, we focus on the recent advances in emerging energy and catalysis applications based on beyond-graphene elemental 2D materials. First, we briefly introduce the general classification, structure, and properties of elemental 2D materials and the new advances in material preparation. We then discuss various applications in energy harvesting and storage, including solar cells, piezoelectric and triboelectric nanogenerators, thermoelectric devices, batteries, and supercapacitors. We further discuss the explorations of beyond-graphene elemental 2D materials for electrocatalysis, photocatalysis, and heterogeneous catalysis. Finally, the challenges and perspectives for the future development of elemental 2D materials in energy and catalysis are discussed.

Properties of S-Functionalized Nitrogen-Based MXene (Ti2NS2) as a Hosting Material for Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries have received extensive attention due to their high theoretical specific capacity and theoretical energy density. However, their commercialization is hindered by the shuttle effect caused by the dissolution of lithium polysulfide. To solve this problem, a method is proposed to improve the performance of Li-S batteries using Ti₂N(Ti₂NS₂) with S-functional groups as the sulfur cathode host material. The calculation results show that due to the mutual attraction between Li and S atoms, Ti₂NS₂ has the moderate adsorption energies for Li₂S_x species, which is more advantageous than Ti₂NO₂ and can effectively inhibit the shuttle effect. Therefore, Ti₂NS₂ is a potential cathode host material, which is helpful to improve the performance of Li-S batteries. This work provides a reference for the design of high-performance sulfur cathode materials.

Mechanistic Insights into Interactions of Polysulfides at VS2 Interfaces in Na-S Batteries: A DFT Study

Room temperature sodium-sulfur (Na-S) batteries, because of their high theoretical energy density and low cost, are considered as a promising candidate for next-generation energy storage devices. However, the practical utilization of the Na-S batteries is greatly hindered by various deleterious factors such as dissolution of sodium polysulfides (Na₂S_n) into the electrolyte commonly termed as "shuttle effect," sluggish decomposition of solid Na₂S, and poor electronic conductivity of sulfur. To overcome the challenges, we introduced single-layer vanadium disulfide (VS₂) as an anchoring material (AM) to immobilize higher-order polysulfides from the dissolution and also to accelerate the otherwise sluggish kinetics of insoluble short-chain polysulfides. We employ density functional theory (DFT) calculations to elucidate the Na₂S_n interactions at the VS₂ interfaces. We show that the adsorption strengths of various Na₂S_n species on the VS₂ basal plane are adequate (1.21-4.3 eV) to suppress the shuttle effect, and the structure of Na₂S_n are maintained without any decomposition, which is necessary to mitigate capacity fading. The calculated projected density of states (PDOS) reveals that the metallic character of the pristine VS₂ is retained even after Na₂S_n adsorption. The calculated Gibbs free energy of each elementary sulfur reduction reaction indicates a significant decrement in the free energy barrier due to the catalytic activity of the VS₂ surface. Furthermore, VS₂ is found to be an excellent catalyst to significantly reduce the oxidative decomposition barrier of Na₂S, which facilitates accelerated electrode kinetics and higher utilization of sulfur. Overall, VS₂ with strong adsorption behavior, enhanced electronic conductivity, and improved oxidative decomposition kinetics of polysulfides can be considered as an effective AM to prevent the shuttle effect and to improve the performance of Na-S batteries.

Self-Assembled Polyoxometalate Nanodots as Bidirectional Cluster Catalysts for Polysulfide/Sulfide Redox Conversion in Lithium-Sulfur Batteries

Polyoxometalates (POMs) are a class of discrete molecular inorganic metal-oxide clusters with reversible multielectron redox capability. Taking advantage of their redox properties, POMs are thus expected to be directly involved in the lithium-sulfur batteries (Li-S, LSBs) system as a bidirectional molecular catalyst. Herein, we design a three-dimensional porous structure of reduced graphene-carbon nanotube skeleton supported POM catalyst as a high-conductive and high-stability host material. Based on various spectroscopic techniques and in situ electrochemical studies together with computational methods, the catalytic mechanism of POM clusters in Li-S battery was systematically clarified at the molecular level. The constructed POM-based sulfur cathode delivers a reversible capacity 1110 mAh g^-1 at 1.0 C and cycling stability up to 1000 cycles at 3.0 C. Furthermore, Li-S pouch/beaker batteries with a POM-based cathode were successfully demonstrated. This work provides essential inputs to promote molecular catalyst design and its application in LSBs.

A Biomass-Based Integral Approach Enables Li-S Full Pouch Cells with Exceptional Power Density and Energy Density

Lithium-sulfur (Li-S) batteries, as part of the post-lithium-ion batteries (post-LIBs), are expected to deliver significantly higher energy densities. Their power densities, however, are today considerably worse than that of the LIBs, limiting the Li-S batteries to very few specific applications that need low power and long working time. With the rapid development of single cell components (cathode, anode, or electrolyte) in the last few years, it is expected that an integrated approach can maximize the power density without compromising the energy density in a Li-S full cell. Here, this goal is achieved by using a novel biomass porous carbon matrix (PCM) in the anode, as well as N-Co9 S8 nanoparticles and carbon nanotubes (CNTs) in the cathode. The authors' approach unlocks the potential of the electrodes and enables the Li-S full pouch cells with unprecedented power densities and energy densities (325 Wh kg-1 and 1412 W kg-1 , respectively). This work addresses the problem of low power densities in the current Li-S technology, thus making the Li-S batteries a strong candidate in more application scenarios.

Etched ion-track membranes as tailored separators in Li-S batteries

Lithium-sulfur (Li-S) batteries are considered a promising next generation alternative to lithium-ion batteries for energy storage systems due to its high energy density. However, several challenges, such as the polysulfide redox shuttle causing self-discharge of the battery, remain unresolved. In this paper, we explore the use of polymer etched ion-track membranes as separators in Li-S batteries to mitigate the redox shuttle effect. Compared to commercial separators, their unique advantages lie in their very narrow pore size distribution, and the possibility to tailor and optimize the density, geometry, and diameter of the nanopores in an independent manner. Various polyethylene terephthalate membranes with diameters between 22 and 198 nm and different porosities were successfully integrated into Li-S coin cells. The reported coulombic efficiency of up to 97% with minor reduction in capacity opens a pathway to potentially address the polysulfide redox shuttle in Li-S batteries using tailored membranes.

Stable Lithium Metal Anodes with a GaOx Artificial Solid Electrolyte Interphase in Damp Air

As a promising high energy density electrode material for rechargeable batteries, lithium (Li) metal is still suffering from air/water instability due to its highly reactive nature. In addition, the Li dendrite issue in Li metal batteries needs to be resolved to ensure the safety of batteries and for wide applications. Herein, we demonstrate that a simple compact GaO_x layer formed using liquid metal (LM) can act as an artificial solid electrolyte interphase to block moisture and oxygen in the air from corroding the lithium metal. Interestingly, GaO_x that covered the electrode effectively inhibits Li dendrite growth in electrochemistry cycling, ensuring the safety of Li metal batteries. The exposed composite Li metal anode (exposed under ambient air with relative humidity (RA) ≈ 75% for 5 h) not only shows a superior stability (symmetrical cell) but also delivers an elevated cycling stability (>500 cycles at 0.5 and 1 C) with a sulfur@C cathode in the full-cell configuration. Our work provides a new pathway for the large-scale applications of the air/water-tolerant Li metal anode in rechargeable batteries.

Monolayer Fe3GeX2 (X = S, Se, and Te) as Highly Efficient Electrocatalysts for Lithium-Sulfur Batteries

The high energy density, low cost, and environmental friendliness of lithium-sulfur (Li-S) batteries enable them to be promising next-generation energy storage systems. However, the commercialization of Li-S batteries is presently hindered by the bottlenecks, such as the low conductivity of sulfur species, shuttle effect of polysulfides, and poor conversion efficiency in discharging/charging processes. Here, on the basis of first-principles calculations, we predicted that the two-dimensional magnetic Fe₃GeX₂ (X = S, Se, and Te) monolayers are quite promising to overcome the aforesaid problems. The Fe₃GeX₂ monolayer has metallic electronic structures and moderate binding strength to the soluble lithium polysulfides, which are expected to improve the overall electric conductivity of sulfur species and anchor the soluble lithium polysulfides to suppress the shuttle effect. Remarkably, Fe₃GeX₂ monolayers show bifunctional electrocatalytic activity to the S reduction reaction and the Li₂S decomposition reaction, which improves the conversion efficiency in discharging and charging processes. This finding may open up an avenue for the development of high-performance Li-S batteries.

Sb nanosheet modified separator for Li-S batteries with excellent electrochemical performance

An air-stable antimony (Sb) nanosheet modified separator (SbNs/separator) has been prepared by coating exfoliated Sb nanosheets (SbNs) successfully onto a pristine separator through a vacuum infiltration method. The as-prepared Li-S batteries using SbNs/separators exhibit much improved electrochemical performance compared to the ones using commercial separators. The coulombic efficiency (CE) of the Li-S battery using the SbNs/separator after the initial cycle is close to 100% at a current density of 0.1 A g-1, and 660 mA h g-1 capacity retained after 100 cycles. The rate capability of Li-S battery using SbNs/separator delivers a reversible capacity of 425 mA h g-1 when the current density increases to 1 A g-1. The improved electrochemical performance is mainly attributed to the following reasons. Firstly, the combination of physical adsorption and chemical bonding between SbNs and lithium polysulfides (LiPSs), which efficiently inhibits the shuttle phenomena of LiPSs. Secondly, the good electronic conductivity of SbNs improves the utilization of the adsorbed LiPSs, which benefits the capacity release of active materials. Lastly, the fast conversion kinetics of intermediate LiPSs caused by the catalytic effect from SbNs further suppresses the shuttle effect of LiPSs. The SbNs/separators exhibit a great potential for the future high-performance Li-S batteries.

Advanced High-Performance Potassium-Chalcogen (S, Se, Te) Batteries

Current great progress on potassium-chalcogen (S, Se, Te) batteries within much potential to become promising energy storage systems opens a new avenue for the rapid development of potassium batteries as a complementary option to lithium ion batteries. The discussion mainly concentrates on recent research advances of potassium-chalcogen (S, Se, Te) batteries and their corresponding cathode materials in this review. Initially, the development of cathode materials for four types of batteries is introduced, including: potassium-sulfur (K-S), potassium-selenium (K-Se), potassium-selenium sulfide (K-Se_x S_y ), and potassium-tellurium (K-Te) batteries. Next, critical challenges for chalcogen-based electrodes in devices operation are summarized. In addition, some pragmatic strategies are proposed as well to relieve the low electronic conductivity, large volumetric expansion, shuttle effect, and potassium dendrite growth. At last, the perspectives on designing advanced cathode materials for potassium-chalcogen batteries are provided with the goal of developing high-performance potassium storage devices.

The Art of Constructing Black Phosphorus Nanosheet Based Heterostructures: From 2D to 3D

Assembling different kinds of 2D nanosheets into heterostructures presents a promising way of designing novel artificial materials with new and improved functionalities by combining the unique properties of each component. In the past few years, black phosphorus nanosheets (BPNSs) have been recognized as a highly feasible 2D material with outstanding electronic properties, a tunable bandgap, and strong in-plane anisotropy, highlighting their suitability as a material for constructing heterostructures. In this study, recent progress in the construction of BPNS-based heterostructures ranging from 2D hybrid structures to 3D networks is discussed, emphasizing the different types of interactions (covalent or noncovalent) between individual layers. The preparation methods, optical and electronic properties, and various applications of these heterostructures-including electronic and optoelectronic devices, energy storage devices, photocatalysis and electrocatalysis, and biological applications-are discussed. Finally, critical challenges and prospective research aspects in BPNS-based heterostructures are also highlighted.

DFT and experimental study of nano red phosphorus anchoring on sulfurized polyacrylonitrile for lithium-ion batteries

Sulfur atoms can reconstruct the configuration of PAN, which makes the electron transfer more convenient and reduces the energy barriers during Li ion diffusion. The sulfurized polyacrylonitrile plays a crucial role in anchoring the P₄ molecule and electron transport simultaneously. Uniform RP nanoparticles (∼200 nm) are obtained using a simple liquid phase method. SPAN-RP shows an initial reversible capacity of 1214 mA h g^-1 at 0.2C and retains a capacity of 860 mA h g^-1 with a high coulombic efficiency of 99.6% after 200 cycles.

Metal chalcogenide hollow polar bipyramid prisms as efficient sulfur hosts for Na-S batteries

Sodium sulfur batteries require efficient sulfur hosts that can capture soluble polysulfides and enable fast reduction kinetics. Herein, we design hollow, polar and catalytic bipyramid prisms of cobalt sulfide as efficient sulfur host for sodium sulfur batteries. Cobalt sulfide has interwoven surfaces with wide internal spaces that can accommodate sodium polysulfides and withstand volumetric expansion. Furthermore, results from in/ex-situ characterization techniques and density functional theory calculations support the significance of the polar and catalytic properties of cobalt sulfide as hosts for soluble sodium polysulfides that reduce the shuttle effect and display excellent electrochemical performance. The polar catalytic bipyramid prisms sulfur@cobalt sulfide composite exhibits a high capacity of 755 mAh g⁻¹ in the second discharge and 675 mAh g⁻¹ after 800 charge/discharge cycles, with an ultralow capacity decay rate of 0.0126 % at a high current density of 0.5 C. Additionally, at a high mass loading of 9.1 mg cm⁻², sulfur@cobalt sulfide shows high capacity of 545 mAh g⁻¹ at a current density of 0.5 C. This study demonstrates a hollow, polar, and catalytic sulfur host with a unique structure that can capture sodium polysulfides and speed up the reduction reaction of long chain sodium polysulfides to solid small chain polysulfides, which results in excellent electrochemical performance for sodium-sulfur batteries.

Sodium sulfur batteries require efficient sulfur hosts that can capture soluble polysulfides and enable fast reduction kinetics. Here, authors report hollow catalytic bipyramid prism CoS₂/C as efficient sulfur carriers, and investigate the reaction mechanism in the sodium sulfur battery.

Comparative Study on the Adsorption Capacities of the Three Black Phosphorus-Based Materials for Methylene Blue in Water

Dye effluent has attracted considerable attention from worldwide researchers due to its harm and toxicity in recent years; as a result, the treatment for dye has become one of the focuses in the environmental field. Adsorption has been widely applied in water treatment owing to its various advantages. However, the adsorption behaviors of the new materials, such as the 2D black phosphorus (BP), for pollution were urgently revealed and improved. In this work, BP, black phosphorene (BPR), and sulfonated BPR (BPRS) were prepared by the vapor phase deposition method, liquid-phase exfoliating method, and modification with sulfonation, respectively. The three BP-based materials were characterized and used as adsorbents for the removal of methylene blue (MB) in water. The results showed that the specific surface areas (SSAs) of BP, BPR, and BPRS were only 6.78, 6.92, and 7.72 m2·g−1, respectively. However, the maximum adsorption capacities of BP, BPR, and BPRS for MB could reach up to 84.03, 91.74, and 140.85 mg·g−1, which were higher than other reported materials with large SSAs such as graphene (GP), nanosheet/magnetite, and reduced graphene oxide (rGO). In the process of BP adsorbing MB, wrinkles were generated, and the wrinkles would further induce adsorption. BPR had fewer layers (3–5), more wrinkles, and stronger adsorption capacity (91.74 mg·g−1). The interactions between the BP-based materials and MB might cause the BP-based materials to deform, i.e., to form wrinkles, thereby creating new adsorption sites between layers, and then further inducing adsorption. Although the wrinkles had a certain promotion effect, the adsorption capacity was limited, so the sulfonic acid functional group was introduced to modify BPR to increase its adsorption sites and promote the adsorption effect. These findings could provide a new viewpoint and insight on the adsorption behavior and potential application of the BP-based materials.

Molybdenum Boride as an Efficient Catalyst for Polysulfide Redox to Enable High-Energy-Density Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries, despite having high theoretical specific energy, possess many practical challenges, including lithium polysulfide (LiPS) shuttling. To address the issues, here, hydrophilic molybdenum boride (MoB) nanoparticles are presented as an efficient catalytic additive for sulfur cathodes. The high conductivity and rich catalytically active sites of MoB nanoparticles allow for a fast kinetics of LiPS redox in high-sulfur-loading electrodes (6.1 mg cm^-2 ). Besides, the hydrophilic properties and good wettability toward electrolyte of MoB can facilitate electrolyte penetration and LiPS redox, guaranteeing a high utilization of sulfur under a lean-electrolyte condition. Therefore, the cells with MoB achieve impressive electrochemical performance, including a high capacity (1253 mA h g^-1 ) and ultralong lifespan (1000 cycles) with a low capacity fade rate of 0.03% per cycle. Also, pouch cells fabricated with the MoB additive deliver an ultrahigh discharge capacity of 947 mA h g^-1 , corresponding to a low electrolyte-to-capacity ratio of about 4.8 µL (mA h)^-1 , and remain stable over 55 cycles under practically necessary conditions with a low electrolyte-to-sulfur ratio of 4.5 µL mg^-1 .

Enhanced Catalytic Conversion of Polysulfides Using Bimetallic Co7Fe3 for High-Performance Lithium-Sulfur Batteries

Practical applications of lithium-sulfur (Li-S) batteries have been severely hindered by their low capacity, poor rate performance, and fast capacity degradation, which mainly originate from the notorious polysulfide shuttle effect. Herein, with density functional theory calculations, we show that the alloying of Fe into carbon-coated Co not only provides moderate binding interactions with the polysulfides to hinder their diffusion but also serves as an active catalyst in the spontaneous and successive lithiation of S₈ to Li₂S. Based on the fast migration of Li ions and the spontaneous lithiation of Li₂S₂ on the carbon-coated Fe-Co alloy, the entrapping-conversion processes of polysulfides are both thermodynamically and kinetically promoted in redox cycling. Experimentally, rationally designed Co₇Fe₃@porous graphite carbon-carbon nanotubes (Co₇Fe₃@PGC-CNT) electrocatalysts are introduced into Li-S batteries through separator functionalization. Consistent with theoretical predictions, Li-S batteries with Co₇Fe₃@PGC-CNT modified separators exhibit a dramatically enhanced rate capacity (788 and 631 mAh g^-1 at 10 and 15 C rates, respectively) and cycling stability (a slow capacity decay of 0.05% per cycle over 1000 cycles at 2.0 C), which are superior to those of most reported Li-S batteries coupled with state-of-the-art separators. Furthermore, it is shown that the excellent hindering of the shuttle effects enables a high areal capacity of 4.7 mAh cm^-2 after 90 cycles at a high sulfur loading of 6.7 mg cm^-2. Our work provides a feasible method for developing high-energy and long-life Li-S batteries, which might drive the commercialization of Li-S batteries.

Two-Dimensional Black Phosphorus Nanomaterials: Emerging Advances in Electrochemical Energy Storage Science

Two-dimensional black phosphorus (2D BP), well known as phosphorene, has triggered tremendous attention since the first discovery in 2014. The unique puckered monolayer structure endows 2D BP intriguing properties, which facilitate its potential applications in various fields, such as catalyst, energy storage, sensor, etc. Owing to the large surface area, good electric conductivity, and high theoretical specific capacity, 2D BP has been widely studied as electrode materials and significantly enhanced the performance of energy storage devices. With the rapid development of energy storage devices based on 2D BP, a timely review on this topic is in demand to further extend the application of 2D BP in energy storage. In this review, recent advances in experimental and theoretical development of 2D BP are presented along with its structures, properties, and synthetic methods. Particularly, their emerging applications in electrochemical energy storage, including Li-/K-/Mg-/Na-ion, Li-S batteries, and supercapacitors, are systematically summarized with milestones as well as the challenges. Benefited from the fast-growing dynamic investigation of 2D BP, some possible improvements and constructive perspectives are provided to guide the design of 2D BP-based energy storage devices with high performance.

Promoted Deposition of Three-Dimensional Li2S on Catalytic Co Phthalocyanine Nanorods for Stable High-Loading Lithium-Sulfur Batteries

The sulfur redox in Li-S batteries involves a complex sequence of solid-liquid-solid conversions, and reaction catalysis has recently become a focused area for further advancement. The deposition of solid Li₂S from liquid Li₂S₄ contributes to three-quarters of the total theoretical capacity and is therefore of great significance over the entire cathode reaction. This study demonstrates a cathode material composed of carbon nanofibers decorated with catalytic Co phthalocyanine nanorods (CoPc@CNF), which are highly effective in promoting the deposition of Li₂S in three-dimensional (3D) fine particles rather than 2D thin films. This significantly alleviates cathode passivation during cell charge and discharge, leading to obviously improved sulfur utilization and cycling stability for high loading cathodes. DFT calculations indicate that the promoted 3D deposition of Li₂S is related to the facilitated migration of deposition precursors (Li₂S₄ and Li-ions) to migrate on the CoPc nanorods. Lithium-sulfur (Li-S) pouch cells were prepared with high specific (954 mAh g^-1), areal (4.8 mAh cm^-2), and total (235 mAh) capacities achieved at 0.5 C under high sulfur content. As metal phthalocyanines possess a high structural variability, this study provides opportunities to the design of a new class of Li-S cathode materials.

Single-atom Catalytic Materials for Lean-electrolyte Ultrastable Lithium-Sulfur Batteries

Lithium-sulfur batteries with high energy capacity are promising candidates for advanced energy storage. However, their applications are impeded by shuttling of soluble polysulfides and sluggish conversion kinetics with inferior rate performance and short cycling life. Here, single-atom materials are designed to accelerate polysulfide conversion for Li-S batteries. Nitrogen sites in the structure not only anchor polysulfides to alleviate the shuttle effect but also enable high loading of single-atom irons. Density functional theory calculations indicate that single-atom sites reduce the energy barrier of electrochemical reactions and thus improve the rate and cycling performances of batteries. The coin battery shows impressive energy storage properties, including a high reversible capacity of 1379 mAh g^-1 at 0.1 C and a high rate capacity of 704 mAh g^-1 at 5 C. The ratio of electrolyte dosage/energy density is as low as 5.5 g Ah^1-. It exhibits excellent cycling performance with a capacity retention of 90% even after 200 cycles at 0.2 C.