Low Attenuation Rate Research Articles

Simultaneous modification of Na+-rich and Mn2+-doping on Na3V2(PO4)3 for superior electrochemical performance: Experimental and theoretical study

Recently, the weak intrinsic conductivity limits the application of Na3V2(PO4)3 (NVP). Herein, a simultaneous optimized scheme is proposed to comprehensively improve the kinetic properties and modify the electronic structure of NVP. Significantly, bivalent Mn2+ is introduced to occupy V3+ site, resulting in favorable p-type substitution effects to produce more hole carriers thus accelerating electronic conductivity. Moreover, Mn2+ possesses a larger ionic radius than V3+ (0.067nm vs. 0.064nm), thus Mn2+ behaves efficient pillar effect to enhance the skeleton steadiness and broaden the migration pathway of Na+, indicating notably improved structure stability and ionic transport rate. Moreover, for the electronic equilibrium of the system, more Na+ will be introduced into the NVP bulk system after Mn2+ doping and Na-rich Na3+xV2-xMnx(PO4)3 compounds are designed, supplying more active carriers to participate the de-intercalation process and generating more reversible capacity. In addition, the optimized electronic construction of Mn2+ doped NVP is deeply investigated by DFT calculations, demonstrating the reduced band gap and declined energy barrier for Na+ transportation. Meanwhile, moderate CNTs are introduced together with coated carbon layers to construct an effective three-dimensional conductive network, significantly elevating the electron transfer property. The enwrapped CNTs also restrain the overgrowth and reunion of powders, thereby reducing the grain size and cutting down the transportation ways of Na+. Finally, the modified Na3.04V1.96Mn0.04(PO4)3@CNTs reveals superior electrochemical performance. It releases 120.8 mAh g-1 at 0.1C. It maintains remarkable retention value of 89.8% at 10C after 1000 cycles, suggesting a relatively low attenuation rate of 0.011% per cycle. Even at 50C, it still delivers a capacity of 63.6 mAh g-1 and keeps 68.2% after 4000 cycles.

Ionic Covalent Organic Framework Membrane as Active Separator for Highly Reversible Zinc-Sulfur Battery.

Zinc-sulfur (Zn-S) batteries exhibit a high theoretical energy density, nontoxicity, and cost-effectiveness, demonstrating significant potential for integration into large-scale energy storage systems. However, the phenomenon of polysulfide (including dissolved S8 and Sx2-) shuttling is a major issue that results in rapid capacity decay and a short lifespan, limiting the practical performance of sulfur-based batteries. Herein, we fabricated an ionic covalent organic framework (iCOF) membrane as an active separator for the Zn-S battery. Sulfonic acid groups were introduced to the COF membrane, providing abundant negative charge sites in its pore wall. By combining size sieving and charge interaction between the polysulfide and pore wall, the iCOF membrane inhibited the crossover of polysulfides to the Zn metal anode without affecting the transport of metal ions. The Zn-S battery with the iCOF membrane as the separator shows a high-performance and low attenuation rate of 0.05% per cycle over 300 cycles at 2.5 A g-1. This study emphasizes the significance of separator design in enhancing Zn-S batteries and showcases the potential of functionalized framework materials for the development of high-performance energy storage systems.

Core-shell Ru@Co2P synergistic catalyst as polysulfides adsorption-catalytic conversion mediator with enhanced redox kinetics in lithium-sulfur batteries

Lithium-sulfur batteries (LSBs) have emerged as the research hotspot due to their compelling merits, including high specific capacity (1675 mAh g−1), theoretical energy density (2600 Wh kg−1), environmental friendliness, and economic advantages. However, challenges still exist for further application due to their inherent issues such as the natural insulation, shuttle effect, and volume expansion of sulfur cathode during the continuous cycle processes. These factors obstruct the lithium ions (Li+) transfer process and sulfur utilization, resulting in significant impedance and inducing inferior battery performance. Herein, the core–shell nanocube anchoring ruthenium atoms and dicobalt phosphate (Ru@Co2P@NC) were fabricated as the effective catalyst and inhibited barrier for LSBs. On the one hand, the core–shell structure offers numerous channels to expedite Li+ diffusion. On the other hand, ruthenium (Ru) and dicobalt phosphate (Co2P) active sites facilitate the chemical capture of lithium polysulfides (LiPSs), accelerating sluggish kinetics. Ru@Co2P@NC modified cells not only exhibited a high initial specific capacity (1609.35 mAh g−1) at 0.5C and enduring stability with high specific capacity retention of 906.60 mAh g−1 at 0.5C after 400 cycles but also possessed low capacity attenuation rate of 0.07 % per cycle after 600 cycles (1C, Sulfur loading: 1.2 mg). Interestingly, the modified cells demonstrated a high specific capacity and long-cycle stability with high sulfur loading (from 1.984 to 3.137 mg), which provides a promising research approach for high-performance LSBs.

3D attenuation tomography of the Uttarakhand, NW Himalaya: Linkage to fluid or partial melt zones - Seismic hazard

This work proposes the shear-wave attenuation tomography of the Garhwal and Kumaun regions, Uttarakhand Himalaya, to investigate the crustal state. Based on attenuation characteristics, the high attenuated layer identified starts at ∼10 km in the Garhwal region and ∼5 km in the Kumaun region. The obtained model revealed that quality factor (Q) values vary from 16 to 664 and 49 to 866 at 1 Hz frequency for the Kumaun and Garhwal regions, respectively. The high attenuation rate (1/Q) in the Kumaun region compared to the Garhwal region may be due to the high attenuated layer at a shallower depth in the Kumaun region. The comparatively low attenuation rate of the Garhwal characterizes it as a region with high seismic hazard potential. Pioneeringly, layered frequency-dependent attenuation models are proposed up to a depth of 30 km for six different layers with 5 km thickness each, which will provide new insight into seismic hazard evaluation.

Rational design of hollow C@SnS2/SnS@C cubes with N-doping to realize stepwise sodium storage induced structural stability for highly stable cycling performance

Current application of SnS2-based anodes in sodium-ion batteries fails to meet the demand for higher Na+ storage capacity due to the structural pulverization induced by significant volume changes during cycling. Herein, a novel composite of hollow C@SnS2/SnS@C cubes with excellent diffusion kinetics and structural stability from stepwise Na+ storage is designed. The SnS with gentle pseudocapacitive reaction acts as the self-supporter to prevent the collapse of SnS2/SnS heterostructure during the Na+ insertion/extraction. Together with the clamping of double carbon layers and hollow construction, the volume change caused structural instability in heterostructure is effectively alleviated. The rapid transport of electrons and ions within the built-in electric field of heterostructure endows the composite an excellent diffusion kinetics, which is generated from the narrow bandgap and outstanding Na+ absorption of heterostructure according to the first-principle calculation. Thus, the as-prepared composite maintains a remarkable capacity of 547.9 mAh g−1 after 200 cycles at current density of 0.5 A g−1. Even a capacity of 502.5 mAh g−1 with a low attenuation rate of 0.035 % per cycle is achieved at 2 A g−1 after 1000 cycles. The work proposes an effective approach to achieve effective Na + storage of SnS2-based anodes with long-lasting structural stability.

Organic-inorganic hybrids of BiI3-polymers with embedded conductive carbon fillers displaying high SNR for direct X-ray imaging detectors

Organic polymers are light weight, low toxic and environmentally stable candidates of interest in X-ray detection application. But low attenuation and high recombination rate of charge carriers cause low sensitivity is major limitation of these detectors. In this work, organic polymers (PS/PMMA) composites were prepared with high-Z inorganic BiI3 by simple dry mixing technique. The organic-inorganic hybrid further embedded with conductive carbon filler (MWCNT, CB, GP) to improve the charge collection of the samples. Resistivity and mobility of the samples were studied with help of Hall measurements and mobility-lifetime was calculated by Hecth equation and found (2.1 ± 0.2) × 10−3 cm2V−1. The elemental analysis of the samples had been done by XPS analysis. The X-ray investigations done by using dental X-ray source and the sensitivity of the samples increases from 3.4 to 200 μGy−1 cm−3 by incorporating CB filler with a low leakage current of order of 33.3 pA/cm2.

P-doped Mo2C nanoparticles embedded on carbon nanofibers as an efficient electrocatalyst for Li-S batteries

Designing a reliable sulfur host that can simultaneously catalyze sulfur redox reactions and suppress polysulfides shuttling is highly desired for the development of advancing Li-S batteries. In this work, P-doped Mo2C nanoparticles anchoring on carbon nanofibers (CNF) is prepared via an organic–inorganic nanohybridization process. The interwoven CNF networks establish continuous electrons transport pathways and provide a large surface area for loading P-Mo2C nanoparticles. The P dopant tunes the electronic structure of Mo2C, which endows P-Mo2C with enhanced polysulfides adsorption ability and improved sulfur redox kinetics. Leveraging these advantages, the Li-S battery shows excellent electrochemical properties, delivering a high specific capacity of 1174 mA·h·g−1 at 0.2 C, and maintaining over 1200 stable cycles at 1 C with a low capacity attenuation rate of 0.043 % per cycle. At a S loading of 4.88 mg·cm−2 and E/S ratio of 8.25 μL·mg−1, the Li-S battery attains an areal capacity of 6.50 mA·h·cm−2 at 0.05 C. These results highlight the promising application potential of P-Mo2C@CNF as an effective electrocatalyst for Li-S batteries.

Reinforced Lewis covalent bond by twinborn nitride heterostructure for lithium-sulfur batteries

The practical application of lithium-sulfur (Li-S) batteries, as promising next-generation batteries, is hindered by their shuttle effect and the slow redox kinetics. Herein, a tungsten and molybdenum nitride heterostructure functionalized with hollow metal-organic framework-derived carbon (W2N/Mo2N) was proposed as the sulfur host. The hollow spherical structure provides storage space for sulfur, enhances electrical conductivity, and inhibits volume expansion. The metal atoms in the nitrides bonded with lithium polysulfides (LiPSs) through Lewis covalent bonds, enhancing the high catalytic activity of the nitrides and effectively reducing the energy barrier of LiPSs redox conversion. Moreover, the high intrinsic conductivity of nitrides and the ability of the heterostructure interface to accelerate electron/ion transport improved the Li+ transmission. By leveraging the combined properties of strong adsorption and high catalytic activity, the sulfur host effectively inhibited the shuttle effect and accelerated the redox kinetics of LiPSs. High-efficiency Li+ transmission, strong adsorption, and the efficient catalytic conversion activities of LiPSs in the heterostructure were experimentally and theoretically verified. The results indicate that the W2N/Mo2N cathode provides stable, and long-term cycling (over 2000 cycles) at 3 C with a low attenuation rate of 0.0196% per cycle. The design strategy of a twinborn nitride heterostructure thus provides a functionalized solution for advanced Li-S batteries.

NiSe nanoparticles decorated corn stalk derived 2D carbon nanosheet as separator modifier for high-performance lithium-sulfur batteries

Lithium-sulfur (Li–S) batteries are considered as the most promising successors of lithium-ion batteries, however, the shuttle effect and sluggish reaction kinetics are the biggest obstacles hindering their commercialization. In this work, a kind of NiSe nanoparticles embedded in corn stalk-derived two-dimensional (2D) porous carbon nanosheet (NiSe@CSC) is constructed as a separator modifier for advanced Li–S batteries. The rich pore structure of the corn stalk-derived carbon nanosheets enables uniform distribution of NiSe and provides more deposition sites for lithium polysulfides (LiPS). Electrochemical analyses show that NiSe increases the affinity for LiPS to suppress the shuttle effect, thereby effectively preventing the corrosion of polysulfide on the lithium anode. NiSe@CSC is found to accelerate the redox conversion of sulfur species in the kinetic study. Consequently, the assembled Li–S cells with NiSe@CSC coating layer exhibit a high-rate performance of 710 mAh g−1 at 3 C and a low capacity attenuation rate of 0.046% per cycle after 800 cycles at 1 C. Furthermore, it can still maintain 2.8 mAh cm−2 at 0.5 C in near-commercial application scenarios of 4.1 mg cm−2 sulfur loading. The NiSe@CSC-based Li–Li symmetric cells also demonstrate stability and low overpotential in protecting the lithium anode. This combination of renewable biomass-based carbons and transition metal selenides enriches the exploration of biomass materials in separators and provides new ideas for designing practical Li–S batteries.

Rationalizing the impact of oxygen vacancy on polysulfide conversion kinetics for highly efficient lithium-sulfur batteries

The “shuttle effect” of lithium polysulfides (LiPSs) is a huge challenge for practical use of high-energy-density lithium-sulfur (Li-S) batteries, and one of the main reasons is the sluggish kinetics of sulfur conversion. Metal oxides are able to expedite the sulfur electrochemistry, and the structural defects enhance the adsorption-conversion ability of metal oxides for polysulfides. However, a significant research gap still remains regarding the relationship between the oxygen vacancy concentration and the adsorptive-catalytic performance of metal oxides. Herein, we establish a correlation between oxygen vacancy concentration and adsorptive-catalytic properties by using tungsten oxide (WOx) as model catalysts. It is revealed that high-concentration oxygen vacancy is beneficial for enhancing the binding between tungsten oxide and LiPSs, reducing the energy barrier of Li2S decomposition, and promoting polysulfide conversion kinetics. Consequently, the Li-S batteries using the tungsten oxide with high-concentration oxygen vacancies deliver high initial discharge capacity of 1169 mA h g−1 at 0.2 C and 865 mA h g−1 at 2 C, low attenuation rate of 0.064% per cycle over 1100 cycles at 2 C. With a high sulfur area loading of 5.34 mg cm−2, the Li-S batteries still exhibit high initial gravimetric capacity of 982 mA h g−1 at 0.1 C and areal capacity of 5.92 mA h cm−2. This work promotes the feasibility of defect engineering on metal oxides as an effective mean to enhance the practicality of Li-S batteries.

Separator modified by ternary iron molybdenum nitride and nitrogen-doped carbon composite enabling efficient polysulfide conversion for lithium-sulfur batteries

Lithium-sulfur batteries (LSBs) are appealing energy storage systems by virtue of the high theoretical energy density and abundant resources of sulfur. However, the sluggish redox reaction kinetics and shuttle effect of soluble lithium polysulfides (LiPSs) seriously restrict their practical applications. Searching for highly efficient and low cost electrocatalysts towards LiPSs conversion is one of the most promising approaches to relieve the shuttle effect and enhance the sulfur utilization. In this work, we first demonstrate the application of ternary iron molybdenum nitride hybridized with nitrogen-doped carbon, denoted as (Fe0.81Mo0.19)MoN2/NC composite, as an advanced separator modifier to boost the bidirectional catalytic conversion of LiPSs. Impressively, the as-fabricated LSBs with (Fe0.81Mo0.19)MoN2/NC modified separator display an ultrahigh initial discharge capacity of 1366.1 mAh g−1 at 0.1 C and still remains a high value of 809.1 mAh g−1 at a high rate of 4 C. Furthermore, a remarkable discharge capacity of 569.2 mAh g−1 is retained when cycling at a high rate of 1 C for 700 cycles (corresponding to a low attenuation rate of 0.065 % per cycle), indicating the good long-term cycling stability. The excellent performance could be attributed to the multiple advantages of high electrical conductivity, numerous active sites, strong adsorption ability and excellent catalytic activity, thereby effectively suppressing the shuttle effect of LiPSs. The present work indicates that the ternary transition metal nitrides could be promising separator modifiers for high-performance LSBs.

Vapor-phase biodegradation and natural attenuation of petroleum VOCs in the unsaturated zone: A microcosm study

Traditional natural attenuation studies focus on aqueous process in the saturated zone while vapor-phase biodegradation and natural attenuation in the unsaturated zone received much less attention. This study used microcosm experiments to explore the vapor-phase biodegradation and natural attenuation of 23 petroleum VOCs in the unsaturated zone including 7 monoaromatic hydrocarbons, 6 n-alkanes, 4 cycloalkanes, 3 alkylcycloalkanes and 3 fuel ethers. We found that monoaromatic hydrocarbon vapors were easily attenuated with significantly high first-order attenuation rates (9.48 d−1-43.20 d−1) in live yellow earth, of which toluene and benzene had the highest rates (43.20 d−1 and 28.32 d−1, respectively). The 13 aliphatic hydrocarbons and 3 fuel ethers all have relatively low attenuation rates (<0.54 d−1) in live soil and negligible biodegradation contribution. We explored the effects of soil types (black soil, yellow earth, lateritic red earth and quartz sand), soil moisture (2, 5, 10, and 17 wt%) contents and temperatures (4, 15, 25, 35 and 45 °C) on the vapor attenuation. Results showed that increasing soil organic matter (SOM) content, silt content, porosity and soil microorganism numbers enhanced contaminant attenuation and remediation efficiency. Increasing moisture content reduced the apparent first-order biodegradation rates of monoaromatic hydrocarbon vapors. The vapor-phase biodegradation had optimal temperature (∼25 °C in yellow earth) and increasing or decreasing temperature slowed down biodegradation rate. Overall, this study enhanced our understanding of vapor-phase biodegradation and natural attenuation of petroleum VOCs in the unsaturated zone, which is critical for the long-term management and remediation of petroleum contaminated site.

Construction of porous MoS2-Mo2C@C aerogel for use as superior lithium-ion battery anode

Anode materials based on molybdenum disulfide (MoS2) have been extensively investigated for lithium-ion battery (LIB) applications. Herein, a MoS2-Mo2C heterostructure was implanted into a porous carbon aerogel. Morphological analysis showed that a porous structure was obtained, with MoS2 nanosheets and Mo2C nanoparticles integrated in the bulky structure. Electrochemical analysis showed that good long-term cycling stability and superb rate performance were achieved when the prepared aerogel was used as an LIB anode. At 2.0 A g−1, a large specific capacity of 598.1 mAh g−1 was achieved. Moreover, after 3000 cycles at a current density of 10.0 A g−1, the aerogel anode maintained a 375.1 mAh g−1 specific capacity, demonstrating a low attenuation rate. Based on the characterization and analysis, a reaction mechanism was proposed. The outstanding electrochemical performance of this anode was ascribed to its porous structure, large surface area, and the defect-rich heterostructure, which synergistically improved its performance. Therefore, this material exhibits great potential for application in LIBs and other energy-related fields.

Conductive metal-organic framework flowers facilitate the anchoring and conversion kinetics of polysulfides for lithium‑sulfur batteries

Enhancing the trapping and catalytic conversion of polysulfides is the main path to restrain their shuttling for durable lithium‑sulfur batteries (LSBs). Herein, we report a flower-like metal-organic framework (MOF) MIL-47 layer as an interlayer material to achieve this purpose. The proposed MOF material possesses a unique flower-like structure that is composed of two-dimensional nanosheets, which is conducive to the mass transfer and the exposure of active sites, enabling an efficient adsorption towards polysulfides. Moreover, the high conductivity combined with sufficient catalytic active centers are instrumental in accelerating the redox processes of polysulfides conversion. Consequently, this flowery MOF-based interlayer endows LSBs an amazing capacity of 1003.6 mAh g−1 and an ultralong cycling stability with a low attenuation rate of 0.029 % over 1000 cycles under 1C, together with an exceptional rate performance (a capacity high as 696.9 mAh g−1 under 5C). In addition to this, an elevated sulfur loading and reduced electrolyte content do not affect its excellent cycling and rate performance. This work provides a new mentality to exploit multi-role nanostructured materials for LSBs.

Numerical prediction of ground vibrations induced by LPG boiling liquid expansion vapour explosion (BLEVE) inside a road tunnel

Accidental boiling liquid expansion vapour explosions (BLEVEs) caused by the bursting of liquified petroleum gas (LPG) tank inside a tunnel can induce vibrations of its surrounding geological media and threaten the stability of adjacent tunnels and structures. Therefore, it is essential to understand the characteristics of vibrations induced by LPG BLEVEs inside the tunnel for the safety design of its adjacent structures. Owing to the difficulty in effectively predicting the LPG BLEVE loads, the current practice usually employs equivalent methods, e.g., the TNT-equivalency method, in LPG BLEVE load predictions for structural response analysis, which may lead to inaccurate response predictions. This study compares ground vibrations induced by a BLEVE inside an arched road tunnel with those induced by its equivalent TNT explosion via high-fidelity numerical simulations. The results demonstrate that the frequency of BLEVE-induced vibrations is lower than that induced by the TNT explosion at the same scaled distance. The intensity of LPG BLEVE-induced vibrations at relatively small-scaled distances is lower than that of TNT explosion-induced vibrations at the same scaled distance, but becomes higher after a certain scaled distance because of the relatively low attenuation rate. In addition, parametric analysis is conducted to evaluate the effects of various factors on the characteristics of LPG BLEVE-induced ground vibrations. It is found that the surrounding rock type, the rock porosity, and the cover depth of the tunnel have more significant influences than the concrete grade of the tunnel lining. The recommendation for the tunnel design is also given based on the intensity and frequency characteristics of BLEVE-induced vibrations.

Dual-Mediation pathways promote redox kinetics for High-Loading Lithium–Sulfur batteries under lean electrolyte

The high energy density (2500 Wh kg−1) makes that lithium–sulfur batteries (LSBs) have a great potential in energy storages. However, the practical application of LSBs is severely hampered by several inherent problems, including the sluggish sulfur redox kinetics, the shuttling of lithium polysulfides (LiPSs) and poor electronic conductivity. Although heterogeneous or homogeneous mediators could improve the cycling performance of LSBs to a certain extent, single mediators could not completely promote sulfur conversions, especially under high sulfur loading and lean electrolyte. Herein, dual-mediator systems consist of heterogeneous and homogeneous mediators that are introduced to address the above issues. Density functional theory (DFT) calculations and electrochemical analysis indicate that CoSe nanoparticles embedded in urchin-like nitrogen-doped porous carbon with in-situ growth of CNTs (CoSe@CNTs) as heterogeneous mediators and soluble CoCp2 as homogeneous mediators could effectively accelerate the bidirectional conversion kinetics of liquid LiPSs ↔ solid Li2S through the synergistic effect. As a consequence, the cell with dual-mediators delivers a high initial specific capacity of 1005 mAh/g with a low attenuation rate of 0.045 % per cycle at a current density of 1.0C under sulfur loading of 2.8 mg cm−2 after 800cycles. Importantly, it still maintains a high areal capacity of 6.53 mAh cm−2 under lower electrolyte/sulfur ratio (E/S, 4.2 µL mg−1) and higher sulfur loading of 7.3 mg cm−2 over 100cycles at 0.1C.

Enhancement of polysulfide trapping induced by faceted ferroelectric for high-performance Li-S batteries

Facet engineering is viewed as an effective approach to tune the surface structure of electrode materials and thus influence their electrochemical performances. Herein, we report the introduction of faceted lead zirconate titanate with exposed (110) plane as the additive into the cathode of Li-S batteries to restrain the shuttle effect. The findings reveal that the faceted ferroelectric with strong internal electric field and sufficient surface polar sites can achieve the more efficient anchoring towards polysulfides than its partial- and un-faceted counterparts. By combining with the porous carbon host, the elaborately designed cathode therefore delivered excellent cycling stability with a low capacity attenuation rate of 0.047% per cycle after 300 cycles at 1 C. This work advances our understanding for the engineering of ferroelectric materials and the electric field effects on the stability of Li-S batteries, which could potentially inspire new strategies for the design of high-performance ferroelectric based energy devices.

Effect of copper foam on the explosion suppression in hydrogen/air with different equivalence ratios

This study investigates the effect of copper foam sheets on explosion suppression in hydrogen/air mixtures with different equivalence ratios (φ). The explosion experiment is conducted in a circular tube with a large aspect ratio (108). The phenomenon of flame quenching can be observed distinctly in the case of φ = 0.5. In the case of φ = 1.5, the copper foam sheets are destroyed by the reflected shock wave, and the overpressure rises by 65 %. In addition, a longer duration of peak overpressure and a lower attenuation rate can be observed due to the interaction between the shock wave and flame front. For the cases of φ = 1.0 and 2.0, the copper foam sheet effectively prevents flames and shock waves from reflecting. The experimental results provide an essential reference for the design of hydrogen flame arresters, the safety of hydrogen pipeline transportation, and engineering application.

Facile synthesis of amorphous carbon-coated bismuth phosphate nanocomposite for lithium-ion battery anode with ultra-long cycle stability

Herein, we report a novel BiPO4@Ketjen Black nanocomposite as long cycle life lithium-ion battery anode. The BiPO4@Ketjen Black nanocomposite is obtained via a simple and mild molten salt preparation followed by post-milling. When assembled with metal lithium sheets for half battery, BiPO4@Ketjen Black nanocomposite delivers a high capacity and rate performance as 317 ​mAh g−1 with current density of 100 ​mA ​g−1 after 100 discharge-charge cycles and 210 ​mAh g−1 delithiation capacity at 200 ​mA ​g−1 after 1500 cycles. A superior result as 100 ​mAh g−1 delithiation capacity at 1 ​A g−1 after 5000 cycles is acquired with a very low capacity attenuation rate of 0.013% per cycle. The enhanced electrochemical performance of BiPO4@Ketjen Black nanocomposite can be attributed to the formation of Bi nanoparticles uniformly dispersed in Li3PO4 inert matrix and amorphous carbon during the lithium impregnation process in the first cycle. This work revealed that the as-prepared BiPO4@Ketjen Black anode has great potential for development in lithium ion batteries.

Azo-Branched Covalent Organic Framework Thin Films as Active Separators for Superior Sodium-Sulfur Batteries.

Sodium-Sulfur (Na-S) batteries are outstanding for their ultrahigh capacity, energy density, and low cost, but they suffer from rapid cell capacity decay and short lifespan because of serious polysulfide shuttle and sluggish redox kinetics. Herein, we synthesize thin films of covalent organic frameworks (COFs) with azobenzene side groups branched to the pore walls. The azobenzene branches deliver dual functions: (1) narrow the pore size to the sub-nanometer scale thus inhibiting the polysulfide shuttle effect and (2) act as ion-hopping sites thus promoting the Na+ migration. Consequently, the Na-S battery using the COF thin film as the separator exhibits a high capacity of 1295 mA h g-1 at 0.2 C and an extremely low attenuation rate of 0.036% per cycle over 1000 cycles at 1 C. This work highlights the importance of separator design in upgrading Na-S batteries and demonstrates the possibility of functionalizable framework materials in developing high-performance energy storage systems.