Vacancy defect MoSeTe embedded in N and F co-doped carbon skeleton for high performance sodium ion batteries and hybrid capacitors

Sodium-ion batteries(SIBs) and hybrid capacitors(SIHCs) have garnered significant attention in energy storage due to their inherent advantages,including high energy density,cost-effectiveness,and enhanced safety.However,developing high-performance anode materials to improve sodium storage performa nce still remains a major challenge.Here,a facile one-pot method has been developed to fabricate a hybrid of MoSeTe nanosheets implanted within the N,F co-doped honeycomb carbon skeleton(MoSeTe/N,F@C).Experimental results demonstrate that the incorporation of large-sized Te atoms into MoSeTe nanosheets enlarges the layer spacing and creates abundant anion vacancies,which effectively facilitate the insertion/extraction of Na^(+) and provide numerous ion adsorption sites for rapid surface capacitive behavior.Additionally,the heteroatoms N,F co-doped honeycomb carbon skeleton with a highly conductive network can restrain the volume expansion and boost reaction kinetics within the electrode.As anticipated,the MoSeTe/N,F@C anode exhibits high reversible capacities along with exceptional cycle stability.When coupled with Na_(3)V_(2)(PO_(4))_(3)@C(NVPF@C) to form SIB full cells,the anode delivers a reversible specific capacity of 126 mA h g^(-1) after 100 cycles at 0.1 A g^(-1).Furthermore,when combined with AC to form SIHC full cells,the anode demonstrates excellent cycling stability with a reversible specific capacity of50 mA h g^(-1) keeping over 3700 cycles at 1.0 A g^(-1).In situ XRD,ex situ TEM characterization,and theoretical calculations(DFT) further confirm the reversibility of sodium storage in MoSeTe/N,F@C anode materials during electrochemical reactions,highlighting their potential for widespread practical application.This work provides new insights into the promising utilization of advanced transition metal dichalcogenides as anode materials for Na^(+)-based energy storage devices.

Rational design of carbon skeleton interfaces for highly reversible sodium metal battery anodes

Sodium metal batteries(SMBs)have attracted increasing attention over time due to their abundance of sodium resources and low cost.However,the widespread application of SMBs as a viable technology remains a great challenge,such as uneven metallic deposition and dendrite formation during cycling.Carbon skeletons as sodiophilic hosts can alleviate the dendrite formation during the plating/stripping.For the carbon skeleton,how to rationalize the design sodiophilic interfaces between the sodium metal and carbon species remains key to developing desirable Na anodes.Herein,we fabricated four kinds of structural features for carbon skeletons using conventional calcination and flash Joule heating.The roles of conductivity,defects,oxygen content,and the distribution of graphite for the deposition of metallic sodium were discussed in detail.Based on interface engineering,the J1600 electrode,which has abundant Na-C species on its surface,showed the highest sodiophilic.There are uniform and rich F-Na species distributed in the inner solid electrolyte interface layer.This study investigated the different Na-deposition behavior in carbon hosts with distinct graphitic arrangements to pave the way for designing and optimizing advanced electrode materials.

Sodiophilic skeleton based on the packing of hard carbon microspheres for stable sodium metal anode without dead sodium

The propensity of metallic Na dendrites from uneven electrodeposits and the low Coulombic efficiency due to the inevitable existence of "dead sodium" are crucial barriers to realizing the Na metal anode.Herein,we report a multifunctional sodiophilic skeleton based on the packing of hard carbon(HC)microspheres for stable sodium metal electrodeposition without "dead sodium".Firstly,HC is sodiophilic substrate due to the intrinsic heteroatoms or defects which is a favor for the nucleation of Na.Secondly,silver nanoparticles electroplating on HC(Ag-HC)was adopted to boost the Na diffusion and further regulate the uniform Na metal epitaxial deposition due to well compatibility with AIMD simulation.Finally,the packing of HC microspheres provides the inner space for Na plating.Importantly,it was first found by Cryo-TEM that Na metal deposition in nanoscale is achieved by oriented attachment along[110]direction,leading to the formation of polycrystalline Na metal film on Ag-HC.Such epitaxial deposition can efficiently reduce the formation of "dead sodium" as revealed by chromatography tests,allowing the high Coulombic efficiency and good cycling stability robust kinetics.Finally,HC-Ag||Na_(3)V_(2)(PO_(4))_(3)full cell with a low negative/positive ratio of 0.6 is firstly achieved and displays good cycling stability.This finding provides a new practical strategy without pre-plating of Na metals and demonstrates a highly reversible polycrystalline Na metal anode toward a high-energy Na-based battery.

Amorphous Se species anchored into enclosed carbon skeleton bridged by chemical bonding toward advanced K-Se batteries

Potassium-selenium(K-Se)batteries have attracted significant attention as one of the most promising alternatives of lithium-ion storage systems owing to high energy density and low cost.In the design of Se-based cathode materials,however,the low utilization rate of active Se and the rapid dissolution of polyselenides seriously weaken the capacity and cycle stability.Therefore,how to make full use of Se species without loss during the charge and discharge process is the key to design high-performance Se-based cathode.In this paper,a 3 D"water cube"-like Se/C hybrid(denoted as Se-O-PCS)is constructed with the assistance of Na_(2)CO_(3) templates.Thanks to the abundant carbonate groups(CO_(3)^(2-))originated from the Na_(2)CO_(3) templates,the molten Se species are firmly anchored into the pore of carbon skeleton by strong C-O-Se bonding.Thus,this unique Se-O-PCS model not only improves the utilization of active Se species,but also can reduce the contact with the electrolyte to inhibit the shuttle effect of polyselenides.Moreover,flexible carbon skeleton gives Se-O-PCS hybrid a good electrical conductivity and excellent structural robustness.Consequently,the resultant Se-O-PCS hybrid is endowed with an obviously enhanced K-ions storage property.

Recent Developments of Transition Metal Compounds-Carbon Hybrid Electrodes for High Energy/Power Supercapacitors

Due to their rapid power delivery,fast charging,and long cycle life,supercapacitors have become an important energy storage technology recently.However,to meet the continuously increasing demands in the fields of portable electronics,transportation,and future robotic technologies,supercapacitors with higher energy densities without sacrificing high power densities and cycle stabilities are still challenged.Transition metal compounds(TMCs)possessing high theoretical capacitance are always used as electrode materials to improve the energy densities of supercapacitors.However,the power densities and cycle lives of such TMCs-based electrodes are still inferior due to their low intrinsic conductivity and large volume expansion during the charge/discharge process,which greatly impede their large-scale applications.Most recently,the ideal integrating of TMCs and conductive carbon skeletons is considered as an effective solution to solve the above challenges.Herein,we summarize the recent developments of TMCs/carbon hybrid electrodes which exhibit both high energy/power densities from the aspects of structural design strategies,including conductive carbon skeleton,interface engineering,and electronic structure.Furthermore,the remaining challenges and future perspectives are also highlighted so as to provide strategies for the high energy/power TMCs/carbon-based supercapacitors.

3D uniform nitrogen-doped carbon skeleton for ultra-stable sodium metal anode

Sodium metal batteries are arousing extensive interest owing to their high energy density,low cost and wide resource.However,the practical development of sodium metal batteries is inherently plagued by the severe volume expansion and the dendrite growth of sodium metal anode during long cycles under high current density.Herein,a simple electrospinning method is applied to construct the uniformly nitrogen-doped porous carbon fiber skeleton and used as three-dimensional(3D)current collector for sodium metal anode,which has high specific surface area(1,098 m^2/g)and strong binding to sodium metal.As a result,nitrogen-doped carbon fiber current collector shows a low sodium deposition overpotential and a highly stable cyclability for 3,500 h with a high coulombic effciency of 99.9%at 2 mA/cm^2 and 2 mAh/cm^2.Moreover,the full cells using carbon coated sodium vanadium phosphate as cathode and sodium pre-plated nitrogen-doped carbon fiber skeleton as hybrid anode can stably cycle for 300 times.These results illustrate an effective strategy to construct a 3D uniformly nitrogen-doped carbon skeleton based sodium metal hybrid anode without the formation of dendrites,which provide a prospect for further development and research of high performance sodium metal batteries.

Transient NOE driven signal enhancement of INADEQUATE solid-state NMR spectroscopy for the structural analysis of rubbers

INADEQUATE(Incredible Natural Abundance DoublE QUAntum Transfer Experiment)is one of the most important techniques in revealing the carbon skeleton of organic solids in solid-state NMR spectroscopy.Nevertheless,its use for structural analysis is quite limited due to the low natural abundance of^(13)C-^(13)C connectivity(~0.01%)and thus low sensitivity.Particularly,in semi-solids like rubbers,the sensitivity will be further significantly reduced by the inefficient cross polarization from 1H to^(13)C due to molecular motions induced averaging of^(1)H-^(13)C dipolar couplings.Herein,in this study,we demonstrate that transient nuclear Overhauser effect(NOE)can be used to efficiently enhance^(13)C signals,and thus enable rapid acquisition of two-dimensional(2D)^(13)C INADEQUATE spectra of rubbers.Using chlorobutyl rubber as the model system,it is found that an overall signalto-noise ratio(SNR)enhancement about 22%can be achieved,leading to significant timesaving by about 33%as compared to the direct polarization-based INADEQUATE experiment.Further experimental results on natural rubber and ethylene propylene diene monomer(EPDM)rubber are also shown to demonstrate the robust performance of transient NOE enhanced INADEQUATE experiment.

MOF-derived spherical Ni_(x)S_(y)/carbon with B-doping enabling high supercapacitive performance

This work uses a simple Ni-metal organic framework(Ni-MOF)to generate a uniform metal-containing carbon hybrid structure of Ni/C by in-situ pyrolysis.Then,after NaBH_(4) treatment and hydrothermal vul-canization of Ni/C,multiphase B-doped Ni_(x)S_(y) nanoparticles can be obtained and uniformly anchored in the carbon skeleton,forming a highly porous flower-shaped B-Ni_(x)S_(y)/C composite.The positive role of B doping was theoretically confirmed by Density Function Theory(DFT)calculations.The MOF-derived car-bon framework has porous,conductive,and continuous features beneficial for fast charge transfer.There are also multiple Ni-sulfide phases in B-Ni_(x)S_(y)/C,dominated by hexagonal NiS,hexagonal Ni 2 S 3,and cu-bic Ni_(3)S_(4),which give rich valance state and are expected to bring active electrochemical reactions.In addition,the boronation process by the reducing agent of NaBH_(4) is also proved beneficial to bring high capacitance,possibly due to the incorporation of more active sites by B.Therefore,the B-Ni_(x)S_(y)/C compos-ite electrode delivers a high specific capacity of 1250.4 C g^(-1) at 1 A g^(-1) and excellent rate performance.The B-Ni_(x)S_(y)/C-based asymmetric supercapacitor also shows promising prospects for future energy stor-age devices,delivering high cyclability with capacitance retention of 87.6%after 7000 cycles.This work proves the efficiency of MOF-derived carbon framework and B-doping in improving metal sulfide’s electrochemical performances.

High-performance porous carbon foams via catalytic pyrolysis of modified isocyanate-based polyimide foams for electromagnetic shielding

Porous carbon skeletons(PCSs)derived from isocyanate-based aromatic polyimide foams(PIFs)by high-temperature pyrolysis are very promising in the fabrication of high-performance polymer composite foams for electromagnetic interference(EMI)shielding due to their efficient conductive networks and facile preparation process.However,severe volumetric shrinkage and low graphitization degree is not conducive to enhancing the shielding efficiency of the PCSs.Herein,ferric acetylacetonate and carbon-nanotube coating have been introduced in isocyanate-based PIFs to greatly suppress the serious shrinkage during pyrolysis and improve the graphitization degree of the final carbon foams through the Fe-catalytic graphitization process,thereby endowing them with better EMI-shielding performance even at lower pyrolysis temperature compared to the control samples.Moreover,compressible polydimethylsiloxane(PDMS)composite foams with the as-prepared carbon foams as prefabricated PCSs have also been fabricated,which could provide not only stable shielding effectiveness(SE)performance even after a thousand compressions,but also multiple functions of Joule heating,thermal insulation and infrared stealth.This study offers a feasible route to prepare high-performance PCSs in a more energy-efficient manner via PIF pyrolysis,which is very promising in the manufacture of multifunctional conductive polymer composite foams.