Low-Temperature Carbonized Nitrogen-Doped Hard Carbon Nanofiber Toward High-Performance Sodium-Ion Capacitors

Carbon nanofiber(CNF)was widely utilized in the field of electrochemical energy storage due to its superiority of conductivity and mechanics.However,CNF was generally prepared at relatively high temperature.Herein,nitrogen-doped hard carbon nanofibers(NHCNFs)were prepared by a lowtemperature carbonization treatment assisted with electrospinning technology.Density functional theory analysis elucidates the incorporation of nitrogen heteroatoms with various chemical states into carbon matrix would significantly alter the total electronic configurations,leading to the robust adsorption and efficient diffusion of Na atoms on electrode interface.The obtained material carbonized at 600°C(NHCNF-600)presented a reversible specific capacity of 191.0 mAh g^(−1)and no capacity decay after 200 cycles at 1 A g^(−1).It was found that the sodium-intercalated degree had a correlation with the electrochemical impedance.A sodium-intercalated potential of 0.2 V was adopted to lower the electrochemical impedance.The constructed sodium-ion capacitor with activated carbon cathode and presodiated NHCNF-600 anode can present an energy power density of 82.1 Wh kg^(−1)and a power density of 7.0 kW kg^(−1).

Mechanically flexible reduced graphene oxide/carbon composite films for high-performance quasi-solid-state lithium-ion capacitors

Practical applications of diverse flexible wearable electronics require electrochemical energy storage(EES)devices with multiple configurations.Moreover,to fabricate flexible EES devices with high energy density and stability,organic integration from electrode design to device assembly is required.To address these challenges,a free-standing reduced graphene oxide(rGO)/carbon film with a unique sandwich structure has been designed via the assistance of vacuum-assistant filtration for lithium-ion capacitors(LICs).The graphene acts as not only a binder to construct a three-dimensional conductive network but also an active material to provide additional capacitive lithium storage sites,thus enabling fast ion/electron transport and improving the capacity.The designed rGO/hard carbon(rGO/HC)and rGO/activated carbon(rGO/AC)free-standing films exhibit enhanced specific capacities(513.7 mA h g^(-1)for rGO/HC and 102.8 mA h g^(-1)for rGO/AC)and excellent stability.Moreover,the integrated flexible quasi-solid-state rGO/AC//rGO/HC LIC devices possess a maximum energy density of 138.3 Wh kg^(-1),a high power density of 11 kW kg^(-1),and improved cycling performance(84.4%capacitance maintained after 10,000 cycles),superior to the AC//HC LIC(43.5%retention).Such a strategy enlightens the development of portable flexible LICs.

Sustainable Lignin-Derived Carbon as Capacity-Kinetics Matched Cathode and Anode towards 4.5 V High-Performance Lithium-Ion Capacitors

The Li-ion capacitors(LICs)develop rapidly due to their double-high features of high-energy density and high-power density.However,the relative low capacity of cathode and sluggish kinetics of anode seriously impede the development of LICs.Herein,the precisely pore-engineered and heteroatomtailored defective hierarchical porous carbons(DHPCs)as large-capacity cathode and high-rate anode to construct high-performance dual-carbon LICs have been developed.The DHPCs are prepared based on triple-activation mechanisms by direct pyrolysis of sustainable lignin with urea to generate the interconnected hierarchical porous structure and plentiful heteroatominduced defects.Benefiting from these advanced merits,DHPCs show the well-matched high capacity and fast kinetics of both cathode and anode,exhibiting large capacities,superior rate capability and long-term lifespan.Both experimental and computational results demonstrate the strong synergistic effect of pore and dopants for Li storage.Consequently,the assembled dual-carbon LIC exhibits high voltage of 4.5 V,high-energy density of 208 Wh kg^(−1),ultrahigh power density of 53.4 kW kg^(−1)and almost zerodecrement cycling lifetime.Impressively,the full device with high mass loading of 9.4 mg cm^(−2)on cathode still outputs high-energy density of 187 Wh kg^(−1),demonstrative of their potential as electrode materials for high-performance electrochemical devices.

Carbon nanocages bridged with graphene enable fast kinetics for dual-carbon lithium-ion capacitors

Lithium-ion capacitors(LICs) combining the advantages of lithium-ion batteries and supercapacitors are considered a promising nextgeneration energy storage device. However, the sluggish kinetics of battery-type anode cannot match the capacitor-type cathode, restricting the development of LICs. Herein, hierarchical carbon framework(HCF) anode material composed of 0D carbon nanocage bridged with 2D graphene network are developed via a template-confined synthesis process. The HCF with nanocage structure reduces the Li^(+) transport path and benefits the rapid Li^(+) migration, while 2D graphene network can promote the electron interconnecting of carbon nanocages. In addition, the doped N atoms in HCF facilitate to the adsorption of ions and enhance the pseudo contribution, thus accelerate the kinetics of the anode. The HCF anode delivers high specific capacity, remarkable rate capability. The LIC pouch-cell based on HCF anode and active HCF(a-HCF) cathode can provide a high energy density of 162 Wh kg^(-1) and a superior power density of 15.8 kW kg^(-1), as well as a long cycling life exceeding 15,000cycles. This study demonstrates that the well-defined design of hierarchical carbon framework by incorporating 0D carbon nanocages and 2D graphene network is an effective strategy to promote LIC anode kinetics and hence boost the LIC electrochemical performance.

Co-doped BaFe_(2)As_(2) Josephson junction fabricated with a focused helium ion beam

Josephson junction plays a key role not only in studying the basic physics of unconventional iron-based superconductors but also in realizing practical application of thin-film based devices,therefore the preparation of high-quality iron pnictide Josephson junctions is of great importance.In this work,we have successfully fabricated Josephson junctions from Co-doped BaFe_(2)As_(2)thin films using a direct junction fabrication technique which utilizes high energy focused helium ion beam(FHIB).The electrical transport properties were investigated for junctions fabricated with various He^(+)irradiation doses.The junctions show sharp superconducting transition around 24 K with a narrow transition width of 2.5 K,and a dose correlated foot-structure resistance which corresponds to the effective tuning of junction properties by He^(+)irradiation.Significant J_c suppression by more than two orders of magnitude can be achieved by increasing the He^(+)irradiation dose,which is advantageous for the realization of low noise ion pnictide thin film devices.Clear Shapiro steps are observed under 10 GHz microwave irradiation.The above results demonstrate the successful fabrication of high quality and controllable Co-doped BaFe_(2)As_(2)Josephson junction with high reproducibility using the FHIB technique,laying the foundation for future investigating the mechanism of iron-based superconductors,and also the further implementation in various superconducting electronic devices.

Recent advances in carbon nanostructures prepared from carbon dioxide for high-performance supercapacitors

The burgeoning global economy during the past decades gives rise to the continuous increase in fossil fuels consumption and rapid growth of CO_(2) emission,which demands an urgent exploration into green and sustainable devices for energy storage and power management.Supercapacitors based on activated carbon electrodes are promising systems for highly efficient energy harvesting and power supply,but their promotion is hindered by the moderate energy density compared with batteries.Therefore,scalable conversion of CO_(2) into novel carbon nanostructures offers a powerful alternative to tackle both issues:mitigating the greenhouse effect caused by redundant atmospheric CO_(2) and providing carbon materials with enhanced electrochemical performances.In this tutorial review,the techniques,opportunities and barriers in the design and fabrication of advanced carbon materials using CO_(2) as feedstock as well as their impact on the energy-storage performances of supercapacitors are critically examined.In particular,the chemical aspects of various Cv2 conversion reactions are highlighted to establish a detailed understanding for the science and technology involved in the microstructural evolution,surface engineering and porosity control of CO_(2)-converted carbon nanostructures.Finally,the prospects and challenges associated with the industrialization of CO_(2) conversion and their practical application in supercapacitors are also discussed.

A 10-μm Ultrathin Lithium Metal Composite Anodes with Superior Electrochemical Kinetics and Cycling Stability

Lithium metal is a promising candidate for the promotion of the next generation high energy density batteries.The employment of ultrathin Li metal anode with controllable thickness could enable a higher efficiency of Li utilization.Herein,a simple method to fabricate free-standing 10μm ultrathin Li metal anode is developed in this work.A three-dimensional MnO_(x)-coated CNT framework is constructed through a facile hydrothermal process,utilizing as a host for molten Li infusion,which could not only put forward a simple strategy to modulate the thickness of Li metal film but also restricts the volume expansion.The abundant MnO_(x)nanoparticles acting as lithiophilic sites reduce the Li nucleation barrier and optimize the electrochemical kinetics at the anode/electrolyte interface.As a result,the ultrathin Li composite anode exhibits a superior lifespan expanded to 2000 cycles in a symmetric cell,as well as a better capacity and rate capability than that of bare Li anode in full cell,fulfilling the requirements of high energy density and stable cycling life.Furthermore,a wave-shaped Li metal pouch cell based on the ultrathin Li composite anode is assembled that exhibits remarkable mechanical bending toleration and cyclic stability,demonstrating large potential application in the field of flexible wearable devices.

Effects of electrothermal ageing on dielectric performance of metallised biaxial orientation polypropylene film capacitors in strong magnetic fields

The dielectric performance of the pristine and the electrothermal-aged metallised polypropylene capacitors are investigated under different magnetic fields.The energy storage capacity decreases under the magnetic field.At 12 T,the capacitance value of the pristine capacitors decreases by 8.4%-17%and that of the aged capacitors declines by 15%-20%.The dielectric loss is reduced by 2.6%-6.3%,but the equivalent series resistance shows an 8.3%-23.1%growth.The leakage conductivity increases to 202%-354%,which leads to a weakened voltage holding capacity.In addition to the effects of the magnetic fields,the impacts of ageing have also been investigated.The effects of the magnetic field and ageing on the electrical parameters of the capacitors are discussed separately.The molecular chains of the dielectric are oxidised and decomposed during the ageing process,which reduces the insulating properties of the dielectric.The magnetic field inhibits polarisation by changing the polarisation behaviour through Lorentz force and excites the electrons to enhance charge transmission.

A safe,low-cost and high-efficiency presodiation strategy for pouch-type sodium-ion capacitors with high energy density

Sodium-ion capacitors(SICs)have attracted appreciable attention in virtue of the higher energy and power densities compared with their rivals,supercapacitors and sodium-ion batteries.Due to the lack of sodium resources in cathode,presodiation is critical for SICs to further augment performances.However,current presodiation strategy utilizes metallic sodium as the presodiation material.In this strategy,assembling/disassembling of half-cells is required,which is dangerous and in creases the time and cost of SIC leading to the restriction of their industrialization and commercialization.Herein we present a safe,low-cost and high-efficiency presodiation strategy by first employing Na_(2)C_(2)O_(4) as the sacrificial salt applied in SICs.Na_(2)C_(2)O_(4) is environmentally friendly and possesses considerably low expenditure.No additional residues remain after sodium extraction ascribed to its"zero dead mass"property.When paired with commercial activated carb on as the cathode and commercial hard carbon as the ano de,the constructed pouch-type SICs exhibit high energy and power densities of 91.7 Wh/kg and 13.1 kW/kg,respectively.This work shows a prospect of realizing the safe and low-cost manufacturing for high-performance SICs commercially.

Slow Vortex Creep Induced by Strong Grain Boundary Pinning in Advanced Ba122 Superconducting Tapes

We report the temperature, magnetic field and time dependences of magnetization in advanced Ba122 superconducting tapes. The sample exhibits peculiar vortex creep behavior. Below 10 K, the normalized magnetization relaxation rate S = d ln(-M)/d ln(t) shows a temperature-insensitive plateau with a value comparable to that of low-temperature superconductors, which can be explained within the framework of collective creep theory. It then enters into a second collective creep regime when the temperature increases. Interestingly, the relaxation rate below 20 K tends to reach saturation with increasing the field. However, it changes to a power law dependence on the field at a higher temperature. A vortex phase diagram composed of the collective and the plastic creep regions is shown. Benefiting from the strong grain boundary pinning, the advanced Bal22 superconducting tape has potential to be applied not only in liquid helium but also in liquid hydrogen or at temperatures accessible with cryocoolers.

High-performance Ba_(1-x)K_(x)Fe_(2)As_(2) superconducting tapes with grain texture engineered via a scalable fabrication

Nowadays the development of high-field magnets strongly relies on the performance of superconducting materials.Iron-based superconductors(IBSs)exhibit high upper critical fields and low electromagnetic anisotropy,making them particularly attractive for high-field applications,especially in particle accelerator magnets,nuclear magnetic resonance spectrometers,medical magnetic resonance imaging systems and nuclear fusion reactors.Herein,through an industrially scalable manufacturing strategy,a practical-level critical current density up to 1.1×10^(5)A cm^(-2)at4.2 K in an external magnetic field of 10 T was achieved in Cu/Ag composite-sheathed Ba_(1-x)K_(x)Fe_(2)As_(2)(Ba122)superconducting tapes.The preparation strategy combines flat rolling to induce grain texture and subsequent hot-isostaticpressing densification.By varying the parameters of rolling,the degree of grain texture was engineered.It is found that the transport properties of the Ba122 tapes can be enhanced by applying a large amount of deformation during rolling,which can be attributed to the improved degree of c-axis texture.Microstructure characterizations on the highest-performance tape demonstrate that the Ba122 phase has a uniform element distribution and small grains with good connectivity.Grain boundary pinning is consequently enhanced as proved by large currents circulating through the sample even at 25 K.Our work proves that Cu/Ag composite-sheathed Ba122 superconducting tapes can be a promising competitor for practical high-field applications in terms of the viable,scalable and cost-effective fabrication strategy applied and the high transport properties achieved in this work.

Carbon-coated Li3VO4 with optimized structure as high capacity anode material for lithium-ion capacitors

Due to the high capacity,moderate voltage platform,and stable structure,Li3VO4(LVO) has attracted close attention as feasible anode material for lithium-ion capacitor.However,the intrinsic low electronic conductivity and sluggish kinetics of the Li+ insertion process severely impede its practical application in lithium-ion capacitors(LICs).Herein,a carbon-coated Li3VO4(LVO/C) hierarchical structure was prepared by a facial one-step solid-state method.The synthesized LVO/C composite delivers an impressive capacity of 435 mAh/g at 0.07 A/g,remarkable rate capability,and nearly 100% capacity retention after 500 cycles at 0.5 A/g.The superior electrochemical properties of LVO/C composite materials are attributed to the improved conductivity of electron and stable carbon/LVO composite structures.Besides,the LIC device based on activated carbon(AC) cathode and optimal LVO/C as anode reveals a maximum energy density of 110 Wh/kg and long-term cycle life.These results provide a potential way for assembling the advanced hybrid lithium-ion capacitors.

Cationic intermediates assisted self-assembly two-dimensional Ti_(3)C_(2)T_(x)/rGO hybrid nanoflakes for advanced lithium-ion capacitors

Two-dimensional(2 D)material MXenes have been intensively concerned in energy-storage field due to these unique properties of metallic-like conductivity,good hydrophilicity and high volumetric capacity.However,the self-restocking of ultra-thin 2 D materials seriously hinders these performances,which significantly inhibits the full exploitation of MXenes in the field of energy storage.To solve this issue,a strategy to prepare delaminated Ti_(3)C_(2)T_(x)(MXene)nanoflakes/reduced graphene oxide(r GO)composites is proposed using the electrostatic self-assembly between positively charged Ti_(3)C_(2)T_(x) with tetrabutylammonium ion(TBA+)modification and negatively charged graphene.The nanoflakes of Ti_(3)C_(2)T_(x)/rGO are well dispersed and arranged in a face-to-face structure to effectively alleviate the self-restacking and provide more electroactive sites for accessible of electrolyte ions.The prepared delaminated Ti_(3)C_(2)T_(x)/r GO anode shows a high reversible capacity up to 1394 m Ah g^(-1) at a current density of 50 m A g^(-1).Moreover,a lithium-ion capacitor(LIC)was assembled with delaminated Ti_(3)C_(2)T_(x)/r GO anode and activated carbon(AC)cathode which can exhibit a specific capacity of 70.7 F g^(-1) at a current density of 0.1 A g^(-1) and deliver an ultrahigh energy density of 114 Wh kg^(-1) at a relatively high power density of 3125 W kg^(-1).These good electrochemical performances demonstrate the potential of delaminated Ti_(3)C_(2)T_(x)/r GO as an anode material for lithium-ion capacitors.

Accordion-like titanium carbide(MXene) with high crystallinity as fast intercalative anode for high-rate lithium-ion capacitors

Two-dimensional transition-metal carbide materials,or MXenes,have attracted great attention in energy-related fields due to their excellent electrical conductivity,and large interlayer spacing.In this work,a simple method involving combustion synthesis and acid treatment to prepare accordion-like Ti3C2Tx MXene with open structure and high crystallinity,which is employed as anode materials in lithium-ion capacitors.Due to the improved ion diffusion and electron transportation of Ti3C2Tx anode,the mismatched electrode kinetics can be largely alleviated to acquire an enhanced power perfo rmance.The assembled Ti3C2Tx-based lithium-ion capacitors provides a maximum energy density of 106 Wh/kg and still exhibits a superior energy density of 79 Wh/kg even at a higher power density of 5.2 kW/kg,which provides a new platform for MXene materials with porous and crystalline features toward both high energy and power densities.

Progress in the development of the 122-type IBS wires

Profit from their low anisotropy and high upper critical field,iron-based superconductors(IBSs)have great potential for high magnetic fields applications.Significant progress has been made for the current density improvement of(Sr,Ba)0.6K0.4Fe2As2(122-type)IBS wires over the past fourteen years.In this article,an overview of the preparation procedures and key issues affecting the critical current performance of 122-type IBS wires is given,to provide a fundamental understanding of what controls the transport critical current density of 122-type IBS wires.Additionally,the recent developments for 122-type IBS wires are presented and future prospect and challenges in the development of 122-type IBS wires for practical applications are discussed.