Fast charge transport motivated by tunable Mo2C/Mo2N high-quality heterointerface for superior pseudocapacitive storage

The development of potential transition-metal carbide/nitride heterojunctions is hindered by overall understanding and precise modulation for heterointerface effects.Herein,we demonstrate that Mo_(2)C/Mo_(2)N heterojunction with the precisely regulated high-quality interface can achieve marvelous rate performance and energy output via enlarging the interface-effect range and maximizing "accelerated charge" amount The heterointerface mechanism improving properties is synergistically revealed from kinetics and thermodynamics perspectives.Kinetics analysis confirms that the self-built electric field affords a robust force to drive rapid interface electrons/ions migration.The small adsorption energy,high density of states and quite low diffusion barrier thermodynamically enhance the electrochemical reaction dynamics on heterointerface.Consequently,the almost optimal performance of ultrahigh capacitance retention(85.6% even at 10 A g^(-1)) and pronounced energy output(96.4 Wh kg^(-1))in hybridsupercapacitors than other Mo_(2)C/Mo_(2)N-based materials is presented.This work gives new insight into the energy storage mechanism of heterojunction and guides the design of advanced electrodes.

Microwave-assisted conversion of biomass wastes to pseudocapacitive mesoporous carbon for high-performance supercapacitor

Developing an efficient approach of transforming biomass waste to functional carbon-based electrode materials applied in supercapacitor offers an important and high value-added practical application due to the abundance and considerable low price of biomass wastes.Herein,a hierarchical carbon functionalized with electrochemical-active oxygen-containing groups was fabricated by microwave treatment from the biomass waste of camellia oleifera.The obtained mesoporous carbon(MAC)owns nanosheet morphology,rich mesoporosity,large surface area(1726 m2/g)and very high oxygenic functionalities(16.2 wt%)with pseudocapacitive activity.Prepared electrode of supercapacitor and tested in 2.0 M H2 SO4,the MAC exhibits an obvious pseudocapacitive activity and achieved a superior supercapacitive performance to that of directly activated carbon(DAC-800)including high specific capacitance(367 F/g vs.298 F/g)and better rate performance(66%vs.44%).The symmetrical supercapacitor based on MAC shows a high capacity of275 F/g,large energy density of 9.55 Wh/kg(at power density of 478 W/kg)and excellent cycling stability with 99%capacitance retention after 10000 continuous charge-discharge,endowing the obtained MAC a promising functional material for electrochemical energy storage.

Bifunctional Li6CoO4 serving as prelithiation reagent and pseudocapacitive electrode for lithium ion capacitors

Lithium ion capacitors(LICs)have been widely used as energy storage devices due to their high energy density and high power density.For LICs,pre-lithiation of negative electrode is necessary.In this work,we employ a bifunctional Li6CoO4(LCO)as cathodic pre-lithiation reagent to improve the electrochemical performance of LICs.The synthesized LCO exhibited high first charge specific capacity of 721 mAh g-1and extremely low initial coulombic efficiency of 3.19%,providing sufficient Li+ for the pre-lithiation of negative electrode in the first charge.Simultaneously,Li6–xCoOy is generated from LCO during the first charge process,which exhibits pseudocapacitive property and contributes to capacity in form of surface capacitance during subsequent cycles,increasing the capacity of capacitive positive electrode.With the appropriate amounts of addition to the positive side in LICs,this bifunctional prelithiation reagent LCO shows significantly improved the electrochemical performance with the energy density of 78.5 Wh kg-1after 300 cycles between 2.0 and 4.2 V at 250 mA g-1.

Definitions of Pseudocapacitive Materials: A Brief Review

Pseudocapacitive materials generally offer both high capacitance and high rate capability, which has stimulated great efforts in developing the materials system and related energy storage devices. In recent years, however, with the extensive use of nanomaterials in batteries, fast redox kinetics comparable to pseudocapacitive have been achieved in many kinds of battery materials due to the much shortened ion diffusion lengths and highly exposed surface/interface as a result of nanosize effect. Consequently, the terms"pseudocapacitive materials" and "battery materials" are becoming more and more confusing. In this review, different opinions on the definition of pseudocapacitive materials and the evolution of the definitions as well as the resulting confusion will be firstly reviewed. Then, to accurately distinguish pseudocapacitive and battery materials, method with the consideration of both the electrochemical signatures(CVs and GCD) and quantitative kinetics analysis as a supplement is proposed. Finally, we end this review by discussing the possible device configurations of asymmetric supercapacitors and hybrid supercapacitors. The present review will help understanding the differences between pseudocapacitive materials and battery materials, and thus avoiding the definition confusion.

High Rate and Long Lifespan Sodium‑Organic Batteries Using Pseudocapacitive Porphyrin Complexes‑Based Cathode

Sodium-organic batteries utilizing natural abundance of sodium element and renewable active materials gain great attentions for grid-scale applications.However,the development is still limited by lack of suitable organic cathode materials with high electronic conductivity that can be operated stably in liquid electrolyte.Herein,we present 5,15-bis(ethynyl)-10,20-diphenylporphyrin(DEPP)and[5,15-bis(ethynyl)-10,20-diphenylporphinato]copper(II)(CuDEPP)as new cathodes for extremely stable sodium-organic batteries.The copper(II)ion partially contributes the charge storage and significantly stabilizes the structure of porphyrin complex for electrochemical energy storage.In situ electrochemical stabilization of organic cathode with a lower charging current density was identified which enables both improved high energy density and power density.An excellent longterm cycling stability up to 600 cycles and an extremely high power density of 28 kW kg−1 were achieved for porphyrin-based cathode.This observation would open new pathway for developing highly stable sodium-organic cathode for electrochemical energy storage.

Superior Pseudocapacitive Storage of a Novel Ni3Si2/ NiOOH/Graphene Nanostructure for an All‑Solid‑State Supercapacitor

Recent developments in the synthesis of graphene-based structures focus on continuous improvement of porous nanostructures,doping of thin films,and mechanisms for the construction of threedimensional architectures.Herein,we synthesize creeper-like Ni3Si2/NiOOH/graphene nanostructures via low-pressure all-solid meltingreconstruction chemical vapor deposition.In a carbon-rich atmosphere,high-energy atoms bombard the Ni and Si surface,and reduce the free energy in the thermodynamic equilibrium of solid Ni–Si particles,considerably catalyzing the growth of Ni–Si nanocrystals.By controlling the carbon source content,a Ni3Si2 single crystal with high crystallinity and good homogeneity is stably synthesized.Electrochemical measurements indicate that the nanostructures exhibit an ultrahigh specific capacity of 835.3 C g^−1(1193.28 F g^−1)at 1 A g^−1;when integrated as an all-solidstate supercapacitor,it provides a remarkable energy density as high as 25.9 Wh kg^−1 at 750 W kg^−1,which can be attributed to the freestanding Ni3Si2/graphene skeleton providing a large specific area and NiOOH inhibits insulation on the electrode surface in an alkaline solution,thereby accelerating the electron exchange rate.The growth of the high-performance composite nanostructure is simple and controllable,enabling the large-scale production and application of microenergy storage devices.

High-Power and Ultralong-Life Aqueous Zinc-Ion Hybrid Capacitors Based on Pseudocapacitive Charge Storage

Rechargeable aqueous zinc-ion hybrid capacitors and zincion batteries are promising safe energy storage systems.In this study,amorphous RuO2·H2O for the first time was employed to achieve fast and ultralong-life Zn2+storage based on a pseudocapacitive storage mechanism.In the RuO2·H2O||Zn zinc-ion hybrid capacitors with Zn(CF3SO3)2 aqueous electrolyte,the RuO2·H2O cathode can reversibly store Zn2+in a voltage window of 0.4-1.6 V(vs.Zn/Zn2+),delivering a high discharge capacity of 122 mAh g?1.In particular,the zinc-ion hybrid capacitors can be rapidly charged/discharged within 36 s with a very high power density of 16.74 kW kg?1 and a high energy density of 82 Wh kg?1.Besides,the zinc-ion hybrid capacitors demonstrate an ultralong cycle life(over 10,000 charge/discharge cycles).The kinetic analysis elucidates that the ultrafast Zn2+storage in the RuO2·H2O cathode originates from redox pseudocapacitive reactions.This work could greatly facilitate the development of high-power and safe electrochemical energy storage.

Highly Sensitive Pseudocapacitive Iontronic Pressure Sensor with Broad Sensing Range

Flexible pressure sensors are unprecedentedly studied on monitoring human physical activities and robotics.Simultaneously,improving the response sensitivity and sensing range of flexible pressure sensors is a great challenge,which hinders the devices’practical application.Targeting this obstacle,we developed a Ti_(3)C_(2)T_(x)-derived iontronic pressure sensor(TIPS)by taking the advantages of the high intercalation pseudocapacitance under high pressure and rationally designed structural configuration.TIPS achieved an ultrahigh sen-sitivity(S_(min)>200 kPa^(−1),S_(max)>45,000 kPa^(−1))in a broad sensing range of over 1.4 MPa and low limit of detection of 20 Pa as well as stable long-term working durability for 10,000 cycles.The practical application of TIPS in physical activity monitoring and flexible robot manifested its versatile potential.This study provides a demonstration for exploring pseudocapacitive materials for building flexible iontronic sensors with ultrahigh sensitivity and sensing range to advance the development of high-performance wearable electronics.

Pseudocapacitive Vanadium-based Materials toward High-Rate Sodium-Ion Storage

Sodium-ion battery materials and devices are promising candidates for largescale applications,owing to the abundance and low cost of sodium sources.Emerging sodium-ion pseudocapacitive materials provide one approach for achieving high capacity at high rates,but are currently not well understood.Herein,a comprehensive overview of the fundamentals and electrochemical behaviors of vanadium-based pseudocapacitive materials for sodium-ion storage is presented.The insight of sodium-ion storage mechanisms for various vanadium-based materials,including vanadium oxides,vanadates,vanadium sulfides,nitrides,and carbides are systematically discussed and summarized.In particular,areas for further development to improve fundamental understanding of electrochemical and structural properties of materials are identified.Finally,we provide a perspective on the application of pseudocapacitive materials in high-power and high-energy sodium-ion storage devices(e.g.,sodium-ion capacitors).

Tailored amorphous titanium oxide and carbon composites for enhanced pseudocapacitive sodium storage

As an effective and competitive supplement to the commercialized lithium ion batteries(LIBs),sodium ion batteries(SIBs)have been receiving increasing attention in recent years due to lower cost,richer content,and broader distribution of sodium[1–7].Sodium has similar electrochemical properties to lithium,and thus the concepts for the preparation of electrode materials for SIBs can be borrowed from LIBs[8,9].

Tuning coordination environment of iron ions to ensure ultra-high pseudocapacitive capability in iron oxide

The mechanism governing the pseudocapacitive lithium storage behavior is one of the most critical unsolved issues in conversion-type anodes for lithium-ion batteries.In this work,we,for the first time,demonstrate that the pseudocapacitive capability of iron oxide-based anodes is closely associated with the electronic structures of iron ions.As proof of concept,the introduction of amorphization,nitrogen doping,oxygen vacancies reduces the coordination of iron ions and contributes significantly to the pseudocapacitive lithium storage capability of iron oxide,reaching up to 96%of the specific capacity at 1 mV·s^(−1).Due to the significantly modulated coordination environment,the 3d electrons of Fe(II)are delocalized with increased spin state and the energy band gap is narrowed,accompanied by an upshift of Fermi energy.The redox activity and carrier mobility of iron oxides are substantially increased,which substantially enhance the exchange current density and thereby improve the pseudocapacitive capability of iron oxide.

SnP entangled by carbon nanotube networks as anode for pseudocapacitive half/full battery

Due to the lower operating voltage and higher theoretical specific capacity,tin phosphide is considered a class of materials with prospects as an anode material for lithium-ion batteries(LIBs).Among them,tin monophosphide has attracted people's attention due to its unique layered structure.Unfortunately,because of the challenging synthesis method and metastable nature,the application of SnP is limited.In this work,tin phosphide/carbon nanotubes(SnP/CNTs)are prepared by controlling the nucleation and adjusting the ratio of phosphorus/carbon using carbon nanotube as initiator.Sn-MOF is used as a template to make the morphology of SnP more evenly,and carbon nanotubes can also be used as a conductive network to increase the speed of electron transmission.As an anode material for LIBs,SnP/CNTs reveals superior rate performances(reversible capability of 610 mA·h·g^(-1)at 2000 mA·g^(-1)).The full-cell was assembled and tested,after 50 cycles at 0.1 C,the capacity can maintain 292 mA·h·g^(-1),and its capacity retention rate can reach 80.5%.After 230 cycles,its capacity can maintain at around 223 mA·h·g
1.In addition,SnP/CNTs materials exhibit 89%pseudocapacitance contribution upon cycling,which indicates the robust Lit storage and satisfactory fast-charging capability.Hence,SnP/CNTs suggests a promising anode material for energy storage system.

Oxygen functional groups modified amorphous hollow carbon bowls for pseudocapacitive Zn-ion storage

Carbon is a promising capacitive electrode material for Zn-ion hybrid supercapacitors(ZHSCs),as it is low-cost,environmentally friendly,controllable and adjustable.By now,achieving both high energy and high power with carbon electrodes is still challenging,limited by their intrinsic properties.In this work,we have designed and presented an amorphous hollow carbon bowl material with surface chemical modifications of oxygen groups to figure out these concerns.The preparation of bowl-like structures and the storage behavior between Zn^(2+)and oxygen functional groups have also been discussed.With the contributions from its unique hollow structure and surface functional groups,it can significantly enhance the electrode pseudocapacitance and the entire electrochemical performance.

An in-situ self-etching enabled high-power electrode for aqueous zinc-ion batteries

Sluggish storage kinetics is considered as the main bottleneck of cathode materials for fast-charging aqueous zinc-ion batteries(AZIBs).In this report,we propose a novel in-situ self-etching strategy to unlock the Palm tree-like vanadium oxide/carbon nanofiber membrane(P-VO/C)as a robust freestanding electrode.Comprehensive investigations including the finite element simulation,in-situ X-ray diffraction,and in-situ electrochemical impedance spectroscopy disclosed it an electrochemically induced phase transformation mechanism from VO to layered Zn_(x)V_(2)O_5·nH_(2)O,as well as superior storage kinetics with ultrahigh pseudocapacitive contribution.As demonstrated,such electrode can remain a specific capacity of 285 mA h g^(-1)after 100 cycles at 1 A g^(-1),144.4 mA h g^(-1)after 1500 cycles at 30 A g^(-1),and even 97 mA h g^(-1)after 3000 cycles at 60 A g^(-1),respectively.Unexpectedly,an impressive power density of 78.9 kW kg^(-1)at the super-high current density of 100 A g^(-1)also can be achieved.Such design concept of in-situ self-etching free-standing electrode can provide a brand-new insight into extending the pseudocapacitive storage limit,so as to promote the development of high-power energy storage devices including but not limited to AZIBs.

F-doped orthorhombic Nb_(2)O_(5) exposed with 97% (100) facet for fast reversible Liþ-Intercalation

Orthorhombic Nb_(2)O_(5)(T-Nb_(2)O_(5))is attractive for fast-charging Li-ion batteries,but it is still hard to realize rapid charge transfer kinetics for Li-ion storage.Herein,F-doped T-Nb_(2)O_(5) microflowers(F-Nb_(2)O_(5))are rationally synthesized through topotactic conversion.Specifically,F-Nb_(2)O_(5) are assembled by single-crystal nanoflakes with nearly 97%exposed(100)facet,which maximizes the exposure of the feasible Li^(+)transport pathways along loosely packed 4g atomic layers to the electrolytes,thus effectively enhancing the Li^(+)-intercalation performance.Besides,the band gap of F-Nb_(2)O_(5) is reduced to 2.87 eV due to the doping of F atoms,leading to enhanced electrical conductivity.The synergetic effects between tailored exposed crystal facets,F-doping,and ultrathin building blocks,speed up the Li^(+)/electron transfer kinetics and improve the pseudocapacitive properties of F-Nb_(2)O_(5).Therefore,F-Nb_(2)O_(5) exhibit superior rate capability(210.8 and 164.9 mAh g^(-1) at 1 and 10 C,respectively)and good long-term 10 C cycling performance(132.7 mAh g^(-1) after 1500 cycles).

Addressing the Achilles'heel of pseudocapacitive materials:Long-term stability

Electrode materials with high energy densities and long-lasting performances are crucial to durable and reliable electrochemical energy storage devices for modern information technologies(eg,Internet of things).In terms of supercapacitors,their low energy densities could be enhanced by using pseudocapacitive electrodes,but meanwhile,their ultralong lifetimes are compromised by the limited chargedischarge cycling stabilities of pseudocapacitive materials.This review article discusses on the cycling instability issues of five common pseudocapacitive materials:conjugated polymers(or conducting polymers),metal oxides,metal nitrides,metal carbides,and metal sulfides.Specifically,the article includes the fundamentals of the failure modes of these materials,as well as thoroughly surveys the design rationales and technical details of the cycling-stability-boosting tactics for pseudocapacitive materials that reported in the literature.Additionally,promising opportunities,future challenges,and possible solutions associated with pseudocapacitive materials are discussed.

A novel Li-ion supercapattery by K-ion vacant ternary perovskite fluoride anode with pseudocapacitive conversion/insertion dual mechanisms

An innovative K+vacant ternary perovskite fluoride(K_(0.89)Ni_(0.02)Co_(0.03)Mn_(0.95)F_(3.0),KNCMF-3#)anode was designed for advanced Li-ion supercapattery(i.e.,Li-ion capacitors/batteries,LIC/Bs).Owing to the conversion/insertion dual mechanisms and fast pseudocapacitive con-trol dynamics,the KNCMF-3#electrode exhibits superior electrochemical performance,especially the excellent cycle performance(467%(229 mAh·g^(-1))/1000 cycles/2 A·g^(-1)).Moreover,the hybrid KNCMF-3#/reduced gra-phene oxide(rGO)electrode can further increase the electrochemical performance(217-97 mAh·g^(-1)/0.1-3.2 A·g^(-1),150%(197 mAh·g^(-1))/1000 cycles/2 A·g^(-1)).Also,a novel capacitor/battery cathode,activated carbon(AC)+LiFePO_(4)+graphene(AC+LFP+G),exhibits impres-sive performance(128-82 mAh·g^(-1)/0.1-3.2 A·g^(-1),84%/1000 cycles/2 A·g^(-1)).By the synergistic optimization of anode and cathode,the Li-ion supercapattery KNCMF-3#@rGO//AC+LFP+G demonstrates remarkable per-formance,for example,111.9-23.8 Wh·kg^(-1)/0.4-8.0 kW·kg^(-1)/82%/2000 cycles/5 A·g^(-1)/0-4 V,which is superior to KNCMF-3#//AC LICs,KNCMF-3#@rGO//AC LICs,KNCMF-3#//AC+LFP+G LIC/Bs.In all,the novel Li-ion supercapattery idea adds a promising per-spective to develop advanced energy storage devices.

Carbon-doped surface unsaturated sulfur enriched CoS2@rGO aerogel pseudocapacitive anode and biomass-derived porous carbon cathode for advanced lithium-ion capacitors

As a hybrid energy storage device of lithium-ion batteries and supercapacitors,lithium-ion capacitors have the potential to meet the demanding needs of energy storage equipment with both high power and energy density.In this work,to solve the obstacle to the application of lithium-ion capacitors,that is,the balancing problem of the electrodes kinetic and capacity,two electrodes are designed and adequately matched.For the anode,we introduced in situ carbon-doped and surface-enriched unsaturated sulfur into the graphene conductive network to prepare transition metal sulfides,which enhances the performance with a faster lithium-ion diffusion and dominant pseudocapacitive energy storage.Therefore,the lithium-ion capacitors anode material delivers a remarkable capacity of 810 mAh·g^(−1) after 500 cycles at 1 A·g^(−1).On the other hand,the biomass-derived porous carbon as the cathode also displays a superior capacity of 114.2 mAh·g^(−1) at 0.1 A·g^(−1).Benefitting from the appropriate balance of kinetic and capacity between two electrodes,the lithium-ion capacitors exhibits superior electrochemical performance.The assembled lithium-ion capacitors demonstrate a high energy density of 132.9 Wh·kg^(−1) at the power density of 265 W·kg^(−1),and 50.0 Wh·kg^(−1) even at 26.5 kW·kg^(−1).After 10000 cycles at 1 A·g^(−1),lithium-ion capacitors still demonstrate the high energy density retention of 81.5%.

Vanadium nitride nanoparticles embedded in carbon matrix with pseudocapacitive behavior for high performance lithium-ion capacitors

Lithium-ion capacitors(LICs)have attracted wide attention due to their potential of achieving merits of high-power output as well as high energy density.How-ever,the key issue of kinetics mismatch between anode and cathode hinders the electrochemical performance of LICs.Therefore,a vanadium nitride composite with nanoparti-cles embedded in carbon matrix(VN-C)was prepared as an efficiently pseudocapacitive anode material with high electronic conductivity and fast Li-ion diffusion rate.The VN-C composites were synthesized through one-step ammonia heating treatment at different temperatures among which the sample annealed at 600℃exhibits high specific capacity(513 mAh·g^(-1)at 0.1 A·g^(-1)),outstanding rate performance(~300 mAh·g^(-1)at 10 A·g^(-1)),and excellent cyclic steadiness(negligible capacity decay over 2000 cycles)in half-cell devices.A high-performance lithium-ion capacitor device was also fabricated by using VN-C-600 as the anode and activated carbon as the cath-ode,delivering a maximum energy density of 112.6 Wh·kg^(-1)and an extreme power density of 10 kW·kg^(-1).

Pulse-potential electrochemistry to boost real-life application of pseudocapacitive dual-doped polypyrrole

Polypyrrole(PPy)is a very promising pseudocapacitive electrode material for supercapacitors.However,the poor electrochemical performances and cycling stability caused by volumetric change and counterion drain severely limited its practical application and commercialization.Herein,we present a pulsepotential polymerization strategy for uniformly depositing a dual-doped PPy with ordered and shorter molecular structure by balancing the concentration polarization.Such a strategy ensures more homogeneous stress distribution of PPy during ultralong cycling tests and improves the cycle stability.Moreover,the pulse-potential polymerized PPy with dual anion doping behavior induces enhanced protonation level and improved electrical conductivity,which boosting the charge transfer kinetics.Therefore,the as-synthesized PPy exhibits a remarkable capacitance performance(7250 mF/cm^(2)@3 mA/cm^(2)),outstanding rate capability(3073 mF/cm^(2)@200 mA/cm^(2))and a long cycle life.The assembled symmetric and asymmetric supercapacitors(ASC)exhibit good energy densities(0.8 mWh/cm^(2) for ASC and 0.5 mWh/cm^(2) for symmetric supercapacitor),and excellent durability with zero capacitive loss after 35,000 cycles.In addition,we have fabricated small pouch devices,which can effectively operate a variety of electronic products(including the high-voltage 5 V smartphone,and tablet)and well withstand the external extreme tests during operation,demonstrating the quantitative investigation of the real-life application of aqueous supercapacitors.