Capacitive energy storage from single pore to porous electrode identified by frequency response analysis

Rate capability,peak power,and energy density are of vital importance for the capacitive energy storage(CES)of electrochemical energy devices.The frequency response analysis(FRA)is regarded as an efficient tool in studying the CES.In the present work,a bi-scale impedance transmission line model(TLM)is firstly developed for a single pore to a porous electrode.Not only the TLM of the single pore is reparameterized but also the particle packing compactness is defined in the bi-scale.Subsequently,the CES properties are identified by FRA,focused on rate capability vs.characteristic frequency,peak power vs.equivalent series resistance,and energy density vs.low frequency limiting capacitance for a single pore to a porous electrode.Based on these relationships,the CES properties are numerically simulated and theoretically predicted for a single pore to a porous electrode in terms of intra-particle pore length,intra-particle pore diameter,inter-particle pore diameter,electrolyte conductivity,interfacial capacitance&exponent factor,electrode thickness,electrode apparent surface area,and particle packing compactness.Finally,the experimental diagnosis of four supercapacitors(SCs)with different electrode thicknesses is conducted for validating the bi-scale TLM and gaining an insight into the CES properties for a porous electrode to a single pore.The calculating results suggest,to some extent,the inter-particle pore plays a more critical role than the intra-particle pore in the CES properties such as the rate capability and the peak power density for a single pore to a porous electrode.Hence,in order to design a better porous electrode,more attention should be given to the inter-particle pore.

Model reduction of fractional impedance spectra for time–frequency analysis of batteries, fuel cells, and supercapacitors

Joint time–frequency analysis is an emerging method for interpreting the underlying physics in fuel cells,batteries,and supercapacitors.To increase the reliability of time–frequency analysis,a theoretical correlation between frequency-domain stationary analysis and time-domain transient analysis is urgently required.The present work formularizes a thorough model reduction of fractional impedance spectra for electrochemical energy devices involving not only the model reduction from fractional-order models to integer-order models and from high-to low-order RC circuits but also insight into the evolution of the characteristic time constants during the whole reduction process.The following work has been carried out:(i)the model-reduction theory is addressed for typical Warburg elements and RC circuits based on the continued fraction expansion theory and the response error minimization technique,respectively;(ii)the order effect on the model reduction of typical Warburg elements is quantitatively evaluated by time–frequency analysis;(iii)the results of time–frequency analysis are confirmed to be useful to determine the reduction order in terms of the kinetic information needed to be captured;and(iv)the results of time–frequency analysis are validated for the model reduction of fractional impedance spectra for lithium-ion batteries,supercapacitors,and solid oxide fuel cells.In turn,the numerical validation has demonstrated the powerful function of the joint time–frequency analysis.The thorough model reduction of fractional impedance spectra addressed in the present work not only clarifies the relationship between time-domain transient analysis and frequency-domain stationary analysis but also enhances the reliability of the joint time–frequency analysis for electrochemical energy devices.

Decouple charge transfer reactions in the Li-ion battery

In the development of Li-ion batteries(LIBs)with high energy/power density,long cycle-life,fast charging,and high safety,an insight into charge transfer reactions is required.Although electrochemical impedance spectroscopy(EIS)is regarded as a powerful diagnosis tool,it is not a direct but an indirect measurement.With respect to this,some critical questions need to be answered:(i)why EIS can reflect the kinetics of charge transfer reactions;(ii)what the inherent logical relationship between impedance models under different physical scenes is;(iii)how charge transfer reactions compete with each other at multiple scales.This work aims at answering these questions via developing a theory framework so as to mitigate the blindness and uncertainty in unveiling charge transfer reactions in LIBs.To systematically answer the above questions,this article is organized into a three-in-one(review,tutorial,and research)type and the following contributions are made:(i)a brief review is given for impedance model development of the LIBs over the past half century;(ii)an open source code toolbox is developed based on the unified impedance model;(iii)the competive mechanisms of charge transfer reactions are unveiled based on the developed EIS-Toolbox@LIB.This work not only clarifies theoretical fundamentals,but also provides an easy-to-use open source code for EIS-Toolbox@LIB to optimize fast charge/discharge,mitigate cycle aging,and improve energy/power density.

A review of carbon dots and their composite materials for electrochemical energy technologies

Carbon dots(CDs)and their composites as energy storage materials and electrocatalysts have emerged as new types of quasi-zero-dimensional carbon materials.CDs can provide a large specific surface area,numerous electron-electron hole pairs,adjustable heteroatom doping,rich surface functional groups,and so on.However,the roles and functional mechanisms of CDs and their composite materials in the enhancement of electrochemical performance remain unclear and need to be understood in depth.Based on the most recent literature,this paper comprehensively reviews the synthesis methods and applications of various categories of CDs and their composites as electrode materials of supercapacitors,lithium-ion batteries,sodium-ion batteries,and potassium-ion batteries,and as electrocatalysts for hydrogen evolution,oxygen evolution,and oxygen reduction reactions in metal-air batteries,fuel cells,and water electrolysis.To facilitate further research and development,several important aspects related to CDs and their composite materials are summarized with analysis of the technical challenges in practical applications and discussion of the possible development perspectives.

A Review of In‑Situ Techniques for Probing Active Sites and Mechanisms of Electrocatalytic Oxygen Reduction Reactions

Electrocatalytic oxygen reduction reaction(ORR)is one of the most important reactions in electrochemical energy technologies such as fuel cells and metal–O2/air batteries,etc.However,the essential catalysts to overcome its slow reaction kinetic always undergo a complex dynamic evolution in the actual catalytic process,and the concomitant intermediates and catalytic products also occur continuous conversion and reconstruction.This makes them difficult to be accurately captured,making the identification of ORR active sites and the elucidation of ORR mechanisms difficult.Thus,it is necessary to use extensive in-situ characterization techniques to proceed the real-time monitoring of the catalyst structure and the evolution state of intermediates and products during ORR.This work reviews the major advances in the use of various in-situ techniques to characterize the catalytic processes of various catalysts.Specifically,the catalyst structure evolutions revealed directly by in-situ techniques are systematically summarized,such as phase,valence,electronic transfer,coordination,and spin states varies.In-situ revelation of intermediate adsorption/desorption behavior,and the real-time monitoring of the product nucleation,growth,and reconstruction evolution are equally emphasized in the discussion.Other interference factors,as well as in-situ signal assignment with the aid of theoretical calculations,are also covered.Finally,some major challenges and prospects of in-situ techniques for future catalysts research in the ORR process are proposed.

A porous Co_(3)O_(4)-carbon paper electrode enabling nearly 100% electrocatalytic reduction of nitrate to ammonia

Co_(3)O_(4) was synthesized on carbon paper(CP)using a facile method to improve electrochemical nitrate-toammonia conversion efficiency.The resulting Co_(3)O_(4)-CP electrode demonstrated an exceptional Faradaic efficiency of almost 100% across a broad range of application conditions,with a peak NH3 yield of 3.43 mmol h^(-1) cm^(-2)(2.25 mol gCo^(-1) h^(-1)).

Tuning composite solid-state electrolyte interface to improve the electrochemical performance of lithium-oxygen battery

Thin and flexible composite solid-state electrolyte(SSE) is considered to be a prospective candidate for lithium-oxygen(Li-O_(2)) batteries with the aim to address the problems of unsatisfied safety, terrible durability as well as inferior electrochemical performance. Herein, in order to improve the safety and durability, a succinonitrile(SN) modified composite SSE is proposed. In this SSE, SN is introduced for eliminating the boundary between ceramic particles, increasing the amorphous region of polymer and ensuring fast ionic transport. Subsequently, the symmetric battery based on the proposed SSE achieves a long cycle life of 3000 h. Moreover, the elaborate cathode interface through the SN participation effectively reduces the barriers to the combination between lithium ions and electrons, facilitating the corresponding electrochemical reactions.As a result, the solid-state Li-O_(2)battery based on this SSE and tuned cathode interface achieves improved electrochemical performance including large specific capacity over 12,000 m Ah g^(-1), enhanced rate capacity as well as stable cycle life of 54 cycles at room temperature. This ingenious design provides a new orientation for the evolution of solid-state Li-O_(2)batteries.

Supported dual-atom catalysts: Preparation, characterization, and potential applications

Developing sustainable and clean electrochemical energy conversion technologies is a crucial step in addressing the challenges of energy shortage and environmental pollution. Exploring and developing new electrocatalysts with excellent performance and low cost will facilitate the commercial use of these energy conversion technologies. Recently, dual-atom catalysts(DACs) have attracted considerable research interest since they exhibit higher metal atom loading and more flexible active sites compared to single-atom catalysts(SACs). In this paper, the latest preparation methods and characterization techniques of DACs are systematically reviewed. The advantages of homonuclear and heteronuclear DACs and the catalytic mechanism and identification technologies between the two DACs are highlighted. The current applications of DACs in the field of electrocatalysis are summarized. The development opportunities and challenges of DACs in the future are prospected. The ultimate goal is to provide new ideas for the preparation of new catalysts with excellent properties by customizing diatomic catalysts for electrochemical applications.

Regulating Zn Deposition via an Artificial Solid–Electrolyte Interface with Aligned Dipoles for Long Life Zn Anode

Aqueous zinc ion batteries show prospects for next-generation renewable energy storage devices.However,the practical applications have been limited by the issues derived from Zn anode.As one of serious problems,Zn dendrite growth caused from the uncontrollable Zn deposition is unfavorable.Herein,with the aim to regulate Zn deposition,an artificial solid–electrolyte interface is subtly engineered with a perovskite type material,BaTiO3,which can be polarized,and its polarization could be switched under the external electric field.Resulting from the aligned dipole in BaTiO3 layer,zinc ions could move in order during cycling process.Regulated Zn migration at the anode/electrolyte interface contributes to the even Zn stripping/plating and confined Zn dendrite growth.As a result,the reversible Zn plating/stripping processes for over 2000 h have been achieved at 1 mA cm^(−2) with capacity of 1 mAh cm−2.Furthermore,this anode endowing the electric dipoles shows enhanced cycling stability for aqueous Zn-MnO2 batteries.The battery can deliver nearly 100%Coulombic efficiency at 2 Ag^(−1) after 300 cycles.

Host-guest supramolecular interaction behavior at the interface between anode and electrolyte for long life Zn anode

The hydrogen evolution reaction (HER) and dendrite growth associated with Zn anode have become the main bottlenecks for the further development of zinc ion batteries (ZIBs).In this work,the electrochemical activity of H_(3)O^(+) is inhibited by the supramolecular host–guest complex composed of H_(3)O^(+) as guest and 18-crown-6 as host.The even Zn plating is induced by the host–guest complex electrostatic shielding layer on Zn anode,as detected by in-situ optical microscopy.The lamellar Zn is plated which profits from the improved Zn plating behavior.Density functional theory (DFT) calculation presents the stable structure of complex.The less produced H_(2) content is monitored online by a mass spectrometer during Zn plating/stripping,which indicates HER can be hampered by the host–guest behavior.Thus,the ZIBs with long life and high Coulombic efficiency are achieved via introducing 18-crown-6.The proposed host–guest supramolecular interaction is expected to facilitate the furthermore development of Zn batteries.

Novel design and synthesis of 1D bamboo-like CNTs@Sn_(4)P_(3)@C coaxial nanotubes for long-term sodium ion storage

In this work,a novel bamboo-like carbon nanotubes@Sn4P3@carbon(BLCNTs@Sn_(4)P_(3)@C)coaxial nanotubes are designed and prepared using a newly developed hydrothermal method followed by a phophidation process.The prepared Sn_(4)P_(3) nanoparticles are uniformly coated and wrapped on the one-dimensional(1D)bamboo-like CNTs,which is covered by a uniform carbon layer to form a sandwich-like structure with Sn_(4)P_(3) in between.The inner CNT and outer carbon can effectively maintain the structural stability and serve as the good electron conductors.Additionally,the outer carbon coating layer can effectively keep BLCNTs@Sn_(4)P_(3)@C nanotubes separate each other,preventing aggregation of Sn_(4)P_(3) during charge/discharge when this material is used as anode for sodium ion batteries.The anode of BLCNTs@Sn_(4)P_(3)@C shows excellent reversible capacity and a long cycling of over 2000 cycles.The unique design of coaxial nanotubes is greatly beneficial to the electrochemical performance of Sn_(4)P_(3) for sodium ion storage.

Pd nanocluster-decorated CoFe composite supported on nitrogen carbon nanotubes as a high-performance trifunctional electrocatalyst

Rational design and synthesis of low-cost trifunctional electrocatalysts with improved stability and superior electrocatalytic activity for oxygen reduction reaction(ORR),oxygen evolution reaction(OER),and hydrogen evolution reaction(HER) are highly desirable but remain as the bottlenecks at the current state of technology.In this paper,the cobalt-iron(Co-Fe) composite supported on nitrogen-doped carbon nanotubes(CoFe composite/NCNTs) is synthesized.The intrinsic OER and HER catalytic activities of this CoFe composite/NCNTs composite are significantly improved with palladium(Pd) nanocluster decoration [Pd-coated(CoFe composite/NCNTs)].The as-prepared Pd-coated(CoFe composite/NCNTs) catalyst exhibits excellent trifunctional electrocatalytic activity and stability due to the interfacial coupling between Pd and(CoFe composite/NCNTs).This catalyst is successfully employed in the water electrolysis cell as both OER and HER electrode catalysts,flexible rechargeable Zn-air battery as the bifunctional ORR and OER electrode catalyst.The cell voltage of this catalyst-coated electrodes requires only 1.60 V to achieve 10 mA cm^(-2) current density for water electrolysis cell,which is comparable to and even better than that of Pt/C and Ir/C based cell.The primary Zn-air battery using this catalyst shows a constant high open-circuit voltage(OCV) of 1.47 V and a maximum power density of 261 mW cm^(-2) in the flooded mode configuration.Most importantly,a flexible Zn-air battery with this catalyst runs very smoothly without a change in voltage gap during flat,bending,and twisting positions.

Oxygen reduction electrocatalysis:From conventional to single-atomic platinum-based catalysts for proton exchange membrane fuel cells

Platinum(Pt)-based materials are still the most efficient and practical catalysts to drive the sluggish kinetics of cathodic oxygen reduction reaction(ORR)in proton exchange membrane fuel cells(PEMFCs).However,their catalysis and stability performance still need to be further improved in terms of corrosion of both carbon support and Pt catalyst particles as well as Pt loading reduction.Based on the developed synthetic strategies of alloying/nanostructuring Pt particles and modifying/innovating supports in developing conventional Pt-based catalysts,Pt single-atom catalysts(Pt SACs)as the recently burgeoning hot materials with a potential to achieve the maximum utilization of Pt are comprehensively reviewed in this paper.The design thoughts and synthesis of various isolated,alloyed,and nanoparticlecontained Pt SACs are summarized.The single-atomic Pt coordinating with non-metals and alloying with metals as well as the metal-support interactions of Pt single-atoms with carbon/non-carbon supports are emphasized in terms of the ORR activity and stability of the catalysts.To advance further research and development of Pt SACs for viable implementation in PEMFCs,various technical challenges and several potential research directions are outlined.

A comprehensive review of electrochemical hybrid power supply systems and intelligent energy managements for unmanned aerial vehicles in public services

The electric unmanned aerial vehicles (UAVs) are rapidly growing due to their abilities to perform some difficult or dangerous tasks as well as many public services including real-time monitoring, wireless coverage, search and rescue, wildlife surveys, and precision agriculture. However, the electrochemical power supply system of UAV is a critical issue in terms of its energy/power densities and lifetime for service endurance. In this paper, the current power supply systems used in UAVs are comprehensively reviewed and analyzed on the existing power configurations and the energy management systems. It is identified that a single type of electrochemical power source is not enough to support a UAV to achieve a long-haul flight;hence, a hybrid power system architecture is necessary. To make use of the advantages of each type of power source to increase the endurance and achieve good performance of the UAVs, the hybrid systems containing two or three types of power sources (fuel cell,battery, solar cell, and supercapacitor,) have to be developed. In this regard, the selection of an appropriate hybrid power structure with the optimized energy management system is critical for the efficient operation of a UAV. It is found that the data-driven models with artificial intelligence (AI) are promising in intelligent energy management. This paper can provide insights and guidelines for future research and development into the design and fabrication of the advanced UAV power systems.

Manipulating dielectric property of polymer coatings toward highretention-rate lithium metal full batteries under harsh critical conditions

Lithium(Li)metal batteries(LMBs)can potentially deliver much higher energy density but remain plagued by uncontrollable Li plating with dendrite growth,unstable interfaces,and highly abundant excess Li(>50 mAh·cm^(-2)).Herein,different from the artificial layer or three-dimensional(3D)matrix host constructions,various dielectric polymers are initially well-comprehensively investigated from experimental characterizations to theoretical simulation to evaluate their functions in modulating Li ion distribution.As a proof of concept,a 3D interwoven high dielectric functional polymer(HDFP)nanofiber network with polar C-F dipole moments electrospun on copper(Cu)foil is designed,realizing uniform and controllable Li deposition capacity up to 5.0 mAh·cm^(-2),thereby enabling stable Li plating/stripping cycling over 1400 h at 1.0 mA·cm^(-2).More importantly,under the highcathode loading(~3.1 mAh·cm^(-2))and only 0.6×excess Li(N/P ratio of 1.6),the full cells retain capacity retention of 97.4%after 200 cycles at 3.36 mA·cm^(-2)and achieve high energy density(297.7 Wh·kg^(-1)at cell-level)under lean electrolyte conditions(15μL),much better than ever-reported literatures.Our work provides a new direction for designing high dielectric polymer coating toward high-retention-rate practical Li full batteries.

A Review of Solid Electrolyte Interphase(SEI)and Dendrite Formation in Lithium Batteries

Lithium-metal batteries with high energy/power densities have significant applications in electronics,electric vehicles,and stationary power plants.However,the unstable lithium-metal-anode/electrolyte interface has induced insufficient cycle life and safety issues.To improve the cycle life and safety,understanding the formation of the solid electrolyte interphase(SEI)and growth of lithium dendrites near the anode/electrolyte interface,regulating the electrodeposition/electrostripping processes of Li^(+),and developing multiple approaches for protecting the lithium-metal surface and SEI layer are crucial and necessary.This paper comprehensively reviews the research progress in SEI and lithium dendrite growth in terms of their classical electrochemical lithium plating/stripping processes,interface interaction/nucleation processes,anode geometric evolution,fundamental electrolyte reduction mechanisms,and effects on battery performance.Some important aspects,such as charge transfer,the local current distribution,solvation,desolvation,ion diffusion through the interface,inhibition of dendrites by the SEI,additives,models for dendrite formation,heterogeneous nucleation,asymmetric processes during stripping/plating,the host matrix,and in situ nucleation characterization,are also analyzed based on experimental observations and theoretical calculations.Several technical challenges in improving SEI properties and reducing lithium dendrite growth are analyzed.Furthermore,possible future research directions for overcoming the challenges are also proposed to facilitate further research and development toward practical applications.

Facile construction of a water-defendable Li anode protection enables rechargeable Li-O_(2) battery operating in humid atmosphere

The rechargeable Li-O_(2) battery endowed with high theoretical specific energy density has sparked intense research interest as a promising energy storage system. However, the intrinsic high activity of Li anode,especially to moisture, usually leads to inferior electrochemical performance of Li-O_(2) battery in humid environments, hindering its widespread application. To settle the trouble of poor moisture tolerance, fabricating a water-proof layer on the Li-metal anode could be an effective tactic. Herein, a facile strategy for constructing an ibuprofen-based protective layer on the Li anode has been proposed to realize highly rechargeable Li-O_(2) battery in humid atmosphere. Due to the in-situ reaction between ibuprofen reagent and metallic Li, the protective layer with a thickness of ~30 μm has been uniformly deposited on the surface of Li anode. Particularly, the protective layer, consisting of a large amount of hydrophobic alkyl group and benzene ring, can significantly resist water ingress and enhance the electrochemical stability of Li anode. As a result, the Li-O_(2) battery based on the protected Li anode achieves a long cycle life of 210 h(21 cycles at 1000 m Ah/g, 200 m A/g) in highly moist atmosphere with relative humidity(RH) of68%. This convenient and efficient strategy offers novel design concept of water-resistant metal anode,and paves the way to the promising future prospect for the high-energy Li-O_(2) battery implementing in the ambient atmosphere.

Advanced Noncarbon Materials as Catalyst Supports and Non‑noble Electrocatalysts for Fuel Cells and Metal–Air Batteries

Electrochemical energy systems such as fuel cells and metal–air batteries can be used as clean power sources in the field of electric transportation and possess great potential in the reduction of various energy and environmental issues.In these systems,the oxygen reduction reaction(ORR)at the cathode is the rate-determining factor for overall system performance,and up to now,platinum group metals supported on carbon materials,especially Pt,remain the highest performing and the most practical ORR electrocatalysts.However,corresponding carbonaceous catalyst supports are extremely susceptible to corrosion under electrochemical operation,and therefore,the extensive exploration of alternative stable materials for ORR electrocatalysts with both high electrochemical stability and catalytic performance is essential.Here,noncarbon materials with high corrosion resistance have been explored to substitute traditional carbon supports or even act directly as low-cost non-noble metal electrocatalysts,and based on this,this review will present a comprehensive overview and deep analysis of the recent progress in noncarbon materials,including metals,oxides,nitrides,carbides,sulfides,and so on.Overall,general attributes associated with noncarbon materials include high corrosion resistance,strong metal–support interaction,and impressive porous structure retention.However,major drawbacks include low electrical conductivity,insufficient chemical stability in acidic or alkaline media,and poor electrochemical stability at ORR electrode potentials.To overcome these challenges,this review will also summarize efficient strategies such as combining with highly conductive materials,introducing dopants and forming vacancies to result in promising electrocatalytic ORR performances.Finally,this review will propose possible research directions to facilitate future research and development toward the practical application of noncarbon-based ORR electrocatalysts.

Trace Nb-doped Na_(0.7)Ni_(0.3)Co_(0.1)Mn_(0.6)O_(2) with suppressed voltage decay and enhanced low temperature performance

The P2-type manganese-based Na_(0.7)MnO_(2) cathode materials attract great interest due to their high theoretical capacity.However,these materials suffer from rapid capacity fading,poor rate performance and severe voltage decay resulting from phase transition and sluggish reaction kinetics.In this work we report a novel Nb-doped Na_(0.7)[Ni_(0.3)Co_(0.1)Mn_(0.6)]_(1-x)Nb_(x)O_(2) with significantly suppre ssed voltage decay and enhanced cycling stability.The strong Nb-O bond can efficiently stabilize the TMO fra mework,and the as prepared material demonstrates much lower discharge midpoint voltage decay(0.132 V) than that of pristine one(0.319 V) after 200 cycles.Consequently,a remarkably improved cycling perfo rmance with a capacity retention of 87.9% after 200 cycle at 0.5 C is achieved,showing a 2.4 fold improvement as compared to the control sample Na_(0.7)Ni_(0.3)Co_(0.1)Mn_(0.6)O_(2)(~37% rotation).Even at 2 C,a capacity retention of 68.4% is retained after 500 cycles.Remarkably,the as prepared material can be applied at low temperature of-20℃,showing a capacity retention of 81% as compared to that at room temperature.

Synthesis of SnS2 Ultrathin Nanosheets as Anode Materials for Potassium Ion Batteries

Potassium(K)ion batteries present their promising application for large-scale energy storage systems with cost-effective characteristic.Unfortunately,the large K ion radius results in sluggish K ion diffusion kinetics and volume expansion of the electrode during the K ion insertion/extraction process.It is a challenge to explore capable anode materials with remarkable K ion storage ability.Herein,we design and prepare SnS2 ultrathin nanosheets via a facile hydrothermal process.When severing as anode materials for K ion batteries with optimized electrolyte,SnS2 presents an improved capacity and rate ability.The capable electrochemical performance is ascribed to the reduced ion diffusion pathway and capacitor-dominated K-ion storage process.In addition,the K ion storage mechanism of SnS2 is investigated by the ex-situ X-ray diffraction technique.