Insights into Nano-and Micro-Structured Scaffolds for Advanced Electrochemical Energy Storage

Adopting a nano-and micro-structuring approach to fully unleashing the genuine potential of electrode active material benefits in-depth understandings and research progress toward higher energy density electrochemical energy stor-age devices at all technology readiness levels.Due to various challenging issues,especially limited stability,nano-and micro-structured(NMS)electrodes undergo fast electrochemical performance degradation.The emerging NMS scaffold design is a pivotal aspect of many electrodes as it endows them with both robustness and electrochemical performance enhancement,even though it only occupies comple-mentary and facilitating components for the main mechanism.However,extensive efforts are urgently needed toward optimizing the stereoscopic geometrical design of NMS scaffolds to minimize the volume ratio and maximize their functionality to fulfill the ever-increasing dependency and desire for energy power source supplies.This review will aim at highlighting these NMS scaffold design strategies,summariz-ing their corresponding strengths and challenges,and thereby outlining the potential solutions to resolve these challenges,design principles,and key perspectives for future research in this field.Therefore,this review will be one of the earliest reviews from this viewpoint.

Dual-Functional Electrode Promoting Dendrite-Free and CO_(2) Utilization Enabled High-Reversible Symmetric Na-CO_(2) Batteries

Sodium-carbon dioxide(Na-CO_(2))batteries are regarded as promising energy storage technologies because of their impressive theoretical energy density and CO_(2)reutilization,but their practical applications are restricted by uncontrollable sodium dendrite growth and poor electrochemical kinetics of CO_(2)cathode.Constructing suitable multifunctional electrodes for dendritefree anodes and kinetics-enhanced CO_(2)cathodes is considered one of the most important ways to advance the practical application of Na-CO_(2)batteries.Herein,RuO2 nanoparticles encapsulated in carbon paper(RuCP)are rationally designed and employed as both Na anode host and CO_(2)cathode in Na-CO_(2)batteries.The outstanding sodiophilicity and high catalytic activity of RuCP electrodes can simultaneously contribute to homogenous Na+distribution and dendrite-free sodium structure at the anode,as well as strengthen discharge and charge kinetics at the cathode.The morphological evolution confirmed the uniform deposition of Na on RuCP anode with dense and flat interfaces,delivering enhanced Coulombic efficiency of 99.5%and cycling stability near 1500 cycles.Meanwhile,Na-CO_(2)batteries with RuCP cathode demonstrated excellent cycling stability(>350 cycles).Significantly,implementation of a dendrite-free RuCP@Na anode and catalytic-site-rich RuCP cathode allowed for the construction of a symmetric Na-CO_(2)battery with long-duration cyclability,offering inspiration for extensive practical uses of Na-CO_(2)batteries.

Recent progress and future prospects of high-entropy materials for battery applications

Due to the energy crisis caused by limited fossil fuel reserves,extensive use of the renewable energy sources such as wind or solar energy is deemed to replace the use of traditional fossil fuels in the future^([1−3]).However,most renewable energy sources face the same problem,which is the intermittency of energy.For example,solar energy cannot be utilized at night.That means the continuous energy demand required for large-scale power grids can’t be satisfied by a single solar panel model.

Anode materials for potassium-ion batteries: Current status and prospects

Potassium-ion batteries(KIBs)as one of the most promising alternatives to lithium-ion batteries have been highly valued in recent years.However,progress in KIBs is largely restricted by the sluggish development in anode materials.Therefore,it is imperative to systematically outline and evaluate the recent research advances in the field of anode materials for KIBs toward promoting the development of high-performance anode materials for KIBs.In this review,the recent achievements in anode materials for KIBs are summarized.The electrochemical properties(ie.charge storage mechanism,capacity,rate performance,and cycling stability)of these reported anode materials,as well as their advantages/disadvantages,are discerned and analyzed,enabling high-performance KIBs to meet the requirements for practical applications.Finally,technological developments,scientific challenges,and future research opportunities of anode materials for KIBs are briefly reviewed.

Micro-nano structural electrode architecture for high power energy storage

The necessity and superiorities of micro-nano structural electrodes toward high power:Electrochemical energy storage(EES)technologies have achieved great success in portable electronics and electric vehicles owing to their environmental friendliness and cost effectiveness.With the promotional concepts such as the Internet of Things and ultra-high efficiency self-powered systems in recent years,there are substantial demand for superior EES systems,including but not limited to high-performance,miniaturization and multifunction[1−4].In a particular EES cell,active materials are carried by electrodes as the basic building blocks of energy storage or release.Material innovation(includes composition,structure,size and morphology)has revealed remarkable energy density,power density and lifespan for associated devices in the lab setting of low mass loading slurry-coating electrodes[5].

Highly-rough surface carbon nanofibers film as an effective interlayer for lithium–sulfur batteries

Lithium–sulfur(Li–S)battery with a new configuration is demonstrated by inserting a flexible nitrogen-doping carbon nanofiber(N-CNFs)interlayer between the sulfur cathode and the separator.The N-CNFs film with high surface roughness and surface area is fabricated by electrospinning and a subsequent calcination process.The N-CNFs film interlayer not only effectively traps the shuttling migration of polysulfides but also gives the whole battery reliable electronic conductivity,which can effectively enhance the electrochemical performance of Li–S batteries.Finally,Li–S batteries with long cycling stability of 785 mAh/g after 200 cycles and good rate capability of 573 mAh/g at 5 C are achieved.

Recent Research Progress of Anode Materials for Potassium-ion Batteries

The next-generation smart grid for the storage and delivery of renewable energy urgently needs to develop a low-cost and rechargeable energy storage technology beyond lithium-ion batteries(LIBs).Owing to the abundance of potassium(K) resources and the similar electrochemical performance to that of LIBs,potassium-ion batteries(PIBs) have been attracted considerable interest in recent years,and significant progress has been achieved concerning the discovery of high-performance electrode materials for PIBs.This review especially summarizes the latest research progress regarding anode materials for PIBs,including carbon materials,organic materials,alloys,metal-based compounds,and other new types of compounds.The reversible K-ion storage principle and the electrochemical performance(i.e.,capacity,potential,rate capability,and cyclability) of these developed anode materials are summarized.Furthermore,the challenges and the corresponding effective strategies to enhance the battery performance of the anode materials are highlighted.Finally,prospects of the future development of high-performance anode materials for PIBs are discussed.

Review on Recent Advances of Cathode Materials for Potassium-ion Batteries

Potassium-ion batteries(PIBs) as a promising supplement to lithium-ion batteries have drawn great attention attributing to the abundant potassium resources, the fast-ionic conductivity of potassium ions in electrolyte, and the low standard redox potential of potassium. However, the development of PIBs is still in its infancy, which is largely restricted by the fact that the electrode materials, especially the cathode materials of PIBs, are far from satisfactory in practical applications regarding the capacity, voltage, and cycle life. Therefore, most of current research efforts have been devoted to exploring new and high-performance electrode materials for achieving PIBs with high capacity and voltage as well as excellent cyclability. In this review,the recent advancements on cathode materials for PIBs are specially summarized. Besides, technological developments, scientific challenges, and future research opportunities of cathode materials for PIBs are also briefly outlooked.

Research progress of transition metal compounds as bifunctional catalysts for zinc-air batteries

Zinc-air batteries(ZABs)are widely studied because of their high theoretical energy density,high battery voltage,environmental protection,and low price.However,the slow kinetics of oxygen reduction reaction(ORR)and oxygen evolution reaction(OER)on the air electrode limits the further application of ZABs,so that how to develop a cheap,efficient,and stable catalyst with bifunctional catalytic activity is the key to solving the development of ZABs.Transition metal compounds are widely used as cathode materials for ZABs due to their low cost,high electrocatalytic activity,and stable structure.This review summarizes the research progress of transition metal compounds as bifunctional catalysts for ZABs.The development history,operation principle,and mechanism of ORR and OER reactions are introduced first.The application and development of transition metal compounds as bifunctional catalysts for ZABs in recent years are systematically introduced,including transition metal oxides(TMOs),transition metal nitrides(TMNs),transition metal sulfides(TMSs),transition metal carbides(TMCs),transition metal phosphates(TMPs),and others.In addition,the shortcomings of transition metal compounds as bifunctional catalysts for ZABs were summarized and reasonable design strategies and improvement measures were put forward,aiming at providing a reference for the design and construction of high-performance ZABs cathode materials.Finally,the challenges and future in this field are discussed and prospected.

A mini review： Functional nanostructuring with perfectly-ordered anodic aluminum oxide template for energy conversion and storage

Nanostructures have drawn great attentions for functional device applications. Among the various techniques developed for fabricating arrayed nanostructures of functional materials, nanostructuring technique with porous anodic aluminum oxide （AAO） membrane as templates becomes more attractive owing to the superior geometrical characteristics and low-cost preparation process. In this mini review, progress about functional we summarize our recent nanostructuring based on perfectly-ordered AAO membrane to prepare perfectly- ordered nanostructure arrays of functional materials toward constructing high-performance energy conversion and storage devices. By employing the perfectly-ordered AAO membrane as templates, arrayed nanostructures in the form ofnanodot, nanorod, nanotube and nanopore have been synthesized over a large area. These as-obtained nanostructure arrays have large specific surface area, high regularity, large-scale implementation, and tunable nanos- cale features. All these advanced features enable them to be of great advantage for the performance improvement of energy conversion and storage devices, including photo- electrochemical water splitting cells, supercapacitors, and batteries, etc.

Advances on three-dimensional electrodes for micro-supercapacitors:A mini-review

Owing to the high power density,long cycle life and maintain-free,micro-supercapacitors(MSCs)stand out as preferred miniaturized energy source for themiscellaneous autonomous electronic components.However,the shortage of energy density is the main stumbling block for their practical applications.To solve this energy issue,constructing a three-dimensional(3D)electrode within the limited footprint area is proposed as a new solution for improving the energy storage capacity ofMSCs.In the last few years,extensive efforts have been devoted to developing 3D electrodes for MSCs,and significant progress and breakthrough have been achieved.While,there is still lack of systematic summary on the 3D electrode design strategies.To this end,it is imperative to outline the basic design conception,summarize the current states,and discuss the future research about 3D electrodes in MSCs based on the latest development.

Unexpected intercalation-dominated potassium storage in WS2 as a I potassium-ion battery anode

Unexpected intercalation-dominated process is observed duri ng K^+insertion in WS2 in a voltage range of 0.01-3.0 V.This is different fromthe previously reported two-dimensional(2D)transition metal dichalcogenides that undergo a conversion reaction in a low voltage rangewhen used as anodes in potassium-ion batteries.Charge/discharge processes in the K and Na cells are studied in parallel to demonstrate thedifferention storage mechanisms.The Na^+storage proceeds through intercalation and conversion reactions while the K^+storage is governedby an intercalation reaction.Owing to the reversible K^+intercalation in the van der Waals gaps,the WS2 anode exhibits a low decay rate of 0.07%per cycle,delivering a capacity of 103 mAh·g^-1 after 100 cycles at 100 mA·g^-1.It maintains 57%capacity at 800 mA·g^-1 and shows stablecyclability up to 400 cycles at 500 mA·g^-1.Kinetics study proves the facilitation of K^+transport is derived from the intercalation-dominatedmecha nism.Furthermore,the mechanismis verified by the density functional theory(DFT)calculations,showing that the progressive expansion of the interlayer space can account for the observed results.

Emerging smart design of electrodes for micro-supercapacitors:A review

Owing to high power density and long cycle life,micro-supercapacitors(MSCs)are regarded as a prevalent energy storage unit for miniaturized electronics in modern life.A major bottleneck is achieving enhanced energy density without sacrificing both power density and cycle life.To this end,designing electrodes in a“smart”way has emerged as an effective strategy to achieve a trade-off between the energy and power densities of MSCs.In the past few years,considerable research efforts have been devoted to exploring new electrode materials for high capacitance,but designing clever configurations for electrodes has rarely been investigated from a structural point of view,which is also important for MSCs within a limited footprint area,in particular.This review article categorizes and arranges these“smart”design strategies of electrodes into three design concepts:layer-by-layer,scaffoldassisted and rolling origami.The corresponding strengths and challenges are comprehensively summarized,and the potential solutions to resolve these challenges are pointed out.Finally,the smart design principle of the electrodes of MSCs and key perspectives for future research in this field are outlined.

Nickel nanopore arrays as promising current collectors for constructing solid-state supercapacitors with ultrahigh rate performance

In this work, nickel nanopore arrays with a highly-oriented nanoporous structure inherited from por- ous alumina membranes were used as nanostructured current collectors for constructing ultrahigh rate solid-state supercapacitors. A thin layer of poly（3,4-ethylenediox- ythiophene） （PEDOT） as electroactive materials was conformally coated onto nickel nanopores to form heterostructured electrodes. The as-prepared electrodes have a large specific surface area to ensure a high capacity, and the highly-oriented nanoporous structure of nickel nanopores reduces the ion transport resistance, allowing the ions in the solid-state electrolytes to quickly access the PEDOT surface during the fast charge-discharge process. As a result, the assembled solid-state supercapacitor in a symmetric configuration exhibits an ideal capacitive behavior and a superior rate capability even at an ultrahigh scan rate of 50 V· s^-1.