Recent advances in 3D printed electrode materials for electrochemical energy storage devices

Electrochemical energy storage(EES)systems like batteries and supercapacitors are becoming the key power sources for attempts to change the energy dependency from inadequate fossil fuels to sustainable and renewable resources.Electrochemical energy storage devices(EESDs)operate efficiently as a result of the construction and assemblage of electrodes and electrolytes with appropriate structures and effective materials.Conventional manufacturing procedures have restrictions on regulating the morphology and architecture of the electrodes,which would influence the performance of the devices.3D printing(3DP)is an advanced manufacturing technology combining computer-aided design and has been recognised as an artistic method of fabricating different fragments of energy storage devices with its ability to precisely control the geometry,porosity,and morphology with improved specific energy and power densities.The capacity to create mathematically challenging shape or configuration designs and high-aspect-ratio 3D architectures makes 3D printing technology unique in its benefits.Nevertheless,the control settings,interactive manufacturing processes,and protracted post-treatments will affect the reproducibility of the printed components.More intelligent software,sophisticated control systems,high-grade industrial equipment,and post-treatment-free methods are necessary to develop.3D printed(3DPd)EESDs necessitate dynamic printable materials and composites that are influenced by performance criteria and fundamental electrochemistry.Herein,we review the recent advances in 3DPd electrodes for EES applications.The emphasis is on printable material synthesis,3DP techniques,and the electrochemical performance of printed electrodes.For the fabrication of electrodes,we concentrate on major 3DP technologies such as direct ink writing(DIW),inkjet printing(IJP),fused deposition modelling(FDM),and stereolithography3DP(SLA).The benefits and drawbacks of each 3DP technology are extensively discussed.We provide an outlook on the integration of synthesis of emerging nanomaterials and fabrication of complex structures from micro to macroscale to construct highly effective electrodes for the EESDs.

Recent advances in electrochemical performance of Mg-based electrochemical energy storage materials in supercapacitors:Enhancement and mechanism

The application of Mg-based electrochemical energy storage materials in high performance supercapacitors is an essential step to promote the exploitation and utilization of magnesium resources in the field of energy storage.Unfortunately,the inherent chemical properties of magnesium lead to poor cycling stability and electrochemical reactivity,which seriously limit the application of Mg-based materials in supercapacitors.Herein,in this review,more than 70 research papers published in recent 10 years were collected and analyzed.Some representative research works were selected,and the results of various regulative strategies to improve the electrochemical performance of Mg-based materials were discussed.The effects of various regulative strategies(such as constructing nanostructures,synthesizing composites,defect engineering,and binder-free synthesis,etc.)on the electrochemical performance and their mechanism are demonstrated using spinelstructured MgX_(2)O_(4) and layered structured Mg-X-LDHs as examples.In addition,the application of magnesium oxide and magnesium hydroxide in electrode materials,MXene's solid spacers and hard templates are introduced.Finally,the challenges and outlooks of Mg-based electrochemical energy storage materials in high performance supercapacitors are also discussed.

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.

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.

MXene-based materials for electrochemical energy storage

Rechargeable batteries and supercapacitors are widely investigated as the most important electrochemical energy storage devices nowadays due to the booming energy demand for electric vehicles and hand-held electronics. The large surface-area-to-volume ratio and internal surface areas endow two-dimensional（2D） materials with high mobility and high energy density; therefore, 2D materials are very promising candidates for Li ion batteries and supercapacitors with comprehensive investigations. In 2011, a new kind of 2D transition metal carbides, nitrides and carbonitrides, MXene, were successfully obtained from MAX phases. Since then about 20 different kinds of MXene have been prepared. Other precursors besides MAX phases and even other methods such as chemical vapor deposition（CVD） were also applied to prepare MXene, opening new doors for the preparation of new MXene. Their 2D nature and good electronic properties ensure the inherent advantages as electrode materials for electrochemical energy storage. In this review, we summarize the recent progress in the development of MXene with emphasis on the applications to electrochemical energy storage. Also, future perspective and challenges of MXene-based materials are briefly discussed regrading electrochemical energy storage.

Redox-active conjugated microporous polymers as electron-accepting organic pseudocapacitor electrode materials for flexible energy storage

Efficient energy storage devices,i.e.pseudocapacitors,are being intensively pursued to address the environmental and energy crises.Most high-performance pseudocapacitors are based on inorganic materials,while organic materials with broader synthetic tunability have attracted increasing interest.Despite recent progress,electron-deficient(n-type)organic pseudocapacitive materials for flexible energy storage are highly demanded yet remain largely unexplored.Here a novel set of n-type perylene diimide(PDI)based conjugated microporous polymers(CMPs),namely,CMP-1,CMP-2 and CMP-3,have been created to integrate excellent desirable characteristics as organic pseudocapacitor electrode materials for flexible energy storage.In light of electron-accepting redox-active sites,hierarchically porous structures,as well as amide-linked networks,the PDI-CMPs electrodes displayed n-type pseudocapacitive behaviors with high capacity(139-205 F g^(-1)at 0.5 A g^(-1)),wide and negative biases(-1.0 to 0 V vs.Ag/AgCl),and long cycling stability.CMP-3 consisting of tetraphenylmethane three-dimensional(3D)building block and PDI units demonstrates not only higher capacitance but also better performance stability because of the higher specific surface area and faster diffusion kinetics as compared to its counterpart CMP-1.Asymmetric supercapacitors(SCs)based on CMP-3 and poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate)(PEDOT/PSS)exhibited wider potential window(1.8 V)and higher capacitance(17.4 m F cm^(-2))compared with symmetric SCs based on PEDOT/PSS electrodes.Notably,CMP-3 also demonstrates attractive potentials as the anode for rechargeable Li-ion batteries.The study sheds light on the fundamental understanding of the key structural parameters that determine their electrochemical and transport properties,thus opening a new door for the rational design of efficient and stable n-type organic electrode materials for flexible energy storage applications.

New insights on(V_(10)O_(28))^(6-)-based electrode materials for energy storage:a brief review

Progress in humanity has intensified the demand for efficient and renewable energy storage,which warrants the development of advanced rechargeable batteries such as lithium-ion batteries(LIBs),sodium-ion batteries(SIBs),zinc-ion batteries(ZIBs),and lithium-sulfur batteries(Li-S batteries).Nevertheless,these batteries still suffer from certain limitations,such as the insufficient capacity and inferior stability in their electrode materials.Therefore,developing a feasible electrode material for Li/Na/Zn ion storage represents a critical challenge.Recently,polyoxovanadates(POVs)materials,particularly decavanadate anion(V_(10)O_(28))^(6-)clusters,have attracted considerate attention as promising battery electrodes,due to their rich multi-electron redox process,high structural stability,simple preparation process,and abundant ligand environment.In this review,we provide an overview of the research progress of(V_(10)O_(28))^(6-)-based materials in various metal-ion battery systems,including LIBs,SIBs,ZIBs,and Li-S batteries.We also discuss the underlying challenges associated with this type of materials,and we provide alternative strategies to overcome these issues.This review aims to facilitate the research and development of the nextgeneration(V_(10)O_(28))^(6-)-based battery materials.

Preparation of nano-PANI@MnO_2 by surface initiated polymerization method using as a nano-tubular electrode material:The amount effect of aniline on the microstructure and electrochemical performance

In this study,nano-polyanline and manganese oxide nanometer tubular composites（nano-PANI@MnO2）were prepared by a surface initiated polymerization method and used as electrochemical capacitor electrode materials; and the effect of aniline amount on the microstructure and electrochemical performance was investigated. The microstructures and surface morphologies of nano-PANI@MnO2 were characterized by X-ray diffraction,scanning electron microscopy and fourier transformation infrared spectroscope. The electrochemical performance of these composite materials was performed with cyclic voltammetry,charge–discharge test and electrochemical impedance spectroscopy,respectively. The results demonstrate that the feed ratio of aniline to MnO2 played a very important role in constructing the hierarchically nano-structure,which would,hence,determine the electrochemical performance of the materials. Using the templateassisted strategy and controlling the feed ratio of aniline to MnO2,the nanometer tubular structure of nanoPANI@MnO2 was obtained. A maximum specific capacitance of 386 F/g was achieved in aqueous 1 mol/L Na NO3 electrolyte with the potential range from 0 to 0.6 V（vs. SCE）.

Lignocellulosic biomass as sustainable feedstock and materials for power generation and energy storage

Lignocellulosic biomass has attracted great interest in recent years for energy production due to its renewability and carbon-neutral nature.There are various ways to convert lignocellulose to gaseous,liquid and solid fuels via thermochemical,chemical or biological approaches.Typical biomass derived fuels include syngas,bio-gas,bio-oil,bioethanol and biochar,all of which could be used as fuels for furnace,engine,turbine or fuel cells.Direct biomass fuel cells mediated by various electron carriers provide a new direction of lignocellulose conversion.Various metal and non-metal based carriers have been screened for mediating the electron transfer from biomass to oxygen thus generating electricity.The power density of direct biomass fuel cells can be over 100 mW cm^(-2),which shows promise for practical applications.Lignocellulose and its isolated components,primarily cellulose and lignin,have also been paid considerable attention as sustainable carbonaceous materials for preparation of electrodes for supercapacitors,lithium-ion batteries and lithium-sulfur batteries.In this paper,we have provided a state-of-the-art review on the research progress of lignocellulosic biomass as feedstock and materials for power generation and energy storage focusing on the chemistry aspects of the processes.It was recommended that process integration should be performed to reduce the cost for thermochemical and biological conversion of lignocellulose to biofuels,while efforts should be made to increase efficiency and improve the properties for biomass fuelled fuel cells and biomass derived electrodes for energy storage.

Defect engineering in molybdenum-based electrode materials for energy storage

Molybdenum-based materials have stepped into the spotlight as promising electrodes for energy storage systems due to their abundant valence states,low cost,and high theoretical capacity.However,the performance of conventional molybdenum-based electrode materials has been limited by slow diffusion dynamics and deficient thermodynamics.Applying defect engineering to molybdenum-based electrode materials is a viable method for overcoming these intrinsic limitations to realize superior electrochemical performance for energy storage.Herein,we systematically review recent progress in defect engineering for molybdenum-based electrode materials,including vacancy modulation,doping engineering,topochemical substitution,and amorphization.In particular,the essential optimization mechanisms of defect engineering in molybdenum-based electrode materials are pre-sented:accelerating ion diffusion,enhancing electron transfer,adjusting potential,and maintaining structural stability.We also discuss the existing challenges and future objectives for defect engineering in molybdenum-based electrode materials to realize high-energy and high-power energy storage devices.

Carbon-Based Electrode Materials for Supercapacitor： Progress, Challenges and Prospective Solutions

Carbon-based materials are typical and commercially active electrode for supercapacitors due to their advantages such as low cost, good stability and easy availability. In the light of energy storage, supercapacitors mechanism is classified into EDLCs （electrochemical double layer capacitors） and pseudocapacitors. Multidimensional carbon nanomaterials （active carbon, carbon nanotube, graphene, etc.）, carbon-based composite and corresponding electrolyte are the critical and important factor in the eyes of researcher. In this minireview, we will discuss the storage mechanism and summarize recent developed novel carbon and carbon-based materials in supercapacitors. The techniques to design the novel nanostructure and high performance electrodematerials that facilitate charge transfer to achieve high energy and power densities will also be discussed.

Organic Electrode Materials for Non-aqueous K-Ion Batteries

The demands for high-performance and low-cost batteries make K-ion batteries(KIBs) considered as promising supplements or alternatives for Li-ion batteries(LIBs). Nevertheless, there are only a small amount of conventional inorganic electrode materials that can be used in KIBs, due to the large radius of K^+ ions. Diff erently, organic electrode materials(OEMs) generally own sufficiently interstitial space and good structure flexibility, which can maintain superior performance in K-ion systems. Therefore, in recent years, more and more investigations have been focused on OEMs for KIBs. This review will comprehensively cover the researches on OEMs in KIBs in order to accelerate the research and development of KIBs. The reaction mechanism, electrochemical behavior, etc., of OEMs will all be summarized in detail and deeply. Emphasis is placed to overview the performance improvement strategies of OEMs and the characteristic superiority of OEMs in KIBs compared with LIBs and Na-ion batteries.

Surface chemistry of electrode materials toward improving electrolyte-wettability:A method review

The electrolyte-wettability at electrode material/electrolyte interface is a criticalfactor that governs the fundamental mechanisms of electrochemical reactionefficiency and kinetics of electrode materials in practical electrochemicalenergy storage. Therefore, the design and construction of electrode materialsurfaces with improved electrolyte-wettability has been demonstrated to beimportant to optimize electrochemical energy storage performance of electrodematerial. Here, we comprehensively summarize advanced strategies and keyprogresses in surface chemical modification for enhancing electrolytewettabilityof electrode materials, including polar atom doping by post treatment,introducing functional groups, grafting molecular brushes, and surfacecoating by in situ reaction. Specifically, the basic principles, characteristics,and challenges of these surface chemical strategies for improving electrolytewettabilityof electrode materials are discussed in detail. Finally, the potentialresearch directions regarding the surface chemical strategies and advancedcharacterization techniques for electrolyte-wettability in the future are provided.This review not only insights into the surface chemical strategies forimproving electrolyte-wettability of electrode materials, but also provides strategicguidance for the electrolyte-wettability modification and optimization ofelectrode materials in pursuing high-performance electrochemical energy storagedevices.

Recent advances in zinc-ion hybrid energy storage: Coloring high-power capacitors with battery-level energy

Zinc-ion hybrid capacitors(ZICs) are considered as newly-emerging and competitive candidates for energy storage devices due to the integration of characteristic capacitor-level power and complementary battery-level energy. The practical application of rising ZICs still faces the specific capacity and dynamics mismatch between the two electrodes with different energy storage mechanisms, which cannot meet the ever-growing indicator demand for portable electronic displays and public traffic facilities. Focusing on these unresolved issues, this mini-review presents recent advances in ZICs referring to the hybrid energy storage mechanism, design strategies of both capacitor-type and battery-type electrode materials, and electrolyte research toward advanced performances(e.g., high operational potential, wide adaptive temperature). Finally, current challenges and future outlook have been proposed to guide further exploration of next-generation ZICs with a combination of high-power delivery, high-energy output and high-quality service durability.

Nanomaterials for electrochemical energy storage

The development of nanotechnology in the past two decades has generated great capability of controlling materials at the nanometer scale and has enabled exciting opportunities to design materials with desirable electronic, ionic, photonic, and mechanical properties. This development has also contributed to tile advance in energy storage, which is a critical technology in this century. In this article, we will review how the rational design of nanostructured materials has addressed the challenges of batteries and electrochemical capacitors and led to high-performance electrochemical energy storage devices. Four specific material systems will be discussed： i） nanostructured alloy anodes for Li-batteries, ii） nanostructured sulfur cathodes for Li-batteries, iii） nanoporous open- framework battery electrodes, and iv） nanostructured electrodes for electrochemical capacitors.

Exploration and progress of high-energy supercapacitors and related electrode materials

As one of new electrical energy storage systems, supercapacitors possess higher energy density than conventional capacitors and larger power density than batteries, integrating substantial merits with high energy, large power delivery, long cycle life, obvious safety, and low cost. However, the unsatisfying energy density is the inhabiting issue for the wide commercial applications. As the energy density(E, W h kg?1) is directly proportional to specific capacitance(C, F g?1) and the square of operating voltage(V, V), in this review, we summarize the recent progress in two sections: the exploration of high-performance electrode materials to achieve high specific capacitance and the construction of high-voltage supercapacitor systems for high working voltage. The progressive explorations and developments in supercapacitors could guide the future research towards high-performance, low-cost, and safe energy storage devices.

Supercapacitor and nanoscale research towards electrochemical energy storage

Electrochemical capacitors,also known as supercapacitors or ultracapacitors,have received much attention from research and development to industrialization,owing to their promise to deliver high levels of electrical power and offer long operating lifetimes.They are considered ideal candidates for energy storage in high-power applications.Benefiting from intensive nanoscale research in recent decades,remarkable improvements and development of supercapacitive energy storage systems have been achieved.Both the energy density and power density for supercapacitors have been substantially improved.In this review article,we endeavor to assess the profound impacts of nanoscale research on the development of supercapacitors,in terms of the substantial improvement of capacitive performance for electrode materials,and revolutionary advances in electrode and device configurations.In addition,recent progress in basic energy storage mechanisms and prototypes of supercapacitors are also reviewed,including a new kinetically-favored intercalation mechanism introduced for the first time.The review concludes with descriptions of the demonstration of already-realized practical applications of commercially-available supercapacitor devices,especially focusing on real usage in vehicles that are highly anticipated by future communities to further heighten the wide attention on clean energy storage systems.

High‑Entropy Electrode Materials:Synthesis,Properties and Outlook

High-entropy materials represent a new category of high-performance materials,first proposed in 2004 and extensively investigated by researchers over the past two decades.The definition of high-entropy materials has continuously evolved.In the last ten years,the discovery of an increasing number of high-entropy materials has led to significant advancements in their utilization in energy storage,electrocatalysis,and related domains,accompanied by a rise in techniques for fabricating high-entropy electrode materials.Recently,the research emphasis has shifted from solely improving the performance of high-entropy materials toward exploring their reaction mechanisms and adopting cleaner preparation approaches.However,the current definition of high-entropy materials remains relatively vague,and the preparation method of high-entropy materials is based on the preparation method of single metal/low-or medium-entropy materials.It should be noted that not all methods applicable to single metal/low-or medium-entropy materials can be directly applied to high-entropy materials.In this review,the definition and development of high-entropy materials are briefly reviewed.Subsequently,the classification of high-entropy electrode materials is presented,followed by a discussion of their applications in energy storage and catalysis from the perspective of synthesis methods.Finally,an evaluation of the advantages and disadvantages of various synthesis methods in the production process of different high-entropy materials is provided,along with a proposal for potential future development directions for high-entropy materials.

Germanium-Carbdiyne: A 3D Well-Defined sp-Hybridized Carbon-Based Material with Superhigh Li Storage Property

Carbyne delivers various excellent properties for the existence of the larger number of sp-hybridized carbon atoms.Here,a 3D well-defined porous carbon material germanium-carbdiyne(Ge-CDY)which is comprised of only sp-hybridized carbon atoms bridging by Ge atoms has been developed and investigated.The unique diamond-like structure constructed by linear butadiyne bonds and sp 3-hybridized Ge atoms ensures the stability of Ge-CDY.The large percentage of conjugated alkyne bonds composed of sp-C guarantees the good conductivity and the low band gap,which were further confirmed experimentally and theoretically,endowing Ge-CDY with the potential in electrochemical applications.The well-defined 3D carbon skeleton of Ge-CDY provides abundant uniform nanopores,which is suitable for metal ions storage and diffusion.Further half-cell evaluation also demonstrated Ge-CDY exhibited an excellent performance in lithium storage.All those indicating sp-hybridized carbon-based materials can exhibit great potential to possess excellent properties and be applied in the field of energy,electronic,and so on.

V_(2)CT_(x) MXene and its derivatives:synthesis and recent progress in electrochemical energy storage applications

With the continuous development of two-dimensional (2D) transition metal carbides and nitrides(collectively referred to as MXene).Nowadays,more than 70 MXene materials have been discovered,and the number is still increasing.Among them,the V_(2)CT_(x) MXene has attracted considerable attentions due to its outstanding physical and chemical properties.In this review,we mainly discussed the emerging V_(2)CT_(x) MXene and its derivative systems in various energy storage devices.Firstly,an introduction of the V-based MXene and its derivatives along with their synthetic methodologies is provided,then we summarize their applications in specific energy storage devices,such as metal (Li,Na,K,Mg,Zn and Al) ion batteries,lithium-sulfur batteries,supercapacitors and metal-ion capacitors.Finally,the main challenges and future perspectives existing in V-based MXene and its derivatives are reasonably put forward.