Progress on Transition Metal Ions Dissolution Suppression Strategies in Prussian Blue Analogs for Aqueous Sodium-/Potassium-Ion Batteries

Aqueous sodium-ion batteries(ASIBs)and aqueous potassium-ion batteries(APIBs)present significant potential for large-scale energy storage due to their cost-effectiveness,safety,and environmental compatibility.Nonetheless,the intricate energy storage mechanisms in aqueous electrolytes place stringent require-ments on the host materials.Prussian blue analogs(PBAs),with their open three-dimensional framework and facile synthesis,stand out as leading candidates for aqueous energy storage.However,PBAs possess a swift capacity fade and limited cycle longevity,for their structural integrity is compromised by the pronounced dis-solution of transition metal(TM)ions in the aqueous milieu.This manuscript provides an exhaustive review of the recent advancements concerning PBAs in ASIBs and APIBs.The dissolution mechanisms of TM ions in PBAs,informed by their structural attributes and redox processes,are thoroughly examined.Moreover,this study delves into innovative design tactics to alleviate the dissolution issue of TM ions.In conclusion,the paper consolidates various strategies for suppressing the dissolution of TM ions in PBAs and posits avenues for prospective exploration of high-safety aqueous sodium-/potassium-ion batteries.

Research progress on vanadium oxides for potassium-ion batteries

Potassium-ion batteries(PIBs)have been considered as promising candidates in the post-lithium-ion battery era.Till now,a large number of materials have been used as electrode materials for PIBs,among which vanadium oxides exhibit great potentiality.Vanadium oxides can provide multiple electron transfers during electrochemical reactions because vanadium possesses a variety of oxidation states.Meanwhile,their relatively low cost and superior material,structural,and physicochemical properties endow them with strong competitiveness.Although some inspiring research results have been achieved,many issues and challenges remain to be further addressed.Herein,we systematically summarize the research progress of vanadium oxides for PIBs.Then,feasible improvement strategies for the material properties and electrochemical performance are introduced.Finally,the existing challenges and perspectives are discussed with a view to promoting the development of vanadium oxides and accelerating their practical applications.

Cocoon-shaped P3-type K0.5Mn0.7Ni0.3O2 as an advanced cathode material for potassium-ion batteries

Potassium ion batteries(PIBs)are emerging as potential next-generation energy storage systems on account of their low cost and high theoretical energy density.Nevertheless,they also face challenges of low specific capacity and suboptimal cycling stability.Herein,we synthesize a cocoon-like P3-type K_(0.5)Mn_(0.7)Ni_(0.3)O_(2)(KMNO)cathode material by a self-template method.The KMNO cocoons possess a hierarchical layered architecture composed of nanoparticle stacking,which can accelerate the transport kinetics of potassium ions,mitigate the stress caused by K^(+)intercalation and deintercalation,and improve structural stability.In addition,Ni can not only alleviate the Jahn-Teller distortion and suppress the phase transition to stabilize the structure,but also act as an electrochemically active element,providing the capacity of two electrons from Ni2+to Ni4+.Combining the advantages of structure and nickel substitution,the P3-type KMNO cocoons are used for electrochemical performance testing of PIB cathodes,delivering an excellent rate capability of 57.1 m A h g^(-1)at 500 m A g^(-1)and a remarkable cycling stability of 77.0%over 300 cycles at 100 m A g^(-1).Impressively,the KMNO cocoons//pitch-derived soft carbon assembled full battery exhibits superior electrochemical performance with a reversible capacity of 79.7 m A h g^(-1)at 50 m A g^(-1).Moreover,ex-situ XRD also further reveals a solid solution phase reaction with a volume change of only 1.46%.This work furnishes a suitable approach to fabricating highperformance layered oxide cathodes for PIBs with outstanding cycling stability and rate capability.

Regulating solid electrolyte interphases on phosphorus/carbon anodes via localized high-concentration electrolytes for potassium-ion batteries

The resourceful and inexpensive red phosphorus has emerged as a promising anode material of potassium-ion batteries(PIBs) for its large theoretical capacities and low redox potentials in the multielectron alloying/dealloying reactions,yet chronically suffering from the huge volume expansion/shrinkage with a sluggish reaction kinetics and an unsatisfactory interfacial stability against volatile electrolytes.Herein,we systematically developed a series of localized high-concentration electrolytes(LHCE) through diluting high-concentration ether electrolytes with a non-solvating fluorinated ether to regulate the formation/evolution of solid electrolyte interphases(SEI) on phosphorus/carbon(P/C) anodes for PIBs.Benefitting from the improved mechanical strength and structural stability of a robust/uniform SEI thin layer derived from a composition-optimized LHCE featured with a unique solvation structure and a superior K+migration capability,the P/C anode with noticeable pseudocapacitive behaviors could achieve a large reversible capacity of 760 mA h g^(-1)at 100 mA g^(-1),a remarkable capacity retention rate of 92.6% over 200 cycles at 800 mA g^(-1),and an exceptional rate capability of 334 mA h g^(-1)at8000 mA g^(-1).Critically,a suppressed reduction of ether solvents with a preferential decomposition of potassium salts in anion-derived interfacial reactions on P/C anode for LHCE could enable a rational construction of an outer organic-rich and inner inorganic-dominant SEI thin film with remarkable mechanical strength/flexibility to buffer huge volume variations and abundant K+diffusion channels to accelerate reaction kinetics.Additionally,the highly reversible/durable full PIBs coupling P/C anodes with annealed organic cathodes further verified an excellent practical applicability of LHCE.This encouraging work on electrolytes regulating SEI formation/evolution would advance the development of P/C anodes for high-performance PIBs.

KVPO_(4)F/carbon nanocomposite with highly accessible active sites and robust chemical bonds for advanced potassium-ion batteries

KVPO_(4)F(KVPF)has been extensively investigated as the potential cathode material for potassium-ion batteries(PIBs)owing to its high theoretical capacity,superior operating voltage,and three-dimensional Kt conduction pathway.Nevertheless,the electrochemical behavior of KVPF is limited by the inherent poor electronic conductivity of the phosphate framework and unstable electrode/electrolyte interface.To address the above issues,this work proposes an infiltration-calcination method to confine the in-situ grown KVPF into the mesoporous carbon CMK-3(denoted KVPF@CMK-3).The assembled KVPF@CMK-3 nanocomposite features three-dimensional interconnected carbon channels,which not only offer abundant active sites and significantly accelerate K t/electron transport,but also prevent the growth of KVPF nanoparticle agglomerates,hence stabilizing the structure of the material.Additionally,V–F–C bonds are created at the interface of KVPF and CMK-3,which reduce the loss of F and stabilize the electrode interface.Thus,when tested as a cathode material for PIBs,the KVPF@CMK-3 nanocomposite delivers superior reversible capacitiy(103.2 mAh g^(-1) at 0.2 C),outstanding rate performance(90.1 mAh g^(-1) at 20 C),and steady cycling performance(92.2 mAh g^(-1) at 10 C and with the retention of 88.2%after 500 cycles).Moreover,its potassium storage mechanism is further examined by ex-situ XRD and ex-situ XPS techniques.The above synthetic strategy demonstrates the potential of KVPF@CMK-3 to be applied as the cathode for PIBs.

Coupling Ternary Selenide SnSb_(2)Se_(4) with Graphene Nanosheets for High-Performance Potassium-Ion Batteries

Although chalcogenide anodes possess higher potassium storage capacity than intercalated-based graphite,their drastic volume change and the irreversible electrochemical reactions still hinder the effective electron/ion transfer during the potassiation/depotassiation process.To solve the above problems,this article proposes the synthesis of a lamellar nanostructure where graphene nanosheets are embedded with SnSb_(2)Se_(4)nanoparticles(SnSb_(2)Se_(4)/GNS).In the product,fine monodisperse SnSb_(2)Se_(4)nanoparticles are coupled with graphene nanosheets to form a porous network framework,which can effectively mitigate the drastic volume changes during electrode reactions and guarantee efficient potassium-ion storage through the synergistic interactions among multiple elements.Various electrochemical analyses prove that SnSb_(2)Se_(4)inherits the advantages of the binary Sb2Se3 and SnSe while avoiding their disadvantages,confirming the synergistic effect of the ternary–chalcogenide system.When tested for potassium storage,the obtained composite delivers a high specific capacity of 368.5 mAh g^(-1)at 100 mA g^(-1)and a stable cycle performance of 265.8 mAh g^(-1)at 500 mA g^(-1)over 500 cycles.Additionally,the potassium iron hexacyanoferrate cathode and the SnSb_(2)Se_(4)/GNS anode are paired to fabricate the potassium-ion full cell,which shows excellent cyclic stability.In conclusion,this strategy employs atomic doping and interface interaction,which provides new insights for the design of high-rate electrode materials.

Bi/Bi_(3)Se_(4) nanoparticles embedded in hollow porous carbon nanorod:High rate capability material for potassium-ion batteries

Considering their superior theoretical capacity and low voltage plateau,bismuth(Bi)-based materials are being widely explored for application in potassium-ion batteries(PIBs).Unfortunately,pure Bi and Bibased compounds suffer from severe electrochemical polarization,agglomeration,and dramatic volume fluctuations.To develop an advanced bismuth-based anode material with high reactivity and durability,in this work,the pyrolysis of Bi-based metal-organic frameworks and in-situ selenization techniques have been successfully used to produce a Bi-based composite with high capacity and unique structure,in which Bi/Bi_(3)Se_(4)nanoparticles are encapsulated in carbon nanorods(Bi/Bi_(3)Se_(4)@CNR).Applied as the anode material of PIBs,the Bi/Bi_(3)Se_(4)@CNR displays fast potassium storage capability with 307.5 m A h g^(-1)at 20 A g^(-1)and durable cycle performance of 2000 cycles at 5 A g^(-1).Notably,the Bi/Bi_(3)Se_(4)@CNR also showed long cycle stability over 1600 cycles when working in a full cell system with potassium vanadate as the cathode material,which further demonstrates its promising potential in the field of PIBs.Additionally,the dual potassium storage mechanism of the Bi/Bi_(3)Se_(4)@CNR based on conversion and alloying reaction has also been revealed by in-situ X-ray diffraction.

Research progress on carbon materials as negative electrodes in sodium-and potassium-ion batteries

Carbon materials,including graphite,hard carbon,soft carbon,graphene,and carbon nanotubes,are widely used as high-performance negative electrodes for sodium-ion and potassium-ion batteries(SIBs and PIBs).Compared with other materials,carbon materials are abundant,low-cost,and environmentally friendly,and have excellent electrochemical properties,which make them especially suitable for negative electrode materials of SIBs and PIBs.Compared with traditional carbon materials,modifications of the morphology and size of nanomaterials represent effective strategies to improve the quality of electrode materials.Different nanostructures make different contributions toward improving the electrochemical performance of electrode materials,so the synthesis of nanomaterials is promising for controlling the morphology and size of electrode materials.This paper reviews the progress made and challenges in the use of carbon materials as negative electrode materials for SIBs and PIBs in recent years.The differences in Na+and K+storage mechanisms among different types of carbon materials are emphasized.

Facile fabrication of MoP nanodots embedded in porous carbon as excellent anode material for potassium-ion batteries

Molybdenum phosphide(MoP),owing to its abundant reserve and high theoretical capacity,is regarded as a promising anode material for potassium-ion batteries.However,it still suffers from the problems of acute volume expansion and weak diffusion kinetics.This study reports a simple method to synthesize a composite of molybdenum phosphide and porous carbon(MoP@PC)through simple mixing and annealing treatment.In the MoP@PC,lots of MoP nanodots with an average diameter of about 4 nm uniformly embedded in the petal-like porous carbon.The MoP@PC shows reversible capacities of 330 mAh g^(-1) at100 mA g^(-1) after 100 cycles,and ultra-long cycling stability with a capacity of 240 mAh g^(-1) after 1000 cycles at 1 A g^(-1) and 161 mAh g^(-1) after 1000 cycles at 5 A g^(-1).The structure of MoP@PC after charging-discharging cycles is also investigated by high resolution transmission electron microscope(HRTEM)and the result shows that MoP can still maintain the nanodot morphology without any agglomeration after 1000 cycles at 5 A g^(-1).The storage mechanism of potassium ions was studied as well,which reveals that MoP and potassium ion have a conversion reaction.

Carbon-Coated Three-Dimensional MXene/Iron Selenide Ball with Core–Shell Structure for High-Performance Potassium-Ion Batteries

Two-dimensional(2D)MXenes are promising as electrode materials for energy storage,owing to their high electronic conductivity and low diffusion barrier.Unfortunately,similar to most 2D materials,MXene nanosheets easily restack during the electrode preparation,which degrades the electrochemical performance of MXene-based materials.A novel synthetic strategy is proposed for converting MXene into restacking-inhibited three-dimensional(3D)balls coated with iron selenides and carbon.This strategy involves the preparation of Fe_(2)O_(3)@carbon/MXene microspheres via a facile ultrasonic spray pyrolysis and subsequent selenization process.Such 3D structuring effectively prevents interlayer restacking,increases the surface area,and accelerates ion transport,while maintaining the attractive properties of MXene.Furthermore,combining iron selenides and carbon with 3D MXene balls offers many more sites for ion storage and enhances the structural robustness of the composite balls.The resultant 3D structured microspheres exhibit a high reversible capacity of 410 mAh g^(−1) after 200 cycles at 0.1 A g^(−1) in potassium-ion batteries,corresponding to the capacity retention of 97% as calculated based on 100 cycles.Even at a high current density of 5.0 A g^(−1),the composite exhibits a discharge capacity of 169 mAh g^(−1).

Elucidating electrochemical intercalation mechanisms of biomass-derived hard carbon in sodium-/potassium-ion batteries

Hard carbon materials are characterized by having rich resources,simple processing technology,and low cost,and they are promising as one of the anode electrodes for commercial applications of sodium-/potassium-ion batteries.Simultaneously,exploring the alkali metal ion storage mechanism is particularly important for designing high-performance electrode materials.However,the structure of hard carbon is more complex,and the description of energy storage behavior is quite controversial.In this study,the Magnolia grandiflora Lima leaf is used as a precursor,combined with simple pyrolysis and impurity removal processes,to obtain biomass-derived hard carbon material(carbonized Magnolia grandiflora Lima leaf[CMGL]).When it is used as an anode for sodium-ion batteries,it exhibits a high specific capacity of 315mAh/g,and the capacity retention rate is 90.0%after 100 cycles.For potassium-ion batteries,the charge specific capacity is 263.5mAh/g,with a capacity retention rate of 85.5%at the same cycling.Furthermore,different electrochemical analysis methods and microstructure characterization techniques were used to further elucidate the sodium/potassium storage mechanism of the material.All the results indicate that the high potential slope region represents the adsorption/desorption characteristics on the surface active sites,whereas the low-potential quasiplateau region belongs to the ion insertion/extraction in the graphitic microcrystallites interlayer.It is noteworthy that potassium ion is randomly intercalated between the graphitic microcrystallite layer without forming a segmented intercalation compound structure.

Hierarchical Bimetallic Selenides CoSe_(2)–MoSe_(2)/rGO for Sodium/Potassium-Ion Batteries Anode: Insights into the Intercalation and Conversion Mechanism

As anode materials for high-performance sodium-ion batteries and potassium-ion batteries,bimetallic selenides have attracted great concern due to their relatively high electrical conductivity and electrochemical activity.However,the formidable challenge in the reaction process is the large volume change,leading to the structural collapse of material,and eventually the decline in electrochemical performance.Herein,a composite of hierarchical CoSe_(2)–MoSe_(2) tubes anchored on reduced graphene oxide nanosheets(CoSe_(2)–MoSe_(2)/rGO)is designed by an in situ hydrothermal selenization treatment.Benefiting from the synergistic effects between CoSe_(2) and MoSe_(2),unique hierarchical structure,and effective reduced graphene oxide coating,the CoSe_(2)–MoSe_(2)/rGO exhibited improved reaction kinetics and structural stability,and thus good electrochemical properties.A combination mechanism of intercalation and conversion of CoSe_(2)–MoSe_(2)/rGO by forming NaxCoSe_(2) and Mo_(15)Se_(19) as intermediate states is put forward on the basis of in situ and ex situ XRD analyses.

Ultrafine nano-scale Cu_(2)Sb alloy confined in three-dimensional porous carbon as an anode for sodium-ion and potassium-ion batteries

Ultrafine nano-scale Cu2Sb alloy confined in a three-dimensional porous carbon was synthesized using NaCl template-assisted vacuum freeze-drying followed by high-temperature sintering and was evaluated as an anode for sodium-ion batteries(SIBs)and potassium-ion batteries(PIBs).The alloy exerts excellent cycling durability(the capacity can be maintained at 328.3 mA·h·g^(-1) after 100 cycles for SIBs and 260 mA·h·g^(-1) for PIBs)and rate capability(199 mA·h·g^(-1) at 5 A·g^(-1) for SIBs and 148 mA·h·g^(-1) at 5 A·g^(-1) for PIBs)because of the smooth electron transport path,fast Na/K ion diffusion rate,and restricted volume changes from the synergistic effect of three-dimensional porous carbon networks and the ultrafine bimetallic nanoalloy.This study provides an ingenious design route and a simple preparation method toward exploring a high-property electrode for K-ion and Na-ion batteries,and it also introduces broad application prospects for other electrochemical applications.

Sn_(4)P_(3)nanoparticles confined in multilayer graphene sheets as a high-performance anode material for potassium-ion batteries

Phosphorus-based anodes are highly promising for potassium-ion batteries(PIBs)because of their large theoretical capacities.Nevertheless,the inferior potassium storage properties caused by the poor electronic conductivity,easy self-aggregation,and huge volumetric changes upon cycling process restrain their practical applications.Now we impregnate Sn_(4)P_(3)nanoparticles within multilayer graphene sheets(Sn_(4)P_(3)/MGS)as the anode material for PIBs,greatly improving its potassium storage performance.Specifically,the graphene sheets can efficiently suppress the aggregation of Sn_(4)P_(3)nanoparticles,enhance the electronic conductivity,and sustain the structural integrity.In addition,plenty of Sn_(4)P_(3)nanoparticles impregnated in MGS offer a large accessible area for the electrolyte,which decreases the diffusion distance for K^(+)and electrons upon K^(+)insertion/extraction,resulting in an improved rate capability.Consequently,the optimized Sn_(4)P_(3)/MGS containing 80 wt%Sn_(4)P_(3)(Sn_(4)P_(3)/MGS-80)exhibits a high reversible capacity of 378.2 and 260.2 m Ah g;at 0.1 and 1 A g^(-1),respectively,and still delivers a large capacity retention of 76.6%after the 1000th cycle at 0.5 A g^(-1).

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.

Development of Metal and Metal-Based Composites Anode Materials for Potassium-Ion Batteries

Potassium-ion batteries(KIBs)are considered the next powerful potential generation energy storage system because of substantial potassium resource availability and similar characteristics with lithium.Unfortunately,the actual application of KIBs is inferior to that of lithium-ion batteries(LIBs),in which the fi nite energy density,ordinary circular life,and underdeveloped fabrication technique dominate the key constraints.Various works have recently been directed to growing novel anode electrodes with superior electrochemical capability.Noticeably,metals/metal oxides materials(e.g.,Sb,Sn,Zn,SnO_(2),and MoO_(2))have been widely investigated as KIBs anodes because of high theoretical capacity,suggesting outstanding promise for high-energy KIBs.In this review,the latest research of metals/metal oxides electrodes for potassium storage is summarized.The major strategies to control the electrochemical property of metals/metal oxides electrodes are discussed.Finally,the future investigation foreground for these anode electrodes has been proposed.

Recent Developments of Antimony-Based Anodes for Sodiumand Potassium-Ion Batteries

The development of sodium-ion(SIBs)and potassium-ion batteries(PIBs)has increased rapidly because of the abundant resources and cost-effectiveness of Na and K.Antimony(Sb)plays an important role in SIBs and PIBs because of its high theoretical capacity,proper working voltage,and low cost.However,Sb-based anodes have the drawbacks of large volume changes and weak charge transfer during the charge and discharge processes,thus leading to poor cycling and rapid capacity decay.To address such drawbacks,many strategies and a variety of Sb-based materials have been developed in recent years.This review systematically introduces the recent research progress of a variety of Sb-based anodes for SIBs and PIBs from the perspective of composition selection,preparation technologies,structural characteristics,and energy storage behaviors.Moreover,corresponding examples are presented to illustrate the advantages or disadvantages of these anodes.Finally,we summarize the challenges of the development of Sb-based materials for Na/K-ion batteries and propose potential research directions for their further development.

Bismuth nanorods confined in hollow carbon structures for high performance sodium-and potassium-ion batteries

Bismuth has drawn widespread attention as a prospective alloying-type anode for sodium-ion batteries(SIBs)and potassium-ion batteries(PIBs)due to its large volumetric capacity.However,such material encounters drastic particle pulverization and overgrowth of solid-electrolyte interphase(SEI)upon repeated(de)alloying,thus causing poor rate and cycling degradation.Herein,we report a unique structure design with bismuth nanorods confined in hollow N,S-codoped carbon nanotubes(Bi@NS-C)fabricated by a solvothermal method and in-situ thermal reduction.Ex-situ SEM observations confirm that such a design can significantly suppress the size fining of Bi nanorods,thus inhibiting the particle pulverization and repeated SEI growth upon charging/discharging.The as achieved Bi@NS-C demonstrates outstanding rate capability for SIBs(96.5%capacity retention at 30 A g^(-1) vs.1 A g^(-1)),and a record high rate performance for PIBs(399.5 m Ah g^(-1)@20 A g^(-1)).Notably,the as constructed full cell(Na_(3)V_(2)(PO_(4))_(3)@C|Bi@NS-C)demonstrates impressive performance with a high energy density of 219.8 W h kg^(-1) and a high-power density of 6443.3 W kg^(-1)(based on the total mass of active materials on both electrodes),outperforming the state-of-the-art literature.

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.

Biomass Template Derived Boron/Oxygen Co-Doped Carbon Particles as Advanced Anodes for Potassium-Ion Batteries

Among various anode candidates for potassium-ion batteries,carbonaceous materials have attracted significant attention due to their overwhelming advantages including cost-effectiveness and environmental benignity.However,the inferior specific capacity and the sluggish reaction kinetics hinder the further development in this realm.Herein,we report biomass templated synthesis of boron/oxygen heteroatom co-doped carbon particles(BO-CPs)via direct plasma-enhanced chemical vapor deposition.With the combined advantages of abundant active sites,large accessible surface area,and functional groups,BO-CP anode exhibits high reversible specific capacity(426.5 mAh g^(-1)at 0.1 A g^(-1))and excellent rate performance(166.5 mAh g^(-1)at 5 A g^(-1)).The K-ion storage mechanism is probed by operando Raman spectroscopy,ex situ X-ray photoelectron spectroscopy/electrochemical impedance spectroscopy,galvanostatic intermittent titration technique measurements,and theoretical simulations.The synergistic effect of boron and oxygen co-doping greatly facilitates the performance of carbon-based anode,wherein boron dopant improves the conductivity of carbon framework and the oxygen dopant affords ample active sites and thus harvests additional specific capacity.This work is anticipated to propel the development of high-performance anode materials for emerging energy storage devices.