Advanced Anode Materials of Potassium Ion Batteries:from Zero Dimension to Three Dimensions

Potassium ion batteries(PIBs)with the prominent advantages of sufficient reserves and economical cost are attractive candidates of new rechargeable batteries for large-grid electrochemical energy storage systems(EESs).However,there are still some obstacles like large size of K+to commercial PIBs applications.Therefore,rational structural design based on appropriate materials is essential to obtain practical PIBs anode with K+accommodated and fast diffused.Nanostructural design has been considered as one of the effective strategies to solve these issues owing to unique physicochemical properties.Accordingly,quite a few recent anode materials with different dimensions in PIBs have been reported,mainly involving in carbon materials,metal-based chalcogenides(MCs),metal-based oxides(MOs),and alloying materials.Among these anodes,nanostructural carbon materials with shorter ionic transfer path are beneficial for decreasing the resistances of transportation.Besides,MCs,MOs,and alloying materials with nanostructures can effectively alleviate their stress changes.Herein,these materials are classified into 0D,1D,2D,and 3D.Particularly,the relationship between different dimensional structures and the corresponding electrochemical performances has been outlined.Meanwhile,some strategies are proposed to deal with the current disadvantages.Hope that the readers are enlightened from this review to carry out further experiments better.

Advanced metal sulfide anode for potassium ion batteries

Potassium-ion batteries（KIBs） are a promising alternative to lithium-ion batteries owning to the abundance of potassium on Earth and the relatively low K/K＋redox couple. To date, KIBs remains its infancy and the investigation of anode materials mainly focused on carbon-based materials, which deliver limited reversible capacity. Hence, it is imperative to explore alternative anode materials with high reversible capacity for KIBs. Recently, a pioneering work from Chen’s group reported a nanocomposite of Sb2S3 nanoparticles anchored on porous S,N-codoped graphene（denoted as Sb2S3-SNG） as an advanced anode material for KIBs, which exhibited remarkable enhancements of both capacity and cycling stability, highlighting the rational structure design of Sb2S3-SNG for maximum utilization of Sb2S3 nanoparticles and graphene layers for energy storage applications in high-performance KIBs.

Improvement in potassium ion batteries electrodes: Recent developments and efficient approaches

Demand for efficient and continuous application for high-grid energy storage systems involves the study towards novel battery technologies. Hence, considering the vast naturally available resources of potassium all over the world and its encouraging intercalation chemistries, it has recently enticed attention in electrochemical energy storage industry in the form of potassium ion batteries (PIBs). The major factor in this K+ based battery, is to develop efficient approaches to manufacture electrode substance to intercalate its big size potassium ions with considerable voltage, kinetics, charge/discharge capacity, capacity retention, cost, etc. This study contributes in the recent developments of anode and cathode materials for PIBs, including several electrode materials in regards to synthesis, structure, electrochemical performance, and K-storage mechanisms. Finally, the review contributes to provide helpful sources for the increasing number of scientists working in this industry regarding its critical issues and challenges and also to indicate the future direction of electrode materials in PIBs.

Cross-Linked Hollow Graphitic Carbon as Low-Cost and High-Performance Anode for Potassium Ion Batteries

Large-scale and low-cost preparation of carbon-based potassium anode with long life and high capacity is one of the footstones for the development of potassium ion batteries(PIBs).Herein,a low-cost carbon-based material,cross-linked hollow graphitic carbon(HGC),is large scale synthesized to apply for PIBs anode.Its hollow structure can afford sufficient space to overcome the damage caused by the volume expansion of graphitic carbon(GC).While the cross-linked structure forms a compact interconnection network that allows electrons to rapid transfer between different GC frameworks.Electrochemical measurements demonstrated that the HGC anode exhibited low charge/discharge plateau(about 0.25 V and 0.1 V)and excellent specific capacity as high as 298 m A h g^(-1)at the current density of 50 m A g^(-1).And more important,after 200 cycles the capacity of HGC anode still shows 269 m A h g^(-1)(the decay rate of per cycle is only 0.048%).Meanwhile,the use of commercial traditional electrolyte(KPF_(6))and cheap raw materials that provide new hope for trying and realizing the large-scale production of PIBs based on carbon anode materials.

Dealloying-induced dual-scale nanoporous indium-antimony anode for sodium/potassium ion batteries

InSb alloy is a promising candidate for sodium/potassium ion batteries(SIBs/PIBs)but challenged with achieving high performance by dramatic volumetric changes.Herein,nanoporous(np)-InSb with dualscale phases(cubic/hexagonal(C/H)-InSb)was fabricated by chemical dealloying of ternary Mg-In-Sb precursor.Operando X-ray diffraction(XRD)and ex-situ characterizations well rationalize the dealloying/alloying mechanisms and the formation of dual-scale microstructures/phases.As an anode for SIB/PIBs,the np-InSb electrode exhibits superior reversible capacities and lifespan compared with the monometallic porous(p)-In electrode,stemming from the dealloying-induced dual-scale nanoporous architecture and alloying strategy with proper composition.The operando XRD results demonstrate that the(de)sodiated mechanism of the np-InSb electrode involves a two-step(de)alloying process,while the(de)potassiated mechanism is associated with a full electrochemically-driven amorphization upon cycling.Additionally,the gas evolution during the(dis)charge process was monitored by on-line mass spectrometry.

Metal–organic compounds as promising anode materials for potassium ion batteries: A mini review

Potassium-ion batteries(PIBs)represent one of the most promising alternatives to lithium-ion batteries(LIBs),owing to their exceptional attributes such as high voltages,potent power capabilities,and cost-effectiveness.Nonetheless,challenges arise from the sluggish kinetics and significant volume expansion observed during the insertion/extraction of large-radii potassium ions,leading to subpar rate performance and considerable capacity degradation in potassium-ion batteries.Consequently,it becomes imperative to explore advanced anode materials exhibiting high electrochemical activity and robust structural stability.In this regard,the present review focuses on recent progress in metal-organic compounds(MOCs)as anode materials for potassium-ion batteries,systematically discussing their outstanding merits from the perspective of metal speciation.Additionally,the principal mechanism of K ion storage within relevant MOCs is presented.Furthermore,a comprehensive summary of existing drawbacks that hinder the broader application of MOCs-based materials is provided,along with proposed guidelines and strategies for addressing the inferior performance characteristics.This review serves to illuminate the development of MOCs-based anode materials for potassium-ion batteries and offers a valuable reference for future research endeavors.

Delving into the dissimilarities in electrochemical performance and underlying mechanisms for sodium and potassium ion storage in N-doped carbon-encapsulated metallic Cu_(2)Se nanocubes

The large volumetric variations experienced by metal selenides within conversion reaction result in inferior rate capability and cycling stability,ultimately hindering the achievement of superior electrochemical performance.Herein,metallic Cu_(2)Se encapsulated with N-doped carbon(Cu_(2)Se@NC)was prepared using Cu_(2)O nanocubes as templates through a combination of dopamine polymerization and hightemperature selenization.The unique nanocubic structure and uniform N-doped carbon coating could shorten the ion transport distance,accelerate electron/charge diffusion,and suppress volume variation,ultimately ensuring Cu_(2)Se@NC with excellent electrochemical performance in sodium ion batteries(SIBs)and potassium ion batteries(PIBs).The composite exhibited excellent rate performance(187.7 mA h g^(-1)at 50 A g^(-1)in SIBs and 179.4 mA h g^(-1)at 5 A g^(-1)in PIBs)and cyclic stability(246,8 mA h g^(-1)at 10 A g^(-1)in SIBs over 2500 cycles).The reaction mechanism of intercalation combined with conversion in both SIBs and PIBs was disclosed by in situ X-ray diffraction(XRD)and ex situ transmission electron microscope(TEM).In particular,the final products in PIBs of K_(2)Se and K_(2)Se_(3)species were determined after discharging,which is different from that in SIBs with the final species of Na_(2)Se.The density functional theory calculation showed that carbon induces strong coupling and charge interactions with Cu_(2)Se,leading to the introduction of built-in electric field on heterojunction to improve electron mobility.Significantly,the theoretical calculations discovered that the underlying cause for the relatively superior rate capability in SIBs to that in PIBs is the agile Na~+diffusion with low energy barrier and moderate adsorption energy.These findings offer theoretical support for in-depth understanding of the performance differences of Cu-based materials in different ion storage systems.

Modulating Co-Co bonds average length in Co_(0.85)Se_(1-x)S_(x) to enhance conversion reaction for potassium storage

While alloying transition metal chalcogenides(TMCs)with other chalcogen elements can effectively improve their conductivity and electrochemical properties,the optimal alloying content is still uncertain.In this study,we study the influence of dopant concentration on the chemical bonds in TMC and reveal the associated stepwise conversion reaction mechanism for potassium ion storage.According to density function theory calculations,appropriate S-doping in Co0.85Se(Co_(0.85)Se_(1-x)S_(x))can reduce the average length of Co-Co bonds because of the electronegativity variation,which is thermodynamically favourable to the phase transition reactions.The optimal Se/S ratio(x=0.12)for the conductivity has been obtained from experimental results.When assembled as an anode in potassium-ion batteries(PIBs),the sample with optimized Se/S ratio exhibits extraordinary electrochemical performance.The rate performance(229.2 mA h g^(-1)at 10 A g^(-1))is superior to the state-of-the-art results.When assembled with Prussian blue(PB)as a cathode,the pouch cell exhibits excellent performance,demonstrating its great potential for applications.Moreover,the stepwise K+storage mechanism caused by the coexistence of S and Se is revealed by in-situ X-ray diffraction and ex-situ transmission electron microscopy techniques.Hence,this work not only provides an effective strategy to enhance the electrochemical performance of transition metal chalcogenides but also reveals the underlying mechanism for the construction of advanced electrode materials.

Pillar effect boosting the electrochemical stability of Prussian bluepolypyrrole for potassium ion batteries

Due to the high theoretical capacity and electrode potential,Prussian blue is regarded as promising cathode material for potassium ion batteries.However,inferior structural stability,poor electronic conductivity,ambiguous energy storage mechanism have limited the application of Prussian blue materials.Herein,a highly stable Prussian blue-polypyrrole(PB-PPY)composite has been prepared by a facile one-step method.PB-PPY displays higher discharging capacity,better rate capacity,and longer cycling lifespan than that of pure Prussian blue in potassium ion batteries.The superior electrochemical performance can be attributed to the unique synthesis strategy to reduce the content of vacancies and crystal water in Prussian blue and enhance the conductivity.Furthermore,partial K ions have been evidenced that could remain in the Prussian blue framework,which contributes the long-term cycling stability.The K ions in the framework play the role of“pillars”to support the framework of Prussian blue and relieve the structural stress during the intercalation and de-intercalation of K ions.This work will reveal a new energy storage mechanism of Prussian blue and promote the design of high stability Prussian blue in the future.

Strengthening synergistic effects between hard carbon and soft carbon enabled by connecting precursors at molecular level towards high-performance potassium ion batteries

Synergistic effects between hard carbons and soft carbons are proven to be helpful for improving the electrochemical performance of carbonaceous anode for potassium-ion batteries(PIBs).However,the phase separation of precursors limits the synergistic effects and improvement of electrochemical performance.Here,inspired by the esterification reaction,the precursors of two sorts of carbon are connected at the molecular level,which boosts the synergistic effects in hybrid carbon,resulting in excellent electrochemical kinetics and low charge/discharge voltage.Consequently,the hybrid carbon anode exhibited a high specific capacity of 121 mAh·g^(−1)at 3.2 A·g^(−1),a high-rate capability,and stable cycling performance.After 500 cycles at 1 A·g^(−1),the average capacity fading is only 0.078%per cycle.

Constructing oxygen-deficient V_(2)O_(3)@C nanospheres for high performance potassium ion batteries

Potassium ion batteries(PIBs) have been regarded as promising alternatives to lithium ion batteries(LIBs)on account of their abundant resource and low cost in large scale energy storage applications. However,it still remains great challenges to explore suitable electrode materials that can reversibly accommodate large size of potassium ions. Here, we construct oxygen-deficient V_(2)O_(3)nanoparticles encapsulated in amorphous carbon shell(Od-V_(2)O_(3)@C) as anode materials for PIBs by subtly combining the strategies of morphology and deficiency engineering. The MOF derived nanostructure along with uniform carbon coating layer can not only enables fast K+migration and charge transfer kinetics, but also accommodate volume change and maintain structural stability. Besides, the introduction of oxygen deficiency intrinsically tunes the electronic structure of materials according to DFT calculation, and thus lead to improved electrochemical performance. When utilized as anode for PIBs, Od-V_(2)O_(3)@C electrode exhibits superior rate capability(reversible capacities of 262.8, 227.8, 201.5, 179.8, 156.9 mAh/g at 100, 200, 500, 1000 and2000 mA/g, respectively), and ultralong cycle life(127.4 mAh/g after 1000 cycles at 2 A/g). This study demonstrates a feasible way to realize high performance PIBs through morphology and deficiency engineering.

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.

Sulfur/nitrogen/oxygen tri-doped carbon nanospheres as an anode for potassium ion storage

Carbonaceous materials are considered as ideal anode for potassium ion batteries(PIBs)due to their abundant resources and stable physical and chemical properties.However,improvements of reversible capacity and cycle performance are still needed,aiming to the practical application.Herein,S/N/O tridoped carbon(SNOC)nanospheres are prepared by in-situ vulcanized polybenzoxazine.The S/N/O tridoped carbon matrix provides abundant active sites for potassium ion adsorption and effectively improves potassium storage capacity.Moreover,the SNOC nanospheres possess large carbon interlayer spacing and high specific surface area,which broaden the diffusion pathway of potassium ions and accelerate the electron transfer speed,resulting in excellent rate performance.As an anode for PIBs,SNOC shows attractive rate performance(438.5 mA h g^(-1) at 50 mA g^(-1) and 174.5 mA h g^(-1) at2000 mA g^(-1)),ultra-high reversible capacity(397.4 mA h g^(-1) at 100 mA g^(-1) after 700 cycles)and ultra-long cycling life(218.9 mA h g^(-1) at 2000 mA g^(-1) after 7300 cycles,123.1 mA h g^(-1) at3000 mA g^(-1) after 16500 cycles and full cell runs for 4000 cycles).Density functional theory calculation confirms that S/N/O tri-doping enhances the adsorption and diffusion of potassium ions,and in-situ Fourier-transform infrared explores explored the potassium storage mechanism of SNOC.

Recent advances in alloy-based anode materials for potassium ion batteries

Potassium ion batteries(PIBs)are regarded as one of promising low-cost energy storage technologies.Achieving long cycle life and high energy density has been considered as important tasks for developing high-performance PIBs.The alloy-based anodes for PIBs have attracted great attentions because of their high theoretical capacity and relatively low operating voltage.In this review,the latest advance in the related alloy-based anodes was overviewed.Specifically,the correlations among the morphology and potassium storage performance,phase transition mechanisms,the formation of solid electrolyte interphases and ionic transport kinetics are critically discussed.It is expected that this review will provide meaningful guidance and possible pathways for the developments of alloy-based anodes for PIBs.

A review of hard carbon anode: Rational design and advanced characterization in potassium ion batteries

K-ion batteries(KIBs)have attracted tremendous attention and seen significant development because of their low price,high operating voltage,and properties similar to those of Li-ion batteries.In the field of development of full batteries,exploring high-performing and low-cost anode materials for K-ion storage is a crucial challenge.Owing to their excellent cost effectiveness,abundant precursors,and environmental benignancy,hard carbons(HCs)are considered promising anode materials for KIBs.As a result,researchers have devoted much effort to quantify the properties and to understand the underlying mechanisms of HC-based anodes.In this review,we mainly introduce the electrochemical reaction mechanism of HCs in KIBs,and summarize approaches to further improve the electrochemical performance in HC-based materials for K-ion storage.In addition,we also highlight some advanced in situ characterization methods for understanding the evolutionary process underlying the potassiation–depotassiation process,which is essential for the directional electrochemical performance optimization of KIBs.Finally,we raise some challenges in developing smart-structured HC anode materials for KIBs,and propose rational design principles and perspectives serving as the guidance for the targeted optimization of HC-based KIBs.

Deciphering the potassium storage phase conversion mechanism of phosphorus by combined solid-state NMR spectroscopy and density functional theory calculations

Phosphorus is the potential anode material for emerging potassium-ion batteries(PIBs)owing to the highest specific capacity and relatively low operation plateau.However,the reversible delivered capacities of phosphorus-based anodes,in reality,are far from the theoretical capacity corresponding to the formation of K3P alloy.And,their underlying potassium storage mechanisms remain poorly understood.To address this issue,for the first time,we perform high-resolution solid-state31P NMR combined with XRD measurements,and density functional theory calculations to yield a systemic quantitative understanding of(de)potassiation reaction mechanism of phosphorus anode.We explicitly reveal a previously unknown asymmetrical nanocrystalline-to-amorphous transition process via rP←→(K_(3)P_(11),K_(3)P_(7),beta-K_(4)P_(6))←→(alpha-K4P6)←→(K_(1-x)P,KP,K_(4-x)P3,K_(1+x)P)←→(amorphous K4P3,amorphous K3P)that are proceed along with the electrochemical potassiation/depotassiation processes.Additionally,the corresponding KP alloys intermediates,such as the amorphous phases of K_(4)P_(3),K_(3)P,and the nonstoichiometric phases of“K_(1-x)P”,“K_(1+x)P”,“K_(4-x)P_(3)”are experimentally detected,which indicating various complicated K-P alloy species are coexisted and evolved with the sluggish electrochemical reaction kinetics,resulting in lower capacity of phosphorus-based anodes.Our findings offer some insights into the specific multi-phase evolution mechanism of alloying anodes that may be generally involved in conversion-type electrode materials for PIBs.

Constructing Carbon Nanobubbles with Boron Doping as Advanced Anode for Realizing Unprecedently Ultrafast Potassium Ion Storage

Carbonaceous material with favorable K^(+)intercalation feature is considered as a compelling anode for potassium-ion batteries(PIBs).However,the inferior rate performance and cycling stability impede their large-scale application.Here,a facile template method is utilized to synthesize boron doping carbon nanobubbles(BCNBs).The incorporation of boron into the carbon structure introduces abundant defective sites and improves conductivity,facilitating both the intercalation-controlled and capacitivecontrolled capacities.Moreover,theoretical calculation proves that boron doping can effectively improve the conductivity and facilitate electrochemical reversibility in PIBs.Correspondingly,the designed BCNBs anode delivers a high specific capacity(464 mAh g^(-1)at 0.05 A g^(-1))with an extraordinary rate performance(85.7 mAh g^(-1)at 50 A g^(-1)),and retains a considerable capacity retention(95.2%relative to the 100th charge after 2000 cycles).Besides,the strategy of pre-forming stable artificial inorganic solid electrolyte interface effectively realizes high initial coulombic efficiency of 79.0%for BCNBs.Impressively,a dual-carbon potassium-ion capacitor coupling BCNBs anode displays a high energy density(177.8 Wh kg^(-1)).This work not only shows great potential for utilizing heteroatom-doping strategy to boost the potassium ion storage but also paves the way for designing high-energy/power storage devices.

Atomic layer deposition of core-shell structured V_(2)O_(5)@CNT sponge as cathode for potassium ion batteries

Potassium-ion batteries(KIBs)represent one of the most promising alternatives to lithium-ion batteries(LIBs)considering the potential low cost and abundant potassium resource.In this work,we demonstrate a core-shell structured sponge cathode for KIBs,where amorphous V_(2)O_(5) uniformly coats on carbon nanotube(CNT)sponge via atomic layer deposition(ALD).The V_(2)O_(5)@CNT sponge shows several advantages as cathode:(1)the three-dimensional(3D)conductive network of CNT sponge offers a fast electron transport pathway,(2)the porous nature and high surface area of CNT sponge enables enough access for electrolyte to V_(2)O_(5),(3)the amorphous structure of V_(2)O_(5) offers a fast kinetics upon K-ion insertion/deinsertion.The V_(2)O_(5)@CNT sponge cathode delivers a high capacity of 206mA h/g and moderate cycling and rate performance in common carbonate-based electrolyte system.

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.

Dealloying-constructed hierarchical nanoporous bismuth-antimony anode for potassium ion batteries

Bi-Sb alloys are appealing anode materials for potassium ion batteries(PIBs)but challenged by their enormous volumetric variation during operation.Herein,a facile one-step dealloying protocol was devised and utilized to prepare the Bi-Sb alloys that manifest an exotic bicontinuous hierarchical nanoporous(np)microstructure ideal for volume-change mitigation and K+transport percolation.The growth mechanism fostering the peculiar morphology of the np-(Bi,Sb)alloys was investigated and clarified via operando X-ray(XRD)and ex-situ scanning electron microscopy(SEM).In particular,the np-Bi6Sb2 electrode,optimized for comprehensive electrochemical performance,achieves decent reversible capacities and a superior lifespan,as benchmarked with the monometallic references and other Bi-Sb alloy electrodes.The(de)potassiation mechanism of the np-(Bi,Sb)alloys was studied by operando XRD and further rationalized by density functional theory(DFT)calculations,whereby a homogeneous(segregation-free)and robust two-step electrochemically-driven phase transformations’catenation of(Bi,Sb)↔K(Bi,Sb)2↔K3(Bi,Sb)was reliably established to substantiate the outstanding reversibility of the np-(Bi,Sb)anodes in PIBs.