Potassium Storage Mechanism Research Articles

Dual-Carbon confinement strategy of antimony anode material enabling advanced potassium ion storage

Antimony (Sb) has attracted considerable attention as an anode material for potassium ion batteries (PIBs) because of its high theoretical capacity. Nevertheless, owing to the large radius of K+, apparent volume expansion occurs during the reaction between Sb and K+, which will undermine the stability of the electrode. Accordingly, a dual-carbon confinement strategy is regarded as an effective method for handling this issue. Herein, Sb is firstly captured by mesoporous carbon sphere (MCS) to form a composite of Sb/MCS, and then reduced graphene oxide (rGO) is adopted as an outer layer to wrap the Sb/MCS to obtain the dual-carbon confinement material (Sb/MCS@rGO). Given the synergistic confinement effects of the MCS and rGO, the Sb/MCS@rGO electrode realizes an excellent rate capacity of 341.9 mAh g−1 at 1000 mA g−1 and prominent cycling stability with around 100% retention at 50 mA g−1 after 100 cycles. Besides, the discussion on galvanostatic charge–discharge test, cyclic voltammetry and ex-situ XRD illustrates the stepwise potassium storage mechanism of Sb. Benefiting from the dual-carbon confinement effects, the Sb/MCS@rGO electrode processes promising electrochemical reaction kinetics. Furthermore, the application of the Sb/MCS@rGO in full cells also demonstrates its superior rate capacity (212.3 mAh g−1 at 1000 mA g−1).

Charge–Discharge Behavior of Graphite Negative Electrodes in FSA-Based Ionic Liquid Electrolytes: Comparative Study of Li-, Na-, K-Ion Systems

K-ion batteries utilizing ionic liquid (IL) electrolytes are promising candidates for next-generation batteries because of the abundance of potassium resources, low redox potential of potassium, and high safety of ILs. Our major interest is in the comprehensive understanding of electrochemical alkali metal intercalation/deintercalation into graphite negative electrodes, because graphite can easily form graphite intercalation compounds (GICs) with various ionic species, but not with sodium. In this study, we investigated the potassium storage mechanism of graphite negative electrodes in bis(fluorosulfonyl)amide (FSA)-based ILs, and compared the electrochemical GIC formation of Li-, Na-, and K-ion systems. Charge–discharge tests of graphite in K[FSA]–[C3C1pyrr][FSA] IL (C3C1pyrr = N-methyl-N-propylpyrrolidinium) at 313 K yielded an initial discharge capacity as high as 268 mAh (g-C)−1, leading to the formation of several K-GICs including stage-3 KC36, stage-2 KC24, and stage-1 KC8. The rate capability and long-term cycling tests indicated stable potassiation/depotassiation behavior for 225 cycles. A comparison of the electrochemical behavior of graphite among M[FSA]–[C3C1pyrr][FSA] (M = Li, Na, and K) ILs at 298 K indicated that the formation of binary M-GICs is localized in the potential range below −2.85 V vs. Fc+/Fc (Fc = ferrocene), which possibly hinders Na-GIC formation.

Graphene wrapped Cobalt/Tin bimetallic sulfides composites with abundant active facets and extended interlayer spacing for stable sodium/potassium storage

In this work, graphene wrapped Cobalt/Tin bimetallic sulfides composites (Co1Sn6.75-sulfides/rGO, CSSG) were prepared via soft template-assisted solvothermal reactions, the electrostatic assembly and high-temperature calcination strategies. Compared with pure SnS, Co1Sn6.75-sulfides show extended interlayer spacings and abundant active facets, which can accelerate the intercalation/extraction of Na+/K+ and improve the diffusion kinetics. Graphene can increase the electrical conductivity of composites and induce the formation of stable electrode/electrolyte interfaces. Therefore, CSSG exhibit superior cycle performance (391.7 mAh/g at 2.0 A/g after 1000 cycles, 240 mAh/g at 5.0 A/g over 5000 cycles) and outstanding rate capability (326.3 mAh/g at 10.0 A/g) for sodium ion half-cells. In addition, Na3V2(PO4)3||CSSG full-cells deliver a high reversible capacity of 339.3 mAh/g at 0.5 A/g after 100 cycles. Similarly, CSSG still exhibits high cycle capacities for potassium ion half-cells (306.6 mAh/g at 0.5 A/g after 1000 cycles). A variety of analysis methods and ex-situ characterizations are adopted to explore the diffusion kinetics of Na+/K+ and potassium storage mechanism. The structural evolution of CSSG during the long-term cycle process for sodium storage is investigated to analyze the capacity growth and attenuation.

Nanoconfinement Synthesis of Ultrasmall Bismuth Oxyhalide Nanocrystals with Size‐Induced Fully Reversible Potassium‐Ion Storage and Ultrahigh Volumetric Capacity

AbstractBismuth oxyhalide (BiOX, X = Cl, Br, I) nanomaterials have attracted enormous attention because their unique layered structure and nano‐size effect endows them with fascinating physicochemical properties and wide application potential. However, synthesis of ultrasmall BiOX nanocrystals with sizes down to sub‐10 nm remains a considerable challenge and the investigation of such ultrasmall BiOX nanocrystals in alkali‐metal ion batteries have not yet been explored so far. The fabrication of ultrasmall BiOX nanocrystals with an average size of 6 nm on reduced graphene oxide by a versatile nanoconfinement strategy is reported here. The obtained ultrasmall BiOCl nanocrystals‐based monolithic composites are evaluated as free‐standing anodes for potassium‐ion batteries (PIBs) and exhibit the highest reversible capacity of 521 mAh g−1 at 0.05 A g−1 among all reported Bi‐based PIB anodes and ultrahigh volumetric capacity of 1148 mAh cm‐3, along with excellent rate capability (205 mAh g−1 at 5 A g−1 ) and extraordinary cycling stability with 94.7% capacity retention after 3000 cycles. More importantly, a fully reversible potassium storage mechanism of BiOCl (BiOCl ↔ Bi ↔ K3Bi) induced by the ultrasmall nano‐size effect is revealed for the first time by detailed characterizations, providing new fundamental insights for boosting the electrochemical performance of nanostructured materials.

Heteroatom-doped carbon anode materials for potassium-ion batteries: From mechanism, synthesis to electrochemical performance

Carbonaceous materials are attractive anode candidates for potassium-ion batteries (PIBs) because of their cost-effectiveness, high conductivity, and considerable architecture. However, these carbon materials usually exhibit slow diffusion kinetics and huge volume variation induced by the large ionic size of K-ions, resulting in poor rate capability and cycling stability. Compared to pure carbon, heteroatom (N, S, P, and O)-doped carbons can well improve potassium storage performance by optimizing K-adsorption ability and conductivity, and, hence, exhibit a significant potential in PIBs. This review in-detail summarizes the recent progress of heteroatom-doped carbon anodes based on potassium storage mechanism, design or synthesis strategies, and electrochemical performance, mainly including single-, bi-, and tri-element doped carbons. Moreover, some critical issues and possible solutions for the development of heteroatom-doped carbon in the future are discussed. This review aims at providing a deep insight into the understanding, designing, and application of heteroatom-doped carbon anodes in PIBs and is expected to make an obvious effect on the exploration of other anodes.

Exploration of CrPO4@N-doped carbon composite as advanced anode material for potassium-ion batteries

Metal phosphates are attracting great attention as anode materials for alkali-ion batteries due to their chemical stability, low working voltage, and high theoretical capacity. However, there are few reports on the application of metal phosphate as potassium-ion batteries (PIBs) anode material, and the potassium storage mechanism remains mysterious. Herein, a core–shell chromium phosphate@N-doped carbon (denoted as CrPO4@NC) composite is newly synthesized and demonstrated as conversion-type anode material for PIBs. The N-doped carbon coating layer effectively relieves the mechanical strain and improves electrical conductivity during repetitive cycling. The formed P–C bonding between CrPO4 core and nitrogen-doped carbon shell can help to maintain structural integrity and accelerate charge transfer. As a consequence, the CrPO4@NC composite exhibits a decent capacity (304.6 mAh g−1 at 50 mA g−1), good rate capability (135.1 mAh g−1 at 500 mA g−1), and superior stability (133.2 mAh g−1 at 200 mA g−1 after 100 cycles). Particularly noteworthy, we also provide experimental evidence that a conversion reaction occurs at CrPO4@NC electrode with metallic Cr and K3PO4 formed during the potassiation process. This work illustrates that CrPO4 may be a kind of anode material for applications in energy storage systems.

Nature of bismuth and antimony based phosphate nanobundles/graphene for superior potassium ion batteries

A novel architecture with bismuth (Bi) and antimony (Sb) based phosphate nanobundles well dispersed on graphene nanosheet is devised as outstanding anode for potassium-ion batteries (PIBs). The Bi and Sb based (in a ratio of 47:53) phosphate nanobundles can deliver a favourable cycling performance for 400 cycles under 500 mA g−1, obtaining a gravimetric capacity of 288 mAh g−1 with a remarkable capacity maintenance of 99%, in addition to displaying promising voltage plateaus. Meanwhile, it shows a superior performance in the full battery test, reaching an admired capacity of 372 mAh g−1 at 100 mA g−1. Nature of Bi and Sb based phosphate nanobundles during battery operation, including the lattice evolution, chemical bond cleavage, and phase transformation, is revealed. This study is notable for providing a promising anode for PIBs, and unveiling the nature of potassium storage mechanism of bismuth and antimony based phosphate, which is significant for the electrode development in PIBs.

Construction of Novel Bimetallic Oxyphosphide as Advanced Anode for Potassium Ion Hybrid Capacitor.

Potassium ion hybrid capacitors (PIHCs) have attracted considerable interest due to their low cost, competitive power/energy densities, and ultra‐long lifespan. However, the more sluggish insertion kinetics of battery‐type anodes than capacitor‐type cathodes in PIHCs seriously limits their practical application. Therefore, developing advanced anodes with high capacitor and suitable K+ intercalation is imperative and significant. A novel core–shell structure of Ni—Co oxide/Ni—Co oxyphosphide (NCOP) nanowires are designed and constructed in this study via efficient and facile strategy. Combining the merits of the core–shell structure and the massive active sites in the oxyphosphide layer, the as‐prepared NCOP composites manifest highly reversible capacitors and outstanding rate capability. Meanwhile, the insertion and conversion potassium storage mechanisms of the NCOP are successfully revealed through in situ X‐ray diffraction and density functional theory calculations, respectively. Furthermore, the PIHC was assembled with NCOP anode and borocarbonitride cathode, which displays a large energy density and high‐power density, along with an exceptional capacity retention of ≈90% over 10 000 cycles at 1.0 A g−1. This work provides the anion regulation strategy for modifying the transition metal oxide and constructing the advancing electrode materials for next‐generation energy storage and beyond.

Interfacial Engineered Vanadium Oxide Nanoheterostructures Synchronizing High-Energy and Long-Term Potassium-Ion Storage.

Potassium ion hybrid capacitors (KICs) have drawn tremendous attention for large-scale energy storage applications because of their high energy and power densities and the abundance of potassium sources. However, achieving KICs with high capacity and long lifespan remains challenging because the large size of potassium ions causes sluggish kinetics and fast structural pulverization of electrodes. Here, we report a composite anode of VO2–V2O5 nanoheterostructures captured by a 3D N-doped carbon network (VO2–V2O5/NC) that exhibits a reversible capacity of 252 mAh g–1 at 1 A g–1 over 1600 cycles and a rate performance with 108 mAh g–1 at 10 A g–1. Quantitative kinetics analyses demonstrate that such great rate capability and cyclability are enabled by the capacitive-dominated potassium storage mechanism in the interfacial engineered VO2–V2O5 nanoheterostructures. The further fabricated full KIC cell consisting of a VO2–V2O5/NC anode and an active carbon cathode delivers a high operating voltage window of 4.0 V and energy and power densities up to 154 Wh kg–1 and 10 000 W kg–1, respectively, surpassing most state-of-the-art KICs.

Ultra-stable potassium storage and hybrid mechanism of perovskite fluoride KFeF3/rGO.

Potassium-ion batteries (PIBs) are promising for large-scale energy storage due to the abundant reserves of the element potassium yet few satisfactory cathode materials have been developed due to the limitation of the large ionic radius of the potassium ion. Cubic perovskite fluorides have three-dimensional diffusion channels and a robust structure, which are favorable for ion transfer, but their poor electronic conductivity needs to be compensated. Here, we synthesized cubic KFeF3 powder by a solvothermal procedure. After the combination with reduced graphene oxide (rGO) and carbon coating, its electronic conductivity is greatly improved. In the optimal sample KFeF3/rGO-PVA-500, KFeF3 nano-particles (smaller than 50 nm) distribute on the rGO surface evenly. Owing to the special structure, KFeF3/rGO-PVA-500 provides an excellent rate performance and cycling stability. In particular, a high capacity retention of 94% is obtained after 1000 cycles at 200 mA g-1. In addition, a hybrid reaction mechanism combining mainly solid solution and partly conversion processes is revealed by employing in situ and ex situ characterization.

AMORPHOUS CUSEP2/GRAPHENE COMPOSITES AS ANODE MATERIAL FOR ADVANCED POTASSIUM-ION BATTERY

The ternary amorphous CuSeP2 was designed and prepared as the anode material of potassium ion battery for the first time, and its electrochemical performance was also investigated. After ball-milling with commercial graphene powder, it is used as the anode material for potassium ion battery with reversible specific capacity up to 300 mAh g-1, and the corresponding initial coulombic efficiency is close to 60%. What’s more, the specific capacity remains above 150 mAh g-1 after 100 cycles at 200 mA g-1. When increasing the current density to 1000 mA g-1, the CuSeP2/graphene composites still has a potassium storage specific capacity of 100 mAh g-1. Our results show that the potassium storage mechanism of the ternary CuSeP2 anode material is a typical conversion reaction and the introduction of Cu can not only buffer the volume expansion during the subsequent electrochemical reaction, but also effectively enhance the electrochemical reversibility of potassium ion.

Facile synthesis of KVPO4F/reduced graphene oxide hybrid as a high-performance cathode material for potassium-ion batteries

Potassium-ion batteries (PIBs) as a substitute for lithium-ion batteries have aroused widespread attention and have been rapidly developed. In the positive electrode materials, polyanionic compound has a high working voltage and large reversible capacity on account of its distinct framework and the strong inducing effect of the anionic group. Herein, a KVPO4F/reduced graphene oxide (KVPF/rGO) hybrid was fabricated via a simple multi-step approach as the polyanionic cathode material for PIBs. Profiting from the small size of KVPF nanoparticles and their uniform distribution in the rGO framework, the as-synthesized KVPF/rGO hybrid manifests a large discharge capacity of 103.2 mAh g−1 with an outstanding energy density of 436.5 Wh kg−1. Through rGO decoration, the hybrid also demonstrates remarkable rate and cycling properties. By employing ex-situ X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) techniques, the potassium storage mechanism of KVPF was clearly revealed. The facile preparation procedure and superior properties endow it great application prospects in large-scale energy storage.

An Adsorption-Insertion Mechanism of Potassium in Soft Carbon.

Soft carbon (SC) has become a promising anode for potassium ion batteries (PIBs) benefiting from its structural flexibility. However, the evolution of potassium storage behavior with the microstructure (the average size of the crystallites La and the average interlayer spacing a3 ) is still unclear, which hinders the understanding of the potassium storage mechanism. Herein, a series of soft carbon with different microstructures is prepared through pyrolysis of petroleum pitch. Based on the analysis of the relationship between electrochemical behavior and microstructure, an adsorption-insertion mechanism is proposed: the capacity in the voltage range of 0.45-1.1V is originated from the adsorption of potassium ions on edge-defect sites whereas the capacity below 0.45V is attributed to the insertion of potassium ions into interlayers. When La equals to 10.56Å, SCs exhibit an adsorption-controlled mechanism. However, as La increases to 120.98Å, the insertion process is dominant. With La increasing from 21.9 to 93.02Å, SCs have two mixed behaviors. The initial insertion coefficients do not change until a3 decreases to 3.46Å. These findings highlight the relation of potassium storage behavior with different microstructures and the adsorption-insertion mechanism can provide insights into the design of SC anodes for PIBs.

In-Depth Mechanism Understanding for Potassium-Ion Batteries by Electroanalytical Methods and Advanced In Situ Characterization Techniques.

The advancement of potassium ion batteries (PIBs) stimulated by the dearth of lithium resources is accelerating. Major progresses on the electrochemical properties are based on the optimization of electrode materials, electrolytes, and other components. More significantly, the prerequisites for optimizing these key compositions are in-depth and comprehensive exploration of electrochemical reaction processes, including the evolution of morphology and structure, phase transition, interface behaviors, and K+ movement, etc. As a result, the obtained K+ storage mechanism via analyzing aforementioned reaction processes sheds light on furthering practical application of PIBs. Typical electrochemical analysis methods are capable of obtaining physical and chemical characteristics. The advent of in situ electrochemical measurements enables dynamic observation and monitoring, thereby gaining extensive insights into the intricate mechanism of capacity degradation and interface kinetics. By coupling with these powerful electrochemical characterization techniques, inspiring works in PIBs will burgeon into wide realms of energy storage fields. In this review, some typical electroanalytical tests and in situ hyphenated measurements are described with the main concentration on how these techniques play a role in investigating the potassium storage mechanism for PIBs and achieving encouraging results.

Potassium storage mechanism of In2S3/C nanofibers as the anode for potassium ion batteries

The excellent electrochemical performance of indium sulfide (In2S3) in lithium ion batteries (LIBs) and sodium ion batteries (SIBs) prompted us to explore its energy storage mechanism in potassium ion batteries (PIBs). In this work, In2S3/C nanofibers are successfully synthesized by simple electrospinning and subsequent vulcanization. In K half cells, compared to commercial In2S3 electrodes, In2S3/C nanofibers as anode materials for PIBs show outstanding electrochemical performance, which can deliver reversible capacities of 397.6 (25), 366.2 (50), 335.2 (100), 307.8 (200), 260.4 (500) and 212.2 mAh g−1 (1000 mA g−1), respectively. In K full cells, In2S3/C nanofibers can also show good potassium storage performance and can light up 15 light emitting diodes (LEDs). The superb electrochemical performance of In2S3/C nanofibers is due to the in-situ composite with self-nitrogen-doped carbon matrix and the nanoization of In2S3 particles, which buffers the volume effect and improves the conductivity of the material during the potassium storage process. In addition, the mechanism of potassium storage of In2S3/C nanofibers was systematically studied by cyclic voltammetry (CV), ex-situ XRD, TEM and XPS methods. The mechanism of In2S3 for K-ion storage can be described as the conversion reaction: In2S3 + 6K+ + 6e− ⇌ In + 3K2S.

Construction of three-dimensional nitrogen doped porous carbon flake electrodes for advanced potassium-ion hybrid capacitors

It is of great significance to develop a new kind of green and environmentally friendly potassium ion energy storage device, with stable structures and large specific capacity. In this manuscript, a facile and robust way is reported to construct nitrogen doped porous carbon flake (NPCF) through NaCl template and pyrolysis method. 3D porous structures can be formed and interconnected NPCF are used as potassium ion batteries (PIBs) anode. High content of pyridinic N/pyrrolic N and enlarged interlayer distance of NPCF are obtained. Specifically, the anode delivers a high reversible capacity of 326.3 mAh g−1 at the current density of 50 mA g−1, and shows up outstanding cycle stability and represents long cycle life of 10,000 cycles at a current density of 5000 mA g−1. Moreover, the cyclic voltammetry kinetic analysis shows that the main capacitive process plays a leading role in the potassium storage mechanism. Consequently, equipped with activate carbon (AC) as cathode and NPCF as anode, the assembled potassium ion hybrid capacitors (PIHCs) achieve an energy density of 65.8 Wh kg−1 at 100 mA g−1, and maintains 30 Wh kg−1 even at a high current density of 5000 mA g−1.

Special Issue on the 40th Anniversary of University of Macau

Special Issue on the 40th Anniversary of University of Macau

Spray drying derived wrinkled pea-shaped carbon-matrixed KVP2O7 as a cathode material for potassium-ion batteries

Searching for advanced cathode materials is indispensable for the eventual practical applications of potassium-ion batteries (KIBs). Herein, we design and synthesize a carbon-matrixed potassium vanadium pyrophosphate powder (KVP2O7@C) with a wrinkled pea-shaped particle morphology via a spray drying process. As a cathode material for KIBs, this KVP2O7@C exhibits a reversible capacity of 60 mA h g−1 with two discharge plateaus at 4.1 V and 4.5 V (vs. K+/K), leading to a high energy density of 250 W h kg−1 at 0.2 C in half cells. The potassium storage mechanism of KVP2O7 is revealed by ex-situ X-ray diffraction technology as an intercalation/de-intercalation reaction during electrochemical cycling, i.e. KVP2O7 (P21/c + P1¯) ↔ KxVP2O7 (x ≈ 0.4, P1¯). A full cell constructed by coupling KVP2O7@C cathode with a hard carbon anode can achieve a high operating voltage (3.55 V), high energy density (184 W h kg−1) and superior cycling stability (89% capacity retention after 400 cycles).

Fast and Durable Potassium Storage Enabled by Constructing Stress-Dispersed Co3Se4 Nanocrystallites Anchored on Graphene Sheets.

Transition metal dichalcogenides are regarded as promising anode materials for potassium-ion batteries (PIBs) because of their high theoretical capacities. However, due to the large atomic radius of K+, the structural damage caused by the huge volume expansion upon potassiation is much more severe than that of their lithium counterparts. In this research, a stress-dispersed structure with Co3Se4 nanocrystallites orderly anchored on graphene sheets is achieved through a two-step hydrothermal treatment to alleviate the structural deterioration. The ability to reduce the contact stress by the well-dispersed Co3Se4 nanocrystallites during K+ intercalation, together with the highly conductive graphene matrix, provides a more reliable and efficient anode architecture than its two agminated counterparts. Given these advantages, the optimized electrode delivers excellent cycling stability (301.8 mA h g-1 after 500 cycles at 1 A g-1), as well as an outstanding rate capacity (203.8 mA h g-1 at 5 A g-1). Further in situ and ex situ characterizations and density functional theory calculations elucidate the potassium storage mechanism of Co3Se4 during the conversion reaction and reveal the fast electrochemical kinetics of the rationally designed electrode. This work provides a practical approach for constructing stable metal-selenide anodes with long cycle life and high-rate performance for PIBs.

Carbon‐based anode materials for potassium‐ion batteries: From material, mechanism to performance

AbstractPotassium‐ion batteries (PIBs) show great potential in the application of large‐scale energy storage devices due to the comparable high operating voltage with lithium‐ion batteries and lower cost. Carbon‐based materials are promising candidates as anodes for PIBs, for their low cost, high abundance, nontoxicity, environmental benignity, and sustainability. In this review, we will first discuss the potassium storage mechanisms of graphitic and defective carbon materials and carbon‐based composites with various compositions and microstructures to comprehensively understand the potassium storage behavior. Then, several strategies based on heteroatoms doping, unique nanostructure design, and introduction of the conductive matrix to form composites are proposed to optimize the carbon‐based materials and achieve high performance for PIBs. Finally, we conclude the existing challenges and perspectives for further development of carbon‐based materials, which is believed to promote the practical application of PIBs in the future.