Low-Cost High-Energy Potassium Cathode

Organic phosphomolybdate: a high capacity cathode for potassium ion batteries

This work firstly introduces tetra-n-butylammonium phosphomolybdate into potassium ion batteries as a high capacity cathode.

MXene-Based Dendrite-Free Potassium Metal Batteries

Potassium metal batteries are considered as attractive alternatives beyond lithium-ion batteries. However, uncontrollable dendrite growth on the potassium metal anode has restrained their practical applications. A high-performance potassium anode achieved by confining potassium metal into a titanium-deficient nitrogen-containing MXene/carbon nanotube freestanding scaffold is reported. The high electronic transport and fast potassium diffusion in this scaffold enable reduced local current density and homogeneous ionic flux during plating/stripping processes. Furthermore, as verified by theoretical calculations and experimental investigations, such "potassium-philic" MXene sheets can induce the nucleation of potassium, and guide potassium to uniformly distribute in the scaffold upon cycling. Consequently, the as-developed potassium metal anodes exhibit a dendrite-free morphology with high Coulombic efficiency and long cycle life during plating/stripping processes. Such anodes also deliver significantly improved electrochemical performances in potassium-sulfur batteries compared with bare potassium metal anodes. This work can provide a new avenue for developing potassium metal-based batteries.

Reversible Alloying of Phosphorene with Potassium and Its Stabilization Using Reduced Graphene Oxide Buffer Layers

High specific capacity materials that can store potassium (K) are essential for next-generation K-ion batteries. One such candidate material is phosphorene (the 2D allotrope of phosphorus (P)), but the potassiation capability of phosphorene has not yet been established. Here we systematically investigate the alloying of few-layer phosphorene (FLP) with K. Unlike lithium (Li) and sodium (Na), which form Li₃P and Na₃P, FLP alloys with K to form K₄P₃, which was confirmed by ex situ X-ray characterization as well as density functional theory calculations. The formation of K₄P₃ results in high specific capacity (∼1200 mAh g^-1) but poor cyclic stability (only ∼9% capacity retention in subsequent cycles). We show that this capacity fade can be successfully mitigated by the use of reduced graphene oxide (rGO) as buffer layers to suppress the pulverization of FLP. We studied the performance of rGO and single-walled carbon nanotubes (sCNTs) as buffer materials and found that rGO being a 2D material can better encapsulate and protect FLP relative to 1D sCNTs. The half-cell performance of FLP/rGO could also be successfully reproduced in a full-cell configuration, indicating the possibility of high-performance K-ion batteries that could offer a sustainable and low-cost alternative to Li-ion technology.

Layered K0.28MnO2·0.15H2O as a Cathode Material for Potassium-Ion Intercalation

Here, we present K_0.28MnO₂·0.15H₂O, which has a two-dimensional open framework, as an intercalation host for potassium ions. K_0.28MnO₂·0.15H₂O has a layered structure consisting of edge-sharing MnO₆ octahedra with a large basal spacing of ∼7.3 Å, which facilitates K⁺-ion mobility. Water molecules in the interlayers between the MnO₂ layers play an important role as a pillar to support the structure during repetitive de/potassiation cycles, as confirmed by an operando X-ray diffraction study. As a result, the large K⁺ ions readily migrate into the crystal structure, resulting in satisfactory electrochemical performance in K-cells. With the aid of the structural pillar, the K_0.28MnO₂·0.15H₂O cathode delivers a high reversible capacity of 150 mA h g^-1 over 100 cycles at a rate of 0.1 C (15 mA g^-1), with acceptable power capability up to 5 C-rates.

Rational Design of a Polyimide Cathode for a Stable and High-Rate Potassium-Ion Battery

Potassium has similar chemical characteristics compared with lithium while it is more abundant and of low cost, resulting in widespread research attention on potassium-ion batteries (PIBs). Developing organic polymer cathodes has garnered extensive attention because of their merits of environmental friendship and structure diversity, while confronted with inferior cycle stability and low rate performance. In this paper, we utilize the low-cost graphite nanosheets to stabilize polyimide (PI@G) for PIBs. Additionally, the potassium storage mechanism of PI@G was further evaluated; the highly reversible chemical bonds (C═O) of PI@G are responsible to its long-term stability. Consequently, the PI@G exhibits a maximal capacity of 142 mA h g^-1 at the current density of 100 mA g^-1 and maintains a capacity of 118 mA h g^-1 after 500 cycles (corresponding to a capacity fade of 0.034% per cycle). Moreover, the full battery based on the PI@G cathode also reveals promisingly electrochemical performance. This study may have great significance to the application prospect of the organic cathode for PIBs.

Size-, Water-, and Defect-Regulated Potassium Manganese Hexacyanoferrate with Superior Cycling Stability and Rate Capability for Low-Cost Sodium-Ion Batteries

Potassium manganese hexacyanoferrate (KMHCF) is a low-cost Prussian blue analogue (PBA) having a rigid and open framework that can accommodate large alkali ions. Herein, the synthesis of KMHCF and its application as a high-performance cathode in sodium-ion batteries (NIBs) is reported. High-quality KMHCF with low amounts of crystal water and defects and with homogeneous microstructure is obtained by controlling the nucleation and grain growth by using a high-concentration citrate solution as a precipitation medium. The obtained KMHCF exhibits superior cycling and rate performance as a NIB cathode, showing 80% capacity retention after 1000 cycles at 1 C and a high capacity of 95 mA h g^-1 at 20 C. Unlike conventional single-cation batteries, the hybrid NIB with KMHCF as cathode and Na as anode in Na-ion electrolyte displays three reversible plateaus that involve stepwise insertion/extraction of both K⁺ and Na⁺ in the PBA framework. In later cycling, the K⁺ -Na⁺ cointercalated phase is partially converted into a cubic sodium manganese hexacyanoferrate (NaMHCF) phase due to the increasing replacement of Na⁺ for K⁺ .

High-Energy and High-Power-Density Potassium Ion Batteries Using Dihydrophenazine-Based Polymer as Active Cathode Material

Polymeric aromatic amines were shown to be very promising cathodes for lithium-ion batteries. Surprisingly, these materials are scarcely used for designing post-lithium batteries. In this Letter, we investigate the application of the high-voltage poly(N-phenyl-5,10-dihydrophenazine) (p-DPPZ) cathodes for K-ion batteries. The designed batteries demonstrate an impressive specific capacity of 162 mAh g^-1 at the current density of 200 mA g^-1, operate efficiently at high current densities of 2-10 A g^-1, enabling charge and discharge within ∼1-4 min, and deliver the specific capacity of 125-145 mAh g^-1 with a retention of 96 and 79% after 100 and 1000 charge-discharge cycles, respectively. Finally, these K-ion batteries with polymeric p-DPPZ cathodes showed rather outstanding specific power of >3 × 10⁴ W kg^-1, thus paving a way to the design of ultrafast and durable high-capacity metal-ion batteries matching the increasing demand for high power and high energy density electrochemical energy storage devices.

Iodine encapsulated in mesoporous carbon enabling high-efficiency capacitive potassium-Ion storage

The development of potassium-ion batteries (KIBs) are hampered by the lack of appropriate electrode materials allowing for the reversible insertion/de-insertion of the large K-ion. Iodine, as a conversion-type cathode for rechargeable batteries, has high theoretical capacity and excellent electrochemical reversibility, making it a potential cathode material for KIBs. However, due to the defects of iodine with the poor electronic conductivity and easy dissolution in the electrolyte, an intensive quest for iodine-based KIBs enabling high-performance potassium-ion storage is still underway. In this work, a high-efficiency capacitive K-I₂ battery has been successfully achieved by constructing a nanocomposite of iodine encapsulated in mesoporous carbon (CMK-3). The as-prepared CMK-3/iodine nanocomposite exhibites excellent rate performance (89.3 mA h g^-1 at 0.5 A g^-1) and superior cycling stability, which remarkably exceeds most of reported KIBs cathode materials. Such a excellent electrochemical performance can be ascribed to the engineered structure of CMK-3/iodine hybridized electrode which can alleviate the impact of the shuttle phenomenon, improve electronic conductivity and facilitate ion diffusion. As a consequence, iodine within the conductive protecting CMK-3 can afford an extraordinary pseudo-capacitive potassium-ion storage, which sheds light on the development prospect of conversion-type electrode materials to meet urgent demand for advanced KIBs.

A 4 V Class Potassium Metal Battery with Extremely Low Overpotential

K metal anodes usually have a low Coulombic efficiency and poor safety owing to their large volume variation and high chemical reactivity. In this study, a three-dimensional K (3D-K) anode is formed by plating metallic K into hollow N-doped C polyhedrons/graphene (HNCP/G). Then a Sn-based solid-electrolyte interphase layer is conformably coated onto the surface of 3D-K to construct Sn@3D-K. Compared with the typical K-foil anode, the Sn@3D-K anode can significantly reduce the interfacial resistance, improve the K⁺ ion transport mobility, reduce parasitic reactions, and suppress the formation of K dendrites. Meanwhile, HNCP/G serves as a chemically stable, conductive host to accommodate the volume expansion/shrinkage of Sn@3D-K. Owing to these merits, the symmetric Sn@3D-K cell exhibits low voltage hysteresis (9 mV at 0.2 mA cm^-2 after 500 h; 31 mV at 1 mA cm^-2 after 100 h). When paired with a Prussian blue (PB)/graphene cathode, the K_1.56Mn[Fe(CN)₆]_1.08/G∥Sn@3D-K battery delivers an average discharge plateau of 4.02 V, an ultralow overpotential of 0.01 V, and a high specific capacity of 147.2 mAh g^-1, approaching the theoretical value of K₂MnFe(CN)₆ (156 mAh g^-1). A 4 V class K metal battery that exhibits extremely low overpotential and high specific capacity, which are the best among previously reported PB-based K batteries, is proposed.

Cycling Stability of Layered Potassium Manganese Oxide in Nonaqueous Potassium Cells

Potassium-ion batteries have emerged as an alternative to lithium-ion batteries as energy storage systems. In particular, K_xMnO₂ has attracted considerable attention as a cathode material because of its high theoretical capacity and low cost. In this study, partial substitution of Mn in P3-type K_0.5MnO₂ with divalent Ni is performed, resulting in a first discharge capacity of approximately 121 mAh (g-oxide)^-1 with 82% retention for 100 cycles. Operando synchrotron X-ray diffraction analysis reveals the occurrence of phase transition from P3 to O3 on charge and O3-P3-P'3 transition on discharge at the first cycle, where P'3 is a new distorted form of the P3 phase, accompanied by reversible Mn^4+/3+ and Ni^3+/2+ redox pairs, as evidenced by X-ray absorption spectroscopy. The reduced variation in the lattice parameters during de/potassiation for P3-K_0.5[Ni_0.1Mn_0.9]O₂ relative to P3-K_0.5MnO₂ is suggested as a possible reason for the enhanced electrochemical performance of K_0.5[Ni_0.1Mn_0.9]O₂. These results open the possibility of using inexpensive and high-capacity Mn-based cathode active materials for potassium-ion batteries.

Chemical Properties, Structural Properties, and Energy Storage Applications of Prussian Blue Analogues

Prussian blue analogues (PBAs, A₂ T[M(CN)₆ ], A = Li, K, Na; T = Fe, Co, Ni, Mn, Cu, etc.; M = Fe, Mn, Co, etc.) are a large family of materials with an open framework structure. In recent years, they have been intensively investigated as active materials in the field of energy conversion and storage, such as for alkaline-ion batteries (lithium-ion, LIBs; sodium-ion, NIB; and potassium-ion, KIBs), and as electrochemical catalysts. Nevertheless, few review papers have focused on the intrinsic chemical and structural properties of Prussian blue (PB) and its analogues. In this Review, a comprehensive insight into the PBAs in terms of their structural and chemical properties, and the effects of these properties on their materials synthesis and corresponding performance is provided.

Polypyrrole-Modified Prussian Blue Cathode Material for Potassium Ion Batteries via In Situ Polymerization Coating

Potassium-ion batteries (PIBs) have received significant attention because of the abundant potassium reserves and similar electrochemistry of potassium to that of lithium. Because of the open framework and structural controllability, Prussian blue and its analogues (PB) are considered to be competitive cathodes of PIBs. However, the intrinsic lattice defects and poor electronic conductivity of PBs induce poor cycling performance and rate capability. Herein, we propose a polypyrrole-modified Prussian blue material (KHCF@PPy) via an in situ polymerization coating method for the first time. KHCF@PPy possesses a low defect concentration and improved electronic conductivity, and the electrode was found to exhibit 88.9 mA h g^-1 discharge capacity at 50 mA g^-1, with 86.8% capacity retention after 500 cycles. At a higher current density of 1000 mA g^-1, the initial discharge capacity was 72.1 mA h g^-1, which dropped slightly to 61.8 mA h g^-1 after 500 cycles. The capacity decay rate was 0.03% per cycle. Detailed characterization showed a lack of phase transition during the charge and discharge processes and determined that K ions were not completely extracted from the monoclinic structure, possibly contributing to the excellent cycling stability. This simple surface modification method represents a promising means of mitigating issues currently associated with PB-based cathodes for PIBs.

Birnessite Nanosheet Arrays with High K Content as a High-Capacity and Ultrastable Cathode for K-Ion Batteries

Potassium-ion batteries (PIBs) are one of the emerging energy-storage technologies due to the low cost of potassium and theoretically high energy density. However, the development of PIBs is hindered by the poor K⁺ transport kinetics and the structural instability of the cathode materials during K⁺ intercalation/deintercalation. In this work, birnessite nanosheet arrays with high K content (K_0.77 MnO₂ ⋅0.23H₂ O) are prepared by "hydrothermal potassiation" as a potential cathode for PIBs, demonstrating ultrahigh reversible specific capacity of about 134 mAh g^-1 at a current density of 100 mA g^-1 , as well as great rate capability (77 mAh g^-1 at 1000 mA g^-1 ) and superior cycling stability (80.5% capacity retention after 1000 cycles at 1000 mA g^-1 ). With the introduction of adequate K⁺ ions in the interlayer, the K-birnessite exhibits highly stabilized layered structure with highly reversible structure variation upon K⁺ intercalation/deintercalation. The practical feasibility of the K-birnessite cathode in PIBs is further demonstrated by constructing full cells with a hard-soft composite carbon anode. This study highlights effective K⁺ -intercalation for birnessite to achieve superior K-storage performance for PIBs, making it a general strategy for developing high-performance cathodes in rechargeable batteries beyond lithium-ion batteries.

Red Phosphorus Potassium-Ion Battery Anodes

Phosphorus (P) possesses the highest theoretical specific capacity (865 mA h g-1) among all the elements for potassium-ion battery (PIB) anodes. Although Red P (RP) has intrinsic advantages over its allotropes, including low cost and nontoxicity, and simpler preparation, it is yet unknown to effectively activate it into a high-performance PIB anode. Here, high-performance RP PIB anodes are reported. Two important factors are found to facilitate RP react with K-ions reversibly: i) nanoscale RP particles are dispersed evenly in a conductive carbon matrix composed of multiwall carbon nanotubes and Ketjen black that provide an efficient electrical pathway and a tough scaffold. ii) The results of X-ray photoelectron spectroscopy spectrum and the electrochemical performance perhaps show that no P-C bond formation is beneficial to allow K-ions to react with RP effectively. As a result, the RP/C electrodes deliver a reversible specific capacity of ≈750 mA h g-1 and exhibit a high-rate capability (≈300 mA h g-1 at 1000 mA g-1). RP/C full cells using potassium manganese hexacyanoferrate as cathode show a long cycling life (680 cycles) at a current density of 1000 mA g-1, in addition, a pouch-type battery is built to demonstrate practical applications.

Reverse Dual-Ion Battery via a ZnCl2 Water-in-Salt Electrolyte

Dual-ion batteries are known for anion storage in the cathode coupled to cation incorporation in the anode. We flip the sequence of the anion/cation-storage chemistries of the anode and the cathode in dual-ion batteries (DIBs) by allowing the anode to take in anions and a cation-deficient cathode to host cations, thus operating as a reverse dual-ion battery (RDIB). The anion-insertion anode is a nanocomposite having ferrocene encapsulated inside a microporous carbon, and the cathode is a Zn-insertion Prussian blue, Zn₃[Fe(CN)₆]₂. This unique battery configuration benefits from the usage of a 30 m ZnCl₂ "water-in-salt" electrolyte. This electrolyte minimizes the dissolution of ferrocene; it raises the cation-insertion potential in the cathode, and it depresses the anion-insertion potential in the anode, thus widening the full cell's voltage by 0.35 V compared with a dilute ZnCl₂ electrolyte. RDIBs provide a configuration-based solution to exploit the practicality of cation-deficient cathode materials in aqueous electrolytes.

Polyanionic Compounds for Potassium-Ion Batteries

Lithium-ion batteries have the highest energy density among practical secondary batteries and are widely used for electronic devices, electric vehicles, and even stationary energy-storage systems. Along with the expansion of demand and applications, the concern about resources of lithium and cobalt is growing. Therefore, secondary batteries composed of abundant elements are required to complement lithium-ion batteries. In recent years, the development of potassium-ion batteries has attracted much attention, especially for large-scale energy storage. In order to realize potassium-ion batteries, various compounds are proposed and investigated as positive electrode materials, including layered transition-metal oxides, Prussian blue analogues, and polyanionic compounds. This article offers a review of polyanionic compounds which are typically composed of abundant elements and expected high operating potential. Furthermore, we deliver our new results to partially compensate for lack of studies and provide a future perspective.

Electrochemical Exchange Reaction Mechanism and the Role of Additive Water to Stabilize the Structure of VOPO4 ⋅2 H2 O as a Cathode Material for Potassium-Ion Batteries

VOPO₄ ⋅2 H₂ O is demonstrated as a cathode material for potassium-ion batteries in 0.6 m KPF₆ in ethylene carbonate/diethyl carbonate, and its distinct exchange reaction mechanism between potassium and crystal water is reported. In an anhydrous electrolyte, the cathode shows an initial capacity of approximately 90 mAh g^-1 , with poor capacity retention (32 % after 50 cycles). In contrast, the capacity retention dramatically improved (86 % after 100 cycles) in a wet electrolyte containing 0.1 m of additive water. VOPO₄ ⋅2 H₂ O contains two types of water (structural and crystal). Upon discharge, potassium ions are intercalated whereas the crystal water is simultaneously de-intercalated from the structure. Upon charging, a completely reverse reaction takes place in the wet electrolyte, resulting in high stability of the host structure and excellent cyclability. However, in the anhydrous electrolyte, some portion of the extracted crystal water molecules cannot be reinserted into the host structure because they are distributed over the anhydrous electrolyte. Keeping some concentration of water in the electrolyte turns out to be was the key to achieving such high reversibility. The potassium ions (90 %) and proton or hydronium ions (10 %) seem to be co-intercalated in the wet electrolyte. This work provides a general insight into the intercalation mechanism of crystal-water-containing host materials.

Highly reversible potassium-ion intercalation in tungsten disulfide

Rechargeable potassium-ion batteries (PIBs) show promise beyond Li-ion technology in large-scale electrical-energy storage due to the abundance and low cost of potassium resources. However, the intercalation of large-size K+ generally results in irreversible structural degradation and short lifespan to the hosts, representing a major obstacle. Here, we report a new electrochemical K+-intercalation host, tungsten disulfide (WS2), which can store 0.62 K+ per formula unit with a reversible capacity of 67 mA h g-1 and well-defined voltage plateaus at an intrinsically safe average operation potential of 0.72 V versus K/K+. In situ X-ray diffraction and ex situ electron microscopy revealed the underlying intercalation mechanism, a relatively small cell volume change (37.81%), and high reversibility of this new battery chemistry. Such characteristics impart WS2 with ultrahigh structural stability and a long lifespan, regardless of deep or fast charging. WS2 achieved record-high cyclability among chalcogenides up to 600 cycles with 89.2% capacity retention at 0.3C, and over 1000 cycles with 96.3% capacity retention and an extraordinary average Coulombic efficiency of 99.90% at 2.2C. This intercalation electrochemistry may open up new opportunities for the design of long-cycle-life and high-safety PIBs.

A vanadium-based metal–organic phosphate framework material K2[(VO)2(HPO4)2(C2O4)] as a cathode for potassium-ion batteries

A layered metal–organic phosphate framework K₂[(VO)₂(HPO₄)₂(C₂O₄)] is investigated as a cathode for K-ion batteries.

Enhanced K-ion kinetics in a layered cathode for potassium ion batteries

A layered cathode for K-ion storage was achieved using electrochemical ion-exchange.

Unlocking high capacities of graphite anodes for potassium-ion batteries

Graphite is considered a promising candidate as the anode for potassium-ion batteries (KIBs). Here, we demonstrate a significant improvement in performance through the ball-milling of graphite. Electrochemical techniques show reversible K-intercalation into graphitic layers, with 65% capacity retention after 100 cycles from initial capacities and extended cycling beyond 200 cycles. Such an affinity of the graphite towards storage of K-ions is explained by means of SEM and Raman analyses. Graphite ball-milling results in a gentle mechanical exfoliation of the graphene layers and simultaneous defect formation, leading to enhanced electrochemical performance.

Ball-milling of graphite results in graphene layer exfoliation and defect formation, leading to enhanced performance as a K-ion battery anode.

Potassium manganese hexacyanoferrate/graphene as a high-performance cathode for potassium-ion batteries

A potassium manganese Prussian blue/graphene nanocomposite exhibits a high capacity, excellent rate capability and long high-rate cycle life.

Polydiaminoanthraquinones with tunable redox properties as high performance organic cathodes for K-ion batteries

Polydiaminoanthraquinones with redox-active quinone-based segments linked by polyanilines were developed as advanced K storage cathodes with tunable redox properties.

Two-dimensional transition metal dichalcogenides as promising anodes for potassium ion batteries from first-principles prediction

Although K possesses a larger atomic radius, its migration barriers on TMD monolayers are much smaller than those of Li and Na ions. Among them, both VS₂ and TiS₂ are suggested to be the best electrode for KIBs.

Utilizing an autogenously protective atmosphere to synthesize a Prussian white cathode with ultrahigh capacity-retention for potassium-ion batteries

Prussian white with ultrahigh capacity-retention was synthesized by utilizing an autogenously protective atmosphere.

An Ultrafast and Highly Stable Potassium-Organic Battery

Potassium-organic batteries have a great potential for applications in the grid-scale energy storage owing to their low cost and abundant resources, although they suffer from the inferior cycle stability, fast capacity decay, and low power density. A highly reversible phase transformation of the organic cathode during potassiation/depotassiation is the key factor for the capacity retention, as revealed here. Consequently, the potassium-organic battery achieves a high power density of 9796 W kg^-1 , a remarkable energy efficiency of 89%, a long cycle stability for 1000 cycles, a superior areal capacity around 2 mA h cm^-2 , and a long-term cycling time over 8 months. Besides, the full cells also exhibit a superior rate performance and good cycle stability over 3000 cycles. This work provides new insight into the stabilization of the organic cathode, and demonstrates the enormous potential of organic cathodes for application in high-power potassium-ion batteries (PIBs), which may bring PIBs to new heights.

Rechargeable potassium-ion batteries with honeycomb-layered tellurates as high voltage cathodes and fast potassium-ion conductors

Rechargeable potassium-ion batteries have been gaining traction as not only promising low-cost alternatives to lithium-ion technology, but also as high-voltage energy storage systems. However, their development and sustainability are plagued by the lack of suitable electrode materials capable of allowing the reversible insertion of the large potassium ions. Here, exploration of the database for potassium-based materials has led us to discover potassium ion conducting layered honeycomb frameworks. They show the capability of reversible insertion of potassium ions at high voltages (~4 V for K₂Ni₂TeO₆) in stable ionic liquids based on potassium bis(trifluorosulfonyl) imide, and exhibit remarkable ionic conductivities e.g. ~0.01 mS cm⁻¹ at 298 K and ~40 mS cm^–1 at 573 K for K₂Mg₂TeO₆. In addition to enlisting fast potassium ion conductors that can be utilised as solid electrolytes, these layered honeycomb frameworks deliver the highest voltages amongst layered cathodes, becoming prime candidates for the advancement of high-energy density potassium-ion batteries.

The development of potassium-ion batteries requires cathode materials that can maintain the structural stability during cycling. Here the authors have developed honeycomb-layered tellurates K₂M₂TeO₆ that afford high ionic conductivity and reversible intercalation of large K ions at high voltages.

Enhanced electrochemical properties of SnO2-graphene-carbon nanofibers tuned by phosphoric acid for potassium storage

Potassium-ion batteries (KIBs) are considered as attractive alternatives to commercial lithium-ion batteries. However, the lack of suitable electrodes to host large K⁺ for rapid as well as reversible insertion/extraction hinders the developments of KIBs. As an attempt, the phosphoric acid doped SnO₂-graphene-carbon (P-SGC) nanofibers synthesized with a facile electrospinning method are introduced and applied as anode materials for KIBs. The P-SGC anodes present a reversible capacity of 285.9 mAh g^-1 over 60 cycles at the current density of 100 mA g^-1, and the high rate capacity of 208.53 mAh g^-1 at 1 A g^-1 as well. Emphasis is placed on enhancing the electrochemical properties of the SGC nanofibers by phosphoric acid modification through more active sites and higher electrical conductivity, accounting for improved K⁺ diffusion kinetics. Meanwhile, the coated carbon matrix and dispersive graphene buffer the structural changes and protect the active materials from destruction, leading to the good structural stability. With the presented results, these P-SGC nanofibers show attractive potential for future energy storage application of KIBs.

Boosting potassium-ion batteries by few-layered composite anodes prepared via solution-triggered one-step shear exfoliation

Earth-abundant potassium is a promising alternative to lithium in rechargeable batteries, but a pivotal limitation of potassium-ion batteries is their relatively low capacity and poor cycling stability. Here, a high-performance potassium-ion battery is achieved by employing few-layered antimony sulfide/carbon sheet composite anode fabricated via one-step high-shear exfoliation in ethanol/water solvent. Antimony sulfide with few-layered structure minimizes the volume expansion during potassiation and shortens the ion transport pathways, thus enhancing the rate capability; while carbon sheets in the composite provide electrical conductivity and maintain the electrode cycling stability by trapping the inevitable by-product, elemental sulfur. Meanwhile, the effect of the exfoliation solvent on the fabrication of two-dimensional antimony sulfide/carbon is also investigated. It is found that water facilitates the exfoliation by lower diffusion barrier along the [010] direction of antimony sulfide, while ethanol in the solvent acts as the carbon source for in situ carbonization.

Developing high-performance potassium-ion batteries remains a challenge. Here, the authors show that few-layered Sb₂S₃/carbon composite anode synthesized via simple exfoliation minimizes the volume changes during (de)intercalation of K⁺ ions with boosted rate performance and cyclability.

Self-Templating Synthesis of Cobalt Hexacyanoferrate Hollow Structures with Superior Performance for Na-Ion Hybrid Supercapacitors

Prussian blue (PB) and its analogues (PBA), especially with hollow structures, have attracted growing attention from the researchers of energy storage field. Herein, we have developed a facile self-templating method to synthesize hollow-structured cobalt hexacyanoferrate (CoHCF) with controllable morphologies by using water-soluble precursors as templates. The method is versatile and can be extended to synthesize various PB/PBA hollow structures with tunable composition and morphology. Profiting from the unique hollow structure, the CoHCF hollow prisms manifest exceptional electrochemical performance in the Na₂SO₄ aqueous electrolyte, including a high specific capacitance (284 F g^-1 at 1 A g^-1), a high rate capability, and an excellent cycling stability (92% retention after 5000 cycles). A hybrid supercapacitor device assembled with the CoHCF hollow prisms and activated carbon shows a high specific density of 47 W h kg^-1 at a specific power of 1000 W kg^-1 and stable cycling performance.