Electrolyte-Induced Morphology Evolution to Boost Potassium Storage Performance of Perylene-3,4,9,10-tetracarboxylic Dianhydride

Organic materials have attracted extensive attention for potassium-ion batteries due to their flexible structure designability and environmental friendliness. However, organic materials generally suffer from unavoidable dissolution in aprotic electrolytes, causing an unsatisfactory electrochemical performance. Herein, we designed a weakly solvating electrolyte to boost the potassium storage performance of perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA). The electrolyte induces an in situ morphology evolution and achieves a nanowire structure. The weakly dissolving capability of ethylene glycol diethyl ether-based electrolyte and unique nanowire structure effectively avoid the dissolution of PTCDA. As a result, PTCDA shows excellent cycling stability (a capacity retention of 89.1% after 2000 cycles) and good rate performance (70.3 mAh g-1 at 50C). In addition, experimental detail discloses that the sulfonyl group plays a key role in inducing morphology evolution during the charge/discharge process. This work opens up new opportunities in electrolyte design for organic electrodes and illuminates further developments of potassium-ion batteries.

Selective Lattice Doping Enables a Low-cost, High-capacity and Long-lasting Potassium Layered Oxide Cathode for Potassium and Sodium storage

Layered transition metal oxides are highly promising host materials for K ions, owing to their high theoretical capacities and appropriate operational potentials. To address the intrinsic issues of KxMnO2 cathodes and optimize their electrochemical properties, a novel P3-type oxide doped with carefully chosen cost-effective, electrochemically active and multi-functional elements is proposed, namely K0.57Cu0.1Fe0.1Mn0.8O2. Compared to the pristine K0.56MnO2, its reversible specific is increased from 104 to 135 mAh g-1. In addition, the Cu and Fe co-doping triples the capacity under high current densities, and contributes to long-term stability over 500 cycles with a capacity retention of 68%. Such endeavor holds the potential to make potassium-ion batteries particularly competitive for application in sustainable, low-cost, and large-scale energy storage devices. In addition, the cathode is also extended for sodium storage. Facilitated by the interlayer K ions that protect the layered structure from collapsing and expand the diffusion pathway for sodium ions, the cathode shows a high reversible capacity of 144 mAh g-1, fast kinetics and a long lifespan over 1000 cycles. The findings offer a novel pathway for the development of high-performance and cost-effective sodium-ion batteries.

Steering lithium and potassium storage mechanism in covalent organic frameworks by incorporating transition metal single atoms

Organic electrodes mainly consisting of C, O, H, and N are promising candidates for advanced batteries. However, the sluggish ionic and electronic conductivity limit the full play of their high theoretical capacities. Here, we integrate the idea of metal-support interaction in single-atom catalysts with π-d hybridization into the design of organic electrode materials for the applications of lithium (LIBs) and potassium-ion batteries (PIBs). Several types of transition metal single atoms (e.g., Co, Ni, Fe) with π-d hybridization are incorporated into the semiconducting covalent organic framework (COF) composite. Single atoms favorably modify the energy band structure and improve the electronic conductivity of COF. More importantly, the electronic interaction between single atoms and COF adjusts the binding affinity and modifies ion traffic between Li/K ions and the active organic units of COFs as evidenced by extensive in situ and ex situ characterizations and theoretical calculations. The corresponding LIB achieves a high reversible capacity of 1,023.0 mA h g-1 after 100 cycles at 100 mA g-1 and 501.1 mA h g-1 after 500 cycles at 1,000 mA g-1. The corresponding PIB delivers a high reversible capacity of 449.0 mA h g-1 at 100 mA g-1 after 150 cycles and stably cycled over 500 cycles at 1,000 mA g-1. This work provides a promising route to engineering organic electrodes.

Unveiling the Synergy of Architecture and Anion Vacancy on Bi2Te3-x@NPCNFs for Fast and Stable Potassium Ion Storage

Large volume strain and slow kinetics are the main obstacles to the application of high-specific-capacity alloy-type metal tellurides in potassium-ion storage systems. Herein, Bi2Te3-x nanocrystals with abundant Te-vacancies embedded in nitrogen-doped porous carbon nanofibers (Bi2Te3-x@NPCNFs) are proposed to address these challenges. In particular, a hierarchical porous fiber structure can be achieved by the polyvinylpyrrolidone-etching method and is conducive to increasing the Te-vacancy concentration. The unique porous structure together with defect engineering modulates the potassium storage mechanism of Bi2Te3, suppresses structural distortion, and accelerates K+ diffusion capacity. The meticulously designed Bi2Te3-x@NPCNFs electrode exhibits ultrastable cycling stability (over 3500 stable cycles at 1.0 A g-1 with a capacity degradation of only 0.01% per cycle) and outstanding rate capability (109.5 mAh g-1 at 2.0 A g-1). Furthermore, the systematic ex situ characterization confirms that the Bi2Te3-x@NPCNFs electrode undergoes an "intercalation-conversion-step alloying" mechanism for potassium storage. Kinetic analysis and density functional theory calculations reveal the excellent pseudocapacitive performance, attractive K+ adsorption, and fast K+ diffusion ability of the Bi2Te3-x@NPCNFs electrode, which is essential for fast potassium-ion storage. Impressively, the assembled Bi2Te3-x@NPCNFs//activated-carbon potassium-ion hybrid capacitors achieve considerable energy/power density (energy density up to 112 Wh kg-1 at a power density of 1000 W kg-1) and excellent cycling stability (1600 cycles at 10.0 A g-1), indicating their potential practical applications.

Thermodynamic Origin-Based In Situ Electrochemical Construction of Reversible p-n Heterojunctions for Optimal Stability in Potassium Ion Storage

Heterojunctions in electrode materials offer diverse improvements during the cycling process of energy storage devices, such as volume change buffering, accelerated ion/electron transfer, and better electrode structure integrity, however, obtaining optimal heterostructures with nanoscale domains remains challenging within constrained materials. A novel in situ electrochemical method is introduced to develop a reversible CuSe/PSe p-n heterojunction (CPS-h) from Cu3 PSe4 as starting material, targeting maximum stability in potassium ion storage. The CPS-h formation is thermodynamically favorable, characterized by its superior reversibility, minimized diffusion barriers, and enhanced conversion post K+ interaction. Within CPS-h, the synergy of the intrinsic electric field and P-Se bonds enhance electrode stability, effectively countering the Se shuttling phenomenon. The specific orientation between CuSe and PSe leads to a 35° lattice mismatch generates large space at the interface, promoting efficient K ion migration. The Mott-Schottky analysis validates the consistent reversibility of CPS-h, underlining its electrochemical reliability. Notably, CPS-h demonstrates a negligible 0.005% capacity reduction over 10,000 half-cell cycles and remains stable through 2,000 and 4,000 cycles in full cells and hybrid capacitors, respectively. This study emphasizes the pivotal role of electrochemical dynamics in formulating highly stable p-n heterojunctions, representing a significant advancement in potassium-ion battery (PIB) electrode engineering.

Synergistic Effect of Co-Mo Pinning in Lay-Structured Oxide Cathode for Enhancing Stability toward Potassium-Ion Batteries

Owing to the high economic efficiency and energy density potential, manganese-based layer-structured oxides have attracted great interests as cathode materials for potassium ion batteries. In order to alleviate the continuous phase transition and K+ re-embedding from Jahn-Teller distortion, the [Mn-Co-Mo]O6 octahedra are introduced into P3-K0.45 MnO2 herein to optimize the local electron structure. Based on the experimental and computational results, the octahedral center metal molybdenum in [MoO6 ] octahedra proposes a smaller ionic radius and higher oxidation state to induce second-order JTE (pseudo-JTE) distortion in the adjacent [MnO6 ] octahedra. This distortion compresses the [MnO6 ] octahedra along the c-axis, leading to an increased interlayer spacing in the K+ layer. Meanwhile, the Mn3+ /Mn4+ is balanced by [CoO6 ] octahedra and the K+ diffusion pathway is optimized as well. The proposed P3-K0.45 Mn0.9 Co0.05 Mo0.05 O2 cathode material shows an enhanced cycling stability and rate performance. It demonstrates a high capacity of 80.2 mAh g-1 at 100 mAh g-1 and 77.3 mAh g-1 at 500 mAh g-1 . Furthermore, it showcases a 2000 cycles stability with a 59.6% capacity retention. This work presents a promising solution to the challenges faced by manganese-based layered oxide cathodes and offers a deep mechanism understanding and improved electrochemical performance.

Defect-Free Prussian Blue Analogue as Zero-Strain Cathode Material for High-Energy-Density Potassium-Ion Batteries

Prussian blue analogues (PBAs) have been widely studied as cathodes for potassium-ion batteries (PIBs) due to their three-dimensional framework structure and easily adjustable composition. However, the phase transition behavior and [Fe(CN)6]4- anionic defects severely deteriorate electrochemical performances. Herein, we propose a defect-free potassium iron manganese hexacyanoferrate (K1.47Fe0.5Mn0.5[Fe(CN)6]·1.26H2O, KFMHCF-1/2) as the cathode material for PIBs. The Fe-Mn binary synergistic and defect-free effects can inhibit the cell volume change and octahedral slip during the K-ion insertion/extraction process, so that the phase transformation behavior (monoclinic ↔ cubic) is effectively inhibited, achieving a zero-strain solid solution mechanism employing Fe and Mn as dual active-sites. Thus, KFMHCF-1/2 contributes the highest initial capacity of 155.3 mAh·g-1 with an energy density of 599.5 Wh·kg-1 at 10 mA·g-1 among the reported PBA cathodes, superior rate capability, and cyclic stability over 450 cycles. The assembled K-ion full battery using K deposited on graphite (K@G) as anode also delivers high reversible specific capacity of 131.1 mAh·g-1 at 20 mA·g-1 and ultralong lifespans over 1000 cycles at 50 mA·g-1 with the lowest capacity decay rate of 0.044% per cycle. This work will promote the rapid application of high-energy-density PIBs.

GeV4 S8 : a Novel Bimetallic Sulfide for Robust and Fast Potassium Storage

Potassium-ion batteries (PIBs) have attracted much attention due to their low production cost and abundant resources. Germanium is a promising alloying-type anode with a high theoretical capacity for PIBs, yet suffering significant volume expansion and sluggish potassium-ion transport kinetics. Herein, a rational strategy is formulated to disperse Ge atoms into transition metal V-S sulfide frameworks to form a loosely packed and metallic GeV4 S8 medium. The theoretical prediction shows that GeV4 S8 is conducive to the adsorption and diffusion of K+ . The V-S frameworks provide fast ion/electron diffusion channels and also help to buffer the volume expansion during K+ insertion. In situ and ex situ characterizations manifest that KGe alloy clusters are constrained and dispersed by potassiated VS2 topological structure during discharging, and revert to the original GeV4 S8 after charging. Consequently, as a novel anode for PIBs, GeV4 S8 provides a high specific capacity of ≈400 mAh g-1 at 0.5 C, maintaining 160 mAh g-1 even at 12.5 C and ≈80% capacity after 1000 cycles at 5 C, superior to most of the state-of-the-art anode materials. The proposed strategy of combining alloy and intercalation dual-functional units is expected to open up a new way for high-capacity and high-rate anode for PIBs.

Anchoring π-d Conjugated Metal-Organic Frameworks with Dual-Active Centers on Carbon Nanotubes for Advanced Potassium-Ion Batteries

Potassium-ion batteries (PIBs) are gradually gaining attention owing to their natural abundance, excellent security, and high energy density. However, developing excellent organic cathode materials for PIBs to overcome the poor cycling stability and slow kinetics caused by the large radii of K+ ions is challenging. This study demonstrates for the first time the application of a hexaazanonaphthalene (HATN)-based 2D π-d conjugated metal-organic framework (2D c-MOF) with dual-active centers (Cu-HATNH) and integrates Cu-HATNH with carbon nanotubes (Cu-HATNH@CNT) as the cathode material for PIBs. Owing to this systematic module integration and more exposed active sites with high utilization, Cu-HATNH@CNT exhibits a high initial capacity (317.5 mA h g-1 at 0.1 A g-1 ), excellent long-term cycling stability (capacity retention of 96.8% at 5 A g-1 after 2200 cycles), and outstanding rate capacity (147.1 mA h g-1 at 10 A g-1 ). The reaction mechanism and performance are determined by combining experimental characterization and density functional theory calculations. This contribution provides new opportunities for designing high-performance 2D c-MOF cathodes with multiple active sites for PIBs.

Heteroatoms-Doped Mesoporous Carbon Nanosheets with Dual Diffusion Pathways for Highly Efficient Potassium Ion Storage

The high potassization/depotassization energy barriers and lack of efficient ion diffusion pathways are two serious obstacles for carbon-based materials to achieve satisfactory potassium ion storage performance. Herein, a facile and controllable one-step exfoliation-doping-etching strategy is proposed to construct heteroatoms (N, O, and S)-doped mesoporous few-layer carbon nanosheets (NOS-C). The mixed molten salts of KCl/K2 SO4 are innovatively used as the exfoliators, dopants, and etching agents, which enable NOS-C with expanded interlayer spacing and uniformly distributed mesopores with the adjusted electronic structure of surrounding carbon atoms, contributing efficient dual (vertical and horizontal) K-ion diffusion pathways, low potassization/depotassization energy barriers and abundant active sites. Thus, the NOS anodes achieve a high reversible capacity of 516.8 mAh g-1 at 0.05 A g-1 , superior rate capability of 202.8 mAh g-1 at 5 A g-1 and excellent long-term cyclic stability, and their practical application potential is demonstrated by the assembled potassium-ion full batteries. Moreover, a surface-interlayer synergetic K+ storage mechanism is revealed by a combined theoretical and experimental approach including in situ EIS, in situ Raman, ex situ XPS, and SEM analysis. The proposed K+ storage mechanism and unique structural engineering provide a new pathway for potassium-ion storage devices and even beyond.

Effect of Zwitterionic Additives on Solvation and Transport of Sodium and Potassium Cations in (Ethylene Oxide)10: A Molecular Dynamics Simulation Study

Sodium- (Na+) and potassium- (K+) ion batteries are cost-effective alternatives to lithium-ion (Li+) batteries due to the abundant sodium and potassium resources. Solid polymer electrolytes (SPEs) are essential for safer and more efficient Na+ and K+ batteries because they often exhibit low ionic conductivity at room temperature. While zwitterionic (ZW) materials enhance Li+ battery conductivity, their potential for Na+ and K+ transport in batteries remains unexplored. In this study, we investigated the effect of three ZW molecules (ChoPO4, i.e., 2-methacryloyloxyethyl phosphorylcholine, ImSO3, i.e., sulfobetaine ethylimidazole, and ImCO2, i.e., carboxybetaine ethylimidazole) on the dissociation of Na+ and K+ coordination with ethylene oxide (EO) chains in EO-based electrolytes through molecular dynamics simulations. Our results showed that ChoPO4 possessed the highest cation-EO10 dissociation ability, while ImSO3 exhibited the lowest. Such dissociation ability correlated with the cation-ZW molecule coordination strength: ChoPO4 and ImSO3 showed the strongest and the weakest coordination with cations. However, the cation-ZW molecule coordination could slow the cationic diffusion. The competition of these effects resulted in accelerating or decelerating cationic diffusion. Our simulated results showed that ImCO2 enhanced Na+ diffusion by 20%, while ChoPO4 and ImSO3 led to a 10% reduction. For K+, ChoPO4 reduced its diffusion by 40%, while ImCO2 and ImSO3 caused a similar decrease of 15%. These findings suggest that the ZW structure and the cationic size play an important role in the ionic dissociation effect of ZW materials.

Peapod-Like Structured B/N Co-Doped Carbon Nanotube Array Encapsulating MxPy (M = Fe, Co, and Ni) Nanoparticles for High-Rate Potassium Storage

Potassium-ion batteries (PIBs) have become the desirable alternatives for lithium-ion batteries (LIBs) originating from abundant reserves and appropriate redox potential, while the considerable radius size of K+ leading to poor reaction kinetics and huge volume expansion limits the practical application of PIBs. Hybridization of transition-metal phosphides and carbon substrates can effectively optimize the obstacles of poor conductivity, sluggish kinetics, and huge volume variation. Thus, the peapod-like structural MxPy@BNCNTs (M = Fe, Co, and Ni) composites as anode materials for PIBs were synthesized through a facile strategy. Notably, the unique architecture of B/N codoped carbon nanotube array as fast ion/electron transfer pathways effectively improves the electronic conductivity of composites. The MxPy nanoparticles (NPs) are encapsulated in BNCNTs with an amorphous carbon layer (5-10 nm), which discernibly alleviate the volume changes during potassiation/depotassiation. In conclusion, the composites show a commendable cycling performance, possessing reversible capacities of 111, 152, and 122 mA h g-1 after 1000 cycles at 1.0 A g-1 with a negligible capacity loss for FeP@BNCNT, CoP/Co2P@BNCNT, and Ni2P@BNCNT electrodes, respectively. Especially, after 1000 cycles at 2.0 A g-1, the CoP/Co2P@BNCNT electrode still possesses a capacity of 87.9 mA h g-1, demonstrating excellent rate performance and long-term life. This work may offer an innovative and viable route to construct a stable architecture for solving the issue of poor stability of TMP-based anodes at a high current density.

Elastic Restraint Induced by Carbon Coating Enhances Potassium-Ion Batteries' Performance via Phase Transition

Potassium-ion batteries (PIBs) possess great potential in the next generation of large-scale energy storage due to their abundant sources and suitable operating voltage. However, the serious volume expansion resulting from the large radius of K+ makes it difficult to insert and extract, which greatly limits the development of PIBs. Herein, tin phosphide coated with carbon (Sn4P3@C) is designed for the PIB anode material by in situ construction of robust physical barriers of carbonaceous materials to accommodate the strain induced by volume expansion. Furthermore, the unique elastic restraint induced by the carbon coating in Sn4P3@C blocks the phase transition of α-Sn to β-Sn during the process of potassiation. Meanwhile, the existence of α-Sn facilitates K+ diffusion dynamics, endowing the Sn4P3@C electrode with high reversible discharge ability, good circularity, and a low discharge plateau. Moreover, the electrode can maintain a capacity of 187 mAh g-1 over repeated 1500 cycles at 1 A g-1. This work not only explores the chemical kinetics of K+ in Sn4P3 but also provides a new idea for basic research of tin-based anode materials.

Carbon Nanofibers-Based Anodes for Potassium-Ion Battery

In recent years, with the global warming getting worse and increasing demand for energy, countries around the world are trying to develop new energy storage technologies to solve this problem. Currently, potassium-ion batteries (PIBs) have attracted tremendous attention from researchers as low-cost and high-performance energy storage devices. However, due to the huge ionic radius of K+ , PIBs face significant volume expansion during cycling, which can easily lead to the collapse of electrode structures. In addition, the poor diffusion kinetics of K+ seriously affect the electrochemical performance of the battery. Carbon nanofibers (CNFs)-based materials (including CNFs, metal/CNFs composites, chalcogenide/CNFs composites, and other CNFs-based materials) are widely used as PIBs electrode anode materials due to their three-dimensional conductive network, heteroatom doping and excellent mechanical properties. This review discusses in detail the research progress of CNFs-based materials in PIBs, including material preparation, structural design, and performance optimization. On this basis, this article explores the key issues faced by CNFs-based materials and future development directions, and proposes improvement suggestions for providing new ideas for the development of CNFs-based materials.

Robust Micro-Sized and Defect-Rich Carbon-Carbon Composites as Advanced Anodes for Potassium-Ion Batteries

Pitch-derived carbon (PC) anode features the merits of low-cost, rich edge-defect sites, and tunable crystallization degree for potassium ion batteries (PIBs). However, gaining the PC anode with both rich edge-defect sites and robust structure remains challenging. Herein, micro-sized and robust PC/expanded-graphite (EG) composites (EGC) with rich edge-defect sites are massively synthesized via melting impregnation and confined pyrolysis. The PC is in situ encapsulated in micro-sized EG skeleton with robust chemical bonds between PC and EG after thermal treatment, endowing the structural stability as micro-sized carbon-carbon composites. The confinement effect originating from EG skeleton could suppress the crystallization degree of the PC and contribute rich edge-defect sites in EGC composites. Additionally, the EG skeleton inside EGC could form continuous electronic conduction nets and establish low-tortuosity carbonaceous electrodes, facilitating rapid electron/ion migration. While applied in PIBs, the EGC anode delivers a reversible capacity that up to 338.5 mAh g-1 at 0.1 A g-1 , superior rate performance of 127.5 mAh g-1 at 5.0 A g-1 , and long-term stability with 204.8 mAh g-1 retain after 700 cycles at 1.0 A g-1 . This novel strategy highlights an interesting category of heterogeneous carbon-carbon composite materials to keep pace with the demand for the future PIBs industry.

Metal Selenides Find Plenty of Space in Architecting Advanced Sodium/Potassium Ion Batteries

The rapid evolution of smart grid system urges researchers on exploiting systems with properties of high-energy, low-cost, and eco-friendly beyond lithium-ion batteries. Under the circumstances, sodium- and potassium-ion batteries with the semblable work mechanism to commercial lithium-ion batteries, hold the merits of cost-effective and earth-abundant. As a result, it is deemed a promising candidate for large-scale energy storage devices. Exploiting appropriate active electrode materials is in the center of the spotlight for the development of batteries. Metal selenides with special structures and relatively high theoretical capacity have aroused broad interest and achieved great achievements. To push the smooth development of metal selenides and enhancement of the electrochemical performance of sodium- and potassium-ion batteries, it is vital to grasp the inherent properties and electrochemical mechanisms of these materials. Herein, the state-of-the-art development and challenges of metal selenides are summarized and discussed. Meanwhile, the corresponding electrochemical mechanism and future development directions are also highlighted.

Tetrahedral Occupied V Ions Enabling Reversible Three-Electron Redox of Cr3+ /Cr6+ in Layered Cathode Materials for Potassium-Ion Batteries

Reversible three-electron redox of Cr3+ /Cr6+ in layered cathode materials for rechargeable batteries is very attractive in layered cathode materials, which leads to high capacity and energy density for rechargeable batteries. However, the poor reversibility and Cr-ion migration make it very challenging. In this work, by introducing V ions into tetrahedral sites of layer-structured NaCrO2 , reversible three-electron redox of Cr3+ /Cr6+ is realized successfully in NaCr0.92 V0.05 O2 (NCV05) cathode for potassium-ion batteries with a cut-off voltage of 4.0 V. V ions can weaken the attraction of Cr to electrons, leading to enhanced valence change of Cr ions. On the other hand, V in tetrahedral sites can facilitate the reversible migration of Cr between octahedral and tetrahedral sites via coulombic repulsion to realize the reversible redox between Cr3+ and Cr6+ during charge and discharge processes. In addition, V ions can inhibit the phase transition from O3 phase to O'3 phase during the charge process by adjusting the crystal lattices. As a result, the NaCr0.92 V0.05 O2 cathode exhibits a high reversible capacity of 130 mAh g-1 with promising cycle stability and rate capability. The strategy opens new opportunity for developing high-capacity cathode materials for potassium-ion batteries.

Engineering contact curved interface with high-electronic-state active sites for high-performance potassium-ion batteries

Potassium-ion batteries (PIBs) have attracted ever-increasing interest due to the abundant potassium resources and low cost, which are considered a sustainable energy storage technology. However, the graphite anodes employed in PIBs suffer from low capacity and sluggish reaction kinetics caused by the large radius of potassium ions. Herein, we report nitrogen-doped, defect-rich hollow carbon nanospheres with contact curved interfaces (CCIs) on carbon nanotubes (CNTs), namely CCI-CNS/CNT, to boost both electron transfer and potassium-ion adsorption. Density functional theory calculations validate that engineering CCIs significantly augments the electronic state near the Fermi level, thus promoting electron transfer. In addition, the CCIs exhibit a pronounced affinity for potassium ions, promoting their adsorption and subsequently benefiting potassium storage. As a result, the rationally designed CCI-CNS/CNT anode shows remarkable cyclic stability and rate capability. This work provides a strategy for enhancing the potassium storage performance of carbonaceous materials through CCI engineering, which can be further extended to other battery systems.

Thermal Induced Conversion of CoFe Prussian Blue Analogs Nanocubes Wrapped by Doped Carbon Network Exhibiting Fast and Stable Potassium Ion Storage as Anode

Prussian blue analogs (PBAs) show great promise as anode materials for potassium-ion batteries (PIBs) due to their high specific capacity. However, PBAs still suffer from the drawbacks of low electronic conductivity and poor structural stability, leading to inadequate rate and cyclic performance. To address these limitations, CoFe PBA nanocubes wrapped with N/S doped carbon network (CoFe PBA@NSC) as anode for PIBs is designed by using thermal-induced in situ conversion strategy. As expected, the structural advantages of nanosized PBA cubes, such as abundant interfaces and large surface area, enable the CoFe PBA@NSC electrode to demonstrate superior rate properties (557 and 131 mAh g-1 at 0.05 and 10 A g-1 ) and low capacity degradation (0.093% per cycle over 1000 cycles at 0.5 A g-1 ). Furthermore, several ex situ characterizations revealed the K-ion storage mechanism. Fe+ and Co0 are generated during potassicization, followed by a completely reversible chemical state of iron while some cobalt monomers remained during depotassication. Additionally, the as-built potassium-ion hybrid capacitor based on CoFe PBA@NSC anode exhibits a high energy density of 118 Wh kg-1 . This work presents an alternative but promising synthesis route for Prussian blue analogs, which is significant for the advancement of PIBs and other related energy storage devices.

Oxygen Vacancy-Tailored Schottky Heterojunction Activates Interface Dipole Amplification and Carrier Inversion for High-Performance Potassium-Ion Batteries

An oxygen vacancy-tailored Schottky heterostructure composed of polyvinylpyrrolidone-assisted Bi2 Sn2 O7 (PVPBSO) nanocrystals and moderate work function graphene (mWFG, WF = 4.36 eV) is designed, which in turn intensifies the built-in voltage and interface dipole across the space charge region (SCR), leading to the inversion of majority carriers for facilitating K+ transport/diffusion behaviors. Thorough band-alignment experiments and interface simulations reveal the dynamics between deficient BSO and mWFG, and how charge redistribution within the SCR leads to carrier inversion, demonstrating the impact of different defect engineering degrees on the amplification of Schottky junctions. The ordered transport of bipolar carriers can boost electrons and K ions easily passing through the inner and outer surfaces of the heterostructure. With high activity and low resistance in electrochemical reactions, the PVPBSO/mWFG exhibits an attractive capacity of 430 mA h g-1 and a rate capability exceeding 2000 mA g-1 , accompanied by minimal polarization and efficient utilization of conversion-alloying reactions. The substantial cell capacity and high-redox plateau of PVPBSO/mWFG//PB contribute to the practical feasibility of high-energy full batteries, offering long-cycle retention and high-voltage output. This study emphasizes the direct importance of interface and junction engineering in improving the efficiency of diverse electrochemical kinetic and diffusion processes for potassium-ion batteries.

Reduced Graphene Oxide Modulated FeSe/C Anode Materials for High-Stable and Long-Life Potassium-Ion Batteries

Reduced graphene oxide (rGO) has been demonstrated to effectively enhance the potassium storage performance of transition metal selenides due to its robust mechanical properties and high conductivity. However, the impact of rGO on the electrode-electrolyte interface, a crucial factor in the electrochemical performance of potassium-ion batteries (PIBs), requires further exploration. In this study, we synthesized a seamless architecture of rGO on FeSe/C nanocrystals (FeSe/C@rGO). Comparative analysis between FeSe/C and FeSe/C@rGO reveals that the rGO layer exhibits robust adsorption energies towards EC and DEC, inducing the formation of organic-rich solid-electrolyte interphase (SEI) without damage to the structural integrity. Furthermore, incorporating rGO triggers K+ -ions into the double electrode layer (EDL), markedly improving the transport of K+ -ions. As a PIB anode, FeSe/C@rGO exhibits a reversible capacity of 332 mAh g-1 at 200 mA g-1 after 300 cycles, along with excellent long-term cycling stability, showcasing an ultralow decay rate of only 0.086 % per cycle after 1900 cycles at 1000 mA g-1 .

Hierarchically Superstructured Anisotropic Carbon Particles by Multiscale Assembly Driven by Spinodal Decomposition

Hierarchical superstructures have novel shape-dependent properties, but well-defined anisotropic carbon superstructures with controllable size, shape, and building block dimensionality have rarely been accomplished thus far. Here, a hierarchical assembly technique is presented that uses spinodal decomposition (SD) to synthesize anisotropic oblate particles of mesoporous carbon superstructure (o-MCS) with nanorod arrays by integrating block-copolymer (BCP) self-assembly and polymer-polymer interface behaviors in binary blends. The interaction of major and minor phases in binary polymer blends leads to the formation of an anisotropic oblate particle, and the BCP-rich phase enables ordered packing and unidirectional alignment of carbon nanorods. Consequently, this approach enables precise control over particles' size, shape, and over the dimensionality of their components. Exploiting this functional superstructure, o-MCS are used as an anode material in potassium-ion batteries, and achieve a notable specific capacity of 156 mA h g-1 at a current density of 2 A g-1 , and long-term stability for 3000 cycles. This work presents a significant advancement in the field of hierarchical superstructures, providing a promising strategy for the design and synthesis of anisotropic carbon materials with controlled properties, offering promising applications in energy storage and beyond.

Electrochemical Investigation of Calcium Substituted Monoclinic Li3 V2 (PO4 )3 Negative Electrode Materials for Sodium- and Potassium-Ion Batteries

Herein, the electrochemical properties and reaction mechanism of Li3-2 x Cax V2 (PO4 )3 /C (x = 0, 0.5, 1, and 1.5) as negative electrode materials for sodium-ion/potassium-ion batteries (SIBs/PIBs) are investigated. All samples undergo a mixed contribution of diffusion-controlled and pseudocapacitive-type processes in SIBs and PIBs via Trasatti Differentiation Method, while the latter increases with Ca content increase. Among them, Li3 V2 (PO4 )3 /C exhibits the highest reversible capacity in SIBs and PIBs, while Ca1.5 V2 (PO4 )3 /C shows the best rate performance with a capacity retention of 46% at 20 C in SIBs and 47% at 10 C in PIBs. This study demonstrates that the specific capacity of this type of material in SIBs and PIBs does not increase with the Ca-content as previously observed in lithium-ion system, but the stability and performance at a high C-rate can be improved by replacing Li+ with Ca2+ . This indicates that the insertion of different monovalent cations (Na+ /K+ ) can strongly influence the redox reaction and structure evolution of the host materials, due to the larger ion size of Na+ and K+ and their different kinetic properties with respect to Li+ . Furthermore, the working mechanism of both LVP/C and Ca1.5 V2 (PO4 )3 /C in SIBs are elucidated via in operando synchrotron diffraction and in operando X-ray absorption spectroscopy.

Advancements and Prospects of Graphite Anode for Potassium-Ion Batteries

Potassium-ion batteries (KIBs) have recently attracted considerable attention owing to their resource abundance, low cost and environmental friendliness. Graphite as a mature commercial anode material for lithium-ion batteries, has been proved as a promising anode candidate for KIBs by reversible forming potassium-graphite intercalation compounds. However, large volume expansion and sluggish K+ kinetics caused by the incompatibility between large radius of K+ and the small interlayer spacing of graphite, result in the poor cycle stability and rate performances, hindering its practical application. Extensive research efforts have focused on improving the potassium storage performance of graphite anodes. This review provides an overview of recent advances in addressing these challenges and optimizing the electrochemical performance of graphite anodes for KIBs. Various strategies to improve the electrochemical performance of graphite and graphitic carbon anodes, such as microcrystalline regulation, heteroatom doping, morphological adjustment, and coating modification, are discussed, while the critical issues and challenges associated with graphite anodes and the prospects for their advancement in KIBs are highlighted. The review offers valuable guidelines for rational structural design and promotes the commercial development of high-performance graphite anode materials for KIBs.

Dynamic Electronic and Ionic Transport Actuated by Cobalt-Doped MoSe2 /rGO for Superior Potassium-Ion Batteries

Molybdenum selenium (MoSe2 ) has tremendous potential in potassium-ion batteries (PIBs) due to its large interlayer distance, favorable bandgap, and high theoretical specific capacity. However, the poor conductivity and large K+ insertion/extraction in MoSe2 inevitably leads to sluggish reaction kinetics and poor structural stability. Herein, Coinduced engineering is employed to illuminate high-conductivity electron pathway and mobile ion diffusion of MoSe2 nanosheets anchored on reduced graphene oxide substrate (Co-MoSe2 /rGO). Benefiting from the activated electronic conductivity and ion diffusion kinetics, and an expanded interlayer spacing resulting from Co doping, combined with the interface coupling with highly conductive reduced graphene oxide (rGO) substrate through Mo-C bonding, the Co-MoSe2 /rGO anode demonstrates remarkable reversible capacity, superior rate capability, and stable long-term cyclability for potassium storage, as well as superior energy density and high power density for potassium-ion capacitors. Systematic performance measurement, dynamic analysis, in-situ/ex-situ measurements, and density functional theory (DFT) calculations elucidate the performance-enhancing mechanism of Co-MoSe2 /rGO in view of the electronic and ionic transport kinetics. This work offers deep atomic insights into the fundamental factors of electrodes for potassium-ion batteries/capacitors with superior electrochemical performance.

Bismuth Telluride Nanoplates Hierarchically Confined by Graphene and N-Doped C as Conversion-Alloying Anode Materials for Potassium-Ion Batteries

Potassium-ion batteries (PIBs) have broad application prospects in the field of electric energy storage systems because of its abundant K reserves, and similar "rocking chair" operating principle as lithium-ion batteries (LIBs). Aiming to the large volume expansion and sluggish dynamic behavior of anode materials for storing large sized K-ion, bismuth telluride (Bi2 Te3 ) nanoplates hierarchically encapsulated by reduced graphene oxide (rGO), and nitrogen-doped carbon (NC) are constructed as anodes for PIBs. The resultant Bi2 Te3 @rGO@NC architecture features robust chemical bond of Bi─O─C, tightly physicochemical confinement effect, typical conductor property, and enhanced K-ion adsorption ability, thereby producing superior electrochemical kinetics and outstanding morphological and structural stability. It is visually elucidated via high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) that conversion-alloying dual-mechanism plays a significant role in K-ion storage, allowing 12 K-ion transport per formular unit employing Bi as redox site. Thus, the high first reversible specific capacity of 322.70 mAh g-1 at 50 mA g-1 , great rate capability and cyclic stability can be achieved for Bi2 Te3 @rGO@NC. This work lays the foundation for an in-depth understanding of conversion-alloying mechanism in potassium-ion storage.

Entropy-Stabilized Layered K0.6Ni0.05Fe0.05Mg0.05Ti0.05Mn0.725O2 as a High-Rate and Stable Cathode for Potassium-Ion Batteries

Mn-based layered oxides have been considered the most promising cathode candidates for cost-effective potassium-ion batteries (PIBs). Herein, equiatomic constituents of Ni, Fe, Mg, and Ti have been introduced into the transition metal layers of Mn-based layered oxide to design a high-entropy K0.6Ni0.05Fe0.05Mg0.05Ti0.05Mn0.0725O2 (HE-KMO, S = 1.17R). Consequently, the experimental results manifest that the layered structure of HE-KMO is more stable than conventional low-entropy K0.6MnO2 (LE-KMO, S = 0.66R) during successive cycling and even upon exposure to moisture. Diffraction and electrochemical measurements reveal that HE-KMO undergoes a solid-solution mechanism, contrary to the multistage phase transition processes typically exemplified in K0.6MnO2. Benefiting from the stabilized high-entropy layered framework and the solid-solution K+ storage mechanism, the entropy-stabilized HE-KMO not only demonstrates exceptional rate capability but also shows excellent cyclic stability. Notably, a capacity retention ratio of 86% after 3000 cycles can still be sustained at a remarkable current density of 5000 mA g-1.

Control of Gradient Concentration Prussian White Cathodes for High-Performance Potassium-Ion Batteries

Owing to their abundant resources and low cost, potassium-ion batteries (PIBs) have become a promising alternative to lithium-ion batteries (LIBs). However, the larger ionic radius and higher mass of K+ propose a challenging issue for finding suitable cathode materials. Prussian whites (PWs) have a rigid open framework and affordable synthesis method, but they suffer quick capacity fade due to lattice volume change and structural instability during K+ insertion/extraction. Here, we prepared controllable gradient concentration KxFeaNibMn1-a-b[Fe(CN)6]y·zH2O particles via a facile coprecipitation process, demonstrating high-performance potassium-ion storage. The high-Mn content in the interior can minimize capacity loss caused by electrochemically inert Ni and achieve a high reversible capacity; meanwhile, the high-FeNi content in the exterior can alleviate the volume change of the core material upon cycling, thus enhancing structural stability. Taking the above synergistic effect, the controllable gradient concentration PWs deliver a high reversible capacity of 109.8 mAh g-1 at 100 mA g-1 and good capacity retention of 77.8% after 200 cycles. The gradient concentration PWs can retain structural integrity and stability during long-term cycling. This work provides a prospective strategy to fabricate PWs with stable structure and excellent electrochemical performance for developing high-performance PIBs.

Investigating the Superior Performance of Hard Carbon Anodes in Sodium-Ion Compared With Lithium- and Potassium-Ion Batteries

Emerging sodium-ion batteries (NIBs) and potassium-ion batteries (KIBs) show promise in complementing lithium-ion battery (LIB) technology and diversifying the battery market. Hard carbon is a potential anode candidate for LIBs, NIBs, and KIBs due to its high capacity, sustainability, wide availability, and stable physicochemical properties. Herein, a series of hard carbons is synthesized by hydrothermal carbonization and subsequent pyrolysis at different temperatures to finely tune their structural properties. When tested as anodes, the hard carbons exhibit differing ion-storage trends for Li, Na, and K, with NIBs achieving the highest reversible capacity. Extensive materials and electrochemical characterizations are carried out to study the correlation of structural features with electrochemical performance and to explain the specific mechanisms of alkali-ion storage in hard carbons. In addition, the best-performing hard carbon is tested against a sodium cathode Na3 V2 (PO4 )3 in a Na-ion pouch cell, displaying a high power density of 2172 W kg-1 at an energy density of 181.5 Wh kg-1 (based on the total weight of active materials in both anode and cathode). The Na-ion pouch cell also shows stable ultralong-term cycling (9000 h or 5142 cycles) and demonstrates the promising potential of such materials as sustainable, scalable anodes for beyond Li-batteries.

2D-Layer-Structure Bi to Quasi-1D-Structure NiBi3 : Structural Dimensionality Reduction to Superior Sodium and Potassium Ion Storage

Layer-structured bismuth (Bi) is an attractive anode for Na-ion and K-ion batteries due to its large volumetric capacity and suitable redox potentials. However, the cycling stability and rate capability of the Bi anode are restricted by the large volume expansion and sluggish Na/K-storage kinetics. Herein, a structural dimensionality reduction strategy is proposed and developed by converting 2D-layer-structured Bi into a quasi-1D structured NiBi3 with enhanced reaction kinetics and reversibility to realize high-rate and stable cycling performance for Na/K-ion storage. As a proof of concept, the quasi-1D intermetallic NiBi3 with low formation energy, metallic conductivity, and 3D Na/K-ion diffusion pathways delivers outstanding capacity retention of 94.1% (332 mAh g-1 ) after 15 000 cycles for Na-ion storage, and high initial coulombic efficiency of 93.4% with improved capacity retention for K-ion storage. Moreover, investigations on the highly reversible Na/K-storage reaction mechanisms and cycling-driven morphology reconstruction further reveal the origins of the high reversibility and the accommodation to volume expansion. The finding of this work provides a new strategy for high-performance anode design by structural dimensionality manipulation and cycling-driven morphology reconstruction.

Oxygen Defect Engineering toward Zero-Strain V2O2.8@Porous Reticular Carbon for Ultrastable Potassium Storage

Potassium-ion batteries (KIBs) are promising candidates for large-scale energy storage devices due to their high energy density and low cost. However, the large potassium-ion radius leads to its sluggish diffusion kinetics during intercalation into the lattice of the electrode material, resulting in electrode pulverization and poor cycle stability. Herein, vanadium trioxide anodes with different oxygen vacancy concentrations (V2O2.9, V2O2.8, and V2O2.7 determined by the neutron diffraction) are developed for KIBs. The V2O2.8 anode is optimal and exhibits excellent potassium storage performance due to the realization of expanded interlayer spacing and efficient ion/electron transport. In situ X-ray diffraction indicates that V2O2.8 is a zero-strain anode with a volumetric strain of 0.28% during the charge/discharge process. Density functional theory calculations show that the impacts of oxygen defects are embodied in reducing the band gap, increasing electron transfer ability, and lowering the diffusion energy barriers for potassium ions. As a result, the electrode of nanosized V2O2.8 embedded in porous reticular carbon (V2O2.8@PRC) delivers high reversible capacity (362 mAh g-1 at 0.05 A g-1), ultralong cycling stability (98.8% capacity retention after 3000 cycles at 2 A g-1), and superior pouch-type full-cell performance (221 mAh g-1 at 0.05 A g-1). This work presents an oxygen defect engineering strategy for ultrastable KIBs.

Recent Advances and Challenges in Ti-Based Oxide Anodes for Superior Potassium Storage

Developing high-performance anodes is one of the most effective ways to improve the energy storage performances of potassium-ion batteries (PIBs). Among them, Ti-based oxides, including TiO2, K2Ti6O13, K2Ti4O9, K2Ti8O17, Li4Ti5O12, etc., as the intrinsic structural advantages, are of great interest for applications in PIBs. Despite numerous merits of Ti-based oxide anodes, such as fantastic chemical and thermal stability, a rich reserve of raw materials, non-toxic and environmentally friendly properties, etc., their poor electrical conductivity limits the energy storage applications in PIBs, which is the key challenge for these anodes. Although various modification projects are effectively used to improve their energy storage performances, there are still some related issues and problems that need to be addressed and solved. This review provides a comprehensive summary on the latest research progress of Ti-based oxide anodes for the application in PIBs. Besides the major impactful work and various performance improvement strategies, such as structural regulation, carbon modification, element doping, etc., some promising research directions, including effects of electrolytes and binders, MXene-derived TiO2-based anodes and application as a modifier, are outlined in this review. In addition, noteworthy research perspectives and future development challenges for Ti-based oxide anodes in PIBs are also proposed.

Manipulating Molecular Structure to Trigger Ultrafast and Long-Life Potassium Storage of Fe0.4 Ni0.6 S Solid Solution

Currently, the main obstacle to the widespread utilization of metal chalcogenides (MSx ) as anode for potassium-ion batteries (PIBs) is their poor rate capability and inferior cycling stability as a result of the undesirable electrical conductivity and severe pulverization of the nanostructure during large K-ions intercalation-extraction processes. Herein, an ultrafast and long-life potassium storage of metal chalcogenide is rationally demonstrated by employing Fe0.4 Ni0.6 S solid-solution (FNS/C) through molecular structure engineering. Benefiting from improved electroactivity and intense interactions within the unique solid solution phase, the electrical conductivity and structure durability of Fe0.4 Ni0.6 S are vastly improved. As anticipated, the FNS/C electrode delivers superior rate properties (538.7 and 210.5 mAh g-1 at 0.1 and 10 A g-1 , respectively) and long-term cycle stability (180.8 mAh g-1 at 5 A g-1 after 2000 cycles with a capacity decay of 0.011% per cycle). Moreover, the potassium storage mechanisms of Fe0.4 Ni0.6 S solid solution are comprehensively revealed by several in situ characterizations and theoretical calculations. This innovative molecular structure engineering strategy opens avenues to achieve high-quality metal chalcogenides for future advanced PIBs.

Unlocking Deep and Fast Potassium-Ion Storage through Phosphorus Heterostructure

Potassium-ion battery represents a promising alternative of conventional lithium-ion batteries in sustainable and grid-scale energy storage. Among various anode materials, elemental phosphorus (P) has been actively pursued owing to the ideal natural abundance, theoretical capacity, and electrode potential. However, the sluggish redox kinetics of elemental P has hindered fast and deep potassiation process toward the formation of final potassiation product (K3 P), which leads to inferior reversible capacity and rate performance. Here, it is shown that rational design on black/red P heterostructure can significantly improve K-ion adsorption, injection and immigration, thus for the first time unlocking K3 P as the reversible potassiation product for elemental P anodes. Density functional theory calculations reveal the fast adsorption and diffusion kinetics of K-ion at the heterostructure interface, which delivers a highly reversible specific capacity of 923 mAh g-1 at 0.05 A g-1 , excellent rate capability (335 mAh g-1 at 1 A g-1 ), and cycling performance (83.3% capacity retention at 0.8 A g-1 after 300 cycles). These results can unlock other sluggish and irreversible battery chemistries toward sustainable and high-performing energy storage.

Pseudocapacitive Potassium-Ion Intercalation Enabled by Topologically Defective Soft Carbon toward High-Rate, Large-Areal-Capacity, and Low-Temperature Potassium-Ion Batteries

Carbonaceous materials are widely investigated as anodes for potassium-ion batteries (PIBs). However, the inferior rate capability, low areal capacity, and limited working temperature caused by sluggish K-ions diffusion kinetics are still primary challenges for carbon-based anodes. Herein, a simple temperature-programmed co-pyrolysis strategy is proposed for the efficient synthesis of topologically defective soft carbon (TDSC) based on inexpensive pitch and melamine. The skeletons of TDSC are optimized with shortened graphite-like microcrystals, enlarged interlayer spacing, and abundant topological defects (e.g., pentagons, heptagons, and octagons), which endow TDSC with fast pseudocapacitive K-ion intercalation behavior. Meanwhile, micrometer-sized structure can reduce the electrolyte degradation over particle surface and avoid unnecessary voids, ensuring a high initial Coulombic efficiency as well as high energy density. These synergistic structural advantages contribute to excellent rate capability (116 mA h g-1 at 20 C), impressive areal capacity (1.83 mA h cm-2 with a mass loading of 8.32 mg cm-2 ), long-term cycling stability (capacity retention of 91.8% after 1200 h cycling), and low working temperature (-10 °C) of TDSC anodes, demonstrating great potential for the practical application of PIBs.

Ultrastable Graphite-Potassium Anode through Binder Chemistry

Graphite with abundant reserves has attracted enormous research interest as an anode of potassium-ion batteries (PIBs) owing to its high plateau capacity of 279 mAh g-1 at ≈0.2 V in conventional carbonate electrolytes. Unfortunately, it suffers from fast capacity decay during K+ storage. Herein, an ultrastable graphite-potassium anode is developed through binder chemistry. Polyvinyl alcohol (PVA) is utilized as a water-soluble binder to generate a uniform and robust KF-rich SEI film on the graphite surface, which can not only inhibit the electrolyte decomposition, but also withstand large volume expansion during K+ -insertion. Compared to the PVDF as binder, PVA-based graphite anode can operate for over 2000 cycles (running time of 406 days at C/3) with 97% capacity retention in KPF6 -based electrolytes. The initial Coulombic efficiency (ICE) of graphite anode is as high as 81.6% using PVA as the binder, higher than that of PVDF (40.1%). Benefiting from the strong adhesion ability of PVA, a graphite||fluorophosphate K-ion full battery is further built through 3D printing, which achieves a record-high areal energy of 8.9 mWh cm-2 at a total mass loading of 38 mg cm-2 . These results demonstrate the important role of binder in developing high-performance PIBs.

Vanadium Nitride Nanoparticles Grown on Carbon Fiber Cloth as an Advanced Binder-Free Anode for the Storage of Sodium and Potassium Ions

The escalating demand for sustainable and high-performance energy storage systems has led to the exploration of alternative battery technologies for lithium-ion batteries. Sodium-ion batteries (SIBs) and potassium-ion batteries (PIBs) have emerged as promising candidates because of their abundant Na/K resources, inexpensive costs, and similar chemistries to lithium-ion batteries. However, inherent challenges, such as large ionic radii, sluggish kinetics, and serious volume expansion, necessitate the development of robust and efficient anode materials for SIBs and PIBs. Vanadium nitride has attracted increasing attention as a viable anode due to its high electronic conductivity and potential capacity. In this study, we report on a flexible electrode for SIBs and PIBs that creates binder-free anodes by synthesizing vanadium nitride nanoparticles grown directly on carbon fiber cloths (VN/CFC). The unique architecture and binder-free nature of this anode ensure a robust electrode-electrolyte interface and enhance its electron/ion transport kinetics. The results demonstrate that the material exhibits an outstanding specific discharge capacity of 227 mAh g-1 after undergoing 1000 cycles at a current density of 2 A g-1 for SIBs. An electrochemical analysis indicated that the excellent performance of the material is attributed to the bind-free structure of carbon fiber cloth and the fast kinetics of surface pseudo-capacitive contribution. Furthermore, the material continues to demonstrate an impressive performance, even for PIBs, with a specific discharge capacity of 125 mAh g-1 after 1000 cycles at a current density of 1 A g-1. This study provides a new perspective for designing and developing advanced binder-free anodes for the storage of sodium and potassium ions, paving the way for high-performance energy storage applications.

Short-Range Graphitic Nanodomains in Hypocrystalline Carbon Nanotubes Realize Fast Potassium Ion Migration and Multidirection Stress Release

Defect-rich carbon materials are considered as one of the most promising anodes for potassium-ion batteries due to their enormous adsorption sites of K+ , while the realization of both rate capability and cycling stability is still greatly limited by unstable electrochemical kinetics and inevitable structure degradation. Herein, an Fe3+ -induced hydrothermal-pyrolysis strategy is reported to construct well-tailored hybrid carbon nanotubes network architecture (PP-CNT), in which the short-range graphitic nanodomains are in-situ localized in the pea pod shape hypocrystalline carbon. The N,O codoped hypocrystalline carbon region contributes to abundant defect sites for potassium ion storage, ensuring high reversible capacity. Meanwhile, the short-range graphitic nanodomains with expanded interlayer spacing facilitate stable K+ migration and fast electron transfer. Furthermore, the finite element analysis confirms the volume expansion caused by K+ intercalation can be availably buffered due to the multidirection stress release effect of the unique porous pea pod shape, endowing carbon nanotubes with superior structural integrity. Consequently, the PP-CNT anode exhibits superior potassium-storage performance, including high reversible capacity, exceptional rate capability, and ultralong cycling stability. This work opens a new avenue for the fabrication of advanced carbon materials for achieving durable and fast potassium storage.

Octahedral/Tetrahedral Vacancies in Fe3 O4 as K-Storage Sites: A Case of Anti-Spinel Structure Material Serving as High-Performance Anodes for PIBs

Potassium-ion batteries (PIBs) have attracted more and more attention as viable alternatives to lithium-ion batteries (LIBs) due to the deficiency and uneven distribution of lithium resources. However, it is shown that potassium storage in some compounds through reaction or intercalation mechanisms cannot effectively improve the capacity and stability of anodes for PIBs. The unique anti-spinel structure of magnetite (Fe3 O4 ) is densely packed with thirty-two O atoms to form a face-centered cubic (fcc) unit cell with tetrahedral/octahedral vacancies in the O-closed packing structure, which can serve as K+ storage sites according to the density functional theory (DFT) calculation results. In this work, carbon-coated Fe3 O4 @C nanoparticles are prepared as high-performance anodes for PIBs, which exhibit high reversible capacity (638 mAh g-1 at 0.05 A g-1 ) and hyper stable cycling performance at ultrahigh current density (150 mAh g-1 after 9000 cycles at 10 A g-1 ). In situ XRD, ex-situ Fe K-edge XAFS, and DFT calculations confirm the storage of K+ in tetrahedral/octahedral vacancies.

Achieving Stable and Ultrafast Potassium Storage of Antimony Anode via Dual Confinement of MXene@Carbon Framework

Antimony-based anode materials are recognized for their high potassium storage capacities and appropriate operating potentials. However, the large volume expansion of Sb during the potassiation/depotassiation process, which results in a quick capacity decay, severely limits its practical application in potassium-ion batteries (PIBs). Here, a carbon-coated Sb/MXene heterostructure composite (CSM) is synthesized by adsorption of Sb3+ on MXene nanosheets via Sb-O-Ti bonds followed by carbothermic reduction to construct dual-confined MXene@carbon conductive framework capable of withstanding high volume expansion of Sb and conducive to enabling accelerated electron transfer kinetics. The CSM composite, particularly CSM-700, when configured as an anode for PIBs, realized high capacity (484.4 mAh g-1 at 0.1 A g-1 ), an ultra-stable cycling performance with a high reversible capacity of 435.9 mAh g-1 at 0.1 A g-1 after 100 cycles corresponding to a capacity retention rate of 90.0%, and superior rate performance of 323.0 mAh g-1 at 1 A g-1 . The proposed strategy offers a simple route to construct high-performance Sb-based anodes for advanced PIBs.

Organic-Inorganic Hybrid Interfaces Enable the Preparation of Nitrogen-Doped Hollow Carbon Nanospheres as High-Performance Anodes for Lithium and Potassium-Ion Batteries

An abundant hollow nanostructure is crucial for fast Li⁺ and K⁺ diffusion paths and sufficient electrolyte penetration, which creates a highly conductive network for ionic and electronic transport. In this study, we successfully developed a molecular-bridge-linked, organic-inorganic hybrid interface that enables the preparation of in situ nitrogen-doped hollow carbon nanospheres. Moreover, the prepared HCNSs, with high nitrogen content of up to 10.4%, feature homogeneous and regular morphologies. The resulting HCNSs exhibit excellent lithium and potassium storage properties when used as electrode materials. Specifically, the HCNS-800 electrode demonstrates a stable reversible discharge capacity of 642 mA h g^-1 at 1000 mA g^-1 after 500 cycles for LIBs. Similarly, the electrode maintains a discharge capacity of 205 mA h g^-1 at 100 mA g^-1 after 500 cycles for KIBs. Moreover, when coupled with a high-mass-loading LiFePO₄ cathode to design full cells, the HCNS-800‖LiFePO₄ cells provide a specific discharge capacity of 139 mA h g^-1 at 0.1 C. These results indicate that the HCNS electrode has promising potential for use in high-energy and environmentally sustainable lithium-based and potassium-based batteries.

Uniformly Dispersed Sb-Nanodot Constructed by In Situ Confined Polymerization of Ionic Liquids for High-Performance Potassium-Ion Batteries

Antimony (Sb) is a potential candidate anode for potassium-ion batteries (PIBs) owing to its high theoretical capacity. However; in the process of potassium alloying reaction; the huge volume expansion (about 407%) leads to pulverization of active substance as well as loss of electrical contact resulting in rapidly declining capacity. Herein; uniformly dispersed Sb-Nanodot in carbon frameworks (Sb-ND@C) were constructed by in situ confined polymerization of ionic liquids. Attributed to the uniformly dispersed Sb-ND and confinement effect of carbon frameworks; as anode for PIBs; Sb-ND@C delivered a superior rate capability (320.1 mA h g^-1 at 5 A g^-1) and an outstanding cycling stability (486 mA h g^-1 after 1000 cycles; achieving 89.8% capacity retention). This work offers a facile route to prepare highly dispersed metal-Nanodot via the in situ polymerization of ionic liquid for high-performance metal-ion batteries.

Rechargeable Potassium-Ion Full Cells Operating at -40 °C

Potassium-ion batteries (PIBs) are promising for cryogenic energy storage. However, current researches on low-temperature PIBs are limited to half cells utilizing potassium metal as an anode, and realizing rechargeable full cells is challenged by lacking viable anode materials and compatible electrolytes. Herein, a hard carbon (HC)-based low-temperature potassium-ion full cell is successfully fabricated for the first time. Experimental evidence and theoretical analysis revealed that potassium storage behaviors of HC anodes in the matched low-temperature electrolyte involve defect adsorption, interlayer co-intercalation, and micropore filling. Notably, these unique potassiation processes exhibited low interfacial resistances and small reaction activation energies, enabling an excellent cycling performance of HC with a capacity of 172 mAh g-1 at -40 °C (68% of its room-temperature capacity). Consequently, the HC-based full cells demonstrated impressive rechargeability and high energy density above 100 Wh kg-1cathode at -40 °C, representing a significant advancement in the development of PIBs.

Confined Bismuth-Organic Framework Anode for High-Energy Potassium-Ion Batteries

Metal-organic frameworks (MOFs) with inherent porosity, controllable structures, and designable components are recognized as attractive platforms for designing advanced electrodes of high-performance potassium-ion batteries (PIBs). However, the poor electrical conductivity and low theoretical capacity of many MOFs lead to inferior electrochemical performance. Herein, for the first time, a confined bismuth-organic framework with 3D porous matrix structure (Bi-MOF) as anode for PIBs via a facile wet-chemical approach is reported. Such a porous structure design with double active centers can simultaneously ensure the structure integrity and efficient charge transport to enable high-capacity electrode with super cycling life. As a result, the Bi-MOF for PIBs exhibits high reversible capacity (419 mAh g^-1 at 0.1 A g^-1 ), outstanding cycling stability (315 mAh g^-1 at 0.5 A g^-1 after 1200 cycles), and excellent full battery performance (a high energy density of 183 Wh kg^-1 is achieved, outperforming all reported metal-based anodes for PIBs). Moreover, the K⁺ storage mechanisms of the Bi-MOF are further unveiled by in situ Raman, ex situ high-resolution transmission electron microscopy, and ex situ Fourier-transform infrared spectroscopy. This ingenious electrode design may provide further guidance for the application of MOF in energy storage systems.

Unveiling the Nature of Ultrastable Potassium Storage in Bi0.48Sb1.52Se3 Composite

The conversion and alloying-type anodes for potassium-ion batteries (PIBs) have drawn attention. However, it is still a challenge to relieve the huge volume expansion/electrode pulverization. Herein, we synthesized a composite material comprising Bi_0.48Sb_1.52Se₃ nanoparticles uniformly dispersed in carbon nanofibers (Bi_0.48Sb_1.52Se₃@C). Benefiting from the synergistic effects of the high electronic conductivity of Bi_0.48Sb_1.52Se₃ and the mechanical confinement of the carbon fiber that buffers the large chemomechanical stress, the Bi_0.48Sb_1.52Se₃@C//K half cells deliver a high reversible capacity (491.4 mAh g^-1, 100 cycles at 100 mA g^-1) and an extraordinary cyclability (80% capacity retention, 1000 cycles at 1000 mA g^-1). Furthermore, the Bi_0.48Sb_1.52Se₃@C-based PIB full cells achieve a high energy density of 230 Wh kg^-1. In situ transmission electron microscopy (TEM) reveals an intercalation, conversion, and alloying three-step reaction mechanism and a reversible amorphous transient phase. More impressively, the nanofiber electrode can almost return to its original diameter after the potassiation and depotassiation reaction, indicating a highly reversible volume change process, which is distinct from the other conversion type electrodes. This work reveals the stable potassium storage mechanisms of Bi_0.48Sb_1.52Se₃@C composite material, which provides an effective strategy to enable conversion/alloying-type anodes for high performance PIBs for energy storage applications.

Enhanced Performance of KVPO4F0.5O0.5 in Potassium Batteries by Carbon Coating Interfaces

Potassium vanadium oxyfluoride phosphate of composition KVPO₄F_0.5O_0.5 was modified by a carbon coating to enhance its electrochemical performance. Two distinct methods were used, first, chemical vapor deposition (CVD) using acetylene gas as a carbon precursor and second, an aqueous route using an abundant, cheap, and green precursor (chitosan) followed by a pyrolysis step. The formation of a 5 to 7 nm-thick carbon coating was confirmed by transmission electron microscopy and it was found to be more homogeneous in the case of CVD using acetylene gas. Indeed, an increase of the specific surface area of one order of magnitude, low content of C sp², and residual oxygen surface functionalities were observed when the coating was obtained using chitosan. Pristine and carbon-coated materials were compared as positive electrode materials in potassium half-cells cycled at a C/5 (C = 26.5 mA g^-1) rate within a potential window of 3 to 5 V vs K⁺/K. The formation by CVD of a uniform carbon coating with the limited presence of surface functions was shown to improve the initial coulombic efficiency up to 87% for KVPFO₄F_0.5O_0.5-C₂H₂ and to mitigate electrolyte decomposition. Thus, performance at high C-rates such as 10 C was significantly improved, with ∼50% of the initial capacity maintained after 10 cycles, whereas a fast capacity loss is observed for the pristine material.

Pseudohexagonal Nb2O5 Anodes for Fast-Charging Potassium-Ion Batteries

High-rate batteries will play a vital role in future energy storage systems, yet while good progress is being made in the development of high-rate lithium-ion batteries, there is less progress with post-lithium-ion chemistry. In this study, we demonstrate that pseudohexagonal Nb₂O₅(TT-Nb₂O₅) can offer a high specific capacity (179 mAh g^-1 ∼ 0.3C), good lifetime, and an excellent rate performance (72 mAh g^-1 at ∼15C) in potassium-ion batteries (KIBs), when it is composited with a highly conductive carbon framework; this is the first reported investigation of TT-Nb₂O₅ for KIBs. Specifically, multiwalled carbon nanotubes are strongly tethered to Nb₂O₅ via glucose-derived carbon (Nb₂O₅@CNT) by a one-step hydrothermal method, which results in highly conductive and porous needle-like structures. This work therefore offers a route for the scalable production of a viable KIB anode material and hence improves the feasibility of fast-charging KIBs for future applications.

Regulating the Wettability of Hard Carbon through Open Mesochannels for Enhanced K+ Storage

Hard carbons are deemed as promising anode materials for high-performance potassium-ion battery, but their commercialization is still hindered by the insufficient K⁺ transfer kinetics and poor potassiophilicity. Herein, these issues are addressed by improving the wettability of hard carbon, which can be achieved by the introduction of open mesochannels. A series of such hollow mesoporous carbon capsules with different dimensions are synthesized, which exhibit markedly enhanced wettability with electrolyte compared to the microporous counterparts. Various characterizations confirm its effects on promoting the kinetics and potassiophilicity of as-synthesized carbons, which can be additionally improved by S-doping. As a result, the 2D mesoporous carbon anode exhibits excellent rate capability (122.2 mAh g^-1 at 4 A g^-1 ), high reversible capacity (396.6 mAh g^-1 at 0.1 A g^-1 after 200 cycles), and outstanding cycling stability (197.0 mAh g^-1 at 2 A g^-1 after 1400 cycles). In addition, the hollow mesoporous architecture can effectively buffer the volume expansion and thus stabilize the carbon anodes, as visualized by in situ transmission electron microscopy. This work provides new insight for enhanced K⁺ storage performance from the perspective of anode wettability with electrolyte, as well as a universal anode design that combines mesochannels architecture with heteroatom doping.

Free-Standing Carbon Nanofiber Composite Networks Derived from Bacterial Cellulose and Polypyrrole for Ultrastable Potassium-Ion Batteries

Carbon materials derived from bacterial cellulose have been studied in lithium-ion batteries due to their low cost and flexible characteristics. However, they still face many intractable problems such as low specific capacity and poor electrical conductivity. Herein, bacterial cellulose is used as the carrier and skeleton to creatively realize the composite of polypyrrole on its nanofiber surface. After carbonization treatment, three-dimensional carbon network composites with a porous structure and short-range ordered carbon are obtained for potassium-ion batteries. The introduction of nitrogen doping from polypyrrole can increase the electrical conductivity of carbon composites and provide abundant active sites, improving the comprehensive performance of anode materials. The carbonized bacterial cellulose@polypyrrole (C-BC@PPy) anode exhibits a high capacity of 248 mA h g^-1 after 100 cycles at 50 mA g^-1 and a capacity retention of 176 mA h g^-1 even over 2000 cycles at 500 mA g^-1. Combined with density functional theory calculations, these results indicate that the capacity of C-BC@PPy is contributed by N-doped and defect carbon composite materials as well as pseudocapacitance. This study provides a guideline for the development of novel bacterial cellulose composites in the energy storage field.

Unlock the Potassium Storage Behavior of Single-Phased Tungsten Selenide Nanorods via Large Cation Insertion

Metal chalcogenide anodes with a layered structure have been regarded as potential K-based electrochemical energy storage devices with high energy density for large-scale energy storage applications. However, their development is impeded by the slow K-ion transport kinetics and poor structural stability. In this work, the energy-storage behavior is investigated first and decisively associated them with the capacity-degradation of the promising layer-structured WSe₂ from an integrated chemical and physical point of view. Then, a single-phased WSe₂ with pre-intercalated high K content (SP-K_x WSe₂ ) is designed to overcome the capacity-degradation issue fundamentally. Theoretical calculations clarify the beneficial effect of K-ions inside the interlayer of WSe₂ on boosting its electrochemical performance, including increasing the electronic conductivity, promoting the K-ion diffusivity, and improving the structural stability. The novel design enables the K-ions pre-intercalated WSe₂ anode material to exhibit a high reversible specific capacity of 211 mAh g^-1 at 5 A g^-1 and superior cycling stability (89.3% capacity retention after 5000 cycles at 1 A g^-1 ). Especially, the K-ion hybrid capacitor, assembled from the anode of SP-K_x WSe₂ and the cathode of porous activated carbon, delivers superior energy-density up to 175 Wh kg^-1 , high power-density as well as exceptional cycling stability.