Potassium-ion Batteries Research Articles

Developments and prospects of carbon anode materials in potassium-ion batteries

Developments and prospects of carbon anode materials in potassium-ion batteries

Synthesis, Stable Radical Anion and Energy Storage Performance of Pentacene Tetraimides

Imide functionalization has been widely proved to be an effective approach to enrich optoelectronic properties of polycyclic aromatic hydrocarbons (PAHs). However, appending multiple imide groups onto linear acenes is still a synthetic challenge. Herein, we demonstrate that by taking advantage of a “breaking and mending” strategy, a linear pentacene tetraimides (PeTI) was synthesized through a three‐step sequence started from the naphthalene diimides (NDI). Compared with the parent pentacene, PeTI shows a deeper‐lying lowest unoccupied molecular orbital (LUMO) energy level, narrower bandgap and better stability. The redox behavior of PeTI was firstly evaluated by generating a stable radical anion specie with the assistance of cobaltocene (CoCp2), and the structure of the electron transfer (ET) complex was confirmed by the X‐ray crystallography. Moreover, due to the presence of multiple redox‐active sites, we are able to show that the state‐of‐the‐art energy storage performance of the dealkylated PeTI (designated as PeTCTI) in organic potassium ion batteries (OPIBs) as an anode. Our results shed light on the application of multiple imides functionalized linear acenes, and the reported synthetic strategy provides an effective way to get access to longer nanoribbon imides with fascinating electronic properties.

Synthesis, Stable Radical Anion and Energy Storage Performance of Pentacene Tetraimides.

Imide functionalization has been widely proved to be an effective approach to enrich optoelectronic properties of polycyclic aromatic hydrocarbons (PAHs). However, appending multiple imide groups onto linear acenes is still a synthetic challenge. Herein, we demonstrate that by taking advantage of a "breaking and mending" strategy, a linear pentacene tetraimides (PeTI) was synthesized through a three-step sequence started from the naphthalene diimides (NDI). Compared with the parent pentacene, PeTI shows a deeper-lying lowest unoccupied molecular orbital (LUMO) energy level, narrower bandgap and better stability. The redox behavior of PeTI was firstly evaluated by generating a stable radical anion specie with the assistance of cobaltocene (CoCp2), and the structure of the electron transfer (ET) complex was confirmed by the X-ray crystallography. Moreover, due to the presence of multiple redox-active sites, we are able to show that the state-of-the-art energy storage performance of the dealkylated PeTI (designated as PeTCTI) in organic potassium ion batteries (OPIBs) as an anode. Our results shed light on the application of multiple imides functionalized linear acenes, and the reported synthetic strategy provides an effective way to get access to longer nanoribbon imides with fascinating electronic properties.

Engineering the mass transport properties in potassium-ion intercalated pristine Prussian blue for sustainable potassium-ion batteries

Potassium-ion batteries (PIBs) could be a cheaper and more abundant alternative to lithium-ion batteries, offering faster charging and suitability for large-scale energy storage. Prussian blue (PB) is prepared through a simple wet chemical method, and its intercalation affinity for K+ ions is tested using linear sweep voltammetry (LSV). The diffusion resistance (Rw: ∼116 Ω Hz1/2) and low-frequency region slope (m: ∼0.63) are found high for the third LSV drive (Seg-3), indicating passivation of the PB surface which leads to a double-layer formation. Most of the K+ ions are intercalated into PB until three LSV segments. After that PB surface is passivated and prohibits further LSV-driven K+ ions intercalation. On average, the Seg-3 sample exhibits a 58 % higher lattice strain in comparison to the as-prepared PB. A capacity of 27 mAh g−1 @ 2 mA g−1 in aqueous media is recorded for the Seg-3 sample and a capacity drop of 4 mAh g−1 and Coulombic efficiency of 99.3 % is recorded under 100 cycles. These findings are further comprehensively validated through multi-technique approaches. The observed affinity and single-stage LSV-driven intercalation of K+ ions highlight the perspective of PB as an electrode material for aqueous potassium ion batteries (a-PIBs).

A High-Rate and Ultrastable Re2Te5/MXene Anode for Potassium Storage Enabled by Amorphous/Crystalline Heterointerface Engineering.

The pursuit of anode materials capable of rapid and reversible potassium storage performance is a challenging yet fascinating target. Herein, a heterointerface engineering strategy is proposed to prepare a novel superstructure composed of amorphous/crystalline Re2Te5 anchored on MXene substrate (A/C-Re2Te5/MXene) as an advanced anode for potassium-ion batteries (KIBs). The A/C-Re2Te5/MXene anode exhibits outstanding reversible capacity (350.4 mAh g-1 after 200 cycles at 0.2 A g-1), excellent rate capability (162.5 mAh g-1 at 20 A g-1), remarkable long-term cycling capability (186.1 mAh g-1 at 5 A g-1 over 5000 cycles), and reliable operation in flexible full KIBs, outperforming state-of-the-art metal chalcogenides-based devices. Experimental and theoretical investigations attribute this high performance to the synergistic effect of the A/C-Re2Te5 with a built-in electric field and the elastic MXene, enabling improved pseudocapacitive contribution, accelerated charge transfer behavior, and high K+ ion adsorption/diffusion ability. Meanwhile, a combination of intercalation and conversion reactions mechanism is observed within A/C-Re2Te5/MXene. This work offers a new approach for developing metal tellurides- and MXene-based anodes for achieving stable cyclability and fast-charging KIBs.

Self-grown carbon nanotubes supported fluorine-free Mo2CTx conductive layers for efficient potassium storage

Mo2CTx is relatively less studied among MXenes family, especially for rechargeable alkali metal ion batteries. Herein, a systematic investigation has been conducted to unlock its potential as electrode materials in potassium-ion battery (PIBs), including innovative fluorine-free synthesis strategy, construction of heterostructure, and exploration of suitable electrolyte systems. Firstly, Cetyltriethylammnonium bromide (CTAB)-assisted etching route was provided to fabricate high-quality multilayer Mo2CTx with expanded interlayer space (C-Mo2CTx). The as-obtained C-Mo2CTx demonstrates a large specific capacity of 200 mAh g−1over 300 cycles in potassium-ion battery, surpassing the HF etched counterparts (F-Mo2CTx) by about 300 %. Afterwards, Zeolitic Imidazolate Frameworks (ZIF-67) derived Co, N-codoped carbon nanotubes (Co@NCNTs) were homogenously grown on the surface of Mo2CTx, working as embedding spacer to open the stacked Mo2CTx conductive layers (Mo2CTx-Co@NCNTs). Mo2CTx-Co@NCNTs electrode represents stable reversible capacity of 280 mA h g−1 over 300 cycles. The highly conductive matrix constructed by the strong bond between CNTs arrays and Mo2CTx conductive layer could provide numerous K-ion-diffusion pathways, and buffer volume strain and facilitate electron transfer. The present work proves the potential of Mo2CTx in PIBs and gives the systematic research methodologies on Mo2CTx-based materials in alkali metal ion storage.

Defect engineering of sulfur vacancies in vanadium disulfide integrated with graphene as advanced potassium-ion battery cathode

Potassium-ion batteries (PIBs) have economic and environmental potential, but slow potassium ion diffusion and electrode material degradation hinder the development of effective cathode materials. This research designs a composite cathode material that vanadium disulfide with sulfur vacancies integrated with reduced graphene oxide (VS2-x@rGO). The introduction of sulfur vacancies increases active sites for ion storage, while rGO ensures a stable electronic conductivity and structural integrity. VS2-x@rGO shows a great rate performance of 116.2 mAh g−1 at 20 mA g−1, 77.5 mAh g−1 at 500 mA g−1, and high cycling stability with 94.5 % retention of capacity after 100 cycles at 100 mA g−1. Moreover, the full cell assembled with hard carbon achieves a specific capacity close to 120 mAh g−1. Energy density up to 220 Wh kg−1 in 38.4 W kg−1 and 72 Wh kg−1 in 960 W kg−1. Through in-situ XRD and other ex-situ analyses, the crystal structure rapidly transformed into K0.6VS2 and slight displacement of the crystal plane occurred during K+ insertion until KxVS2 formed in the discharge process. The charging process is reversible and forms VS2. This study provides a novel approach for advancing PIBs cathode materials, contributing valuable insights into the optimization of energy storage solutions.

Internal Space Modulation of Yolk-Shell FeSe2@Carbon Anode with Peanut-Shaped Morphology Enabling Ultra-Stable and Fast Potassium-Ion Storage.

The poor cycling stability and rate performance of transition metal selenides (TMSs) are caused by their intrinsic low conductivity and poor structural stability, which hinders their application in potassium-ion batteries (PIBs). To address this issue, encapsulating TMSs within carbon nanoshells is considered a viable strategy. However, due to the lack and uncontrollability of internal void space, this structure cannot effectively mitigate the volume expansion induced by large K+, resulting in unsatisfactory electrochemical performance. Herein, peanut-shaped FeSe2@carbon yolk-shell capsules are prepared by modulation of the internal space. The active FeSe2 is encapsulated within a robust carbon shell and an optimal void space is retained between them. The outer carbon shell promotes electronic conductivity and avoids FeSe2 aggregation, while the internal void mitigates volume expansion and effectively ensures the structural integrity of the electrode. Consequently, the FeSe2@carbon anode demonstrates exceptional rate performance (242 mAh g-1 at 10 A g-1) and long cycling stability (350 mAh g-1 after 500 cycles at 1 A g-1). Furthermore, the effect of internal space modulation on electrochemical properties is elucidated. Meanwhile, ex situ characterizations elucidate the K+ storage mechanism. This work provides effective guidance for the design and the internal space modulation of advanced TMSs yolk-shell structures.

K-Rich Spinel Interface of Air-Stable Layered Oxide Cathodes for Potassium-Ion Batteries.

Potassium-containing transition metal layered oxides (KxTmO2), although possessing high energy density and suitable operating voltage, suffer from severe hygroscopic properties due to their two dimensional (2D)layered structure. Their air sensitivity compromises structural stability during prolonged air exposure, therefore increasing the cost. The common sense for designing air-stable layered cathode materials is to avoid contact with H2Omolecules. In this study, it is surprisingly found that P3-type KxTmO2 forms an ultra-thin, potassium-rich spinel phase wrapping layer after simply water immersion, remarkedly reduces the reaction activity of the material's surface with air. Combined with Density Function Theory (DFT) calculations, this spinel phase is found to be able to effectively withstand air deterioration and preserving the crystal structure. Consequently, the water-treated material, when exposed to air, can largely maintain its good electrochemical performance, with capacity retention up to 99.15% compared to the fresh samples. Such an in situ surface phase transformation mechanism is also corroborated in other KxTmO2, underscoring its effectiveness in enhancing the air stability of P3-type layered oxides for K+ storage.

Ether-Based Gel Polymer Electrolyte for High-Voltage Potassium Ion Batteries.

Low-concentration ether electrolytes cannot efficiently achieve oxidation resistance and excellent interface behavior, resulting in severe electrolyte decomposition at a high voltage and ineffective electrode-electrolyte interphase. Herein, we utilize sandwich structure-like gel polymer electrolyte (GPE) to enhance the high voltage stability of potassium-ion batteries (PIBs). The GPE contact layer facilitates stable electrode-electrolyte interphase formation, and the GPE transport layer maintains good ionic transport, which enabled GPE to exhibit a wide electrochemical window and excellent electrochemical performance. In addition, Al corrosion under a high voltage is suppressed through the restriction of solvent molecules. Consequently, when using the designed GPE (based on 1 m), the K||graphite cell exhibits excellent cycling stability of 450 cycles with a capacity retention of 91%, and the K||FeFe-Prussian blue cell (2-4.2 V) delivers a high average Coulombic efficiency of 99.9% over 2200 cycles at 100 mA g-1. This study provides a promising path in the application of ether-based electrolytes in high-voltage and long-lasting PIBs.

Synergistic Triple-Action morphological composite Anode: Integrating lattice Softening, Interfacial electric Fields, and dual confinement for superior Potassium-Ion battery performance

Synergistic effects could significantly improve slow redox kinetics and structural pulverization of electrodes in potassium ion batteries (PIBs); however, the performance of single synergistic designs is limited. Multi-synergistic composite, shaped by a blend of factors, substantially boosts performance, yielding outcomes that surpass single synergistic coupling design. Herein, we develop a Bi2Se3/Sb2Se3@NC@G electrode that integrates three key features for enhanced potassium-ion storage: p-n junctions enhance electron transfer through internal electric fields, dual confinement prevents K2Se dissolution into the electrolyte, and lattice softening in the Bi-Sb alloy relieves stress during potassium ion insertion/extraction. These multi-synergistic effects enable the heterostructure to exhibit superior electrochemical performance in potassium-ion batteries.The Bi2Se3/Sb2Se3@NC@G electrode demonstrates notable capacity of 640 mA h g-1 at current density of 50 mA g-1, achieving 95.5 % of its theoretical capacity, maintain stable capacity of 310 mA h g−1 after 5000 cycles at current density of 0.5 A/g with 0.002 % per cycle degradation, and exhibits the fastest rate capability up to 10 A/g (172 mA h g−1). Furthermore, potassium ion hybrid capacitor (PIHC) can achieve a high energy density of 118 Wh kg−1 and a power density of 5200 W kg−1, and full cell shows an attractive energy density of 97 Wh kg-1 and a stable performance after 250 cycling number under 1 A g-1. This study proposes an effective strategy that employs multiple synergistic coupling designs to maximize potassium-ion storage capacity, achieving a breakthrough in extending battery lifecycle.

Polypyrrole-encapsulated TiSe2 with excellent electrochemical performance for potassium-ion storage

TiSe2 as a potential electrode for potassium-ion batteries, has garnered significant attention owing to its stable ion storage property. Nevertheless, the inadequate electronic conductivity of TiSe2 impedes its practical implementation. In this investigation, we adopt a polymerization method to fabricate TiSe2@PPy, which boasts enhanced conductivity and exceptional performance. Once coated with polypyrrole, the TiSe2@PPy composites demonstrate the optimum electrochemical performance, providing a charge capacity of 67.4 mAh g−1 at 1 C with a capacity retention of 68.4 % after 170 cycles. The PPy coating enhances the conductivity of TiSe2 and enables potassium-ion batteries to exhibit outstanding electrochemical performance. Ex-situ Raman and FTIR tests are utilized to comprehend the electrochemical reaction between K+ and the TiSe2@PPy electrode during cycling. Overall, this work introduces a PPy coating on TiSe2, which presents a novel concept for the development.

Optimizing Prussian Blue Analogues for Potassium‐Ion Batteries: Advanced Strategies

Potassium‐ion batteries (PIBs), with the merits of abundant resources and low cost, have rapidly garnered attention as a potential candidate for large‐scale energy storage. Among the various contenders, Prussian Blue analogues (PBAs) are considered the most suitable cathode materials owing to their relatively easy and economical synthesis as well as the open 3D framework which facilitates fast potassium ions intercalation without causing drastic volume expansion. Despite these advantages, integrating PBA as a cathode material for PIBs presents substantial challenges, which hinder their further practical applications. Herein, a fundamental review on the development and advance of PBAs in PIBs is presented with the elucidation of their synthesis methods, structural characteristics, and optimization strategies. Particularly, key areas of focus include regulating crystal structures, doping transition metals, engineering interfaces, and employing innovative techniques such as high‐entropy approaches are highlighted. Finally, critical perspectives for future development of PBAs toward practical potassium‐based energy storage devices are proposed.

The Enormous Potential of Sodium/Potassium-Ion Batteries as the Mainstream Energy Storage Technology for Large-Scale Commercial Applications.

Cost-effectiveness plays a decisive role in sustainable operating of rechargeable batteries. As such, the low cost-consumption of sodium-ion batteries (SIBs) and potassium-ion batteries (PIBs) provides a promising direction for "how do SIBs/PIBs replace Li-ion batteries (LIBs) counterparts" based on their resource abundance and advanced electrochemical performance. To rationalize the SIBs/PIBs technologies as alternatives to LIBs from the unit energy cost perspective, this review gives the specific criteria for their energy density at possible electrode-price grades and various battery-longevity levels. The cost ($ kWh-1 cycle-1) advantage of SIBs/PIBs is ascertained by the cheap raw-material compensation for the cycle performance deficiency and the energy density gap with LIBs. Furthermore, the cost comparison between SIBs and PIBs, especially on cost per kWh and per cycle, is also involved. This review explicitly manifests the practicability and cost-effectiveness toward SIBs are superior to PIBs whose commercialization has so far been hindered by low energy density. Even so, the huge potential on sustainability of PIBs, to outperform SIBs, as the mainstream energy storage technology is revealed as long as PIBs achieve long cycle life or enhanced energy density, the related outlook of which is proceeded as the next development directions for commercial applications.

Modulating polymerization of aromatic polyimides on carbon nanotubes for high-performance organic potassium-ion batteries

Modulating polymerization of aromatic polyimides on carbon nanotubes for high-performance organic potassium-ion batteries

Characterisation and modelling of potassium-ion batteries

Potassium-ion batteries (KIBs) are emerging as a promising alternative technology to lithium-ion batteries (LIBs) due to their significantly reduced dependency on critical minerals. KIBs may also present an opportunity for superior fast-charging compared to LIBs, with significantly faster K-ion electrolyte transport properties already demonstrated. In the absence of a viable K-ion electrolyte, a full-cell KIB rate model in commercial cell formats is required to determine the fast-charging potential for KIBs. However, a thorough and accurate characterisation of the critical electrode material properties determining rate performance—the solid state diffusivity and exchange current density—has not yet been conducted for the leading KIB electrode materials. Here, we accurately characterise the effective solid state diffusivities and exchange current densities of the graphite negative electrode and potassium manganese hexacyanoferrate K2Mn[Fe(CN)6]\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${{{{\\rm{K}}}}}_{2}{{{\\rm{Mn}}}}[{{{\\rm{Fe}}}}{({{{\\rm{CN}}}})}_{6}]$$\\end{document} (KMF) positive electrode, through a combination of optimised material design and state-of-the-art analysis. Finally, we present a Doyle-Fuller-Newman model of a KIB full cell with realistic geometry and loadings, identifying the critical materials properties that limit their rate capability.

Carbon coating engineering enhances the stability of graphite anode in potassium ion batteries

Graphite forms reversible potassium-graphite intercalation compounds electrochemically. Graphite anode possesses a high reversible specific capacity (279 mAh g−1) and an optimal low potential platform, rendering it an ideal anode material for potassium-ion batteries. However, the intercalation of K+ ions in graphite causes a bulk volume expansion of up to 61%, resulting in irreversible damage to the structure of graphite, which leads to inferior cycling stability. In this paper, surface-oxidized graphite (OG) with reduced particle size and increased defect densities was obtained by mechanical ball milling and chemical oxidation. Composites of soft carbon-coated OG (OG@PC) were prepared by soft carbon coating. The soft carbon coating can alleviate the bulk expansion caused by K+ intercalation/deintercalation in OG, thus slowing down the destruction of the crystalline structure of graphite after multiple charging/discharging cycles. OG@PC exhibits increased reversible specific capacity from 267 mAh g−1 to 314 mAh g−1 compared with pristine graphite at a current density of 0.05 A g−1. Moreover, at a high current density of 0.5 A g−1, a reversible specific capacity of 213 mAh g−1 was achieved after 200 cycles. This work investigates simple surface carbon coating strategies to improve the cycling stability of a graphite anode of potassium-ion batteries.

Potassium Alloy Reference Electrodes for Potassium-Ion Batteries: The K-In and K-Bi Systems.

Potassium-ion batteries (KIBs) are a promising alternative to conventional lithium-ion batteries with reduced critical mineral dependency but accurate three-electrode characterization is hindered by the lack of a suitable reference electrode. Potassium metal is frequently used as a reference electrode out of necessity, but its high reactivity and unstable potential limit its reliability. Here we investigate the K-In and K-Bi alloy systems, synthesize two-phase In-In4K and Bi-Bi2K alloys, and identify Bi-Bi2K as a promising material owing to its stable potential of 1.07 V vs K+/K. We prove the use of Bi-Bi2K as a reference electrode by cycling graphite in three-electrode cells and demonstrate that it results in significantly less electrolyte reduction than potassium metal, facilitating the accurate electrochemical characterization necessary to accelerate KIB development.

Phase Engineering and Ion Diffusion Kinetics for High Power and Long Lifespan Potassium-Ion Batteries

Phase Engineering and Ion Diffusion Kinetics for High Power and Long Lifespan Potassium-Ion Batteries

CoSe2 nanocrystals embedded in one-dimensional mesoporous carbon nanofibers as advanced anode for potassium-ion storage

High-performance potassium-ion batteries have received great attention for electrochemical energy storage owing to their low redox potential, abundant natural resources and excellent safety. As an advanced negative material, CoSe2 has been widely investigated for potassium-ion batteries. Unfortunately, the pure CoSe2 anode suffers from the fast capacity decay and sluggish kinetics, preventing its practical application. Herein, we introduce a novel strategy to fabricate the CoSe2 nanoparticles embedded in one-dimensional mesoporous carbon nanofibers (denoted as 1D-CoSe2@CNFs) with superior high-rate property and good cycle stability for the first time. In this designed material, the conductive carbon nanofibers are loaded with CoSe2 particles. The obtained 1D-CoSe2@CNFs anode shows a specific capacity of 706.3 mAh/g at 0.1 A/g and presents a high capacity retention ratio of around 96.3 % at 5 A/g over 400 cycles. Therefore, this fabricated 1D-CoSe2@CNFs nanocomposite can be employed as a novel negative electrode for potassium-ion storage.