Recent advances in rational design for high-performance potassium-ion batteries

The growing global energy demand necessitates the development of renewable energy solutions to mitigate greenhouse gas emissions and air pollution. To efficiently utilize renewable yet intermittent energy sources such as solar and wind power, there is a critical need for large-scale energy storage systems (EES) with high electrochemical performance. While lithium-ion batteries (LIBs) have been successfully used for EES, the surging demand and price, coupled with limited supply of crucial metals like lithium and cobalt, raised concerns about future sustainability. In this context, potassium-ion batteries (PIBs) have emerged as promising alternatives to commercial LIBs. Leveraging the low cost of potassium resources, abundant natural reserves, and the similar chemical properties of lithium and potassium, PIBs exhibit excellent potassium ion transport kinetics in electrolytes. This review starts from the fundamental principles and structural regulation of PIBs, offering a comprehensive overview of their current research status. It covers cathode materials, anode materials, electrolytes, binders, and separators, combining insights from full battery performance, degradation mechanisms, in situ/ex situ characterization, and theoretical calculations. We anticipate that this review will inspire greater interest in the development of high-efficiency PIBs and pave the way for their future commercial applications.

A new strategy to exploit maximum rate performance for aqueous batteries through a judicious selection of MOF-type electrodes

A metal-organic framework (MOF) having a redox active 1,4,5,8-naphthalenetetracarboxdiimide (NDI) derivative in its organic linker shows excellent rate performance as an electrode material for aqueous batteries thanks to its large pores. Among aqueous electrolytes examined, K⁺-based ones exhibit the highest rate performance, which is caused by the highest mobility of the smallest hydrated K⁺ ion not only in the aqueous electrolyte but also in the electrode. Since the use of a counter electrode with insufficiently small pores for the full-cell configuration offsets this merit, our study may lead to a conclusion that the maximum rate performance for aqueous batteries will be accomplished only through further elaboration of both electrode materials with sufficiently large pores, in which hydrated ions can travel equally fast as those in the electrolyte.

Multilayer structure covalent organic frameworks (COFs) linking by double functional groups for advanced K+ batteries

Covalent organic frameworks (COFs) are regarded as the potential and promising anode materials for potassium ion batteries (PIBs) on account of their robust and porous crystalline structure. In this work, multilayer structural COF connected by double functional groups, including imine and amidogent through a simple solvothermalprocess, have been successfully synthesized. The multilayer structure of COF can provide fast charge transfer and combine the merits of imine (the restraint of irreversible dissolution) and amidogent (the supply of more active sites). It presents superior potassium storage performance, including the high reversible capacity of 229.5 mAh g^-1 at 0.2 A g^-1 and outstanding cycling stability of 106.1 mAh g^-1 at the high current density of 5.0 A g^-1 after 2000 cycles, which is superior to the individual COF. The structural advantages of the covalent organic framework linking by double functional groups (d-COF) can develop a new road for that COF anode material for PIBs in further research.

Construction of Fluorine- and Piperazine-Engineered Covalent Triazine Frameworks Towards Enhanced Dual-Ion Positive Electrode Performance

Organic positive electrodes featuring lightweight and tunable energy storage modes by molecular structure engineering have promising application prospects in dual-ion batteries. Herein, a series of highly porous covalent triazine frameworks (CTFs) were synthesized under ionothermal conditions using fluorinated aromatic nitrile monomers containing a piperazine ring. Fluorinated monomers can result in more defects in CTFs, leading to a higher surface area up to 2515 m²  g^-1 and a higher N content of 11.34 wt % compared to the products from the non-fluorinated monomer. The high surface area and abundant redox sites of these CTFs afforded high specific capacities (up to 279 mAh g^-1 at 0.1 A g^-1 ), excellent rate performance (89 mAh g^-1 at 5 A g^-1 ), and durable cycling performance (92.3 % retention rate after 500 cycles at 2.0 A g^-1 ) as dual-ion positive electrodes.

Sustainable Biomass-Derived Carbon Electrodes for Potassium and Aluminum Batteries: Conceptualizing the Key Parameters for Improved Performance

The development of sustainable, safe, low-cost, high energy and density power-density energy storage devices is most needed to electrify our modern needs to reach a carbon-neutral society by ~2050. Batteries are the backbones of future sustainable energy sources for both stationary off-grid and mobile plug-in electric vehicle applications. Biomass-derived carbon materials are extensively researched as efficient and sustainable electrode/anode candidates for lithium/sodium-ion chemistries due to their well-developed tailored textures (closed pores and defects) and large microcrystalline interlayer spacing and therefore opens-up their potential applications in sustainable potassium and aluminum batteries. The main purpose of this perspective is to brief the use of biomass residues for the preparation of carbon electrodes for potassium and aluminum batteries annexed to the biomass-derived carbon physicochemical structures and their aligned electrochemical properties. In addition, we presented an outlook as well as some challenges faced in this promising area of research. We believe that this review enlightens the readers with useful insights and a reasonable understanding of issues and challenges faced in the preparation, physicochemical properties and application of biomass-derived carbon materials as anodes and cathode candidates for potassium and aluminum batteries, respectively. In addition, this review can further help material scientists to seek out novel electrode materials from different types of biomasses, which opens up new avenues in the fabrication/development of next-generation sustainable and high-energy density batteries.

Advanced Covalent Organic Frameworks for Multi-Valent Metal Ion Batteries

Covalent organic frameworks (COFs) have received increased interest in recent years as an advanced class of materials. By virtue of the available monomers, multiple conformations and various linkages, COFs offer a wide range of opportunities for complex structural design and specific functional development of materials, which has facilitated the widespread application in many fields, including multi-valent metal ion batteries (MVMIBs), described as the attractive candidate replacing lithium-ion batteries (LIBs). With their robust skeletons, diverse pores, flexible structures and abundant functional groups, COFs are expected to help realize a high performance MVMIBs. In this review, we present an overview of COFs, describe advances in topology design and synthetic reactions, and study the application of COFs in MVMIBs, as well as discuss challenges and solutions in the preparation of COFs electrodes, in the hope of providing constructive insights into the future direction of COFs.

A 2.75 V ammonium-based dual-ion battery

The popular metal-ion batteries (MIBs) suffer from environmental and economic issues because of their heavy dependency on nonrenewable metals. Here, we propose a metal-free ammonium (NH₄ ⁺ )-based dual-ion battery with a record-breaking operation voltage of 2.75 V. The working mechanism of this sustainable battery involves the reversible anion (PF₆ ^- ) intercalation chemistry in graphite cathode and NH₄ ⁺ intercalation behavior in PTCDI (3,4,9,10-perylenetetracarboxylic diimide) anode. This new battery configuration successfully circumvented the reduction susceptibility of NH₄ ⁺ and the lack of mature NH₄ ⁺ -rich cathodes for NH₄ ⁺ ion batteries (AIBs). The customized organic NH₄ ⁺ electrolyte endows the graphite||PTCDI full battery with durable longevity (over 1000 cycles) and a high energy density (200 Wh kg^-1 ). We show that the development of AIBs should be high-voltage-oriented while circumventing low operation potential to avoid NH₄ ⁺ reduction.

Recent Advances in Polymers for Potassium Ion Batteries

Potassium-ion batteries (KIBs) are considered to be an effective alternative to lithium-ion batteries (LIBs) due to their abundant resources, low cost, and similar electrochemical properties of K⁺ to Li⁺, and they have a good application prospect in the field of large-scale energy storage batteries. Polymer materials play a very important role in the battery field, such as polymer electrode materials, polymer binders, and polymer electrolytes. Here in this review, we focus on the research progress of polymers in KIBs and systematically summarize the research status and achievements of polymer electrode materials, electrolytes, and binders in potassium ion batteries in recent years. Finally, based on the latest representative research of polymers in KIBs, some suggestions and prospects are put forward, which provide possible directions for future research.

Double-layer Composite Gel Polymer Electrolyte for Organic Sodium-metal Batteries

Organic cathode materials have the advantages of abundant raw materials, high theoretical specific capacity, controllable structure and easy recycling. Pyrene-4,5,9,10-tetraone (PTO), as one of the typical organic cathode materials, achieves efficient storage and release of Na + . However, its good solubility in traditional organic liquid electrolytes is detrimental to the cyclic stability of batteries. To address this issue, the double-layer composite gel polymer electrolyte (DLCGPE) consisting of poly (ionic liquid) gel polymer electrolyte and plastic crystal electrolyte was developed and applied to organic sodium-metal batteries. This as-prepared DLCGPE displays an ionic conductivity of 2.17×10 -4 S cm -1 and an electrochemical window of 4.8 V. The as-fabricated sodium-symmetric batteries maintain interfacial stability after 500 h of cycling. Furthermore, the PTO/Na batteries could also retain a specific capacity of 201 mAh g -1 after 300 cycles, confirming that DLCGPE achieves the purpose of inhibiting PTO dissolution and maintaining batteries stability. This work broadens the application of asymmetric electrolytes in organic secondary battery.

Quinone Electrode for Long Lifespan Potassium-Ion Batteries Based on Ionic Liquid Electrolytes

As a class of flexible and designable materials, organic electrode materials would greatly facilitate the progress of potassium-ion batteries (PIBs), especially when the dissolution issue is ameliorated. Ionic liquid electrolytes (ILEs) do not merely alleviate the dissolution of organic materials but provide reliable security. Herein, Pillar[5]quinone (P5Q) as the cathode of PIBs is demonstrated for the first time, and the electrochemical performance of two common ILEs is investigated. In the 0.3 M KFSI-PY13FSI electrolyte with better conductivity, the P5Q cathode maintains a large reversible capacity of 232 mAh g^-1 (450 Wh kg^-1) after 100 cycles at 0.2C at 1.2-4.0 V. When a current density of 2.0C is applied, the cell retains a capacity of 101 mAh g^-1 (211 Wh kg^-1) after 1000 cycles and 61 mAh g^-1 (125 Wh kg^-1) even over 5000 cycles. This research would inspire research on organic electrodes and advance the application of PIBs.

Boosted π-Li Cation Effect in the Stabilized Small Organic Molecule Electrode via Hydrogen Bonding with MXene

The high solubility of the small organic molecule materials in organic electrolytes hinders their development in rechargeable batteries. Hence, this work designs an ultrarobust hydrogen-bonded organic-inorganic hybrid material: the small organic unit of the 1,3,6,8-tetrakis (p-benzoic acid) pyrene (TBAP) molecule connected with the hydroxylated Ti₃C₂T_x MXene through hydrogen bonds between the terminal groups of -COOH and -OH. The robust and elastic hydrogen bonds can empower the TBAP, despite being a low-molecule organic chemical, with unusually low solubility in organic electrolytes and thermal stability. The alkali-treated Ti₃C₂T_x MXene provides a hydroxyl-rich conductive network, and the small organic molecule of TBAP reduces the restacking of MXene layers. Therefore, the combination of these two materials complements each other well, and this organic-inorganic TBAP@D-Ti₃C₂T_x electrode delivers large reversible capacities and long cyclic life. Notably, with the assistance of the in situ FT-IR characterization of the electrode within the fully lithiated (0.005 V) and the delithiated (3.0 V) states, it is revealed that a powerful π-Li cation effect mainly governs the lithium-storage mechanism with the highly activated benzene ring and each C6 aromatic ring, which can reversibly accept six Li-ions to form a 1:1 Li/C complex.

Recent Progress of Carbon-Based Anode Materials for Potassium Ion Batteries

With the increasing demand for clean energy, rechargeable batteries with K⁺ as carriers have attracted wide attention due to their advantages of expandability and low cost. High-performance anode materials are the key to the development of potassium ion batteries (PIBs), improving their competitiveness and feasibility. Carbon materials have become promising anodes for PIBs due to their abundant resources, low cost, non-toxicity and electrochemical diversity. This article reviews the research progress of carbon based anode materials in recent years. Firstly, the unique characteristics of carbon as a competitive anode for advanced PIBs are discussed, which provides guidance for optimal design and exploration. Then, various carbon materials as the anodes towards PIBs are summarized in detail, and the involved problems and corresponding solutions are analyzed. Finally, the future development and perspective of advanced carbons for next-generation PIBs are proposed.

Ultrastable Bioderived Organic Anode Induced by Synergistic Coupling of Binder/Carbon-Network for Advanced Potassium-Ion Storage

Bioderived molecules have been identified as viable anodes for organic potassium-ion batteries (OPIBs) due to the abundance of the necessary natural resources, their high capacity, and their sustainability. However, the high solubility and the inherent nonconductivity cause serious capacity decay and large voltage hysteresis. Here, the biomass molecule juglone was cross-linked with a carbon nanotube network, coupling and cooperating with sodium alginate binder (J@CNT-SA), and was proposed to inhibit small molecule dissolution via weak intermolecular interactions. The synergistic effect of hydrogen bonding and π-π stacking is proven for its outstanding reversible high capacities (262 mA h g^-1 at 0.05 A g^-1), and a remarkable long life span with capacity retention of 77% over 5000 cycles. Further in situ Fourier transform infrared spectroscopy (FTIR) was performed to reveal the electrochemical mechanism. The feasibility of juglone as an anode for PIBs paves the way for other natural organic small molecules to be investigated as potential energy storage materials.

A Stabilized Polyacrylonitrile-Encapsulated Matrix on a Nanolayered Vanadium-Based Cathode Material Facilitating the K-Storage Performance

Layered vanadium-based metal oxides were regarded as promising cathode materials accounting for suitable K⁺ transport channels as well as high work potential in K-ion batteries. Nevertheless, because of the large radius of K⁺ and the rigid structure of inorganic materials, the typical K_0.486V₂O₅ suffers from volume expansion seriously in the repeated charging and discharging processes along with poor ionic and electronic conductivity, consequently determining inevitably poor electrochemical properties. Herein, we proposed a stabilized polymer (PAN) matrix on K_0.486V₂O₅ nanobelts by a liquid-assisted methodology and further electrospinning technology. As a result, a nanocomposite containing a 3D conductive and interconnected mesh structure was thus constructed. By avoiding the full carbonization of polyacrylonitrile (PAN) with appropriate thermal treatment, the elastic properties of the PAN precursor can be retained, effectively inhibiting the volume effect, and the stabilized PAN-encapsulated matrix can also greatly accelerate transport rates of K⁺ and electrons at a high rate as well as restrict the decomposition of organic electrolytes and side reactions. This work can supply significant basic scientific value of the polymer surface coating methodology for the far-reaching development of inorganic cathode materials in K-ion batteries.

Quantitative analysis of molecular surface: systematic application in the sodiation mechanism of a benzoquinone-based pillared compound as a cathode

Quantitative analysis of molecular surface as a novel method for DFT studies of P5Q cathodes, which can simulate reasonable sodiation processes and predict accurate theoretical redox voltages.

A carboxylate- and pyridine-based organic anode material for K-ion batteries

In this work, a new carboxylate- and pyridine-based organic anode material was exploited in K-ion batteries. The results demonstrate the critical role of multiple active centers (CO and CN) in one molecule to enhance the electrochemical performance.

Sb2S3-based conversion-alloying dual mechanism anode for potassium-ion batteries

The large volume expansion and sluggish dynamic behavior are the key bottleneck to suppress the development of conversion-alloying dual mechanism anode for potassium-ion batteries (PIBs). Herein, Sb2S3 nanorods encapsulated by reduced graphene oxide and nitrogen-doped carbon (Sb2S3@rGO@NC) are constructed as anodes for PIBs. The synergistic effect of dual physical protection and robust C-Sb chemical bonding boosts superior electrochemical kinetics and great electrode stability. Thus, Sb2S3@rGO@NC exhibits a high initial charge capacity of 505.6 mAh·g-1 at 50 mA·g-1 and a great cycle stability with the lifetime over 200 cycles at 200 mA·g-1. Ex situ XRD, XPS, and TEM characterizations confirm that the electrode undergoes a multielectron transfer process (Sb2S3↔ Sb + K2S ↔ KSb + K3Sb), where K-ion insert into/extract from the material via dual mechanisms of conversion and alloying. This work sheds a light on the construction of high-performance anode materials and the understanding of K-ion storage mechanism.

Carbon-Free Crystal-like Fe1-xS as an Anode for Potassium-Ion Batteries

Potassium-ion batteries (PIBs) as a new electrochemical energy storage system have been considered as a desirable candidate in the post-lithium-ion battery era. Nevertheless, the study on this realm is in its infancy; it is urgent to develop electrode materials with high electrochemical performance and low cost. Iron sulfides as anode materials have aroused wide attention by virtue of their merits of high theoretical capacities, environmental benignity, and cost competitiveness. Herein, we constructed carbon-free crystal-like Fe_1-xS and demonstrated its feasibility as a PIB anode. The unique structural feature endows the prepared Fe_1-xS with plentiful active sites for electrochemical reactions and short transmission pathways for ions/electrons. The Fe_1-xS electrode retained capacities of 420.8 mAh g^-1 after 100 cycles at 0.1 A g^-1 and 212.9 mAh g^-1 after 250 cycles at 1.0 A g^-1. Even at a high rate of 5.0 A g^-1, an average capacity of 167.6 mAh g^-1 was achieved. In addition, a potassium-ion full cell is assembled by employing Fe_1-xS as an anode and potassium Prussian blue as a cathode; it delivered a discharge capacity of 127.6 mAh g^-1 at 100 mA g^-1 after 50 cycles.

Immobilizing Redox-Active Tricycloquinazoline into a 2D Conductive Metal-Organic Framework for Lithium Storage

Heteroaromatic-conjugated aromatic molecules have inspired numerous interests in rechargeable batteries like Li-ion batteries, but were limited by low conductivity and easy dissolution in electrolytes. Herein, we immobilize a nitrogen-rich aromatic molecule tricycloquinazoline (TQ) and CuO₄ unit into a two-dimensional (2D) conductive metal-organic framework (MOF) to unlock their potential for Li⁺ storage. TQ was identified redox activity with Li⁺ for the first time. With a synergistic effect of TQ and CuO₄ unit, the 2D conductive MOF, named Cu-HHTQ (HHTQ=2,3,7,8,12,13-hexahydroxytricycloquinazoline), can facilitate the Li⁺ /e^- transport and ensure a resilient electrode, resulting in a high capacity of 657.6 mAh g^-1 at 600 mA g^-1 with extraordinary high-rate capability and impressive cyclability. Our findings highlight an efficient strategy of constructing electrode materials for energy storage with combining multiple redox-active moieties into conductive MOFs.

Hybrid nanostructures for electrochemical potassium storage

The wide availability and low cost of potassium resources have made electrochemical potassium storage a promising energy storage solution for sustainable decarbonisation. Research activities have been rapidly increasing in the last few years to investigate various potassium batteries such as K-ion batteries (KIBs), K-S batteries and K-Se batteries. The electrode materials of these battery technologies are being extensively studied to examine their suitability and performance, and the utilisation of hybrid nanostructures has undoubtedly contributed to the advancement of the performance. This review presents a timely summary of utilising hybrid nanostructures as battery electrodes to address the issues currently existing in potassium batteries via taking advantage of the compositional and structural diversity of hybrid nanostructures. The complex challenges in KIBs and K-S and K-Se batteries are outlined and the role of hybrid nanostructures is discussed in detail regarding the characteristics of intercalation, conversion and alloying reactions that take place to electrochemically store K in hybrid nanostructures, highlighting their multifunctionality in addressing the challenges. Finally, outlooks are given to stimulate new ideas and insights into the future development of hybrid nanostructures for electrochemical potassium storage.

Alkynyl-Based Covalent Organic Frameworks as High-Performance Anode Materials for Potassium-Ion Batteries

The development of high-performance organic electrodes for potassium-ion batteries (KIBs) is attracting interest due to their sustainability and low costs. However, the electrolyte systems and moieties that generally proved to be successful in high-performance Li-ion batteries have found relatively little success in KIBs. Herein, two alkynyl-based covalent organic frameworks (COFs) containing 1,3,5-tris(arylethynyl)benzene (TAEB) and dehydrobenzoannulene (DBA) units are utilized as bulk anode materials for KIBs in a localized high-concentration electrolyte. TAEB-COF provides a high capacity value of 254.0 mAh g^-1 at ∼100% efficiency after 300 cycles, and DBA-COF 3 provides a capacity of 76.3 mAh g^-1 with 98.7% efficiency after 300 cycles. DFT calculations suggest that the alkynyl units of TAEB-COF facilitate the binding of K-ions through both enthalpic and geometric driving forces, leading to high reversible capacities.

A review on metal-organic framework-derived anode materials for potassium-ion batteries

In recent years, metal-organic frameworks (MOFs) have been widely used in the field of electrochemical energy storage and conversion because of their excellent properties, such as high specific surface area, adjustable pore size, high porosity, structural diversity, and functional controllability. This paper reviews the applications of metal-organic framework-derived composites such as nitrogen-doped carbon, transition metal sulfides, transition metal selenides, transition metal phosphides and metal selenium compound modifications in potassium ion batteries (PIBs) as anode electrode materials. A variety of MOF-derived composites with different structures and morphologies based on several types of ligands, including 2-methylimidazole, aromatic carboxylic acids, and ferricyanide, have been discussed. Moreover, the current challenges faced by MOF-derived materials and possible countermeasures are proposed.

Revealing better organic sodium battery performance in ionic liquid electrolytes

Ionic liquid (IL) electrolyte conduced to better sodium storage performance for organic electrode materials.