High performance Li-, Na-, and K-ion storage in electrically conducting coordination polymers

Starch as an efficient precursor for hard carbon anodes enables high-performance sodium-ion storage

Starch is an ideal choice for hard carbon anode precursors in sodium-ion batteries because of its diverse sources and high carbon content. Nevertheless, starch experiences melting and foaming in the initial stages of pyrolysis, which results in low yields and hinders the large-scale production and application of starch-derived hard carbon. Herein, we employed phenolic resin and maleic anhydride to esterify and cross-link starch to prepare hard carbon. The starch foaming was successfully inhibited through the synergistic effect among composite precursors. Benefiting from abundant micropores/mesopores and larger microcrystalline structure, the prepared hard carbon delivers a high specific capacity of up to 342.28 mA h g-1 and an impressive initial discharge capacity of 85.89%. The capacity retention is as high as 87.24% after 100 cycles of charge and discharge. Furthermore, the hard carbon demonstrates excellent rate performance with a capacity recovery rate of 95.11%. The stabilized starch-derived hard carbon anode possesses both high sodium storage performance and a lower cost, demonstrating potential for commercialization on a large scale.

Copper Nanoparticles Loaded on N-Doped Carbon Nanotubes with Enhanced Peroxidase-Like Performance for Gallic Acid Detection in Food

The accurate monitoring of gallic acid (GA) in foodstuffs is crucial for safeguarding human health. The application of nanozymes in colorimetric assays offers a promising route for assessing the GA level. However, the development of high-efficiency and cost-effective nanozymes for quick GA detection holds a substantial challenge. In this study, copper (Cu) nanoparticles (NPs) immobilized on N-doped carbon nanotubes (NCNTs) have been prepared, exhibiting exceptional peroxidase (POD)-like activity for GA detection in food. The anchoring of Cu nanoparticles with NCNTs enables their excellent antioxidant capacity. Then, the obtained Cu NPs/NCNTs show remarkable POD-like activity in catalyzing TMB oxidation, with the attributes of long-term storage stability and reproducibility. Electrochemical assays and radical scavenging experiments reveal a dual mechanism action (involving reactive oxygen species and electron transfer) for the POD-mimicking activity. Furthermore, the developed colorimetric catalytic platform is applied to detect GA in actual tea samples, demonstrating high reliability and potential utility for GA monitoring in the food industry.

Regulating the Metal Nodes of In Situ Electropolymerized Metal-Organic Coordination Polymers for High Performance LIBs

Metal-organic coordination polymers (MOPs) comprised of redox-active organic moieties and metal ions emerge as an important class of electroactive materials for battery applications. The bipolar two transition metal-based (Fe and Co) coordination complexes bearing terpyridine-triphenylamine ligand are used as models to investigate the relationships between structure and electrochemical performance. It turned out that the choice of central metal atom has a profound influence on the practical voltage window and specific capacity. The high-performing poly(FeL)n electrode exhibits a reversible capacity of 272.5 mAh g-1 after 100 cycles at 50 mA g-1, excellent cycling stability up to 4000 cycles at 5A g-1 (capacity ration:83.1%), and excellent rate capacity. The poly(CoL)n electrode exhibits a significantly lower capacity of 107 mAh g-1 at the 100th cycle and inferior stability (54 mAh g-1 after 4000 cycles at 5A g-1, capacity retention: 38.7%). DFT analysis indicates that the metal center directly influences the electron cloud density of the metal-terpyridine structure, which in turn affects the redox activity of the polymer by varying the affinity to lithium ions and the charge transfer efficiency. These findings highlight the importance of metal centers in coordination polymers, providing direct guidance for the exploration of MOPs as novel resource-friendly cathode materials.

Three-Dimensional Metal-Organic Frameworks with Selectively Activated Aromatic Rings for High-Capacity and High-Rate Lithium-Ion Storage

Metal-organic frameworks (MOFs) are considered promising candidates for anode materials in Li-ion batteries (LIBs) owing to their designable structure, abundant active sites, and well-organized porosity. However, the structural factors governing active site utilization and Li-ion storage kinetics remain inadequately understood. In particular, the Li-ion storage behaviors of aromatic rings with high LUMO energy levels and situated in varying chemical environments remain a highly debated issue. Herein, a new cobalt-based MOF (Co-NTTA, NTTA ligand: 5,5',5''-((4,4',4''-nitrilotris (benzoyl)) tris-(azanediyl)) triisophthalic acid), featuring aromatic rings situated in diverse local environments, is deliberately designed and synthesized. Experimental characterizations and first-principles calculations have verified the occurrence of a reversible electrochemical reaction involving a total of 51 electrons among the NTTA ligands, cobalt cations, and Li+ ions. Unlike the traditional concept of superlithiation, the three inner aromatic rings are selectively activated by π-aromatic conjugation networks and π ⋯ ${\cdots }$ π stacking, contributing to a reversible 6-electron pseudocapacitive Li+ intercalation reaction. Conversely, the three outer aromatic rings remain inert toward Li+ ions. Impressively, the Co-NTTA MOF anode, with selectively activated aromatic rings, delivers a reversible capacity of up to 956 mAh g-1 at 200 mA g-1 and demonstrates exceptional high-rate durability, further supporting a 4.3 V lithium-ion hybrid electrochemical capacitor with high energy/power density.

Easily Water-Synthesisable Iron-Chloranilate Frameworks as High Energy and High-Power Cathodes for Sustainable Alkali-Ion Batteries

Achieving high battery performance from low-cost, easily synthesisable electrode materials is crucial for advancing energy storage technologies. Metal-organic frameworks (MOFs) combining inexpensive transition metals and organic ligands are promising candidates for high-capacity cathodes. Iron-chloranilate-water frameworks are herein reported to be produced in aqueous media under mild conditions. Removal of reticular water from known [Fe2(CAN)3(H2O)4] ⋅ 4H2O yields a new supramolecular metal-organic framework (SMOF), [Fe2(CAN)3(H2O)4]. Removing coordination water, a new 2D honeycomb-like MOF forms, Fe2(CAN)3, stable without counterions and solvent. This MOF adopts the unusual ABC layer-stacking, as determined using a combination of ab initio random structure searching, electron diffraction, and Rietveld refinement of powder XRD data. Magnetometry, Mossbauer and Raman spectroscopy confirm that all three [Fe2(CAN)3(H2O)x]⋅yH2O phases contain HS-Fe3+ and CAN2-, with magnetic ordering temperatures increasing (5→20 K) as the Fe-CAN connectivity increases. The SMOF and MOF show reversible (de)insertion of >4Li+/f.u. at average 2,59 V and 2,76 V vs Li+/Li, respectively. [Fe2(CAN)3] achieves 146 mAh/g at 1 C, thus specific energy (563 Wh/kg) and power (446 W/kg) in Li half-cells competitive with conventional LiFePO4 (~580 Wh/kg and ~450 W/kg). Beyond Li, [Fe2(CAN)3] delivers 394 Wh/kg and 421 Wh/kg, for Na and K half-cells respectively, becoming a competitive cathode for sustainable batteries.

Air-Stable High-Voltage Li-Ion Organic Cathode Enabled by Localized High-Concentration Electrolyte

While lithium-ion batteries have revolutionized the field of energy storage, their reliance on critical minerals such as cobalt and nickel raises significant concerns over resource availability and supply chain uncertainty. In this study, we revisit dithiin-fused dilithium naphthazarin (5,8-dihydroxy-1,4-naphthoquinone) (DNP-Li) as a high-voltage Li-ion organic cathode and evaluate its performance in conjunction with localized high-concentration electrolyte (LHCE). DNP-Li exhibits remarkable air and thermal stability, a high operating potential of 3.55 V vs. Li+/Li, and a specific capacity of 232 mAh g-1, positioning it as one of the most promising candidates among Li-ion organic cathodes. Furthermore, the electrochemical behavior of DNP-Li is strongly influenced by the electrolyte composition, giving distinct two-plateau or four-plateau voltage profiles accompanied by reversible or irreversible phase transitions in carbonate-based or LHCE electrolyte formulations, respectively. The reduced solubility of DNP-Li-based redox intermediates in LHCE enhances cycling stability, achieving a capacity retention of 85% after 50 cycles at 0.1C and 75% after 160 cycles at 0.5C, demonstrating a significant improvement compared to the carbonate-based electrolyte. This work highlights the critical role of solute-electrolyte interactions in modulating the electrochemical performance of multielectron small-molecule organic cathodes, offering new pathways for advancing sustainable and high-efficiency energy storage technologies.

Ionically conducting Li- and Na-phosphonates as organic electrode materials for rechargeable batteries

Facilitating rapid charge transfer in electrode materials necessitates the optimization of their ionic transport properties. Currently, only a limited number of Li/Na-ion organic cathode materials have been identified, and those exhibiting intrinsic solid-phase ionic conductivity are even rarer. In this study, we present tetra-lithium and sodium salts with the generic formulae: A4-Ph-CH3P and A4-Ph-PhP, wherein A = Li, Na; Ph-CH3P = 2,5-dioxido-1,4-phenylene bis(methylphosphinate); Ph-PhP = 2,5-dioxido-1,4-phenylene bis(phenylphosphinate), as novel alkali-ion reservoir cathode materials. Notably, A4-Ph-PhP exhibits impressive Li-ion and Na-ion conductivities, measured at 2.6 × 10-7 and 1.4 × 10-7 S cm-1, respectively, in a dry state at 30 °C. To the best of our knowledge, these represent the first example of small-molecule organic cathode materials with intrinsic Li+ and Na+ conductivity. Theoretical calculations provide further insight into the electrochemical activity of the Li/Na-phenolate groups, as well as the enhanced electron affinity resulting from -phenyl and -Na substitutions. Additionally, Na4-Ph-PhP displays two distinct charge-discharge plateaus at approximately 2.2 V and 2.7 V, and 2.0 V and 2.5 V vs. Na+/Na, respectively, and demonstrates stable cycling performance, with 100 cycles at a rate of 0.1C and an impressive 1000 cycles at 1C. This study not only expands the portfolio of phenolate-based organic salts for use in metal-ion batteries but also underscores the potential of phosphonate-based organic materials in advancing energy storage technologies.

Alkali Metal Ion Insertion in Polypyrrole Polyoxometalates for Multifunctional Actuator-Sensor-Energy Storage Devices

Modern research technology's goal is to produce multifunctional materials that require low energy. In this work, we have applied polypyrrole (PPy) doped with dodecyl benzenesulfonate (DBS-) with the addition of polyoxometalates (POM) such as phosphotungstic acid (PTA) forming PPyDBS-PT composites. Two different PTA concentrations (4 mM and 8 mM) were used to form PPyDBS-PT4 and PPyDBS-PT8. The higher concentration of PTA created a highly dense and compact film which can be observed from scanning electron microscopy (SEM cross-section image), and also contains fewer phosphotungstate anions (PT3-) inclusion (via energy-dispersive X-ray spectroscopy, EDX). Three different aqueous electrolytes, LiCl (lithium chloride), NaCl (sodium chloride), and KCl (potassium chloride), were applied to investigate how those alkali metal ions perform as typical cation-driven actuators. Cyclic voltammetry with linear actuation revealed the tendency LiCl > NaCl > KCl in view of better strain, charge density, electronic conductivity, and Young's modulus of PPyDBS-PT4 outperformed PPyDBS-PT8. Chronopotentiometric measurements showed high specific capacitance for PPyDBS-PT4 at 260.6 ± 21 F g-1 with capacity retention after 5000 cycles of 88.5%. The sensor calibration of PPyDBS-PT4 revealed that the alkali cations (Li+, Na+, and K+) can be differentiated from each other. The PPyDBS-PT4 has multifunctional applications such as actuators, sensors, and energy storage.

Green and Scalable Preparation of Highly Conductive Alkali Metal-dhta Coordination Polymers

2,5-Dihydroxyterephthalic acid (H4dhta) is well-known for its use in the construction of functional metal-organic frameworks (MOFs). Among them, simple coordination polymers (CPs), such as lithium and sodium coordination polymers with H4dhta, have been used successfully to synthesize electrically conductive MOFs and have also demonstrated great potential as positive or negative electrode materials on their own. However, there has been little exploration of the structure and physicochemical properties of these and other alkali complexes of H4dhta. To address this gap, a series of 1:1 alkali metal-dhta coordination polymers (Li-, Na-, K-, Rb-, Cs-), showing high conductivity with a nonmonotone trend inside the series, were synthesized using green mechanochemical processing. The crystal structures of these metal-organic conductors reveal the rich coordination chemistry of the alkali cations ranging from four to ten. Their electric conductivity was influenced by cation type, coordination environment, the water present in the structure, atmosphere, and temperature. Overall, this study not only sheds light on the fascinating behavior and efficiency of monoalkali metal-dhta CPs and paves the way for the development of more efficient coordination materials for energy storage and conversion applications but also proves that sometimes the smallest changes in materials' structure and composition can make a significant difference in conductivity.

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.

High-capacity dilithium hydroquinone cathode material for lithium-ion batteries

Lithiated organic cathode materials show great promise for practical applications in lithium-ion batteries owing to their Li-reservoir characteristics. However, the reported lithiated organic cathode materials still suffer from strict synthesis conditions and low capacity. Here we report a thermal intermolecular rearrangement method without organic solvents to prepare dilithium hydroquinone (Li2Q), which delivers a high capacity of 323 mAh g-1 with an average discharge voltage of 2.8 V. The reversible conversion between orthorhombic Li2Q and monoclinic benzoquinone during charge/discharge processes is revealed by in situ X-ray diffraction. Theoretical calculations show that the unique Li-O channels in Li2Q are beneficial for Li+ ion diffusion. In situ ultraviolet-visible spectra demonstrate that the dissolution issue of Li2Q electrodes during charge/discharge processes can be handled by separator modification, resulting in enhanced cycling stability. This work sheds light on the synthesis and battery application of high-capacity lithiated organic cathode materials.

Versatile Nitrogen-Centered Organic Redox-Active Materials for Alkali Metal-Ion Batteries

Versatile nitrogen-centered organic redox-active molecules have gained significant attention in alkali metal-ion batteries (AMIBs) due to their low cost, low toxicity, and ease of preparation. Specially, their multiple reaction categories (anion/cation insertion types of reaction) and higher operating voltage, when compared to traditional conjugated carbonyl materials, underscore their promising prospects. However, the high solubility of nitrogen-centered redox active materials in organic electrolyte and their low electronic conductivity contribute to inferior cycling performance, sluggish reaction kinetics, and limited rate capability. This review provides a detailed overview of nitrogen-centered redox-active materials, encompassing their redox chemistry, solutions to overcome shortcomings, characterization of charge storage mechanisms, and recent progress. Additionally, prospects and directions are proposed for future investigations. It is anticipated that this review will stimulate further exploration of underlying mechanisms and interface chemistry through in situ characterization techniques, thereby promoting the practical application of nitrogen-centered redox-active materials in AMIBs.

Covalent Organic Frameworks as Electrode Materials for Alkali Metal-ion Batteries

Covalent organic frameworks (COFs) are a class of porous crystalline polymeric materials constructed by linking organic small molecules through covalent bonds. COFs have the advantages of strong covalent bond network, adjustable pore structure, large specific surface area and excellent thermal stability, and have broad application prospects in various fields. Based on these advantages, rational COFs design strategies such as the introduction of active sites, construction of conjugated structures, and carbon material composite, etc. can effectively improve the conductivity and stability of the electrode materials in the field of batteries. This paper introduces the latest research results of high-performance COFs electrode materials in alkali metal-ion batteries (LIBs, SIBs, PIBs and LSBs) and other advanced batteries. The current challenges and future design directions of COFs-based electrode are discussed. It provides useful insights for the design of novel COFs structures and the development of high-performance alkali metal-ion batteries.

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.

Towards the 4 V-class n-type organic lithium-ion positive electrode materials: the case of conjugated triflimides and cyanamides

Organic electrode materials have garnered a great deal of interest owing to their sustainability, cost-efficiency, and design flexibility metrics. Despite numerous endeavors to fine-tune their redox potential, the pool of organic positive electrode materials with a redox potential above 3 V versus Li+/Li0, and maintaining air stability in the Li-reservoir configuration remains limited. This study expands the chemical landscape of organic Li-ion positive electrode chemistries towards the 4 V-class through molecular design based on electron density depletion within the redox center via the mesomeric effect of electron-withdrawing groups (EWGs). This results in the development of novel families of conjugated triflimides and cyanamides as high-voltage electrode materials for organic lithium-ion batteries. These are found to exhibit ambient air stability and demonstrate reversible electrochemistry with redox potentials spanning the range of 3.1 V to 3.8 V (versus Li+/Li0), marking the highest reported values so far within the realm of n-type organic chemistries. Through comprehensive structural analysis and extensive electrochemical studies, we elucidate the relationship between the molecular structure and the ability to fine-tune the redox potential. These findings offer promising opportunities to customize the redox properties of organic electrodes, bridging the gap with their inorganic counterparts for application in sustainable and eco-friendly electrochemical energy storage devices.

Bimetallic Anionic Organic Frameworks with Solid-State Cation Conduction for Charge Storage Applications

A new phosphonate-based anionic bimetallic organic framework, with the general formula of A4 -Zn-DOBDP (wherein A is Li+ or Na+ , and DOBDP6- is the 2,5-dioxido-1,4-benzenediphosphate ligand) is prepared and characterized for energy storage applications. With four alkali cations per formula unit, the A4 -Zn-DOBDP MOF is found to be the first example of non-solvated cation conducting MOF with measured conductivities of 5.4×10-8  S cm-1 and 3.4×10-8  S cm-1 for Li4 - and Na4 - phases, indicating phase and composition effects of Li+ and Na+ shuttling through the channels. Three orders of magnitude increase in ionic conductivity is further attained upon solvation with propylene carbonate, placing this system among the best MOF ionic conductors at room temperature. As positive electrode material, Li4 -Zn-DOBDP delivers a specific capacity of 140 mAh g-1 at a high average discharge potential of 3.2 V (vs. Li+ /Li) with 90 % of capacity retention over 100 cycles. The significance of this research extends from the development of a new family of electroactive phosphonate-based MOFs with inherent ionic conductivity and reversible cation storage, to providing elementary insights into the development of highly sought yet still evasive MOFs with mixed-ion and electron conduction for energy storage applications.

Polyimides as Promising Materials for Lithium-Ion Batteries: A Review

Lithium-ion batteries (LIBs) have helped revolutionize the modern world and are now advancing the alternative energy field. Several technical challenges are associated with LIBs, such as increasing their energy density, improving their safety, and prolonging their lifespan. Pressed by these issues, researchers are striving to find effective solutions and new materials for next-generation LIBs. Polymers play a more and more important role in satisfying the ever-increasing requirements for LIBs. Polyimides (PIs), a special functional polymer, possess unparalleled advantages, such as excellent mechanical strength, extremely high thermal stability, and excellent chemical inertness; they are a promising material for LIBs. Herein, we discuss the current applications of PIs in LIBs, including coatings, separators, binders, solid-state polymer electrolytes, and active storage materials, to improve high-voltage performance, safety, cyclability, flexibility, and sustainability. Existing technical challenges are described, and strategies for solving current issues are proposed. Finally, potential directions for implementing PIs in LIBs are outlined.

Revealing the reversible solid-state electrochemistry of lithium-containing conjugated oximates for organic batteries

In the rising advent of organic Li-ion positive electrode materials with increased energy content, chemistries with high redox potential and intrinsic oxidation stability remain a challenge. Here, we report the solid-phase reversible electrochemistry of the oximate organic redox functionality. The disclosed oximate chemistries, including cyclic, acyclic, aliphatic, and tetra-functional stereotypes, uncover the complex interplay between the molecular structure and the electroactivity. Among the exotic features, the most appealing one is the reversible electrochemical polymerization accompanying the charge storage process in solid phase, through intermolecular azodioxy bond coupling. The best-performing oximate delivers a high reversible capacity of 350 mAh g^-1 at an average potential of 3.0 versus Li⁺/Li⁰, attaining 1 kWh kg^-1 specific energy content at the material level metric. This work ascertains a strong link between electrochemistry, organic chemistry, and battery science by emphasizing on how different phases, mechanisms, and performances can be accessed using a single chemical functionality.

Structure Design for Ultrahigh Power Density Proton Exchange Membrane Fuel Cell

Next-generation ultrahigh power density proton exchange membrane fuel cells rely not only on high-performance membrane electrode assembly (MEA) but also on an optimal cell structure. To this end, this work comprehensively investigates the cell performance under various structures, and it is revealed that there is unexploited performance improvement in structure design because its positive effect enhancing gas supply is often inhibited by worse proton/electron conduction. Utilizing fine channel/rib or the porous flow field is feasible to eliminate the gas diffusion layer (GDL) and hence increase the power density significantly due to the decrease of cell thickness and gas/electron transfer resistances. The cell structure combining fine channel/rib, GDL elimination and double-cell structure is believed to increase the power density from 4.4 to 6.52 kW L^-1 with the existing MEA, showing nearly equal importance with the new MEA development in achieving the target of 9.0 kW L^-1 .

Emerging Lithiated Organic Cathode Materials for Lithium-Ion Full Batteries

Organic electrode materials have application potential in lithium batteries owing to their high capacity, abundant resources, and structural designability. However, most reported organic cathodes are at oxidized states (namely unlithiated compounds) and thus need to couple with Li-rich anodes. In contrast, lithiated organic cathode materials could act as a Li reservoir and match with Li-free anodes such as graphite, showing great promise for practical full-battery applications. Here we summarize the synthesis, stability, and battery applications of lithiated organic cathode materials, including synthetic methods, stability against O₂ and H₂ O in air, and strategies to improve comprehensive electrochemical performance. Future research should be focused on new redox chemistries and the construction of full batteries with lithiated organic cathodes and commercial anodes under practical conditions. This Minireview will encourage more efforts on lithiated organic cathode materials and finally promote their commercialization.