Conjugated System of PEDOT:PSS-Induced Self-Doped PANI for Flexible Zinc-Ion Batteries with Enhanced Capacity and Cyclability

Supramolecular channels via crown ether functionalized polyaniline for proton-self-doped cathode in aqueous zinc-ion battery

Polyaniline (PANI) has been widely used as a cathode in aqueous zinc-ion batteries (AZIBs) because of its attractive conductivity and energy storage capability. However, the extensive application of PANI is limited by spontaneous deprotonation and slow diffusion kinetics. Herein, an 18-crown-6-functionalised PANI pseudorotaxane (18C6@PANI) cathode is successfully developed through a facile template-directed polymerisation reaction. The 18C6@PANI cathode exhibits a high specific capacity of 256 mAh g-1 at 0.2 A/g, excellent rate performance of 134 mAh g-1 at 6 A/g and outstanding cycle stability at a high current density of 3 A/g over 10,000 cycles. Experimental and theoretical analyses demonstrate the formation of the -N-Zn-O- structure. The abundant supramolecular channels in pseudorotaxane, induced by crown ether functional groups, are beneficial for achieving superior cyclability and rate capability. These encouraging results highlight the potential for designing more efficient PANI-based cathodes for high-performance AZIBs.

Bio-catalyzed oxidation self-charging zinc-polymer batteries

Oxidation self-charging batteries have emerged with the demand for powering electronic devices around the clock. The low efficiency of self-charging has been the key challenge at present. Here, a more efficient autoxidation self-charging mechanism is realized by introducing hemoglobin (Hb) as a positive electrode additive in the polyaniline (PANI)-zinc battery system. The heme acts as a catalyst that reduces the energy barrier of the autoxidation reaction by regulating the charge and spin state of O2. To realize self-charging, the adsorbed O2 molecules capture electrons of the reduced (discharged state) PANI, leading to the desorption of zinc ions and the oxidation of PANI to complete self-charging. The battery can discharge for 12 min (0.5 C) after 50 self-charging/discharge cycles, while there is nearly no discharge capacity in the absence of Hb. This biology-inspired electronic regulation strategy may inspire new ideas to boost the performance of self-charging batteries.

Peelable Microwave Absorption Coating with Reusable and Anticorrosion Merits

The peelable microwave absorption (MA) coating with reversible adhesion for stable presence on substrates and easy release without any residuals is highly desired in temporary electromagnetic protection, which can quickly enter and disengage the electromagnetic protection state according to the real-time changeable harsh surroundings. On the contrary, with the incorporation of abundant absorbent to achieve excellent MA ability, the tunable adhesion and sufficient cohesion are extremely challenging to fulfill the above requirement. The reported peelable coatings still have problems in controlling adhesion/cohesion strength and coating release, facing substantial residuals after peeling even using complex chemical modification or abundant additives. Herein, a peelable MA coating based on the block characteristics of polar and nonpolar segments of poly(styrene-(ethylene-co-butylene)-styrene) (SEBS) is successfully developed. The polyaniline-decorated carbon nanotube as a microwave absorber plays a positive influence on the adhesion/cohesion of the coating due to bonding interaction. The competitive effective absorption bandwidth (EAB) of 8.8 GHz and controllable yet reversible adhesion release on various substrates and complex surfaces have been achieved. The reusability endows peelable MA coating with 93% retention of EAB even after ten coating-peeling cycles. The coating with excellent chemical and adhesion stability can effectively protect substrates from salt/acid/alkali corrosion, showing over 98% retention of EAB even after 8 h of accelerated corrosion. Our peelable MA coating via a general yet reliable approach provides a prospect for temporary electromagnetic protection.

Proton-self-doped PANI@CC as the cathode for high-performance aqueous zinc-ion battery

Aqueous zinc-ion batteries (AZIB) have several advantages such as low cost, large theoretical capacity and good safety. However, the development of polyaniline (PANI) cathode materials has been limited by slow diffusion kinetics. Herein, proton-self-doped polyaniline@carbon cloth (CC) (PANI@CC) was prepared via in-situ polymerization, where polyaniline was deposited on an activated carbon cloth. The PANI@CC cathode exhibits a high specific capacity of 234.3 mA h g-1 at 0.5 A g-1, and excellent rate performance, delivering a capacity of 143 mA h g-1 at 10 A g-1. Furthermore, the reversible redox conversion during the charge-discharge process was studied using ex-situ X-ray photoelectron spectroscopy (XPS) and ex-situ Raman spectra. The results show that the excellent performance of the PANI@CC battery can be attributed to the formation of a conductive network between the carbon cloth and polyaniline. Also, a mixing mechanism involving insertion/extraction of Zn2+/H+ and a double-ion process is proposed. PANI@CC electrode is a novel idea for developing high-performance batteries.

Improving the Cycling Stability of Aqueous Zinc-Ion Batteries by Preintercalation of Polyaniline in Hydrated Vanadium Oxide

This paper reports the synthesis and characterization of hydrated vanadium oxide (VOH) and chemically preintercalated polyanilines in VOH, labeled as PAVO-H as the cathode material for aqueous zinc-ion batteries. Synthesized PAVO-H has a high surface area and rod-shaped morphology. PAVO-H has an increased interlayer distance of 13.36 Å. PAVO-H offers high specific capacities of 330 and 225 mAh g^-1 at 50 mA g^-1 and 4 A g^-1 of current densities, respectively, with a 92% capacity retention rate of over 3000 cycles. The preintercalation of polyaniline is likely to catalyze the redox reaction and facilitate and simplify transport kinetics. It is also possible that the preintercalation of polyaniline permits the insertion of large hydrated Zn ions and reduces the formation of zinc basic salts.

Leaf-like ionic covalent organic framework for the highly efficient and selective removal of non-steroidal anti-inflammatory drugs: Adsorption performance and mechanism insights

In recent years, ionic covalent organic frameworks (iCOFs) have become popular for the removal of contaminants from water. Herein, we employed 2-hydroxybenzene-1,3,5-tricarbaldehyde (TFP) and 1,3-diaminoguanidine monohydrochloride (Dg_Cl) to develop a novel leaf-like iCOF (TFP-Dg_Cl) for the highly efficient and selective removal of non-steroidal anti-inflammatory drugs (NSAIDs). The uniformly distributed adsorption sites, suitable pore sizes, and functional groups (hydroxyl groups, guanidinium groups, and aromatic groups) of the TFP-Dg_Cl endowed it with powerful and selective adsorption capacities for NSAIDs. Remarkably, the optimal leaf-like TFP-Dg_Cl demonstrated an excellent maximum adsorption capacity (1100.08 mg/g) for diclofenac sodium (DCF), to the best of our knowledge, the largest adsorption capacity ever achieved for DCF. Further testing under varying environmental conditions such as pH, different types of anions, and multi-component systems confirmed the practical suitability of the TFP-Dg_Cl. Moreover, the prepared TFP-Dg_Cl exhibited exceptional reusability and stability through six adsorption-desorption cycles. Finally, the adsorption mechanisms of NSAIDs on leaf-like TFP-Dg_Cl were confirmed as electrostatic interactions, hydrogen bonding, and π-π interactions. This work significantly supplements to our understanding of iCOFs and provides new insights into the removal of NSAIDs from wastewater.

Material Choice and Structure Design of Flexible Battery Electrode

With the development of flexible electronics, the demand for flexibility is gradually put forward for its energy supply device, i.e., battery, to fit complex curved surfaces with good fatigue resistance and safety. As an important component of flexible batteries, flexible electrodes play a key role in the energy density, power density, and mechanical flexibility of batteries. Their large-scale commercial applications depend on the fulfillment of the commercial requirements and the fabrication methods of electrode materials. In this paper, the deformable electrode materials and structural design for flexible batteries are summarized, with the purpose of flexibility. The advantages and disadvantages of the application of various flexible materials (carbon nanotubes, graphene, MXene, carbon fiber/carbon fiber cloth, and conducting polymers) and flexible structures (buckling structure, helical structure, and kirigami structure) in flexible battery electrodes are discussed. In addition, the application scenarios of flexible batteries and the main challenges and future development of flexible electrode fabrication are also discussed, providing general guidance for the research of high-performance flexible electrodes.

Comparative Review on the Aqueous Zinc-Ion Batteries (AZIBs) and Flexible Zinc-Ion Batteries (FZIBs)

Lithium-ion batteries (LIBs) have been considered an easily accessible battery technology because of their low weight, cheapness, etc. Unfortunately, they have significant drawbacks, such as flammability and scarcity of lithium. Since the components of zinc-ion batteries are nonflammable, nontoxic, and cheap, AZIBs could be a suitable replacement for LIBs. In this article, the advantages and drawbacks of AZIBs over other energy storage devices are briefly discussed. This review focused on the cathode materials and electrolytes for AZIBs. In addition, we discussed the approaches to improve the electrochemical performance of zinc batteries. Here, we also discussed the polymer gel electrolytes and the electrodes for flexible zinc-ion batteries (FZIBs). Moreover, we have outlined the importance of temperature and additives in a flexible zinc-ion battery. Finally, we have discussed anode materials for both AZIBs and FZIBs. This review has summarized the advantages and disadvantages of AZIBs and FZIBs for future applications in commercial battery technology.

Zinc-Ion Storage Mechanism of Polyaniline for Rechargeable Aqueous Zinc-Ion Batteries

Aqueous multivalent ion batteries, especially aqueous zinc-ion batteries (ZIBs), have promising energy storage application due to their unique merits of safety, high ionic conductivity, and high gravimetric energy density. To improve their electrochemical performance, polyaniline (PANI) is often chosen to suppress cathode dissolution. Herein, this work focuses on the zinc ion storage behavior of a PANI cathode. The energy storage mechanism of PANI is associated with four types of protonated/non-protonated amine or imine. The PANI cathode achieves a high capacity of 74 mAh g⁻¹ at 0.3 A g⁻¹ and maintains 48.4% of its initial discharge capacity after 1000 cycles. It also demonstrates an ultrahigh diffusion coefficient of 6.25 × 10⁻⁹~7.82 × 10⁻⁸ cm⁻² s⁻¹ during discharging and 7.69 × 10⁻¹⁰~1.81 × 10⁻⁷ cm⁻² s⁻¹ during charging processes, which is one or two orders of magnitude higher than other reported studies. This work sheds a light on developing PANI-composited cathodes in rechargeable aqueous ZIBs energy storage devices.

Aqueous Multivalent Charge Storage Mechanism in Aromatic Diamine-Based Organic Electrodes

Rechargeable batteries employing aqueous electrolytes are more reliable and cost-effective as well as possess high ionic conductivity compared to the flammable organic electrolyte solutions. Among these types of batteries, aqueous batteries with multivalent ions attract more attention in terms of providing high energy density. Herein, electrochemical behavior of an organic electrode based on a highly aromatic polymer containing 2,3-diaminophenazine repeating unit, namely poly(ortho-phenylenediamine) (PoPD), is tested in two different multivalent ions (Zn²⁺ and Al³⁺) containing aqueous electrolytes, that is, in zinc sulfate and aluminum chloride solutions. PoPD is synthesized via electropolymerization, and its ion transport and storage mechanism are comprehensively investigated by structural and electrochemical analyses. The electrochemical quartz crystal microbalance, time-dependent Fourier transform infrared, and electrochemical impedance spectroscopy analyses as well as ex situ X-ray diffraction observations established that along with the Zn²⁺ or Al³⁺ ions, reversible proton insertion/extraction also takes place. Contrary to the most of the organic electrodes that requires the use of conductive carbon additives, the electrodeposited PoPD electrode is intrinsically electrically conductive enough, resulting in a binder and additive free electrode assembly. In addition, its discharge products do not dissolve in aqueous medium. As a whole, the resulting PoPD electrode delivers excellent rate performances with prolonged cycle life in which discharge capacities of ∼110 mAh g^-1 in 0.25 M AlCl₃ and ∼93 mAh g^-1 in 1 M ZnSO₄ aqueous electrolyte after 1000 cycles at a current density of 5C have been achieved.

Research Progresses and Challenges of Flexible Zinc Battery

Flexible zinc batteries have great potential in wearable electronic devices due to their high safety, low cost, and environmental friendliness. In the past few years, a great deal of work on flexible zinc batteries has been reported, with exciting results. Therefore, many solutions have been proposed in electrode design and electrolyte preparation to ensure the desired flexibility without sacrificing the capacity. This paper reviews the recent progress of flexible zinc batteries. We discuss the differences between various anode materials, cathode materials, and electrolytes, introduce the differences of electrode preparation methods of active materials on flexible substrates and their influence on the performance of the battery. Finally, the challenges and future research trends of flexible zinc batteries in capacity and mechanical properties are pointed out.

Conjugated Molecules and Polymers in Secondary Batteries: A Perspective

Intrinsically conducting polymers constituting a subclass of macromolecules, as well as a still growing family of large, conjugated molecules, oligomers, and polymers, have attracted research interest for the recent decades. Closely corresponding to the fascination of these materials, combining typical properties of organic polymers and metallic materials, numerous applications have been suggested, explored, and sometimes transferred into products. In electrochemistry, they have been used in various functions beyond the initially proposed and obvious application as active masses in devices for electrochemical energy conversion and storage. This perspective contribution wraps up basic facts that are necessary to understand the behavior and properties of the oligo and polymers and their behavior in electrochemical cells for energy conversion by electrode reactions and associated energy storage. Representative examples are presented and discussed, and an overview of the state of research and development is provided. Particular attention is paid to stability and related aspects of practical importance. Future trends and perspectives are indicated.

Iron-Based NASICON-Type Na4 Fe3 (PO4 )2 (P2 O7 ) Cathode for Zinc-Ion Battery: Zn2+ /Na+ Co-Intercalation Enabling High Capacity

The development of high-performance cathode materials for aqueous zinc-ion batteries (ZIBs) based on nontoxic and earth-abundant elements remains a great challenge. This study introduces the iron-based NASICON-type material Na₄ Fe₃ (PO₄ )₂ (P₂ O7) with carbon layer (NFPP@C) as a cathode material for ZIBs. When Zn²⁺ /Na⁺ dual ion electrolyte is employed, NFPP@C shows a high capacity of 114.4 mAh g^-1 with two voltage plateaus, excellent rate capability (95 mAh g^-1 at 2 A g^-1 ), and long-term cycling stability (66.4 mAh g^-1 after 1800 cycles at 1 A g^-1 ). The outstanding electrochemical performance is ascribed to the synergistic use of NFPP@C and dual ion electrolyte. The NASICON-structure and carbon layer of NFPP@C enable fast ion and electron transport, whereas Na⁺ in the electrolyte reduces the concentration gradient between the electrode and electrolyte, and thus inhibits excessive extraction of Na⁺ from NFPP, maintaining structural stability. Moreover, Zn²⁺ /Na⁺ co-intercalation in NFPP@C brings two potential platforms and enhanced capacity.

A review of π-conjugated polymer-based nanocomposites for metal-ion batteries and supercapacitors

Owing to their extraordinary properties of π-conjugated polymers (π-CPs), such as light weight, structural versatility, ease of synthesis and environmentally friendly nature, they have attracted considerable attention as electrode material for metal-ion batteries (MIBs) and supercapacitors (SCPs). Recently, researchers have focused on developing nanostructured π-CPs and their composites with metal oxides and carbon-based materials to enhance the energy density and capacitive performance of MIBs and SCPs. Also, the researchers recently demonstrated various novel strategies to combine high electrical conductivity and high redox activity of different π-CPs. To reflect this fact, the present review investigates the current advancements in the synthesis of nanostructured π-CPs and their composites. Further, this review explores the recent development in different methods for the fabrication and design of π-CPs electrodes for MIBs and SCPs. In review, finally, the future prospects and challenges of π-CPs as an electrode materials for strategies for MIBs and SCPs are also presented.

Conductive Polymer Composites for Hydrogen Sulphide Sensors Working at Sub-PPM Level and Room Temperature

Hybrid composites based on tin chloride and the conductive polymers, polyaniline (PAni) and poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), were integrated into high-performance hydrogen sulphide (H2S) gas sensors working at room temperature. The morphology and chemical properties were studied by scanning and transmission electron microscopy (SEM, TEM), energy dispersive spectroscopy (EDS) and Fourier-transform infrared (FTIR). The composites demonstrated a slightly porous nanostructure and strong interactions between the polymers and the metal salt, which slightly dopes PAni. The hybrid sensors exhibited a very low detection limit (<85 ppb), fast response, repeatability, reproducibility and stability over one month. Moreover, this work presents how calibration based on the derivative of the signal can give hybrid sensors the ability to quantify the concentration of targeted gas, even during continuous variation of the analyte concentration. Finally, the effect of interfering species, such as water and ammonia, is discussed.

A Polymer/Graphene Composite Cathode with Active Carbonyls and Secondary Amine Moieties for High-Performance Aqueous Zn-Organic Batteries Involving Dual-Ion Mechanism

Aqueous zinc-ion batteries (AZIBs) are regarded as one of the most promising alternative technology to lithium-ion batteries on account of their low flammability and cost-benefits. Among various cathode materials in AZIBs, environment-friendly and sustainable organic electrode materials stand out owing to their structural diversity and tunability. However, their limited rate capability and cycle stability remain the obstacles to their further application in AZIBs. Herein, a mixed cathode design strategy including polymerization and carbon materials hybridization is adopted to assemble high-rate and durable AZIBs. Specifically, a polymer/graphene composite cathode with active carbonyls and secondary amine moieties is prepared to construct high-performance aqueous Zn-organic batteries. Furthermore, a hybrid energy storage mechanism involving dual-ion mechanism is confirmed by various ex situ characterization techniques, providing promising battery chemistry. Thus, this work opens up a new path to high performance AZIBs through a rational cathode design.

Sulfonic-Group-Grafted Ti3C2Tx MXene: A Silver Bullet to Settle the Instability of Polyaniline toward High-Performance Zn-Ion Batteries

Polyaniline (PANI) is a promising cathode material for Zn-ion batteries (ZIBs) due to its intrinsic conductivity and redox activity; however, the achievements of PANI in high-performance ZIBs are largely hindered by its instability during the repeated charge/discharge. Taking advantage of the high conductivity, flexibility, and grafting ability together, a surface-engineered Ti₃C₂T_x MXene is designed as a silver bullet to fight against the deprotonation and swelling/shrinking issues occurring in the redox process of PANI, which are the origins of its instability. Specifically, the sulfonic-group-grafted Ti₃C₂T_x(S-Ti₃C₂T_x) continuously provides protons to improve the protonation degree of PANI and maintains the polymer backbone at a locally low pH, which effectively inhibits deprotonation and brings high redox activity along with good reversibility. Meanwhile, the conductive and flexible natures of S-Ti₃C₂T_x assist the fast redox reaction of PANI and concurrently buffer its corresponding swelling/shrinking. Therefore, the S-Ti₃C₂T_x-enhanced PANI cathode simultaneously achieves a high discharge capacity of 262 mAh g^-1 at 0.5 A g^-1, a superior rate capability of 160 mAh g^-1 at 15 A g^-1, and a good cyclability over 5000 cycles with 100% coulombic efficiency. This work enlightens the development of versatile MXene via surface engineering for advanced batteries.

Aqueous Rechargeable Zn-ion Batteries: Strategies for Improving the Energy Storage Performance

The growing demand for the renewable energy storage technologies stimulated the quest for efficient energy storage devices. In recent years, the rechargeable aqueous zinc-based battery technologies are emerging as a compelling alternative to the lithium-based batteries owing to safety, eco-friendliness, and cost-effectiveness. Among the zinc-based energy devices, rechargeable zinc-ion batteries (ZIBs) are drawing considerable attention. However, they are plagued with several issues, including cathode dissolution, dendrite formation, etc.. Despite several efforts in the recent past, ZIBs are still in their infant stages and have yet to reach the stage of large-scale production. Finding stable Zn²⁺ intercalation cathode material with high operating voltage and long cycling stability as well as dendrite-free Zn anode is the main challenge in the development of efficient zinc-ion storage devices. This Review discusses the various strategies, in terms of the engineering of cathode, anode and electrolyte, adopted for improving the charge storage performance of ZIBs and highlights the recent ZIB technological innovations. A brief account on the history of zinc-based devices and various cathode materials tested for ZIB fabrication in the last five years are also included. The main focus of this Review is to provide a detailed account on the rational engineering of the electrodes, electrolytes, and separators for improving the charge storage performance with a future perspective to achieving high energy density and long cycling stability and large-scale production for practical application.

Intrinsically conducting polymers and their combinations with redox-active molecules for rechargeable battery electrodes: an update

Intrinsically conducting polymers and their copolymers and composites with redox-active organic molecules prepared by chemical as well as electrochemical polymerization may yield active masses without additional binder and conducting agents for secondary battery electrodes possibly utilizing the advantageous properties of both constituents are discussed. Beyond these possibilities these polymers have found many applications and functions for various further purposes in secondary batteries, as binders, as protective coatings limiting active material corrosion, unwanted dissolution of active mass ingredients or migration of electrode reaction participants. Selected highlights from this rapidly developing and very diverse field are presented. Possible developments and future directions are outlined.

Rapid and efficient removal of diclofenac sodium from aqueous solution via ternary core-shell CS@PANI@LDH composite: Experimental and adsorption mechanism study

The efficient removal of Diclofenac sodium (DCF), a nonsteroidal anti-inflammatory drug, has attracted more and more attention. In this work, ternary core-shell CS@PANI@LDH composite was synthesized via the in-situ growth of Mg/Al layered double hydroxide plates onto polyaniline-wrapped carbon sphere and applied for DCF removal. Various influence factors like concentration, pH, time, temperature, and background electrolytes were systematically investigated. The maximum adsorption capacity was 618.16 mg/g. Besides, after 5 regeneration cycles, CS@PANI@LDH still retained high adsorption capacity. The adsorption mechanism was investigated by Fourier transformed infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) characterization analyses. Simultaneously, the Multiwfn program combined the Chimera program was applied to calculate and visualize the localized orbit locator (LOL) of π electrons in DCF^- molecule, which explored the π electronic structure and conjugation characteristics of DCF^- molecule. Moreover, the Independent Gradient Model (IGM) analysis based on pro-molecular density revealed the interaction sites and interaction strength between DCF and LDH. The adsorption mechanism could be explained through electrostatic interaction and hydrogen bonding between LDH and DCF, π-π interaction between DCF and PANI. It was the synergistic effects of different interactions that improved the adsorption of DCF by CS@PANI@LDH composite.

Improving the Performance of a Graphite Foil/Polyaniline Electrode Material by a Thin PEDOT:PSS Layer for Application in Flexible, High Power Supercapacitors

In this study, we present a novel strategy for enhancing polyaniline stability and thus obtaining an electrode material with practical application in supercapacitors. A promising (graphite foil/polyaniline/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) GF/PANI/PEDOT:PSS) electrode material was characterized and used in the construction of a symmetric supercapacitor that provides an outstanding high power density. For this purpose, the electropolymerization of PANI was carried out on a graphite foil and then a thin protective layer of PEDOT:PSS was deposited. The presence of the nanometer PEDOT:PSS layer made it possible to widen the electroactivity potential range of the electrode material. Moreover, the synergy between materials positively affected the amount of accumulated charge, and thus the thin PEDOT:PSS layer contributed to enhancing the specific capacity of the electrode material. The electrochemical performance of the GF/PANI/PEDOT:PSS electrode, as well as the symmetrical supercapacitor, was investigated by cyclic voltammetry and galvanostatic charge/discharge cycles in 1 M H2SO4 at room temperature. The fabricated electrode material shows a high specific capacitance (Csp) of 557.4 Fg-1 and areal capacitance (Careal) of 2600 mF·cm-2 in 1 M H2SO4 at a current density of 200 mA·cm-2 (~4 A·g-1). The supercapacitor performance was studied and the results show that a thin PEDOT:PSS layer enables cycling stability improvement of the device from 54% to 67% after 10,000 cycles, and provides a high specific capacity (159.8 F·g-1) and a maximum specific power (18,043 W·kg-1) for practical applications.

Stable Hydrogel Electrolytes for Flexible and Submarine-Use Zn-Ion Batteries

Due to their intrinsic safety, low cost, and eco-friendliness, aqueous Zn-ion batteries (ZIBs) have shown significant potential for wearable and flexible electronic devices. However, the lack of a stable and durable electrolyte for flexible ZIBs greatly hampers their applications in harsh conditions during daily use. In this work, we reported a stable hydrogel electrolyte, fabricated by coupling the grafted copolymer xanthan gum-polyacrylamide (XG-PAM) with cotton cellulose nanofiber (CNF), denoted XG-PAM/CNF. The designed XG-PAM/CNF hydrogel electrolyte exhibited high ionic conductivity (28.8 mS cm^-1), good adhesion, high mechanical strength, and strong ion adsorption. In addition, it also shows an inhibition effect on the generation of dendrites. The flexible ZIBs with the XG-PAM/CNF hydrogel electrolyte achieved high specific capacity (237 mA·h g^-1) and excellent cycling stability (86.2% retention over 1000 cycles at 4 C). Notably, flexible ZIBs withstand severe conditions, such as bending, folding, poking, washing, soaking, and underwater usage. Furthermore, an underwater warning rescue system application was proposed. Consequently, this work provides a new approach and application for the development of reliable and durable wearable energy storage devices.

Design Strategies for High-Performance Aqueous Zn/Organic Batteries

Organic electroactive compounds are attractive to serve as the cathode materials of aqueous zinc-ion batteries (ZIBs) because of their resource renewability, environmentally friendliness and structural diversity. Up to now, various organic electrode materials have been developed and different redox mechanisms are observed in aqueous Zn/organic battery systems. In this Minireview, we present the recent developments in the energy storage mechanisms and design of the organic electrode materials of aqueous ZIBs, including carbonyl compounds, imine compounds, conductive polymers, nitronyl nitroxides, organosulfur polymers and triphenylamine derivatives. Furthermore, we highlight the design strategies to improve their electrochemical performance in the aspects of specific capacity, output voltage, cycle life and rate capability. Finally, we discuss the challenges and future perspectives of aqueous Zn/organic batteries.

A Covalent Organic Framework with Extended π-Conjugated Building Units as a Highly Efficient Recipient for Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries have recently become a research hotspot because of their tempting theoretical capacity and energy density. Nevertheless, the notorious shuttle of polysulfides hinders the advancement of Li-S batteries. Herein, a two-dimensional covalent organic framework (COF) with extended π-conjugated units has been designed, synthesized, and used as sulfur recipients with 88.4 wt % in loading. The COF offers an elaborate platform for sufficient Li-S redox reactions with almost theoretical capacity release (1617 mA h g^-1 at 0.1 C), satisfactory rate capability, and intensively traps polysulfides for a decent Coulombic efficiency (ca. 98.0%) and extremely low capacity decay (0.077% per cycle after 528 cycles at 0.5 C). The structural factors of the COF on the high-performance batteries are revealed by density functional theory calculations to be the high degrees of conjugation and proper interlayer space. This work not only demonstrates the great potential of COFs as highly efficient sulfur recipients but also provides a viable guidance for further design of COF materials to tackle shuttling issues toward active materials in electrochemical energy storage.

In Situ Encapsulating Metal Oxides into Core-Shell Hierarchical Hybrid Fibers for Flexible Zinc-Ion Batteries toward High Durability and Ultrafast Capability for Wearable Applications

Rechargeable aqueous Zn-ion batteries are promising power sources for the advanced electronics because of their low cost, high safety, environmental friendliness, etc. However, their practical applications are severely restricted by the low energy density, poor rate capability, and low mass loading. In this work, a new type of the core-shell hierarchical structured hybrid fiber with encapsulated metal oxide nanoparticles is reported, which is used as a flexible cathode for aqueous Zn-ion batteries. The hierarchical hybrid fibers, consisting of one-dimensional (1D) central hollow shell and inside carbon network, build bicontinuous conductive pathways and highly porous networks for the in situ formed metal oxide nanoparticles. The core-shell hierarchical structure facilitates fast electron/ion transport and high mass loading; moreover, the 1D structure ensures good pliability and high flexibility. Two transition metal oxides, i.e., Zn₂V₂O₇ and V₂O₅, are employed to construct the hybrid fibers. Both hybrid fibers exhibit excellent electrochemical properties and superior high rate capabilities. They achieve the capacities of 162 mAh g^-1 (for Zn₂V₂O₇) and 409 mAh g^-1 (for V₂O₅) even at a high current density of 8 A g^-1. Moreover, the flexible Zn-ion batteries are fabricated on the basis of the hybrid fibers. The superior energy/power density and good long-term cycling stability demonstrate their good energy storage capability and fast charge/discharge capability. Especially, the well-retained performance under high degree of outside deformations further promotes their applications in wearable electronics.