A Four-Electron Sulfur Electrode Hosting a Cu2+ /Cu+ Redox Charge Carrier

Non-Equilibrium Assembly of Atomically-Precise Copper Nanoclusters

Accurate structure control in dissipative assemblies (DSAs) is vital for precise biological functions. However, accuracy and functionality of artificial DSAs are far from this objective. Herein, a novel approach is introduced by harnessing complex chemical reaction networks rooted in coordination chemistry to create atomically-precise copper nanoclusters (CuNCs), specifically Cu11(µ9-Cl)(µ3-Cl)3L6Cl (L = 4-methyl-piperazine-1-carbodithioate). Cu(I)-ligand ratio change and dynamic Cu(I)-Cu(I) metallophilic/coordination interactions enable the reorganization of CuNCs into metastable CuL2, finally converting into equilibrium [CuL·Y]Cl (Y = MeCN/H2O) via Cu(I) oxidation/reorganization and ligand exchange process. Upon adding ascorbic acid (AA), the system goes further dissipative cycles. It is observed that the encapsulated/bridging halide ions exert subtle influence on the optical properties of CuNCs and topological changes of polymeric networks when integrating CuNCs as crosslink sites. CuNCs duration/switch period could be controlled by varying the ions, AA concentration, O2 pressure and pH. Cu(I)-Cu(I) metallophilic and coordination interactions provide a versatile toolbox for designing delicate life-like materials, paving the way for DSAs with precise structures and functionalities. Furthermore, CuNCs can be employed as modular units within polymers for materials mechanics or functionalization studies.

The role of electrocatalytic materials for developing post-lithium metal||sulfur batteries

The exploration of post-Lithium (Li) metals, such as Sodium (Na), Potassium (K), Magnesium (Mg), Calcium (Ca), Aluminum (Al), and Zinc (Zn), for electrochemical energy storage has been driven by the limited availability of Li and the higher theoretical specific energies compared to the state-of-the-art Li-ion batteries. Post-Li metal||S batteries have emerged as a promising system for practical applications. Yet, the insufficient understanding of quantitative cell parameters and the mechanisms of sulfur electrocatalytic conversion hinder the advancement of these battery technologies. This perspective offers a comprehensive analysis of electrode parameters, including S mass loading, S content, electrolyte/S ratio, and negative/positive electrode capacity ratio, in establishing the specific energy (Wh kg-1) of post-Li metal||S batteries. Additionally, we critically evaluate the progress in investigating electrochemical sulfur conversion via homogeneous and heterogeneous electrocatalytic approaches in both non-aqueous Na/K/Mg/Ca/Al||S and aqueous Zn||S batteries. Lastly, we provide a critical outlook on potential research directions for designing practical post-Li metal||S batteries.

Electrode and Electrolyte Co-Energy-Storage Electrochemistry Enables High-Energy Zn-S Decoupled Batteries

In the search for next-generation green energy storage solutions, Cu-S electrochemistry has recently gained attraction from the battery community owing to its affordability and exceptionally high specific capacity of 3350 mAh gs -1. However, the inferior conductivity and substantial volume expansion of the S cathode hinder its cycling stability, while the low output voltage limits its energy density. Herein, a hollow carbon sphere (HCS) is synthesized as a 3D conductive host to achieve a stable S@HCS cathode, which enables an outstanding cycling performance of 2500 cycles (over 9 months). To address the latter, a Zn//S@HCS alkaline-acid decoupled cell is configured to increase the output voltage from 0.18 to 1.6 V. Moreover, an electrode and electrolyte co-energy storage mechanism is proposed to offset the reduction in energy density resulting from the extra electrolyte required in Zn//S decoupled cells. When combined, the Zn//S@HCS alkaline-acid decoupled cell delivers a record energy density of 334 Wh kg-1 based on the mass of the S cathode and CuSO4 electrolyte. This work tackles the key challenges of Cu-S electrochemistry and brings new insights into the rational design of decoupled batteries.

Zn-based batteries for sustainable energy storage: strategies and mechanisms

Batteries play a pivotal role in various electrochemical energy storage systems, functioning as essential components to enhance energy utilization efficiency and expedite the realization of energy and environmental sustainability. Zn-based batteries have attracted increasing attention as a promising alternative to lithium-ion batteries owing to their cost effectiveness, enhanced intrinsic safety, and favorable electrochemical performance. In this context, substantial endeavors have been dedicated to crafting and advancing high-performance Zn-based batteries. However, some challenges, including limited discharging capacity, low operating voltage, low energy density, short cycle life, and complicated energy storage mechanism, need to be addressed in order to render large-scale practical applications. In this review, we comprehensively present recent advances in designing high-performance Zn-based batteries and in elucidating energy storage mechanisms. First, various redox mechanisms in Zn-based batteries are systematically summarized, including insertion-type, conversion-type, coordination-type, and catalysis-type mechanisms. Subsequently, the design strategies aiming at enhancing the electrochemical performance of Zn-based batteries are underscored, focusing on several aspects, including output voltage, capacity, energy density, and cycle life. Finally, challenges and future prospects of Zn-based batteries are discussed.

Redox-Active Organic Materials: From Energy Storage to Redox Catalysis

Electroactive materials are central to myriad applications, including energy storage, sensing, and catalysis. Compared to traditional inorganic electrode materials, redox-active organic materials such as porous organic polymers (POPs) and covalent organic frameworks (COFs) are emerging as promising alternatives due to their structural tunability, flexibility, sustainability, and compatibility with a range of electrolytes. Herein, we discuss the challenges and opportunities available for the use of redox-active organic materials in organoelectrochemistry, an emerging area in fine chemical synthesis. In particular, we highlight the utility of organic electrode materials in photoredox catalysis, electrochemical energy storage, and electrocatalysis and point to new directions needed to unlock their potential utility for organic synthesis. This Perspective aims to bring together the organic, electrochemistry, and polymer communities to design new heterogeneous electrocatalysts for the sustainable synthesis of complex molecules.

An aqueous alkaline zinc-sulfur flow battery

We demonstrate a rechargeable aqueous alkaline zinc-sulfur flow battery that comprises environmental materials zinc and sulfur as negative and positive active species. Meanwhile, a nickel-based electrode is also obtained by a two-step process to decrease the polarization of the sulfur redox reaction, thus greatly improving the voltage efficiency of the system from 32% to 78% at 10 mA cm-2.

A High-Energy Aqueous All-Sulfur Battery

Rechargeable aqueous batteries are promising energy storage devices because of their high safety and low cost. However, their energy densities are generally unsatisfactory due to the limited capacities of ion-inserted electrode materials, prohibiting their widespread applications. Herein, a high-energy aqueous all-sulfur battery was constructed via matching S/Cu2 S and S/CaSx redox couples. In such batteries, both cathodes and anodes undergo the conversion reaction between sulfur/metal sulfides redox couples, which display high specific capacities and rational electrode potential difference. Furthermore, during the charge/discharge process, the simultaneous redox of Cu2+ ion charge-carriers also takes place and contributes to a more two-electron transfer, which doubles the capacity of cathodes. As a result, the assembled aqueous all-sulfur batteries deliver a high discharge capacity of 447 mAh g-1 based on total mass of sulfur in cathode and anode at 0.1 A g-1 , contributing to an enhanced energy density of 393 Wh kg-1 . This work will widen the scope for the design of high-energy aqueous batteries.

High-Sulfur Loading and Single Ion-Selective Membranes for High-Energy and Durable Decoupled Aqueous Batteries

The decoupled battery design is promising for breaking the energy density limit of traditional aqueous batteries. However, the complex battery configuration and low-selective separator membranes restrict their energy output and service time. Herein, a zinc-sulfur decoupled aqueous battery is achieved by designing a high-mass loading sulfur electrode and single ion-selective membrane (ISM). A vertically assembled nanosheet network constructed with the assistance of a magnetic field enables facile electron and ion conduction in thick sulfur electrodes, which is conducive to boosting the cell-level energy output. For the tailored ISM, the Na ions anchored on its skeleton effectively prevent the crossover of OH- or Cu2+ , facilitating the transport of Na+ and ensuring structural and mechanical stability. Consequently, the Zn-S aqueous battery achieves a reversible energy density of 3988 Wh kgs -1 (by sulfur mass), stable operation over 300 cycles, and an energy density of 53.2 mWh cm-2 . The sulfur-based decoupled system may be of immediate benefit toward safe, reliable, and affordable static energy storage.

Intercalation of Metal into Transition Metal Dichalcogenides in Molten Salts

Van der Waals (vdW)-layered materials have drawn tremendous interests due to their unique properties. Atom intercalation in the vdW gap of layered materials can tune their electronic structure and generate unexpected properties. Here a chemical-scissor-mediated method that enables metal intercalation into transition metal dichalcogenides (TMDCs) in molten salts is reported. By using this approach, various guest metal atoms (Mn, Fe, Co, Ni, Cu, and Ag) are intercalated into various TMDC hosts (such as TiS2 , NbS2 , TaS2 , TiSe2 , NbSe2 , TaSe2 , and Ti0.5 V0.5 S2 ). The structure of the intercalated compound and intercalation mechanism are investigated. The results indicate that the vdW gap and valence state of TMDCs can be modified through metal intercalation, and the intercalation behavior is dictated by the electron work function. The adjustable charge transfer and intercalation endow a channel for rapid mass transfer to enhance the electrochemical performances. Such a chemical-scissor-mediated intercalation provides an approach to tune the physical and chemical properties of TMDCs, which may open an avenue in functional application ranging from energy conversion to electronics.

High-Reversibility Sulfur Anode for Advanced Aqueous Battery

Despite being extensively explored as cathodes in batteries, sulfur (S) can function as a low-potential anode by changing charge carriers in electrolytes. Here, a highly reversible S anode that fully converts from S8 0 to S2- in static aqueous S-I2 batteries by using Na+ as the charge carrier is reported. This S anode exhibits a low potential of -0.5 V (vs standard hydrogen electrode) and a near-to-theoretical capacity of 1404 mA h g-1 . Importantly, it shows significant advantages over the widely used Zn anode in aqueous media by obviating dendrite formation and H2 evolution. To suppress "shuttle effects" faced by both S and I2 electrodes, a scalable sulfonated polysulfone (SPSF) membrane is proposed, which is superior to commercial Nafion in cost (US$1.82 m-2  vs $3500 m-2 ) and environmental benignity. Because of its ultra-high selectivity in blocking polysulfides/iodides, the battery with SPSF displays excellent cycling stability. Even under 100% depth of discharge, the battery demonstrates high capacity retention of 87.6% over 500 cycles, outperforming Zn-I2 batteries with 3.1% capacity under the same conditions. These findings broaden anode options beyond metals for high-energy, low-cost, and fast-chargeable batteries.

High-Energy Aqueous/Organic Hybrid Batteries Enabled by Cu2+ Redox Charge Carriers

Lithium||sulfur (Li||S) batteries are considered as one of the promising next-generation batteries due to the high theoretical capacity and low cost of S cathodes, as well as the low redox potential of Li metal anodes (-3.04 V vs. standard hydrogen electrode). However, the S reduction reaction from S to Li2 S leads to limited discharge voltage and capacity, largely hindering the energy density of Li||S batteries. Herein, high-energy Li||S hybrid batteries were designed via an electrolyte decoupling strategy. In cathodes, S electrodes undergo the solid-solid conversion reaction from S to Cu2 S with four-electron transfer in a Cu2+ -based aqueous electrolyte. Such an energy storage mechanism contributes to enhanced electrochemical performance of S electrodes, including high discharge potential and capacity, superior rate performance and stable cycling behavior. As a result, the assembled Li||S hybrid batteries exhibit a high discharge voltage of 3.4 V and satisfactory capacity of 2.3 Ah g-1 , contributing to incredible energy density. This work provides an opportunity for the construction of high-energy Li||S batteries.

Six-Electron-Redox Iodine Electrodes for High-Energy Aqueous Batteries

Iodine (I2 ) shows great promising as the active material in aqueous batteries due to its distinctive merits of high abundance in ocean and low cost. However, in conventional aqueous I2 -based batteries, the energy storage mechanism of I- /I2 conversion is only two-electron redox reaction, limiting their energy density. Herein, six-electron redox chemistry of I2 electrodes is achieved via the synergistic effect of redox-ion charge-carriers and halide ions in electrolytes. The redox-active Cu2+ ions in electrolytes induce the conversion between Cu2+ ions and I2 to CuI at low potential. Simultaneously, the Cl- ions in electrolytes activate the I2 /ICl redox couple at high potential. As a result, in our case, I2 -based battery system with six-electron redox is developed. Such energy storage mechanism with six-electron redox leads to high discharge potential and capacity, excellent rate capability, as well as stable cycling behavior of I2 electrodes. Impressively, six-electron-redox I2 cathodes can match various aqueous metal (e.g. Zn, Mn and Fe) anodes to construct metal||I2 hybrid batteries. These hybrid batteries not only deliver enhanced capacities, but also exhibit higher operate voltages, which contributes to superior energy densities. Therefore, this work broadens the horizon for the design of high-energy aqueous I2 -based batteries.

Unravelling Twin Topotactic/Nontopotactic Reactive TiSe2 Cathodes for Aqueous Batteries

Titanium selenide (TiSe2 ), a model transition metal chalcogenide material, typically relies on topotactic ion intercalation/deintercalation to achieve stable ion storage with minimal disruption of the transport pathways but has restricted capacity (<130 mAh g-1 ). Developing novel energy storage mechanisms beyond conventional intercalation to break capacity limits in TiSe2 cathodes is essential yet challenging. Herein, the ion storage properties of TiSe2 are revisited and an unusual thermodynamically stable twin topotactic/nontopotactic Cu2+ accommodation mechanism for aqueous batteries is unraveled. In situ synchrotron X-ray diffraction and ex situ microscopy jointly demonstrated that topotactic intercalation sustained the ion transport framework, nontopotactic conversion involved localized multielectron reactions, and these two parallel reactions are miraculously intertwined in nanoscale space. Comprehensive experimental and theoretical results suggested that the twin-reaction mechanism significantly improved the electron transfer ability, and the reserved intercalated TiSe2 structure anchored the reduced titanium monomers with high affinity and promoted efficient charge transfer to synergistically enhance the capacity and reversibility. Consequently, TiSe2 nanoflake cathodes delivered a never-before-achieved capacity of 275.9 mAh g-1 at 0.1 A g-1 , 93.5% capacity retention over 1000 cycles, and endow hybrid batteries (TiSe2 -Cu||Zn) with a stable energy supply of 181.34 Wh kg-1 at 2339.81 W kg-1 , offering a promising model for aqueous ion storage.

A High-Energy Four-Electron Zinc Battery Enabled by Evoking Full Electrochemical Activity in Copper Sulfide Electrode

The growing global demand for sustainable and cost-effective energy storage solutions has driven the rapid development of zinc batteries. Despite significant progress in recent years, enhancing the energy density of zinc batteries remains a crucial research focus. One prevalent strategy involves the development of high-capacity and/or high-voltage cathode materials. CuS, a commonly used electrode material, exhibits a two-electron transfer mechanism; however, the reduced sulfion lacks electrochemical activity and thereby limits its discharge capacity and redox potential. In this study, we activate a CuS cathode to form a high-valence Cu2+&S compound using a deep-eutectic-solvent (DES)-based electrolyte. The presence of Cl- in the DES-based electrolyte is crucial to the reversibility of the redox chemistry, and the liquid-phase-involved electrochemical process facilitates redox kinetics. A four-electron transfer pathway involving five reaction steps is identified for the CuS electrode, which unleashes the full electrochemical activity of the S element. Consequently, the full cell delivers a large discharge capacity of ∼800 mAh g-1 at 0.2 A g-1 and yields a high discharge plateau starting at 1.58 V, contributing to energy densities of up to 650 Wh kg-1 (based on CuS). This work offers a promising approach to developing high-energy zinc batteries.

Trivalent Indium Metal as a High-Capacity, High-Efficiency, Low-Polarization, and Long-Cycling Anode for Aqueous Batteries

Aqueous batteries using multivalent metals hold great promise for energy storage due to their low cost, high energy, and high safety. Presently, divalent metals (zinc, iron, nickel, and manganese) prevail as the leading choice, which, however, suffer from low Coulombic efficiency or dendrite growth. In stark contrast, trivalent metals have received rare attention despite their capability to unlock unique redox reactions. Herein, we investigate trivalent indium as an innovative and high-performance metal anode for aqueous batteries. The three-electron In3+/In redox endows a high capacity of ∼700 mAh g-1, on par with the Zn metal. Besides, indium exhibits a suitable redox potential (-0.34 V vs standard hydrogen electrode) and dendrite-free plating process, which renders an ultrahigh Coulombic efficiency of 99.3-99.8%. More surprisingly, it features an exceedingly low polarization of 1 mV in symmetrical cells, which is 1-2 orders of magnitude lower than any reported metals. The In-MnO2 full cell also delivers impressive performance, with a cell voltage of ∼1.2 V, a high capacity of ∼330 mAh g-1, and a long cycling time of 680 cycles. Our work exemplifies the efficacy of exploiting trivalent metals as an excellent metal anode, which provides an exciting direction for building high-performance aqueous batteries.

Ultrahigh-Speed Aqueous Copper Electrodes Stabilized by Phosphorylated Interphase

High-energy metal anodes for large-scale reversible batteries with inexpensive and nonflammable aqueous electrolytes promise the capability of supporting higher current density, satisfactory lifetime, nontoxicity, and low-cost commercial manufacturing, yet remain out of reach due to the lack of reliable electrode-electrolyte interphase engineering. Herein, in situ formed robust interphase on copper metal electrodes (CMEs) induced by a trace amount of potassium dihydrogen phosphate (0.05 m in 1 m CuSO4 -H2 O electrolyte) to fulfill all aforementioned requirements is demonstrated. Impressively, an unprecedented ultrahigh-speed copper plating/stripping capability is achieved at 100 mA cm-2  for over 12 000 cycles, corresponding to an accumulative areal capacity up to tens of times higher than previously reported CMEs. The use of solid-electrolyte interface-protection strategy brings at least an order of magnitude improvement in cycling stability for symmetric cells (Cu||Cu, 2800 h) and full batteries with CMEs using either sulfur cathodes (S||Cu, 1000 cycles without capacity decay) or zinc anodes (Cu||Zn with all-metal electrodes, discharge voltage ≈1.02 V). The comprehensive analysis reveals that the hydrophilic phosphate-rich interphase nanostructures homogenize copper-ion deposition and suppress nucleation overpotential, enabling dendrite-free CMEs with sustainability and ability to tolerate unusual-high power densities. The findings represent an elegant forerunner toward the promising goal of metal electrode applications.

A triple-synergistic small-molecule sulfur cathode promises energetic Cu-S electrochemistry

Metal-sulfur batteries have received great attention for electrochemical energy storage due to high theoretical capacity and low cost, but their further development is impeded by low sulfur utilization, poor electrochemical kinetics, and serious shuttle effect of the sulfur cathode. To avoid these problems, herein, a triple-synergistic small-molecule sulfur cathode is designed by employing N, S co-doped hierarchical porous bamboo charcoal as a sulfur host in an aqueous Cu-S battery. Expect the enhanced conductivity and chemisorption induced by N, S synergistic co-doping, the intrinsic synergy of macro-/meso-/microporous triple structure also ensures space-confined small-molecule sulfur as high utilization reactant and effectively alleviates the volume expansion during conversion reaction. Under a further joint synergy between hierarchical structure and heteroatom doping, the resulting sulfur cathode endows the Cu-S battery with outstanding electrochemical performance. Cycled at 5 A g-1, it can deliver a high reversible capacity of 2,509.8 mAh g-1 with a good capacity retention of 97.9% after 800 cycles. In addition, a flexible hybrid pouch cell built by a small-molecule sulfur cathode, Zn anode, and gel electrolytes can firmly deliver high average operating voltage of about 1.3 V with a reversible capacity of over 2,500 mAh g-1 under various destructive conditions, suggesting that the triple-synergistic small-molecule sulfur cathode promises energetic metal-sulfur batteries.

Flexible Backbone Effects on the Redox Properties of Perylenediimide-Based Polymers

Organic electrode materials are appealing candidates for a wide range of applications, including heterogeneous electrocatalysis and electrochemical energy storage. However, a narrow understanding of the structure-property relationships in these materials hinders the full realization of their potential. Herein, we investigate a family of insoluble perylenediimide (PDI) polymers to interrogate how backbone flexibility affects their thermodynamic and kinetic redox properties. We verify that the polymers generally access the highest percentage of redox-active groups with K+ ions (vs Na+ and Li+) due to its small solvation shell/energy and favorable soft-soft interactions with reduced PDI species. Through cyclic voltammetry, we show that increasing the polymer flexibility does not minimize barriers to ion-insertion processes but rather increases the level of diffusion-limited processes. Further, we propose that the condensation of imides to iminoimides can truncate the imide polymer chain growth for certain diamine monomers, leading to greater polymer solubilization and reduced cycling stability. Together, our results provide insight into how polymer flexibility, ion-electrode interactions, and polymerization side reactions dictate the redox properties of PDI polymers, paving the way for the development of next-generation organic electrode materials.

Conversion-Type Cathode Materials for Aqueous Zn Metal Batteries in Nonalkaline Aqueous Electrolytes: Progress, Challenges, and Solutions

Aqueous Zn metal batteries are attractive as safe and low-cost energy storage systems. At present, due to the narrow window of the aqueous electrolyte and the strong reliance of the Zn2+ ion intercalated reaction on the host structure, the current intercalated cathode materials exhibit restricted energy densities. In contrast, cathode materials with conversion reactions can promise higher energy densities. Especially, the recently reported conversion-type cathode materials that function in nonalkaline electrolytes have garnered increasing attention. This is because the use of nonalkaline electrolytes can prevent the occurrence of side reactions encountered in alkaline electrolytes and thereby enhance cycling stability. However, there is a lack of comprehensive review on the reaction mechanisms, progress, challenges, and solutions to these cathode materials. In this review, four kinds of conversion-type cathode materials including MnO2 , halogen materials (Br2 and I2 ), chalcogenide materials (O2 , S, Se, and Te), and Cu-based compounds (CuI, Cu2 O, Cu2 S, CuO, CuS, and CuSe) are reviewed. First, the reaction mechanisms and battery structures of these materials are introduced. Second, the fundamental problems and their corresponding solutions are discussed in detail in each material. Finally, future directions and efforts for the development of conversion-type cathode materials for aqueous Zn batteries are proposed.

Initiating Reversible Aqueous Copper-Tellurium Conversion Reaction with High Volumetric Capacity through Electrolyte Engineering

Pursuing conversion-type cathodes with high volumetric capacity that can be used in aqueous environments remains rewarding and challenging. Tellurium (Te) is a promising alternative electrode due to its intrinsic attractive electronic conductivity and high theoretical volumetric capacity yet still to be explored. Herein, the kinetically/thermodynamically co-dominat copper-tellurium (Cu-Te) alloying phase-conversion process and corresponding oxidation failure mechanism of tellurium are investigated using in situ synchrotron X-ray diffraction and comprehensive ex situ characterization techniques. By virtue of the fundamental insights into the tellurium electrode, facile and precise electrolyte engineering (solvated structure modulation or reductive antioxidant addition) is implemented to essentially tackle the dramatic capacity loss in tellurium, affording reversible aqueous Cu-Te conversion reaction with an unprecedented ultrahigh volumetric capacity of up to 3927 mAh cm^-3 , a flat long discharge plateau (capacity proportion of ≈81%), and an extraordinary level of capacity retention of 80.4% over 2000 cycles at 20 A g^-1 of which lifespan thousand-fold longer than Cu-Te conversion using CuSO₄ -H₂ O electrolyte. This work paves a significant avenue for expanding high-performance conversion-type cathodes toward energetic aqueous multivalent-ion batteries.

Unexpected Direct Synthesis of Tunable Redox-Active Benzil-Linked Polymers via the Benzoin Reaction

Strategies for the sustainable synthesis of redox-active organic polymers could lead to next-generation organic electrode materials for electrochemical energy storage, electrocatalysis, and electro-swing chemical separations. Among redox-active moieties, benzils or aromatic 1,2-diones are particularly attractive due to their high theoretical gravimetric capacities and fast charge/discharge rates. Herein, we demonstrate that the cyanide-catalyzed polymerization of simple dialdehyde monomers unexpectedly leads to insoluble redox-active benzil-linked polymers instead of the expected benzoin polymers, as supported by solid-state nuclear magnetic resonance spectroscopy and electrochemical characterization. Mechanistic studies suggest that cyanide-mediated benzoin oxidation occurs by hydride transfer to the solvent, and that the insolubility of the benzil-linked polymers protects them from subsequent cyanolysis. The thiophene-based polymer poly(BTDA) is an intriguing organic electrode material that demonstrates two reversible one-electron reductions with monovalent cations such as Li+ and Na+ but one two-electron reduction with divalent Mg2+. As such, the tandem benzoin-oxidation polymerization reported herein represents a sustainable method for the synthesis of highly tunable and redox-active organic materials.

An aqueous copper battery enabled by Cu2+/Cu+ and Cu3+/Cu2+ redox conversion chemistry

We propose an aqueous copper battery via Cu²⁺/Cu⁺ and Cu³⁺/Cu²⁺ redox conversion chemistry on an activated carbon (AC) electrode enabled by a 30 m ChCl + 1 m CuCl₂ electrolyte, where Cu³⁺/Cu²⁺ redox promotes the discharge capacity by ∼50 mA h g^-1 at ∼1.0 V vs. Ag/AgCl with stable cycling.

Investigation of ion-electrode interactions of linear polyimides and alkali metal ions for next generation alternative-ion batteries

Organic electrode materials offer unique opportunities to utilize ion-electrode interactions to develop diverse, versatile, and high-performing secondary batteries, particularly for applications requiring high power densities. However, a lack of well-defined structure-property relationships for redox-active organic materials restricts the advancement of the field. Herein, we investigate a family of diimide-based polymer materials with several charge-compensating ions (Li+, Na+, K+) in order to systematically probe how redox-active moiety, ion, and polymer flexibility dictate their thermodynamic and kinetic properties. When favorable ion-electrode interactions are employed (e.g., soft K+ anions with soft perylenediimide dianions), the resulting batteries demonstrate increased working potentials and improved cycling stabilities. Further, for all polymers examined herein, we demonstrate that K+ accesses the highest percentage of redox-active groups due to its small solvation shell/energy. Through crown ether experiments, cyclic voltammetry, and activation energy measurements, we provide insights into the charge compensation mechanisms of three different polymer structures and rationalize these findings in terms of the differing degrees of improvements observed when cycling with K+. Critically, we find that the most flexible polymer enables access to the highest fraction of active sites due to the small activation energy barrier during charge/discharge. These results suggest that improved capacities may be accessible by employing more flexible structures. Overall, our in-depth structure-activity investigation demonstrates how variables such as polymer structure and cation can be used to optimize battery performance and enable the realization of novel battery chemistries.

Design Strategies for High-Energy-Density Aqueous Zinc Batteries

In recent years, the increasing demand for high-capacity and safe energy storage has focused attention on zinc batteries featuring high voltage, high capacity, or both. Despite extensive research progress, achieving high-energy-density zinc batteries remains challenging and requires the synergistic regulation of multiple factors including reaction mechanisms, electrodes, and electrolytes. In this Review, we comprehensively summarize the rational design strategies of high-energy-density zinc batteries and critically analyze the positive effects and potential issues of these strategies in optimizing the electrochemistry, cathode materials, electrolytes, and device architecture. Finally, the challenges and perspectives for the further development of high-energy-density zinc batteries are outlined to guide research towards new-generation batteries for household appliances, low-speed electric vehicles, and large-scale energy storage systems.

Ion transport and limited currents in supporting electrolytes and ionic liquids

Supporting electrolytes contain inert dissolved salts to increase the conductivity, to change microenvironments near the electrodes and to assist in electrochemical reactions. This combined experimental and computational study examines the impact of supporting salts on the ion transport and related limited currents in electrochemical cells. A physical model that describes the multi-ion transport in liquid electrolytes and the resulting concentration gradients is presented. This model and its parameterization are evaluated by the measured limited current of the copper deposition in a CuSO₄ electrolyte under a gradually increasing amount of Na₂SO₄ that acts as a supporting salt. A computational sensibility analysis of the transport model reveals that the shared conductance between the ions lowers the limited currents with larger supporting salt concentrations. When the supporting salt supplies most of the conductance, the electric-field-driven transport of the electrochemically active ions becomes negligible so that the limited current drops to the diffusion-limited current that is described by Fick’s first law. The transition from diluted supporting electrolyte to the case of ionic liquids is elucidated with the transport model, highlighting the different physical transport mechanisms in a non-conducting (polar) and a conducting (ionic) solvent.

Synergistic dual conversion reactions assisting Pb-S electrochemistry for energy storage

Based on the analysis of three thermodynamic parameters of various M-S systems (solubility of metal sulfides [M_xS_y] in aqueous solution, volume change of the metal-sulfur [M-S] battery system, and the potential of S/M_xS_y cathode redox couple), an aqueous Pb-S battery operated by synergistic dual conversion reactions (cathode: S⇄PbS, anode: Pb²⁺⇄PbO₂) has been officially reported. Benefitting from the inherent insolubility of PbS and a conversion-type counter electrode, the aqueous Pb-S battery exhibited two advantages: it is shuttle effect free and has a dendrite-free nature. Moreover, the practical value of the Pb-S battery was further certified by the prototype S|Pb(NO₃)₂ǁZn(NO₃)₂|Zn hybrid cell, which afforded an energy density of 930.9 Wh kg⁻¹_sulfur.

As one of the most promising cathode materials for next-generation batteries, sulfur has been widely used in organic metal-sulfur batteries, especially in Li-S batteries. However, to date, Pb-S chemistry has never been officially reported. In this paper, a reliable aqueous Pb-S battery based on a dual conversion reaction was constructed. To clarify the feasibility, three important thermodynamic parameters of the Pb-S system were analyzed, including the solubility of PbS in aqueous solution, the volume change of the Pb-S battery system, and the potential of the S/PbS cathode redox couple. Here, it is demonstrated that the aqueous Pb-S battery possesses a great advantage in theory, and the inherent insolubility of PbS makes an aqueous Pb-S system without a shuttle effect. Moreover, the conversion-type counter electrode of a Pb-S system with a stable nucleation rate endows it with a dendrite-free nature, which is quite different from the traditional metal-sulfur battery with a stripping/plating–type counter electrode. Benefitting from these remarkable natures, the aqueous Pb-S battery exhibits a high discharge capacity of 1,343.9 mAh g⁻¹_sulfur with a capacity retention of 71.4% after 400 cycles. In addition, the feasibility of this Pb-S system is further demonstrated in a hybrid cell consisting of an S cathode and Zn anode, which affords an energy density of 930.9 Wh kg⁻¹_sulfur.

A Cascade Battery: Coupling Two Sequential Electrochemical Reactions in a Single Battery

Currently, rechargeable electrochemical batteries generally operate on one reversible electrochemical reaction during discharging and charging cycles. Here, a cascade battery that couples two sequential electrochemical reactions in a single battery is proposed. Such a concept is demonstrated in an aqueous Zn-S hybrid battery, where solid sulfur serves as the cathode in the first discharge step and the generated Cu₂ S catalyzes Cu²⁺ reduce to Cu/Cu₂ O to provide the second discharge step. The cascade battery shows many merits compared to traditional batteries. First, it integrates two batteries internally, eliminating the use of additional inactive connecting materials required for external integration. Second, it can more fully utilize the inactive reaction chamber of the battery than traditional batteries. Third, cascade battery can bypass the challenges of thick solid electrode to access high areal capacity. An ultrahigh areal capacity of 48 mAh cm^-2 is achieved even at a low solid cathode loading (9.6 mg cm^-2 ). The cascade battery design breaks the stereotype of conventional battery configuration, providing a paradigm for constructing two-in-one batteries.

Vacancy Modulating Co3 Sn2 S2 Topological Semimetal for Aqueous Zinc-Ion Batteries

Weyl semimetals (WSMs) with high electrical conductivity and suitable carrier density near the Fermi level are enticing candidates for aqueous Zn-ion batteries (AZIBs), meriting from topological surface states (TSSs). We propose a WSM Co₃ Sn₂ S₂ cathode for AZIBs showing a discharge plateau around 1.5 V. By introducing Sn vacancies, extra redox peaks from the Sn⁴⁺ /Sn²⁺ transition appear, which leads to more Zn²⁺ transfer channels and active sites promoting charge-storage kinetics and Zn²⁺ storage capability. Co₃ Sn_1.8 S₂ achieves a specific energy of 305 Wh kg^-1 (0.2 Ag^-1 ) and a specific power of 4900 Wkg^-1 (5 Ag^-1 ). Co₃ Sn_1.8 S₂ and Zn_x Co₃ Sn_1.8 S₂ benefit from better conductivity at lower temperatures; the quasi-solid Co₃ Sn_1.8 S₂ //Zn battery delivers 126 mAh g^-1 (0.6 Ag^-1 ) at -30 °C and a cycling stability over 3000 cycles (2 Ag^-1 ) with 85 % capacity retention at -10 °C.

An Energetic CuS-Cu Battery System Based on CuS Nanosheet Arrays

The development of low-cost and high-energy aqueous battery technologies is of significance for renewable and stationary energy applications. However, this development has been bottlenecked by poor conductivity, low capacity, and limited cycling stability of existing electrode materials. In this work, we report on an energetic aqueous copper ion system based on CuS nanosheet arrays, taking profit of high conductivity of CuS and efficient charge carrier of copper ions. Electrochemical results reveal a high capacity of 510 mAh g^-1, robust rate capability of 497 mAh g^-1 at a high rate of 7.5 A g^-1, and ultrastable cycling by retaining 91% of the initial capacity over 2500 cycles. The charge-storage mechanism was systematically investigated by ex situ and in situ techniques involving a reversible transition from CuS to Cu₇S₄ and to Cu₂S through the redox of Cu²⁺/Cu⁺. Moreover, we demonstrate a hybrid ion battery consisting of CuS positive electrode and Zn negative electrode, which affords an energy and power of 286 Wh kg^-1 and 900 W kg^-1, respectively, on the basis of both electrodes, exceeding many aqueous battery systems.

Cu3(PO4)2: Novel Anion Convertor for Aqueous Dual-Ion Battery

A novel anion electrode Cu₃(PO₄)₂ is proposed at the first time. The reaction mechanism of Cu₃(PO₄)₂ electrode is investigated. The dual-ion cell is constructed by using pretreated Cu₃(PO₄)₂ and Na_0.44MnO₂.

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A Low Cost Aqueous Zn-S Battery Realizing Ultrahigh Energy Density

Rechargeable aqueous zinc ion batteries are enabled by the (de)intercalation chemistry, but bottlenecked by the limited energy density due to the low capacity of cathodes. In this work, carbon nanotubes supported 50 wt% sulfur (denoted as S@CNTs-50), as a conversional cathode, is employed and a high energy density aqueous zinc-sulfur (Zn-S) battery is constructed . In the electrolyte of 1 m Zn(CH3COO)2 (pH = 6.5) with 0.05 wt% I2 additive where I2 can serve as medium of Zn2+ ions to reduce the voltage hysteresis of S@CNTs-50 and stabilize Zn stripping/plating, S@CNTs-50 delivers a high capacity of 1105 mAh g-1 with a flat discharge voltage of 0.5 V, realizing an energy density of 502 Wh kg-1 based on sulfur, which is one of the highest values reported in aqueous Zn-based batteries that use mild electrolyte. Moreover, the chemical materials cost of this aqueous Zn-S battery can be lowered to be $45 kWh-1 due to the cheap raw materials, reaching to the level of pumped energy storage. Ex situ X-ray diffraction, Raman spectra, X-ray photoelectron spectrum, and transmission electron microscopy measurements reveal that sulfur cathode undergoes a conversion reaction between S and ZnS.

Thermodynamic analysis and kinetic optimization of high-energy batteries based on multi-electron reactions

Multi-electron reaction can be regarded as an effective way of building high-energy systems (>500 W h kg⁻¹). However, some confusions hinder the development of multi-electron mechanisms, such as clear concept, complex reaction, material design and electrolyte optimization and full-cell fabrication. Therefore, this review discusses the basic theories and application bottlenecks of multi-electron mechanisms from the view of thermodynamic and dynamic principles. In future, high-energy batteries, metal anodes and multi-electron cathodes are promising electrode materials with high theoretical capacity and high output voltage. While the primary issue for the multi-electron transfer process is sluggish kinetics, which may be caused by multiple ionic migration, large ionic radius, high reaction energy barrier, low electron conductivity, poor structural stability, etc., it is urgent that feasible and versatile modification methods are summarized and new inspiration proposed in order to break through kinetic constraints. Finally, the remaining challenges and future research directions are revealed in detail, involving the search for high-energy systems, compatibility of full cells, cost control, etc.