Anion-Cation Competition Chemistry for Comprehensive High-Performance Prussian Blue Analogs Cathodes.

The extensively studied Prussian blue analogs (PBAs) in various batteries are limited by their low discharge capacity, or subpar rate etc., which are solely reliant on the cation (de)intercalation mechanism. In contrast to the currently predominant focus on cations, we report the overlooked anion-cation competition chemistry (Cl-, K+, Zn2+) stimulated by high-voltage scanning. With our designed anion-cation combinations, the KFeMnHCF cathode battery delivers comprehensively superior discharge performance, including voltage plateau >2.0 V (vs. Zn/Zn2+), capacity >150 mAh g-1, rate capability with capacity maintenance above 96 % from 0.6 to 5 A g-1, and cyclic stability exceeding 3000 cycles. We further verify that such comprehensive improvement of electrochemical performance utilizing anion-cation competition chemistry is universal for different types of PBAs. Our work would pave a new and efficient road towards the next-generation high-performance PBAs cathode batteries.

Robust and Corrosion-Resistant Overall Water Splitting Electrode Enabled by Additive Manufacturing.

Electrolysis of water has emerged as a prominent area of research in recent years. As a promising catalyst support, copper foam is widely investigated for electrolytic water, yet the insufficient mechanical strength and corrosion resistance render it less suitable for harsh working conditions. To exploit high-performance catalyst supports, various metal supports are comprehensively evaluated, and Ti6 Al4 V (Ti64) support exhibited outstanding compression and corrosion resistance. With this in mind, a 3D porous Ti64 catalyst support is fabricated using the selective laser sintering (SLM) 3D printing technology, and a conductive layer of nickel (Ni) is coated to increase the electrical conductivity and facilitate the deposition of catalysts. Subsequently, Co0.8 Ni0.2 (CO3 )0.5 (OH)·0.11H2 O (CoNiCH) nanoneedles are deposited. The resulting porous Ti64/Ni/CoNiCH electrode displayed an impressive performance in the oxygen evolution reaction (OER) and reached 30 mA cm-2 at an overpotential of only 200 mV. Remarkably, even after being compressed at 15.04 MPa, no obvious structural deformation is observed, and the attenuation of its catalytic efficiency is negligible. Based on the computational analysis, the CoNiCH catalyst demonstrated superior catalytic activity at the Ni site in comparison to the Co site. Furthermore, the electrode reached 30 mA cm-2 at 1.75 V in full water splitting conditions and showed no significant performance degradation even after 60 h of continuous operation. This study presents an innovative approach to robust and corrosion-resistant catalyst design.

Molecular Structure Engineering of Isomeric Additives for Long Lifetime Zn Anodes.

Modulating the solvation structure of hydrated zinc ions using organic additives stands as a pragmatic approach to suppress dendrite formation and corrosion on zinc metal anodes (ZMAs), thereby enhancing the rechargeability of aqueous Zn-ion batteries. However, fundamental screening principles for organic additives with diverse molecular structures remain elusive, especially for isomers with the same molecular formula. This study delves into the impact of three isomeric hexagonal alcohols (mannitol, sorbitol, and galactitol) as additives in adjusting Zn2+ solvation structural behaviors within ZnSO4 baseline electrolytes. Electrical measurements and molecular simulations reveal the specific molecular structure of mannitol, which features interweaving electron clouds between adjacent hydroxyl groups, achieving a high local electron cloud density. This phenomenon significantly enhances desolvation abilities, thus establishing a more stable anode/electrolyte interface chemistry. Even at 5 mA cm-2 for 2.5 mAh cm-2 capacity, Zn||Zn symmetric cells with mannitol-regulated electrolyte display an impressive 1170 h lifespan, far exceeding those with other isomer additives and is nearly tenfold longer than that with a pure ZnSO4 electrolyte (120 h). Rather than strictly adhering to focusing on chemical composition, this study with emphasis on optimizing molecular structure offers a promising untapped dimension to screen more efficient additives to enhance the reversibility of ZMAs.

Ion Sieve Interface Assisted Zinc Anode with High Zinc Utilization and Ultralong Cycle Life for 61 Wh/kg Mild Aqueous Pouch Battery.

The cycling stability of a thin zinc anode under high zinc utilization has a critical impact on the overall energy density and practical lifetime of zinc ion batteries. In this study, an ion sieve protection layer (ZnSnF@Zn) was constructed in situ on the surface of a zinc anode by chemical replacement. The ion sieve facilitated the transport and desolvation of zinc ions at the anode/electrolyte interface, reduced the zinc deposition overpotential, and inhibited side reactions. Under a 50% zinc utilization, the symmetrical battery with this protection layer maintained stable cycling for 250 h at 30 mA cm-2. Matched with high-load self-supported vanadium-based cathodes (18-20 mg cm-2), the coin battery with 50% zinc utilization possessed an energy density retention of 94.3% after 1000 cycles at 20 mA cm-2. Furthermore, the assembled pouch battery delivered a whole energy density of 61.3 Wh kg-1, surpassing the highest mass energy density among reported mild zinc batteries, and retained 76.7% of the energy density and 85.3% (0.53 Ah) of the capacity after 300 cycles.

MBene with Redox-Active Terminal Groups for an Energy-Dense Cascade Aqueous Battery.

Two-dimensional (2D) transition metal borides (MBenes), new members of the 2D materials family, hold great promise for use in the electrocatalytic and energy storage fields because of their high specific area, high chemical activity, and fast charge carrier mobility. Although various types of MBenes are reported, layered MBenes featuring redox-active terminal groups for high energy output are not yet produced. A facile and energy-efficient method for synthesizing MBenes equipped with redox-active terminal groups for cascade Zn||I2 batteries is presented. Layered MBenes have ordered metal vacancies and ─Br terminal groups, enabling the sequential reactions of I-/I0 and Br-/Br0. The I2-hosting MBene-Br cathode results in a specific energy as high as 485.8 Wh kg-1 at 899.7 W kg-1 and a specific power as high as 6007.7 W kg-1 at 180.2 Wh kg-1, far exceeding the best records for Zn||I2 batteries. The results of this study demonstrate that the challenges of MBene synthesis can be overcome and reveal an efficient path for producing high-performance redox-active electrode materials for energy-dense cascade aqueous batteries.

Development of Inverse-Opal-Structured Charge-Deficient Co9S8@nitrogen-Doped-Carbon to Catalytically Enable High Energy and High Power for the Two-Electron Transfer I+/I- Electrode.

The iodine (I) electrode involving two-electron transfer chemistry by converting between I+ and I-, has the potential to deliver theoretically doubled capacity and higher working voltage platforms, thus achieving higher energy density. However, owing to the slow kinetics of the cascade two-electron transfer reactions, the system suffers from large overpotentials and low power density, especially at high working currents and low temperatures. Here, an inverse-opal-structured cobalt sulfide@nitrogen-doped-carbon (Co9S8@NC) catalyst with unique charge-deficient states is developed to promote the reaction kinetics of the I-/I+ electrode. The charge-deficient Co9S8@NC catalyst not only enables strong physicochemical adsorption with the iodine species but also significantly reduces the activation energy and interfacial charge transfer resistance of the cascade I+/I0/I- conversion reaction. Consequently, the prototypical Zn‖I+/I0/I- battery equipped with the Co9S8@NC catalyst can deliver a high energy density of 554 Wh kg-1 and a stable cycle life of 5000 cycles at 30 °C. Moreover, at a subzero temperature of -30 °C, the battery can exhibit enhanced kinetics and a high power density of 1514 W kg-1, high energy density of 485 Wh kg-1.

Rational Design of Dynamically Super-Tough and Super-Stretchable Hydrogels for Deformable Energy Storage Devices.

Hydrogels possess unique polymer networks that offer flexibility/stretchability, high ionic conductivity, and resistance to electrolyte leakage, making them suitable for deformable energy storage devices. Endowing the mechanical functionality of the hydrogel electrolytes focus on either enhancing the stretchability or the toughness. However, the stretchability and the toughness are generally a trade-off that the stretchable gels are intrinsically prone to damage and sensitive to notches and cracks. Here, the regulating strategies on the hydrogel's mechanical properties are provided to develop the designated hydrogel electrolyte, where different polymeric network structures are constructed, including single network structures, semi-interpenetrating network structures, and interpenetrating dual-network structures. A comprehensive comparison of these polymer network structures is conducted to evaluate their mechanical stretchability and toughness. Designing super-tough and super-stretchable hydrogels based on specific application requirements can be realized by striking a balance by regulating the hydrogel structure. In specific, incorporating semi-interpenetrating networks significantly can enhance stretchability to achieve a break elongation up to 1300%, while the interpenetrating dual-networks can largely improve the toughness to realize the extraordinary fracture toughness of 6.843 kJ m-2 . These findings offer valuable designing guidance for designated hydrogel electrolytes and the deformable zinc-silver battery is demonstrated with high mechanical stability and electrochemical performance.

Deploying Cationic Cellulose Nanofiber Confinement to Enable High Iodine Loadings Towards High Energy and High-Temperature Zn-I2 Battery.

High iodine loading and high-temperature adaptability of the iodine cathode are prerequisites to achieving high energy density at full battery level and promoting the practical application for the zinc-iodine (Zn-I2 ) battery. However, it would aggravate the polyiodide shuttle effect when employing high iodine loading and working temperature. Here, a sustainable cationic cellulose nanofiber (cCNF) was employed to confine the active iodine species through strong physiochemical adsorption to enlarge the iodine loading and stabilize it even at high temperatures. The cCNF could accommodate dual-functionality by enlarging the iodine loading and suppressing the polyiodide shuttle effect, owing to the unique framework structure with abundant surface positive charges. As a result, the iodine cathode based on the cCNF could deliver high iodine mass loading of 14.1 mg cm-2 with a specific capacity of 182.7 mAh g-1 , high areal capacity of 2.6 mAh cm-2 , and stable cycling over 3000 cycles at 2 A g-1 , thus enabling a high energy density of 34.8 Wh kg-1 and the maximum power density of 521.2 W kg-1 at a full Zn-I2 battery level. In addition, even at a high temperature of 60 °C, the Zn-I2 battery could still deliver a stable cycling.

Crystal Orientation Engineering of Perfectly Matched Heterogeneous Textured ZnSe for an Enhanced Interfacial Kinetic Zn Anode.

Uncontrollable dendrite formation in the Zn anode is the bottleneck of the commercialization of rechargeable aqueous zinc-based batteries (RAZBs). Interface, the location of the charge transfer process occuring, can significantly affect the further morphology evolution in ways that have not yet been fully comprehended, for example, the crystal facet and orientation of the coating layer. In this study, we demonstrated that the morphology and kinetics of the Zn anode could be tuned by the crystal facet. The fabricated textured ZnSe (T-ZnSe) layer can significantly enhance the reaction kinetics and induce uniform (0002)Zn deposition. In stark contrast, the polycrystalline P-ZnSe coating hinders the charge transfer process at the interface. With this T-ZnSe@Zn as the anode, the full cell with an I2 cathode and a practical areal capacity (2 mAh cm-2) can work well for 900 cycles. The effectiveness of this anode has also been testified by a pouch cell with an overall capacity of 150 mAh. This research contributes to the understanding of the interface and the feasible strategy for the practical application of the Zn anode.

Manageable Bubble Release Through 3D Printed Microcapillary for Highly Efficient Overall Water Splitting.

Porous metal foams (e.g., Ni/Cu/Ti) are applied as catalyst supports extensively for water splitting due to their large specific area and excellent conductivity, however, intrinsic bubble congestion is unavoidable because of the irregular three-dimensional (3D) networks, resulting in high polarization and degraded electrocatalytic performances. To boost the H2 O decomposition kinetics, the immediate bubble removal and water supply sequential in the gas-liquid-solid interface is essential. Inspired by the high efficiency of water/nutrient transport in the capillaries plants, this work designs a graphene-based capillary array with side holes as catalyst support to manage the bubble release and water supply via a Z-axis controllable digital light processing (DLP) 3D printing technology. Like planting rice, a low-cost, high-active CoNi carbonate hydroxide (CoNiCH) is planted on support. A homemade cell can reach 10 mA cm-2 in 1.51 V, and be kept at 30 mA cm-2 for 60 h without noticeable degradation, surpassing most of the known cells. This research provides a promising avenue to design and prepare advanced catalysts in various fields, including energy applications, pollutant treatment, and chemical synthesis.

3D Carbon Nanonetwork Coated Composite Electrode with Multi-Heteroatom Doping for High-Rate Vanadium Redox Flow Batteries.

With the advantages of benign mechanical property, electrochemical stability, and low cost, graphite fibers (GFs) have been widely used as electrodes for vanadium redox flow batteries (VRFBs). However, GFs usually possess inferior electrochemical activity and ion diffusion kinetics for electrode reaction, vastly limiting their application in VRFBs. Here, a 3D carbon nanonetwork coated GFs with multi-heteroatom doping was constructed for application in VRFBs via low temperature polymerization between linear polymer monomer and phytic acid, and subsequent carbonization (900 °C) on the GFs (GF@PCNs-900). Benefiting from the 3D structural features and multi-heteroatom doping (O, N and P), the composite electrode displayed sufficient diffusion of vanadium ions, rapid electron conduction, and highly enhanced electrochemical activity of reactive site on the electrodes. As a result, the GF@PCNs-900 delivered a high discharge capacity of 21 Ah L-1 and energy efficiency of above 70% with extraordinary stability during 200 cycles at 200 mA cm-2. Even at a huge current density of 400 mA cm-2, the GF@PCNs-900 still maintained a discharge capacity of 5.0 Ah L-1, indicating an excellent rate of performance for VRFBs. Such design strategy opens up a clear view for further development of energy storage field.

Organic electrochromic energy storage materials and device design.

While not affecting electrochemical performance of energy storage devices, integrating multi-functional properties such as electrochromic functions into energy storage devices can effectively promote the development of multifunctional devices. Compared with inorganic electrochromic materials, organic materials possess the significant advantages of facile preparation, low cost, and large color contrast. Specifically, most polymer materials show excellent electrochemical properties, which can be widely used in the design and development of energy storage devices. In this article, we focus on the application of organic electrochromic materials in energy storage devices. The working mechanisms, electrochemical performance of different types of organics as well as the shortcomings of organic electrochromic materials in related devices are discussed in detail.

Chemical Welding of the Electrode-Electrolyte Interface by Zn-Metal-Initiated In Situ Gelation for Ultralong-Life Zn-Ion Batteries.

A compatible and robust electrode-electrolyte interface is favorable in resolving the severe dendritic growth and side reactions of aqueous Zn-ion batteries toward commercial-standard lifespan and charging-discharging rate. Herein, a chemical welding strategy through in situ construction of a gel electrolyte that enables Zn-ion batteries to achieve ultralong life and reversibility is reported. The gel electrolyte is spontaneously formed on the Zn anode surface by redox polymerization with the initiation of Zn metal. The direct participation of the Zn anode in the chemical synthesis of the gel electrolyte brings a well-bonded and water-poor electrode-electrolyte interface, which not only alleviates side reactions but also enables preferential (002) Zn deposition. The in situ symmetric cell thus prepared delivers an ultralong lifespan of 5100 h (>212 days), and a hybrid capacitor with the in situ electrolyte runs smoothly over 40 000 cycles at 20 A g-1 . Even at an ultrahigh current density of 40 mA cm-2  and capacity of 40 mAh cm-2 , the cell still operates stably for 240 h, alongside a high Zn utilization with 87% depth of discharge. The in situ gel electrolyte integrating robust interface and preparation of all-in-one cells demonstrate a commercializable path for aqueous Zn-storage devices.

Few-layer bismuth selenide cathode for low-temperature quasi-solid-state aqueous zinc metal batteries.

The performances of rechargeable batteries are strongly affected by the operating environmental temperature. In particular, low temperatures (e.g., ≤0 °C) are detrimental to efficient cell cycling. To circumvent this issue, we propose a few-layer Bi2Se3 (a topological insulator) as cathode material for Zn metal batteries. When the few-layer Bi2Se3 is used in combination with an anti-freeze hydrogel electrolyte, the capacity delivered by the cell at -20 °C and 1 A g-1 is 1.3 larger than the capacity at 25 °C for the same specific current. Also, at 0 °C the Zn | |few-layer Bi2Se3 cell shows capacity retention of 94.6% after 2000 cycles at 1 A g-1. This behaviour is related to the fact that the Zn-ion uptake in the few-layer Bi2Se3 is higher at low temperatures, e.g., almost four Zn2+ at 25 °C and six Zn2+ at -20 °C. We demonstrate that the unusual performance improvements at low temperatures are only achievable with the few-layer Bi2Se3 rather than bulk Bi2Se3. We also show that the favourable low-temperature conductivity and ion diffusion capability of few-layer Bi2Se3 are linked with the presence of topological surface states and weaker lattice vibrations, respectively.

Ultra-High-Capacity and Dendrite-Free Zinc-Sulfur Conversion Batteries Based on a Low-Cost Deep Eutectic Solvent.

Traditional cathodes for aqueous Zn-ion batteries are afflicted by a limited specific capacity and fearful Zn dendrites. Herein, these troubles are disposed of with a conversion-type Zn-S battery and low-cost deep eutectic solvent (DES). By utilizing the optimized electrolyte, the symmetrical Zn battery can stably cycle over 3920 h, which also confers on the Zn-S battery an ultrahigh specific capacity of ∼846 mA h gS-1 and energy density of 259 W h kg-1 at 0.5 A g-1. Importantly, the conversion chemistry of S and ZnS is responsible for the superior anti-self-discharge behavior (capacity retention: 94.58 and 68.58% after standing for 72 and 288 h versus Zn//VO2 battery: 76.82 and 47.80% after resting for 24 and 72 h versus Zn//MnO2 battery: 95.96 and 91.57% after resting for 24 and 72 h, respectively). This work is the first authentication of Zn-S batteries based on a newly developed low-cost DES-based electrolyte, which meanwhile settles the deep-rooted low specific capacity and infamous Zn dendrite issues in conventional (de)intercalation Zn-ion batteries.

A Self-Healing Crease-Free Supramolecular All-Polymer Supercapacitor.

While traditional three-layer structure supercapacitors are under mechanical manipulations, the high-stress region concentrates, inevitably causing persistent structural problems including interlayer slippage, crease formation, and delamination of the electrode-electrolyte interface. Toward this, an all-polymeric, all-elastic and non-laminated supercapacitor with high mechanical reliability and excellent electrochemical performance is developed. Specifically, a polypyrrole electrode layer is in situ integrated into a silk fibroin-based elastic supramolecular hydrogel film with extensive hydrogen and covalent bonds, where a non-laminate device is realized with structural elasticity at the device level. The non-laminate configuration can avoid slippage and delamination, while the elasticity can preclude crease formation. Furthermore, under more severe mechanical damage, the supercapacitors can restore the electrochemical performance through non-autonomous self-healing capabilities, where the supramolecular design of host-guest interactions in the hydrogel matrix results in a superior self-healing efficiency approaching ≈95.8% even after 30 cutting/healing cycles. The all-elastic supercapacitor delivers an areal capacitance of 0.37 F cm-2 and a volumetric energy density of 0.082 mW h cm-3, which can well-maintain the specific capacitance even at -20 °C with over 85.2% retention after five cut/healing cycles.

Strategies for Stabilization of Zn Anodes for Aqueous Zn-Based Batteries: A Mini Review.

In recent years, thanks to the investigation of the in-depth mechanism, novel cathode material exploitation, and electrolyte optimization, the electrochemical performance of rechargeable Zn-based batteries (RZBs) has been significantly improved. Nevertheless, there are still some persistent challenges locating the instability of the Zn anodes that hinder the commercialization and industrialization of RZBs, especially the obstinate dendrites and hydrogen evolution reaction (HER) on Zn anodes, which will dramatically compromise the cycle stability and Coulombic efficiency. Therefore, various strategies with fundamental design principles focusing on the suppression of dendrite and the HER have been carefully summarized and categorized in this review, which are critically dissected according to the intrinsic mechanisms. Finally, pertinent insights into the challenges and perspectives on the future development of Zn anodes are also emphasized, expecting to supply potential research directions to promote the practical applications of RZBs.

Aqueous Zinc-Tellurium Batteries with Ultraflat Discharge Plateau and High Volumetric Capacity.

Traditional aqueous zinc-ion batteries (ZIBs) based on ion-intercalation or surface redox behaviors at the cathode side suffer severely from an unsatisfactory specific capacity and unstable output potential. Herein, these issues are applied to a conversion-type zinc-tellurium (Zn-Te) battery. Typically, this battery works based on a two-step solid-to-solid conversion with the successive formation of zinc ditelluride (ZnTe2 ) and zinc telluride (ZnTe). It delivers an ultrahigh volumetric capacity of 2619 mAh cm-3 (419 mAh g-1 ), 74.1% of which is from the first conversion (Te to ZnTe2 ) with an ultraflat discharge plateau. Though reported first in a challenging aqueous environment, this Zn-Te battery demonstrates an excellent capacity retention of >82.8% after 500 cycles, which results from the elimination of the notorious "shuttle effect" due to the solid-to-solid conversion behaviors. In addition, a quasi-solid-state Zn-Te battery is also fabricated, exhibiting superior flexibility, robustness, and good electrochemical performance. This work develops a novel cathode material based on conversion-type ion-storage mechanism. The system is attractive due to its ultrastable energy output, which is rarely reported for ZIBs.

Initiating a Reversible Aqueous Zn/Sulfur Battery through a "Liquid Film".

Sulfur cathodes have been under intensive study in various systems, such as Li/S, Na/S, Mg/S, and Al/S batteries. However, to date, Zn/S chemistry has never been reported. The first reliable aqueous Zn/polysulfide system activated by a "liquid film" comprising 4-(3-butyl-1-imidazolio)-1-butanesulfoni ionic liquid (IL) encapsulated within PEDOT:PSS. CF3 SO3 - anions in the IL operating as Zn2+ -transfer channels is reported. Moreover, the PEDOT:PSS network retains the IL, which renders Zn2+ -transfer channels and a polysulfide cathode with enhanced structural stability. The Zn/polysulfide system delivers extraordinary capacity of 1148 mAh g-1 and overwhelming energy density of 724.7 Wh kg-1 cathode at 0.3 Ag-1 . During the discharging phase, S6 2- is dominantly reduced by Zn to S2- (S6   →  S2- ). During the charging phase, these short chains are oxidized to form long-chain Znx Liy S3-6 . A further optimized high-concentrated salt electrolyte is used to improve the reversibility of the battery, demonstrating an extended lifetime over 1600 cycles at 1 Ag-1 with a capacity retention of 204 mAh g-1 . This facile approach and the superior performance of the developed aqueous Zn/S chemistry provide a new platform for sulfur-based battery and potentially solve the problems of other metal/sulfur batteries.

Initiating Hexagonal MoO3 for Superb-Stable and Fast NH4 + Storage Based on Hydrogen Bond Chemistry.

Nonmetallic ammonium (NH4 + ) ions are applied as charge carriers for aqueous batteries, where hexagonal MoO3 is initially investigated as an anode candidate for NH4 + storage. From experimental and first-principle calculated results, the battery chemistry proceeds with reversible building-breaking behaviors of hydrogen bonds between NH4 + and tunneled MoO3 electrode frameworks, where the ammoniation/deammoniation mechanism is dominated by nondiffusion-controlled pseudocapacitive behavior. Outstanding electrochemical performance of MoO3 for NH4 + storage is delivered with 115 mAh g-1 at 1 C and can retain 32 mAh g-1 at 150 C. Furthermore, it remarkably exhibits ultralong and stable cyclic performance up to 100 000 cycle with 94% capacity retention and high power density of 4170 W kg-1 at 150 C. When coupled with CuFe prussian blue analogous (PBA) cathode, the full ammonium battery can deliver decent energy density 21.3 Wh kg-1 and the resultant flexible ammonium batteries at device level are also pioneeringly developed for potential realistic applications.