Pathways towards high energy aqueous rechargeable batteries

Long-Lifespan Fibrous Aqueous Ni//Bi Battery Enabled by Bi2O3-Bi2S3 Hierarchical Heterostructures

Bismuth oxide (Bi2O3) materials are considered as great promising anodes for aqueous batteries on account of the high capacity as well as wide potential plateau. Nevertheless, the low conductivity and severe volumetric change of Bi2O3 in the course of cycling are the main limiting factors for their application in energy-storage systems. Herein, we propose and design unique hierarchical heterostructures constructed by Bi2O3 and Bi2S3 nanosheets (NSs) manufactured immediately on the surface of carbon nanotube fibers (CNTFs). The Bi2O3-Bi2S3 (BO-BS) exhibits enhanced conductivity and increased stability in comparison with pure Bi2O3 and Bi2S3. The BO-BS NSs/CNTF electrode indicates exceptional rate capability and cycling stability, while creating a high reversible capacity of 0.68 mAh cm-2 at 4 mA cm-2, as anticipated. Additionally, the quasi-solid-state fibrous aqueous Ni//Bi battery that was built with the BO-BS NSs/CNTF anode delivers an exceptional cycling stability of 52.7% capacity retention after 4000 cycles at 80 mA cm-2, an ultrahigh capacity of 0.35 mAh cm-2 at 4 mA cm-2, and a high energy density of 340.1 mWh cm-3 at 880 mW cm-3. This work demonstrates the potential of constructing hierarchical heterostructures of bismuth-based materials for high-performance aqueous Ni//Bi batteries and other energy-storage devices.

Recent Functionalized Strategies of Metal-Organic Frameworks for Anode Protection of Aqueous Zinc-Ion Battery

The inherent benefits of aqueous Zn-ion batteries (ZIBs), such as environmental friendliness, affordability, and high theoretical capacity, render them promising candidates for energy storage systems. Nevertheless, the Zn anodes of ZIBs encounter severe challenges, including dendrite formation, hydrogen evolution reaction, corrosion, and surface passivation. These would result in the infeasibility of ZIBs in practical situations. To this end, artificial interfaces with functionalized materials are crafted to protect the Zn anode. They have the capability to modulate the zinc ion flux in proximity to the electrode surface and shield it from aqueous electrolytes by leveraging either size effects or charge effects. Considering metal-organic frameworks (MOFs) with tunable pore size, chemical composition, and stable framework structures, they have emerged as effective materials for building artificial interfaces, prolonging the lifespan, and improving the unitization of Zn anode. In this review, the contributions of MOFs for protecting Zn anode, which mainly involves facilitating homogeneous nucleation, manipulating selective deposition, regulating ion and charge flux, accelerating Zn desolvation, and shielding against free water and anions are comprehensively summarized. Importantly, the future research trajectories of MOFs for the protection of the Zn anode are underscored, which may propose new perspectives on the practical Zn anode and endow the MOFs with high-value applications.

Electrolyte Additives for Stable Zn Anodes

Zn-ion batteries are regarded as the most promising batteries for next-generation, large-scale energy storage because of their low cost, high safety, and eco-friendly nature. The use of aqueous electrolytes results in poor reversibility and leads to many challenges related to the Zn anode. Electrolyte additives can effectively address many such challenges, including dendrite growth and corrosion. This review provides a comprehensive introduction to the major challenges in and current strategies used for Zn anode protection. In particular, an in-depth and fundamental understanding is provided of the various functions of electrolyte additives, including electrostatic shielding, adsorption, in situ solid electrolyte interphase formation, enhancing water stability, and surface texture regulation. Potential future research directions for electrolyte additives used in aqueous Zn-ion batteries are also discussed.

In Situ Fe-Substituted Hexacyanoferrate for High-Performance Aqueous Potassium Ion Batteries

The eco-friendliness, safety, and affordability of aqueous potassium batteries (AKIBs) have made them popular for large-scale energy storage devices. However, the cycling and rate performance of research materials, particularly cobalt hexacyanoferrate, have yet to meet satisfactory standards. Herein, a room-temperature drafted K1.66 Fe0.25 Co0.75 [Fe(CN)6 ]·0.83H2 O (KFCHCF) sample is reported using an in situ substitution strategy. A higher concentration of ferrocyanide ions decreases the water content and increases the potassium content, while citric acid works as a chelating agent and is responsible for Fe-substitution in the KFCHCF sample. The resultant KFCHCF sample exhibits good rate performance, and about 97% and 90.6% of discharge capacity are conserved after 400 and 1000 cycles at 100 and 200 mA g-1 , respectively. The full cell using the KFCHCF cathode and 1,4,5,8-naphthalenetetracarboxylic dianhydride-derived polyimide (PNTCDA) anode maintains ≈74.93% and 74.35% of discharge capacity at 200 mA g-1 and 1000 mA g-1 for 1000 and >10,000 cycles, respectively. Furthermore, ex situ characterizations demonstrate the high reversibility of K-ions and structural stability during the charge-discharge process. Such high performance is attributed to the fast K-ion migration and crystal structure stabilization caused by in situ Fe-substitution in the KFCHCF sample. Other hexacyanoferrates can be synthesized using this method and used in grid-scale storage systems.

Vanadium Hexacyanoferrate Prussian Blue Analogs for Aqueous Proton Storage: Excellent Electrochemical Properties and Mechanism Insights

The significant attraction toward aqueous proton batteries (APBs) is attributable to their expedited kinetics, elevated safety profile, and economical feasibility. Nevertheless, their practical implement is significantly blocked by the unsatisfactory energy density due to the limited cathode materials. Herein, vanadium hexacyanoferrate Prussian blue analog (VOHCF) is introduced as a potentially favorable cathode material for APBs. The findings demonstrate that this VOHCF electrode exhibits a notable reversible capacity of 102.7 mAh g-1 and exceptional cycling stability, with 95.4% capacity retention over 10 000 cycles at 10 A g-1 . It is noteworthy that this is the detailed instance of VOHCF being proposed as a cathode for APBs. Combining the in situ characterization techniques and theoretical simulations, the origins of excellent proton storage performance are revealed as the multiple redox mechanisms with double active centers of ─C≡N group and V═O bond in VOHCF as well as the robust structure stability. A proton full cell with excellent performance is further achieved by coupling the VOHCF cathode and diquinoxalino[2,3-a:2',3'-c] phenazine (HATN) anode, demonstrating the great potential of VOHCF in practical applications. This work could provide fundamental understanding to the development of feasible cathode materials for proton storage device.

Potassium ion pre-intercalated MnO2 for aqueous multivalent ion batteries

Manganese dioxide (MnO2), as a cathode material for multivalent ion (such as Mg2+ and Al3+) storage, is investigated due to its high initial capacity. However, during multivalent ion insertion/extraction, the crystal structure of MnO2 partially collapses, leading to fast capacity decay in few charge/discharge cycles. Here, through pre-intercalating potassium-ion (K+) into δ-MnO2, we synthesize a potassium ion pre-intercalated MnO2, K0.21MnO2·0.31H2O (KMO), as a reliable cathode material for multivalent ion batteries. The as-prepared KMO exhibits a high reversible capacity of 185 mAh/g at 1 A/g, with considerable rate performance and improved cycling stability in 1 mol/L MgSO4 electrolyte. In addition, we observe that aluminum-ion (Al3+) can also insert into a KMO cathode. This work provides a valid method for modification of manganese-based oxides for aqueous multivalent ion batteries.

Aqueous Organic Batteries Using the Proton as a Charge Carrier

Benefiting from the merits of low cost, nonflammability, and high operational safety, aqueous rechargeable batteries have emerged as promising candidates for large-scale energy-storage applications. Among various metal-ion/non-metallic charge carriers, the proton (H+ ) as a charge carrier possesses numerous unique properties such as fast proton diffusion dynamics, a low molar mass, and a small hydrated ion radius, which endow aqueous proton batteries (APBs) with a salient rate capability, a long-term life span, and an excellent low-temperature electrochemical performance. In addition, redox-active organic molecules, with the advantages of structural diversity, rich proton-storage sites, and abundant resources, are considered attractive electrode materials for APBs. However, the charge-storage and transport mechanisms of organic electrodes in APBs are still in their infancy. Therefore, finding suitable electrode materials and uncovering the H+ -storage mechanisms are significant for the application of organic materials in APBs. Herein, the latest research progress on organic materials, such as small molecules and polymers for APBs, is reviewed. Furthermore, a comprehensive summary and evaluation of APBs employing organic electrodes as anode and/or cathode is provided, especially regarding their low-temperature and high-power performances, along with systematic discussions for guiding the rational design and the construction of APBs based on organic electrodes.

Metal-organic frameworks-derived layered double hydroxides: From controllable synthesis to various electrochemical energy storage/conversion applications

Over the past years, metal-organic frameworks (MOF) have been directly used as electrodes or as a precursor for MOF-derived materials in energy storage and conversion systems. In the wide range of existing MOF derivatives, MOF-derived layered double hydroxides (LDHs) are determined to be promising materials due to their unique structure and features. However, MOF-derived LDHs (MDL) materials can suffer from insufficient intrinsic conductivity and agglomeration during formation. Various techniques and approaches were designed and applied to tackle these problems, such as using ternary LDHs, ion-doping, sulphurization, phosphorylation, selenization, direct growth, and conductive substrates. All the mentioned enhancement techniques aim to create the ideal electrode materials with maximum performance. In this review, we gathered and discussed the most recent progressive advances, different synthesis methodologies, unsolved challenges, applications, and electrochemical and electrocatalytic performance of MDL materials. We hope this work will be a reliable source for future progress and synthesis of these materials.

Recent Advances of Transition Metal Chalcogenides as Cathode Materials for Aqueous Zinc-Ion Batteries

In recent years, advances in lithium-ion batteries (LIBs) have pushed the research of other metal-ion batteries to the forefront. Aqueous zinc ion batteries (AZIBs) have attracted much attention owing to their low cost, high capacity and non-toxic characteristics. Among various cathodes, transition metal chalcogenides (TMCs) with a layered structure are considered as suitable electrode materials. The large layer spacing facilitates the intercalation/de-intercalation of Zn²⁺ between the layers. In this mini-review, we summarize a variety of design strategies for the modification of TMCs. Then, we specifically emphasize the zinc storage capacity of the optimized electrodes. Finally, we propose the challenges and future prospects of cathode materials for high-energy AZIBs.

A two-dimensional conductive polymer/V2O5 composite with rapid zinc-ion storage kinetics for high-power aqueous zinc-ion batteries

Vanadium oxides represent a promising cathode material for aqueous zinc ion batteries (ZIBs) owing to their abundant valences and versatile cation-storage capacities. However, the sluggish Zn²⁺ diffusion kinetics in the V₂O₅ framework and poor intrinsic conductivity result in inferior rate capability and unsatisfactory cycling performance of the V₂O₅ cathode, and thus limits its commercial-scale deployment. Herein, a unique conducting polymer intercalation strategy is developed to optimize the ion/electron transport simultaneously based on the rational design of the composite structure and morphology. The poly(3,4-ethylenedioxythiophene) (PEDOT) intercalated V₂O₅ not only remarkably enlarges the interlayer distance for facile Zn²⁺ diffusion, but also diminishes the electron transport resistance by the π-conjugated structure of PEDOT. Additionally, the two-dimensional (2D) morphology enables shorter ion diffusion paths as well as a larger number of exposed sites for Zn²⁺ insertion. As a result, the PEDOT-intercalated V₂O₅ (PEDOT/V₂O₅) exhibits a good high-rate performance (154 mA h g^-1 at an ultrahigh current density of 50 A g^-1) and a long-term cycling life (maintains 170 mA h g^-1 even after 2500 cycles at 30 A g^-1). This universal strategy provides a design principle for constructing efficient Zn²⁺ and electron transport pathways within cathode materials, holding great potential for the development of high-performance and durable ZIB cathodes.

Metal-Organic Framework-Based Materials for Aqueous Zinc-Ion Batteries: Energy Storage Mechanism and Function

Aqueous rechargeable zinc-ion batteries (ZIBs) featuring competitive performance, low cost and high safety hold great promise for applications in grid-scale energy storage and portable electronic devices. Metal-organic frameworks (MOFs), relying on their large framework structure and abundant active sites, have been identified as promising materials in ZIBs. This review comprehensively presents the current development of MOF-based materials including MOFs and their derivatives in ZIBs, which begins with Zn storage mechanism of MOFs, followed by introduction of various types of MOF-based cathode materials (PB and PBA, Mn-based MOF, V-based MOF, conductive MOF and their derivatives), and the regulation approaches for Zn deposition behavior. The key factors and optimization strategies of MOF-based materials that affect ZIBs performance are emphasized and discussed. Finally, the challenges and further research directions of MOF-based materials for advanced zinc-ion batteries are provided.

Regulating Interfacial Desolvation and Deposition Kinetics Enables Durable Zn Anodes with Ultrahigh Utilization of 80

Rechargeable aqueous zinc ion batteries (ZIBs) represent a promising technology for large-scale energy storage due to their high capacity, intrinsic safety and low cost. However, Zn anodes suffer from poor reversibility and cycling stability caused by the side-reactions and dendrite issues, which limit the Zn utilization in the ZIBs. Herein, to improve the durability of Zn under high utilization, an aluminum-doped zinc oxide (AZO) interphase is presented. The AZO interphase inhibits side reactions by isolating active Zn from the bulk electrolyte, and enables facile and uniform Zn deposition kinetics by accelerating the desolvation of hydrated Zn²⁺ and homogenizing the electric field distribution. Accordingly, the AZO-coated Zn (AZO@Zn) anode exhibits a long lifespan of 600 h with Zn utilization of 34.1% at the current density of 10 mA cm^-2 . Notably, even under ultrahigh Zn utilization of 80%, the AZO@Zn remains stable cycling over 200 h. Meanwhile, the V₂ O₅ /AZO@Zn full cell with limited Zn excess displays high capacity retention of 86.8% over 500 cycles at 2 A g^-1 . This work provides a simple and efficient strategy to ensure the reversibility and durability of Zn anodes under high utilization conditions, holding a great promise for commercially available ZIBs with competitive energy density.

Rational Synthesis of "Grape-like" Ni2 V2 O7 Microspheres as High-capacity Anodes for Rechargeable Lithium Batteries

Vanadates have received booming attention recently as promising materials for extensive electrochemical devices such as batteries and electrocatalysis. However, the enormous difficulties of achieving pure-phase transition metal vanadates, especially for nickel-based, hinder their exploitations. Herein, for the first time, by controlling the amount of ethylene glycol (EG) and reaction time, grape-like Ni₂ V₂ O₇ (or V₂ O₅ /Ni₂ V₂ O₇ ) microspheres were rationally fabricated. It is demonstrated that the EG can chelate both Ni²⁺ and VO₃ ^- to form organometallic precursors. As anode in lithium-ion batteries (LIBs), it could deliver superior reversible capacity of 1050 mAh/g at 0.1 A/g and excellent rate capability of 600 mAh/g at 4 A/g. The facile hydrothermal synthesis broadens the material variety of nickel vanadates and offers new opportunities for their wider applications in electrochemistry.