Rechargeable Hydrogen-Chlorine Battery Operates in a Wide Temperature Range

Interface-Controlled Redox Chemistry in Aqueous Mn2⁺/MnO₂ Batteries

Manganese dioxide (MnO2) deposition/dissolution (Mn2+/MnO2) chemistry, involving a two-electron-transfer process, holds promise for safe and eco-friendly large-scale energy storage. However, challenges like electrode/electrolyte interface environment fluctuations (H+ and H2O activity), irreversible Mn degradation, and limited understanding of degradation mechanisms hinder the reversibility of the Mn2+/MnO2 conversion. This study demonstrates a vanadyl/pervanadyl (VO2+/VO2 +) redox-mediated interface designed for high-energy Mn2+/MnO2 batteries. Unlike flow systems, this work uncovers, for the first time, the mechanism of a static redox-mediated interface in regulating interfacial H+ and H2O activities. Significantly, the VO2+/VO2 + chemical redox mediation targets Mn3+ intermediates, suppressing their hydrolysis and enabling 100% Mn2+/MnO2 conversion. The redox-mediated interface enhances the Mn redox electron transfer process, achieving a stable ≈95% coulombic efficiency and ultrahigh capacity of 100 mAh cm- 2 with an areal energy density of 111 mWh cm- 2, outperforming flow systems. The electrode also exhibits an average specific capacity of 593 mAh g-1, approaching the theoretical limit of 616 mAh g-1, and a specific energy density of 721 Wh kg-1 at high MnO2 loadings (50-150 mg cm-2). The findings highlight the critical role of interfacial redox mediation in regulating H+ and H2O activities and underscore the significance of interface dynamics.

Ultrafast Rechargeable Aluminum-Chlorine Batteries Enabled by a Confined Chlorine Conversion Chemistry in Molten Salts

Rechargeable metal chloride batteries, with their high discharge voltage and specific capacity, are promising for next-generation sustainable energy storage. However, sluggish solid-to-gas conversion kinetics between solid metal chlorides and gaseous Cl2 cause unsatisfactory rate capability and limited cycle life, hindering their further applications. Here we present a rechargeable aluminum-chlorine (Al-Cl2) battery that relies on a confined chlorine conversion chemistry in a molten salt electrolyte, exhibiting ultrahigh rate capability and excellent cycling stability. Both experimental analysis and theoretical calculations reveal a reversible solution-to-gas conversion reaction between AlCl4- and Cl2 in the cathode. The designed nitrogen-doped porous carbon cathode enhances Cl2 adsorption, thereby improving the cycling lifespan and coulombic efficiency of the battery. The resulting Al-Cl2 battery demonstrates a high discharge plateau of 1.95 V, remarkable rate capability without capacity decay at different rates from 5 to 50 A g-1, and good cycling stability with over 1200 cycles at a rate of 10 A g-1. Additionally, we implemented a carbon nanofiber membrane on the anode side to mitigate dendrite growth, which further extends the cycle life to 3000 cycles at an ultrahigh rate of 30 A g-1. This work provides a new perspective on the advancement of high-rate metal chloride batteries.

A Highly Reversible Aqueous Sulfur-Dual-Halogen Battery Enabled by a Water-in-Bisalt Electrolyte

The chlorine-based redox reaction applied in aqueous rechargeable batteries (ARBs) has attracted extensive attention owing to the high theoretical capacity and redox potential. However, it generally suffers from low reversibility and poor Coulombic efficiency due to the evolution of toxic Cl2 gas and the decomposition of aqueous electrolytes. Herein, an aqueous sulfur-dual halogen chemistry is demonstrated by employing highly-concentrated water-in-bisalt (WiBS) electrolyte, sulfur anode, and iodine composite electrodes. The freestanding iodine/carbon cloth cathode and Cl--containing WiBS electrolyte not only enable the continuous I+/I0 reaction by forming [IClx]1-x interhalogens but also achieve the oxidation of Cl- in [IClx]1-x at higher redox potential and immobilize Cl0 species via I+─Cl0 chemical bonds. Therefore, the as-assembled aqueous sulfur-dual halogen batteries (ASHBs) based on the dual-halogen conversion on the cathode and the S/Sx 2- redox reaction on the anode deliver a high energy density of 304 Wh kg-1 with an average output voltage of 1.32 V. These key findings open an avenue for the development of low-cost and high-performance ARBs for energy storage applications.

Dynamic Release Electrolyte Design for Stable Proton Batteries

Aqueous proton batteries (APBs) have recently demonstrated unprecedented advantages in the fields of ultralow temperature and high-power energy applications due to kinetically favorable proton chemistry. Proton acids (e. g. H2SO4, H3PO4) as the common proton-conducting electrolyte, however, seriously corrode electrode materials and current collectors, resulting in limited cycle life of APBs. Here we reported protonated amine as a feasible proton transport mediator and releasing source for APBs based on its dynamic chemical dissociation equilibrium. Free protons in the electrolyte are limited to a quite low level. Consequently, the optimized electrolyte with a nearly neutral pH value significantly suppresses corrosion and broadens material selection option for APBs. The CuFe-TBA electrode exhibited a long cycle performance over 40000 cycles with only ~0.0004 % attenuation rate per cycle in the optimized electrolyte. The WO3 and VO2(B) electrode also displayed high cycling stability. Benefiting from enhanced electrode stability in the optimized electrolyte, the resultant CuFe-TBA/WO3 and CuFe-TBA/VO2(B) full batteries display impressive long-term cycling performance with high-capacity retention. Our work presents a proton dynamic-release electrolyte for durable APBs which is highly promising for scalable energy systems.

New Redox Chemistries of Halogens in Aqueous Batteries

Halogen-based redox-active materials represent an important class of materials in aqueous electrochemistry. The existence of versatile halogen species and their rich bonding coordination create great flexibility in designing new redox couples. Novel redox reaction mechanisms and electrochemical reversibility can be unlocked in specifically configurated electrolyte environments and electrodes. In this review, the halogen-based redox couples and their appealing redox chemistries in aqueous batteries, including redox flow batteries and traditional static batteries that have been studied in recent years, are discussed. New aqueous electrochemistry provides hope to outperform the state-of-the-art materials and systems that are facing resources and performance limitation, and to enrich the existing battery chemistries.

Rechargeable Hydrogen Gas Batteries: Fundamentals, Principles, Materials, and Applications

The growing demand for renewable energy sources has accelerated a boom in research on new battery chemistries. Despite decades of development for various battery types, including lithium-ion batteries, their suitability for grid-scale energy storage applications remains imperfect. In recent years, rechargeable hydrogen gas batteries (HGBs), utilizing hydrogen catalytic electrode as anode, have attracted extensive academic and industrial attention. HGBs, facilitated by appropriate catalysts, demonstrate notable attributes such as high power density, high capacity, excellent low-temperature performance, and ultralong cycle life. This review presents a comprehensive overview of four key aspects pertaining to HGBs: fundamentals, principles, materials, and applications. First, detailed insights are provided into hydrogen electrodes, encompassing electrochemical principles, hydrogen catalytic mechanisms, advancements in hydrogen catalytic materials, and structural considerations in hydrogen electrode design. Second, an examination and future prospects of cathode material compatibility, encompassing both current and potential materials, are summarized. Third, other components and engineering considerations of HGBs are elaborated, including cell stack design and pressure vessel design. Finally, a techno-economic analysis and outlook offers an overview of the current status and future prospects of HGBs, indicating their orientation for further research and application advancements.

High Efficiency Alkaline Iodine Batteries with Multi-Electron Transfer Enabled by Bi/Bi2O3 Redox Mediator

The multi-electron transfer I-/IO3 - redox couple is attractive for high energy aqueous batteries. Shifting from an acidic to an alkaline electrolyte significantly enhances the IO3 - formation kinetics due to the spontaneous disproportionation reaction, while the alkaline environment also offers more favorable Zn anode compatibility. However, sluggish kinetics during the reduction of IO3 - persists in both acidic and alkaline electrolytes, compromising the energy efficiency of this glorious redox couple. Here, we establish the fundamental redox mechanism of the I-/IO3 - couple in alkaline electrolytes for the first time and propose that Bi/Bi2O3 acts as a redox mediator (RM) to "catalyze" the reduction of IO3 -. This mediation significantly reduces the voltage gap between charge/discharge from 1.6 V to 1 V with improved conversion efficiency and rate capability. By pairing the Zn anode and the Bi/Bi2O3 RM cathode, the full battery with I-/IO3 - redox mechanism achieves high areal capacity of 12 mAh cm-2 and stable operation at 5 mAh cm-2 for over 400 cycles.

Electrode/Electrolyte Optimization-Induced Double-Layered Architecture for High-Performance Aqueous Zinc-(Dual) Halogen Batteries

Aqueous zinc-halogen batteries are promising candidates for large-scale energy storage due to their abundant resources, intrinsic safety, and high theoretical capacity. Nevertheless, the uncontrollable zinc dendrite growth and spontaneous shuttle effect of active species have prohibited their practical implementation. Herein, a double-layered protective film based on zinc-ethylenediamine tetramethylene phosphonic acid (ZEA) artificial film and ZnF2-rich solid electrolyte interphase (SEI) layer has been successfully fabricated on the zinc metal anode via electrode/electrolyte synergistic optimization. The ZEA-based artificial film shows strong affinity for the ZnF2-rich SEI layer, therefore effectively suppressing the SEI breakage and facilitating the construction of double-layered protective film on the zinc metal anode. Such double-layered architecture not only modulates Zn2+ flux and suppresses the zinc dendrite growth, but also blocks the direct contact between the metal anode and electrolyte, thus mitigating the corrosion from the active species. When employing optimized metal anodes and electrolytes, the as-developed zinc-(dual) halogen batteries present high areal capacity and satisfactory cycling stability. This work provides a new avenue for developing aqueous zinc-(dual) halogen batteries.

Energetic Hypervalent Organoiodine Electrochemistry for Aqueous Zinc Batteries

Hypervalent organoiodine compounds have been extensively utilized in organic synthesis, yet their electrochemical properties remain unexplored despite their theoretically high redox potential compared with inorganic iodine, which primarily relies on the I-/I0 redox couple in battery applications. Here, the fundamental redox mechanism of hypervalent organoiodine in a ZnCl2 aqueous electrolyte is established for the first time using the simplest iodobenzene (PhI) as a model compound. We validated that the PhI to PhICl2 transition is a single-step and reversible reaction, enabling two-electron transfer of I+/I3+ redox chemistry (1.9 V vs Zn2+/Zn) with high capacity (422 mAh giodine-1, and 262.6 mAh g-1 based on PhI) and high theoretical energy density (801.8 Wh kg-1). It was also elucidated that such organoiodine electrochemistry exhibits rich tunability in terms of the global reactivity of various PhI derivatives, including multiple iodine-substituted isomers and functional substituents. Additionally, the stabilizing anion ligands affect the reversibility and stability of trivalent organoiodine compounds. By limiting side reactions and improving the stability of trivalent organoiodine at low temperatures, the zinc-PhI battery demonstrated the feasibility of I+/I3+ conversion and sustained stable performance over 400 cycles. This work bridges the gap between hypervalent organoiodine chemistry and battery technology, highlighting the potential for future high-performance battery applications.

Rechargeable alkali metal-chlorine batteries: advances, challenges, and future perspectives

The emergence of Li-SOCl2 batteries in the 1970s as a high-energy-density battery system sparked considerable interest among researchers. However, limitations in the primary cell characteristics have restricted their potential for widespread adoption in today's sustainable society. Encouragingly, recent developments in alkali/alkaline-earth metal-Cl2 (AM-Cl2) batteries have shown impressive reversibility with high specific capacity and cycle performance, revitalizing the potential of SOCl2 batteries and becoming a promising technology surpassing current lithium-ion batteries. In this review, the emerging AM-Cl2 batteries are comprehensively summarized for the first time. The development history and advantages of Li-SOCl2 batteries are traced, followed by the critical working mechanisms for achieving high rechargeability. The design concepts of electrodes and electrolytes for AM-Cl2 batteries as well as key characterization techniques are also demonstrated. Furthermore, the current challenges and corresponding strategies, as well as future directions regarding the battery are systematically discussed. This review aims to deepen the understanding of the state-of-the-art AM-Cl2 battery technology and accelerate the development of practical AM-Cl2 batteries for next-generation high-energy storage systems.

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.