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

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.

Electron-Donating Conjugation Effect Modulated Zn2+ Reduction Reaction for Separator-Free Aqueous Zinc Batteries

Zinc-based aqueous batteries (ZABs) are attracting extensive attention due to the low cost, high capacity, and environmental benignity of the zinc anode. However, their application is still hindered by the undesired zinc dendrites. Despite Zn-surface modification being promising in relieving dendrites, a thick separator (i.e. glass fiber, 250-700 μm) is still required to resist the dendrite puncture, which limits volumetric energy density of battery. Here, we pivot from the traditional interphase plus extra separator categories, proposing an all-in-one ligand buffer layer (ca. 20 μm) to effectively modulate the Zn2+ transfer and deposition behaviors proved by in situ electrochemical digital holography. Experimental characterizations and density functional theory simulations further reveal that the catechol groups in the buffer layer can accelerate the Zn2+ reduction reaction (ZRR) through the electron-donating p-π conjugation effect, decreasing the negative charge in the coordination environment. Without extra separators, the elaborated system endows low polarization below 28.2 mV, long lifespan of 4950 h at 5 mA cm-2 in symmetric batteries, and an unprecedented volumetric energy density of 99.2 Wh L-1 based on the whole pouch cells. The concomitantly "separator-free" and "dendrite-free" conjugation effect with an accelerated ZRR process could foster the progression of metallic anodes and benefit energetic aqueous batteries.

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.

Zn Anode Surviving Extremely Corrosive Polybromide Environment with Alginate-Graphene Oxide Hydrogel Coating

Zinc-bromine (Zn-Br) redox provides a high energy density and low-cost option for next-generation energy storage systems, and polybromide diffusion remains a major issue leading to Zn anode corrosion, dendrite growth, battery self-discharge and limited electrochemical performance. A dual-functional Alginate-Graphene Oxide (AGO) hydrogel coating is proposed to prevent polybromide corrosion and suppress dendrite growth in Zn-Br batteries through negatively charged carboxyl groups and enhanced mechanical properties. The battery with anode of plain zinc coated with AGO (Zn]AGO) survives a severely corrosive environment with higher polybromide concentration than usual without a membrane, and achieves 80 cycles with 100% Coulombic and 80.65% energy efficiencies, four times compared to plain Zn anode. The promising performance is comparable to typical Zn-Br batteries using physical membranes, and the AGO coating concept can be well adapted to various Zn-Br systems to promote their applications.

Low-Temperature and Fast-Charge Sodium Metal Batteries

Low-temperature operation of sodium metal batteries (SMBs) at the high rate faces challenges of unstable solid electrolyte interphase (SEI), Na dendrite growth, and sluggish Na+ transfer kinetics, causing a largely capacity curtailment. Herein, low-temperature and fast-charge SMBs are successfully constructed by synergetic design of the electrolyte and electrode. The optimized weak-solvation dual-salt electrolyte enables high Na plating/stripping reversibility and the formation of NaF-rich SEI layer to stabilize sodium metal. Moreover, an integrated copper sulfide electrode is in situ fabricated by directly chemical sulfuration of copper current collector with micro-sized sulfur particles, which significantly improves the electronic conductivity and Na+ diffusion, knocking down the kinetic barriers. Consequently, this SMB achieves the reversible capacity of 202.8 mAh g-1 at -20 °C and 1 C (1 C = 558 mA g-1 ). Even at -40 °C, a high capacity of 230.0 mAh g-1 can still be delivered at 0.2 C. This study is encouraging for further exploration of cryogenic alkali metal batteries, and enriches the electrode material for low-temperature energy storage.

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.

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.

A Self-Stratified Thermally Regenerative Battery Using Nanoprism Cu Covering Ni Electrodes for Low-Grade Waste Heat Recovery

Developing a low-cost and high-performance thermally regenerative battery (TRB) is significant for recovering low-grade waste heat. A self-stratified TRB induced by the density difference between electrolytes is proposed to remove the commercial anion exchange membrane (AEM) and avoid ammonia crossover. The simulation and experiment results show the uneven distribution of NH₃, verifying the feasibility of self-stratified electrolytes. For better power generation performance, nanoprism Cu covering Ni electrodes with a high specific surface area and a stable framework are adopted to provide more reaction active sites for fast charge transfer during discharge. A maximum power density (12.7 mW cm^-2) and a theoretical heat-to-electricity conversion efficiency of 2.4% (relative to Carnot efficiency of 27.5%) are obtained in the self-stratified TRB employing nanoprism Cu covering Ni electrodes. Moreover, the cost-effectiveness, simple structure, and sustainable discharge operation indicate that it will be a potential choice for energy conversion from low-grade heat.

Development of long lifespan high-energy aqueous organic||iodine rechargeable batteries

Rechargeable aqueous metal||I₂ electrochemical energy storage systems are a cost-effective alternative to conventional transition-metal-based batteries for grid energy storage. However, the growth of unfavorable metallic deposition and the irreversible formation of electrochemically inactive by-products at the negative electrode during cycling hinder their development. To circumvent these drawbacks, herein we propose 3,4,9,10-perylenetetracarboxylic diimide (PTCDI) as negative electrode active material and a saturated mixed KCl/I₂ aqueous electrolyte solution. The use of these components allows for exploiting two sequential reversible electrochemical reactions in a single cell. Indeed, when they are tested in combination with an active carbon-enveloped I₂ electrode in a glass cell configuration, we report an initial specific discharge capacity of 900 mAh g⁻¹ (electrode mass of iodine only) and an average cell discharge voltage of 1.25 V at 40 A g⁻¹ and 25\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\pm$$\end{document}±1 °C. Finally, we also report the assembly and testing of a PTCDI|KCl-I₂|carbon paper multilayer pouch cell prototype with a discharge capacity retention of about 70% after 900 cycles at 80 mA and 25\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\pm$$\end{document}±1 °C.

Aqueous I₂-based batteries are a promising system for cost-effective and environmentally-friendly electricity storage. Here, the authors propose a high-capacity and long-lasting aqueous I₂ battery system using an electrochemically active organic molecule at the negative electrode.

Voltage-Controlled Divergent Cascade of Electrochemical Reactions for Characterization of Lipids at Multiple Isomer Levels Using Mass Spectrometry

Cascading divergent reactions in a single system is highly desirable for their intrinsic efficiency and potential to achieve multilevel structural characterization of complex biomolecules. In this work, two electrochemical reactions, interfacial electro-epoxidation and cobalt anodic corrosion, are divergently cascaded in nanoelectrospray (nESI) and can be switched at different voltages. We applied these reactions to lipid identification at multiple isomer levels using mass spectrometry (MS), which remains a great challenge in structural lipidomics. The divergent cascade reactions in situ derivatize lipids to produce epoxidized lipids and cobalt-adducted lipids at different voltages. These lipids are then fragmented upon low-energy collision-induced dissociation (CID), generating diagnostic fragments to indicate C═C locations and sn-positions that cannot be achieved by the low-energy CID of native lipids. We have demonstrated that lipid structural isomers show significantly different profiles in the analysis of healthy and cancerous mouse prostate samples using this strategy. The application of divergent cascade reactions in lipid identification allows the four-in-one analysis of lipid headgroups, fatty acyl chains, C═C locations, and sn-positions simply by tuning the nESI voltages within a single experiment. This feature as well as its low sample consumption, no need for an extra apparatus, and quantitative analysis capability show its great potential in lipidomics.

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.

Enabling fast-charging selenium-based aqueous batteries via conversion reaction with copper ions

Selenium (Se) is an appealing alternative cathode material for secondary battery systems that recently attracted research interests in the electrochemical energy storage field due to its high theoretical specific capacity and good electronic conductivity. However, despite the relevant capacity contents reported in the literature, Se-based cathodes generally show poor rate capability behavior. To circumvent this issue, we propose a series of selenium@carbon (Se@C) composite positive electrode active materials capable of delivering a four-electron redox reaction when placed in contact with an aqueous copper-ion electrolyte solution (i.e., 0.5 M CuSO₄) and copper or zinc foils as negative electrodes. The lab-scale Zn | |Se@C cell delivers a discharge voltage of about 1.2 V at 0.5 A g⁻¹ and an initial discharge capacity of 1263 mAh g_Se⁻¹. Interestingly, when a specific charging current of 6 A g⁻¹ is applied, the Zn | |Se@C cell delivers a stable discharge capacity of around 900 mAh g_Se⁻¹ independently from the discharge rate. Via physicochemical characterizations and first-principle calculations, we demonstrate that battery performance is strongly associated with the reversible structural changes occurring at the Se-based cathode.

Aqueous battery Se-based cathodes are based on a two-electron transfer electrochemical reaction and generally show inadequate rate capability behaviour. Here, the authors propose a four-electron Se chemistry with copper ions as charge carriers to enable fast-charging battery cycling.