Theory-Driven Design of a Cationic Accelerator for High-Performance Electrolytic MnO2 -Zn Batteries

Noncovalent Interactions-Driven Self-Assembly of Polyanionic Additive for Long Anti-Calendar Aging and High-Rate Zinc Metal Batteries

Zinc anodes of zinc metal batteries suffer from unsatisfactory plating/striping reversibility due to interfacial parasitic reactions and poor Zn2+ mass transfer kinetics. Herein, methoxy polyethylene glycol-phosphate (mPEG-P) is introduced as an electrolyte additive to achieve long anti-calendar aging and high-rate capabilities. The polyanionic of mPEG-P self-assembles via noncovalent-interactions on electrode surface to form polyether-based cation channels and in situ organic-inorganic hybrid solid electrolyte interface layer, which ensure rapid Zn2+ mass transfer and suppresses interfacial parasitic reactions, realizing outstanding cycling/calendar aging stability. As a result, the Zn//Zn symmetric cells with mPEG-P present long lifespans over 9000 and 2500 cycles at ultrahigh current densities of 120 and 200 mA cm-2, respectively. Besides, the coulombic efficiency (CE) of the Zn//Cu cell with mPEG-P additive (88.21%) is much higher than that of the cell (36.4%) at the initial cycle after the 15-day calendar aging treatment, presenting excellent anti-static corrosion performance. Furthermore, after 20-day aging, the Zn//MnO2 cell exhibits a superior capacity retention of 89% compared with that of the cell without mPEG-P (28%) after 150 cycles. This study provides a promising avenue for boosting the development of high efficiency and durable metallic zinc based stationary energy storage system.

Mesoporous copper-doped δ-MnO2 superstructures to enable high-performance aqueous zinc-ion batteries

Aqueous zinc-ion batteries (AZIBs) are competitive alternatives for large-scale energy-storage devices owing to the abundance of zinc and low cost, high theoretical specific capacity, and high safety of these batteries. High-performance and stable cathode materials in AZIBs are the key to storing Zn2+. Manganese-based cathode materials have attracted considerable attention because of their abundance, low toxicity, low cost, and abundant valence states (Mn2+, Mn3+, Mn4+, and Mn7+). However, as a typical cathode material, birnessite-MnO2 (δ-MnO2) has low conductivity and structural instability. The crystal structure may undergo severe distortion, disorder, and structural damage, leading to severe cyclic instability. In addition, its energy-storage mechanism is still unclear, and most of the reported manganese oxide-based materials do not have excellent electrochemical performance. Herein, we propose a copper-doped Cu0.05K0.11Mn0.84O2·0.54H2O (Cu2-KMO) cathode, which exhibits a large interlayer spacing, a stable structure, and accelerated reaction kinetics. This cathode was prepared using a simple hydrothermal method. The AZIB assembled using Cu2-KMO showed high specific capacity (600 mA h g-1 at 0.1 A g-1 after 75 cycles). The dissolution-deposition energy storage mechanism of Cu-KMO in AZIBs with double electron transfer was revealed using ex situ tests. The good electrochemical performance of the Cu2-KMO cathode fabricated by the doping strategy in this study provides ideas for the subsequent preparation of manganese dioxide using other strategies.

Recent advances in zinc-ion dehydration strategies for optimized Zn-metal batteries

Aqueous Zn-metal batteries have attracted increasing interest for large-scale energy storage owing to their outstanding merits in terms of safety, cost and production. However, they constantly suffer from inadequate energy density and poor cycling stability due to the presence of zinc ions in the fully hydrated solvation state. Thus, designing the dehydrated solvation structure of zinc ions can effectively address the current drawbacks of aqueous Zn-metal batteries. In this case, considering the lack of studies focused on strategies for the dehydration of zinc ions, herein, we present a systematic and comprehensive review to deepen the understanding of zinc-ion solvation regulation. Two fundamental design principles of component regulation and pre-desolvation are summarized in terms of solvation environment formation and interfacial desolvation behavior. Subsequently, specific strategy based distinct principles are carefully discussed, including preparation methods, working mechanisms, analysis approaches and performance improvements. Finally, we present a general summary of the issues addressed using zinc-ion dehydration strategies, and four critical aspects to promote zinc-ion solvation regulation are presented as an outlook, involving updating (de)solvation theories, revealing interfacial evolution, enhancing analysis techniques and developing functional materials. We believe that this review will not only stimulate more creativity in optimizing aqueous electrolytes but also provide valuable insights into designing other battery systems.

Distinguish MnO2/Mn2+ Conversion/ Zn2+ Intercalation/ H+ Conversion Chemistries at Different Potentials in Aqueous Zn||MnO2 Batteries

The rechargeable aqueous Zn||MnO2 chemistry has been extensively explored, but its electrochemical reaction mechanisms, especially in the context of MnO2/Mn2+ conversion and Zn2+/H+ intercalation chemistry, remain not fully understood. Here, we designed an amphiphilic hydrogel electrolyte, which distinguished the MnO2/Mn2+ conversion, Zn2+ intercalation, and H+ intercalation and conversion processes at three distinct discharge plateaus of an aqueous Zn||MnO2 battery. The amphiphilic hydrogel electrolyte is featured with an extended electrochemical stability window up to 3.0 V, high ionic conductivity, Zn2+-selective ion tunnels, and hydrophobic associations with cathode materials. This specifically designed electrolyte allows the MnO2/Mn2+ conversion reaction at a discharge plateau of 1.75 V. More interesting, the discharge plateaus of ~1.33 V, previously assigned as the co-intercalation of Zn2+ and H+ ions in the MnO2 cathode, are specified as the exclusive intercalation of Zn2+ ions, leading to an ultra-flat voltage plateau. Furthermore, with a distinct three-step electrochemical energy storage process, a high areal capacity of 1.8 mAh cm-2 and high specific energy of 0.858 Wh cm-2, even at a low MnO2 loading mass of 0.5 mg cm-2 are achieved. To our knowledge, this is the first report to fully distinguish different mechanisms at different potentials in aqueous Zn||MnO2 batteries.

Insights into the cycling stability of manganese-based zinc-ion batteries: from energy storage mechanisms to capacity fluctuation and optimization strategies

Manganese-based materials are considered as one of the most promising cathodes in zinc-ion batteries (ZIBs) for large-scale energy storage applications owing to their cost-effectiveness, natural availability, low toxicity, multivalent states, high operation voltage, and satisfactory capacity. However, their intricate energy storage mechanisms coupled with unsatisfactory cycling stability hinder their commercial applications. Previous reviews have primarily focused on optimization strategies for achieving high capacity and fast reaction kinetics, while overlooking capacity fluctuation and lacking a systematic discussion on strategies to enhance the cycling stability of these materials. Thus, in this review, the energy storage mechanisms of manganese-based ZIBs with different structures are systematically elucidated and summarized. Next, the capacity fluctuation in manganese-based ZIBs, including capacity activation, degradation, and dynamic evolution in the whole cycle calendar are comprehensively analyzed. Finally, the constructive optimization strategies based on the reaction chemistry of one-electron and two-electron transfers for achieving durable cycling performance in manganese-based ZIBs are proposed.

Carbon Nanotube Network Induces Porous Deposited MnO2 for High-Areal Capacity Zn/Mn Batteries

Mn2+/MnO2 aqueous battery is a promising candidate for large-scale energy storage owing to its feature of low-cost and abundant crustal reserves. However, the inherent MnO2 shedding issue results in a limited areal capacity and poor cycling life, which prohibits its further commercialization. In this manuscript, it is revealed that the cause of shedding is the cracking of MnO2 layer due to stress. To circumvent this challenge, carbon nanotubes framework is introduced on pristine carbon felt, which provides more deposition sites and induces the formation of a porous deposition layer. Compared to the dense deposition layer on pristine carbon felt, the porous structure can effectively avoid cracking and subsequent shedding issue. Moreover, the porous deposited layer is conducive to proton diffusion and rich in defects, which facilitates the subsequent dissolution reaction. As results, the assembled Zn/Mn battery demonstrates more than 200 cycles with the areal capacity of 15 mAh cm-2 at 40 mA cm-2. Even with a high areal capacity of 40 mAh cm-2, it can still run for more than 60 cycles. This breakthrough paves a way toward practical manganese-based batteries, bringing us closer to achieve cost-effective batteries.

Electrolyte-Induced Morphology Evolution to Boost Potassium Storage Performance of Perylene-3,4,9,10-tetracarboxylic Dianhydride

Organic materials have attracted extensive attention for potassium-ion batteries due to their flexible structure designability and environmental friendliness. However, organic materials generally suffer from unavoidable dissolution in aprotic electrolytes, causing an unsatisfactory electrochemical performance. Herein, we designed a weakly solvating electrolyte to boost the potassium storage performance of perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA). The electrolyte induces an in situ morphology evolution and achieves a nanowire structure. The weakly dissolving capability of ethylene glycol diethyl ether-based electrolyte and unique nanowire structure effectively avoid the dissolution of PTCDA. As a result, PTCDA shows excellent cycling stability (a capacity retention of 89.1% after 2000 cycles) and good rate performance (70.3 mAh g-1 at 50C). In addition, experimental detail discloses that the sulfonyl group plays a key role in inducing morphology evolution during the charge/discharge process. This work opens up new opportunities in electrolyte design for organic electrodes and illuminates further developments of potassium-ion batteries.

Intercalation chemistry engineering strategy enabled high mass loading and ultrastable electrodes for High-Performance aqueous electrochemical energy storage devices

Aqueous electrochemical energy storage devices (AEESDs) are considered one of the most promising candidates for large-scale energy storage infrastructure due to their high affordability and safety. Developing electrodes with the merits of high energy density and long lifespan remains a challenging issue toward the practical application of AEESDs. Research attempts at electrode materials, nanostructure configuration, and electronic engineering show the limitations due to the inherent contradictions associated with thicker electrodes and ion-accessible kinetics. Herein, we propose an intercalation chemistry engineering strategy to enhance the electrolyte ion (de)intercalation behaviors during the electrochemical charge-discharge. To validate this strategy, the prototypical model of a high-mass-loading MnO2-based electrode is used with controlled intercalation of Na+ and H2O. Theoretical and experimental results reveal that an optimal content of Na+ and H2O on the MnO2-based electrode exhibits superior electrochemical performance. Typically, the resultant electrode exhibits an impressive areal capacitance of 1551 mF/cm2 with a mass loading of 9.7 mg/cm2 (at 1 mA/cm2). Furthermore, the assembled full-cell with obtained MnO2-based electrode delivers a high energy density of 0.12 mWh/cm2 (at 20.02 mW/cm2) and ultra-high cycling stability with a capacitance retention percentage of 89.63 % (345 mF/cm2) even after 100,000 cycles (tested over 72 days).

Recent advances in battery characterization using in situ XAFS, SAXS, XRD, and their combining techniques: From single scale to multiscale structure detection

Revealing and clarifying the chemical reaction processes and mechanisms inside the batteries will bring a great help to the controllable preparation and performance modulation of batteries. Advanced characterization techniques based on synchrotron radiation (SR) have accelerated the development of various batteries over the past decade. In situ SR techniques have been widely used in the study of electrochemical reactions and mechanisms due to their excellent characteristics. Herein, the three most wide and important synchrotron radiation techniques used in battery research were systematically reviewed, namely X-ray absorption fine structure (XAFS) spectroscopy, small-angle X-ray scattering (SAXS), and X-ray diffraction (XRD). Special attention is paid to how these characterization techniques are used to understand the reaction mechanism of batteries and improve the practical characteristics of batteries. Moreover, the in situ combining techniques advance the acquisition of single scale structure information to the simultaneous characterization of multiscale structures, which will bring a new perspective to the research of batteries. Finally, the challenges and future opportunities of SR techniques for battery research are featured based on their current development.

Alkaline Ni-Zn Rechargeable Batteries for Sustainable Energy Storage: Battery Components, Deterioration Mechanisms, and Impact of Additives

The demand for long-term, sustainable, and low-cost battery energy storage systems with high power delivery capabilities for stationary grid-scale energy storage, as well as the necessity for safe lithium-ion battery alternatives, has renewed interest in aqueous zinc-based rechargeable batteries. The alkaline Ni-Zn rechargeable battery chemistry was identified as a promising technology for sustainable energy storage applications, albeit a considerable investment in academic research, it still fails to deliver the requisite performance. It is hampered by a relatively short-term electrode degradation, resulting in a decreased cycle life. Dendrite formation, parasitic hydrogen evolution, corrosion, passivation, and dynamic morphological growth are all challenging and interrelated possible degradation processes. This review elaborates on the components of Ni-Zn batteries and their deterioration mechanisms, focusing on the influence of electrolyte additives as a cost-effective, simple, yet versatile approach for regulating these phenomena and extending the battery cycle life. Even though a great deal of effort has been dedicated to this subject, the challenges remain. This highlights that a breakthrough is to be expected, but it will necessitate not only an experimental approach, but also a theoretical and computational one, including artificial intelligence (AI) and machine learning (ML).

ZnO Additive Boosts Charging Speed and Cycling Stability of Electrolytic Zn-Mn Batteries

Electrolytic aqueous zinc-manganese (Zn-Mn) batteries have the advantage of high discharge voltage and high capacity due to two-electron reactions. However, the pitfall of electrolytic Zn-Mn batteries is the sluggish deposition reaction kinetics of manganese oxide during the charge process and short cycle life. We show that, incorporating ZnO electrolyte additive can form a neutral and highly viscous gel-like electrolyte and render a new form of electrolytic Zn-Mn batteries with significantly improved charging capabilities. Specifically, the ZnO gel-like electrolyte activates the zinc sulfate hydroxide hydrate assisted Mn2+ deposition reaction and induces phase and structure change of the deposited manganese oxide (Zn2Mn3O8·H2O nanorods array), resulting in a significant enhancement of the charge capability and discharge efficiency. The charge capacity increases to 2.5 mAh cm-2 after 1 h constant-voltage charging at 2.0 V vs. Zn/Zn2+, and the capacity can retain for up to 2000 cycles with negligible attenuation. This research lays the foundation for the advancement of electrolytic Zn-Mn batteries with enhanced charging capability.

Designing Chemically Replaced Interfacial Layer via Unveiling the Influence of Zn Crystal Facets for Practical Zn-Metal Anodes

Zn metal anodes (ZMAs) undergo irregular deposition and unfavorable side reactions, which hinders the practical application of aqueous rechargeable Zn metal batteries (ARZMBs). Chemical replacement reaction (CRR) strategies can achieve stable ZMAs, but the effect of the crystal facets of metallic Zn as reductants remains poorly understood. In this study, based on the observation that preferentially exposed Zn crystal facets affect the surface characteristics of chemically replaced layers in Sn-based CRR, a multifunctional Sn-based interfacial layer (ZnTCF@Sn) is designed on the Zn with textured crystal facets using a novel two-step CRR process. ZnTCF@Sn simultaneously provides abundant zincophilic sites and high surface energy and homogenizes the distribution of current/Zn2+ flux, resulting in fast electrochemical kinetics and dendrite-free deposition. Furthermore, the uniform Sn coverage on the ZnTCF@Sn surface inhibits side reactions and enhances reversibility during Zn deposition/dissolution. Thus, the ZnTCF@Sn achieves exceptional cyclability over 1200 h even under harsh operating conditions with a cumulative capacity of 24 Ah cm-2 . This study contributes to the development of practical ARZMBs by providing new insights into the effect of the Zn crystal facets on the surface modification of ZMAs through various CRRs.

Unraveling the Mechanism of Cooperative Redox Chemistry in High-Efficient Zn2+ Storage of Vanadium Oxide Cathode

The inferior capacity and cyclic durability of V2 O5 caused by inadequate active sites and sluggish kinetics are the main problems to encumber the widespread industrial applications of vanadium-zinc batteries (VZBs). Herein, a cooperative redox chemistry (CRC) as "electron carrier" is proposed to facilitate the electron-transfer by capturing/providing electrons for the redox of V2 O5 . The increased oxygen vacancies in V2 O5 provoked in situ by CRC offers numerous Zn2+ storage sites and ion-diffusion paths and reduces the electrostatic interactions between vanadium-based cathode and intercalated Zn2+ , which enhance Zn2+ storage capability and structural stability. The feasibility of this strategy is fully verified by some CRCs. Noticeably, VZB with [Fe(CN)6 ]3- /[Fe(CN)6 ]4- as CRC displays conspicuous specific capacity (433.3 mAh g-1 ), ≈100% coulombic efficiency and superb cyclability (≈3500 cycles without capacity attenuation). Also, the mechanism and selection criteria of CRC are specifically unraveled in this work, which provides insightful perspectives for the development of high-efficiency energy-storage devices.

Defective construction of vanadium-based cathode materials for high-rate long-cycle aqueous zinc ion batteries

The development of structurally stable, highly conductive layered materials as cathode materials for aqueous zinc-ion batteries (AZIBs) is essential. Herein, polyaniline (PANI) was inserted into the interlayer of a vanadium-metal-organic framework-derived V2O5 to take advantage of the selective growth of the (110) crystal plane of V2O5, facilitating sufficient diffusion of aniline within the V2O5 interlayer along the vertical direction of the spatial c-axis while stabilizing the interlayer structure. The synthesized composite (PANI80-V2O5) exhibited excellent electrochemical properties owing to the increase in the material layer spacing from 5.76 Å to 14.31 Å and the strong synergistic effect of the oxygen vacancies and large specific surface area of the material. In addition, the π-conjugated structure of PANI prevented the active material from dissolving in the electrolyte, further stabilizing its lamellar structure, which tended to collapse during electrochemical cycling. The PANI80-V2O5 electrode exhibited an ultrahigh discharge capacity of 516.90 mAh g-1 at a current density of 0.1 A g-1. Moreover, it exhibited a discharge capacity of 268.80 mAh g-1 at a current density of 10 A g-1 and a capacity retention rate of 97.77% after 3000 cycles. Therefore, this study provided a reference for developing structurally superior cathode materials for AZIBs.

Oxygen vacancies in MnOx regulating reaction kinetics for aqueous zinc-ion batteries

MnO2 cathode materials have presented challenges due to their poor conductivity, unstable structure, and sluggish diffusion kinetics for aqueous zinc-ion batteries (AZIBs). In this study, a nanostructured MnOx cathode material was synthesized using an acid etching method, Which introduced abundant Mn(III) sites, resulting in the formation of numerous oxygen vacancies. Comprehensive characterizations revealed that these oxygen vacancies facilitated the reversible adsorption/desorption of Zn2+ ions and promoted efficient electron transfer. In addition, the designed mesoporous structure offered ample active sites and shortened the diffusion path for Zn2+ and H+ ions. Consequently, the nanosized MnOx cathode exhibited enhanced reaction kinetics, achieving a considerable reversible specific capacity of 388.7 mAh/g at 0.1 A/g and superior durability with 72.0% capacity retention over 2000 cycles at 3.0 A/g. The material delivered a maximum energy density of 639.7 Wh kg-1 at 159.94 W kg-1. Furthermore, a systematic analysis of the zinc storage mechanism was performed. This work demonstrates that engineering oxygen vacancies with nanostructure regulation provides valuable insights into optimizing MnO2 cathode materials for AZIBs.

Nanomicellar Electrolyte To Control Release Ions and Reconstruct Hydrogen Bonding Network for Ultrastable High-Energy-Density Zn-Mn Battery

Zn-Mn batteries with two-electron conversion reactions simultaneously on the cathode and anode harvest a high voltage plateau and high energy density. However, the zinc anode faces dendrite growth and parasitic side reactions while the Mn2+/MnO2 reaction on the cathode involves oxygen evolution and possesses poor reversibility. Herein, a novel nanomicellar electrolyte using methylurea (Mu) has been developed that can encapsulate ions in the nanodomain structure to guide the homogeneous deposition of Zn2+/Mn2+ in the form of controlled release under an external electric field. Consecutive hydrogen bonding network is broken and a favorable local hydrogen bonding system is established, thus inhibiting the water-splitting-derived side reactions. Concomitantly, the solid-electrolyte interface protective layer is in situ generated on the Zn anode, further circumventing the corrosion issue resulting from the penetration of water molecules. The reversibility of the Mn2+/MnO2 conversion reaction is also significantly enhanced by regulating interfacial wettability and improving nucleation kinetics. Accordingly, the modified electrolyte endows the symmetric Zn∥Zn cell with extended cyclic stability of 800 h with suppressed dendrites growth at an areal capacity of 1 mAh cm-2. The assembled Zn-Mn electrolytic battery also demonstrates an exceptional capacity retention of nearly 100% after 800 cycles and a superior energy density of 800 Wh kg-1 at an areal capacity of 0.5 mAh cm-2.

Protocol in Evaluating Capacity of Zn-Mn Aqueous Batteries: A Clue of pH

In the literature, Zn-Mn aqueous batteries (ZMABs) confront abnormal capacity behavior, such as capacity fluctuation and diverse "unprecedented performances." Because of the electrolyte additive-induced complexes, various charge/discharge behaviors associated with different mechanisms are being reported. However, the current performance assessment remains unregulated, and only the electrode or the electrolyte is considered. The lack of a comprehensive and impartial performance evaluation protocol for ZMABs hinders forward research and commercialization. Here, a pH clue (proton-coupled reaction) to understand different mechanisms is proposed and the capacity contribution is normalized. Then, a series of performance metrics, including rated capacity (C_r ) and electrolyte contribution ratio from Mn²⁺ (CfM), are systematically discussed based on diverse energy storage mechanisms. The relationship between Mn (II) ↔ Mn (III) ↔ Mn (IV) conversion chemistry and protons consumption/production is well-established. Finally, the concrete design concepts of a tunable H⁺ /Zn²⁺ /Mn²⁺ storage system for customized application scenarios, opening the door for the next-generation high-safety and reliable energy storage system, are proposed.

Nanoscale Ultrafine Zinc Metal Anodes for High Stability Aqueous Zinc Ion Batteries

Aqueous Zn batteries (AZBs) are a promising energy storage technology, due to their high theoretical capacity, low redox potential, and safety. However, dendrite growth and parasitic reactions occurring at the surface of metallic Zn result in severe instability. Here we report a new method to achieve ultrafine Zn nanograin anodes by using ethylene glycol monomethyl ether (EGME) molecules to manipulate zinc nucleation and growth processes. It is demonstrated that EGME complexes with Zn²⁺ to moderately increase the driving force for nucleation, as well as adsorbs on the Zn surface to prevent H-corrosion and dendritic protuberances by refining the grains. As a result, the nanoscale anode delivers high Coulombic efficiency (ca. 99.5%), long-term cycle life (over 366 days and 8800 cycles), and outstanding compatibility with state-of-the-art cathodes (ZnVO and AC) in full cells. This work offers a new route for interfacial engineering in aqueous metal-ion batteries, with significant implications for the commercial future of AZBs.

High-Capacity Zinc Anode with 96 % Utilization Rate Enabled by Solvation Structure Design

Aqueous zinc-ion batteries (AZBs) show promises for large-scale energy storage. However, the zinc utilization rate (ZUR) is generally low due to side reactions in the aqueous electrolyte caused by the active water molecules. Here, we design a novel solvation structure in the electrolyte by introduction of sulfolane (SL). Theoretical calculations, molecular dynamics simulations and experimental tests show that SL remodels the primary solvation shell of Zn²⁺ , which significantly reduces the side reactions of Zn anode and achieves high ZUR under large capacities. Specifically, the symmetric and asymmetric cells could achieve a maximum of ∼96 % ZUR at an areal capacity of 24 mAh cm^-2 . In a ZUR of ∼67 %, the developed Zn-V₂ O₅ full cell can be stably cycled for 500 cycles with an energy density of 180 Wh kg^-1 and Zn-AC capacitor is stable for 5000 cycles. This electrolyte structural engineering strategy provides new insight into achieving high ZUR of Zn anodes for high performance AZBs.

An Amorphous Anode for Proton Battery

Developing advanced electrode materials is crucial for improving the electrochemical performances of proton batteries. Currently, the anodes are primarily crystalline materials which suffer from inferior cyclic stability and high electrode potential. Herein, we propose amorphous electrode materials for proton batteries by using a general ion-exchange protocol to introduce multivalent metal cations for activating the host material. Taking Al3+ as an example, theoretical and experimental analysis demonstrates electrostatic interaction between metal cations and lattice oxygen, which is the primary barrier for direct introduction of the multivalent cations, is effectively weakened through ion exchange between Al3+ and pre-intercalated K+. The as-prepared Al-MoOx anode therefore delivered a remarkable capacity and outstanding cycling stability that outperforms most of the state-of-the-art counterparts. The assembled full cell also achieved a high voltage of 1.37 V. This work opens up new opportunities for developing high-performance electrodes of proton batteries by introducing amorphous materials.

High-Energy and Long-Lived Zn-MnO2 Battery Enabled by a Hydrophobic-Ion-Conducting Membrane

Alkaline Zn-MnO₂ batteries feature high security, low cost, and environmental friendliness while suffering from severe electrochemical irreversibility for both the Zn anode and MnO₂ cathode. Although neutral electrolytes are supposed to improve the reversibility of the Zn anode, the MnO₂ cathode indeed experiences a capacity degradation caused by the Jahn-Teller effect of the Mn³⁺ ion, thus shortening the lifespan of the neutral Zn-MnO₂ batteries. Theoretically, the MnO₂ cathode undergoes a highly reversible two-electron redox reaction of the MnO₂/Mn²⁺ couple in strongly acidic electrolytes. However, acidic electrolytes would inevitably accelerate the corrosion of the Zn anode, making long-lived acidic Zn-MnO₂ batteries impossible. Herein, to overcome the challenges faced by Zn-MnO₂ batteries, we propose a hybrid Zn-MnO₂ battery (HZMB) by coupling the neutral Zn anode with the acidic MnO₂ cathode, wherein the neutral anode and acidic cathode are separated by a proton-shuttle-shielding and hydrophobic-ion-conducting membrane. Benefiting from the optimized reaction conditions for both the MnO₂ cathode and Zn anode as well as the well-designed membrane, the HZMB exhibits a high working voltage of 2.05 V and a long lifespan of 2275 h (2000 cycles), breaking through the limitations of Zn-MnO₂ batteries in terms of voltage and cycle life.

Proton-Trapping Agent for Mitigating Hydrogen Evolution Corrosion of Zn for an Electrolytic MnO2/Zn Battery

A rechargeable aqueous electrolytic MnO₂/Zn battery (EMZB) based on a reversible Mn²⁺/MnO₂ two-electron redox reaction in an acidic electrolyte is very attractive for large-scale energy storage due to its high output voltage, large gravimetric capacity, and low cost. However, severe hydrogen evolution corrosion (HEC) of the Zn anode in an acidic electrolyte limits its application. Here, a proton-trapping agent (PTA) is introduced in the electrolyte to improve the electrochemical performance of the EMZB. Experimental results and theoretical calculations demonstrate that HEC of the Zn electrode can be effectively mitigated through high binding energy between the protons and PTA. The optimized EMZB regulated by a PTA of acetate (EMZB-20% Ac) delivers a high discharge voltage of 1.91 V and over 400 stable cycles at 1 C, which is more than 5 times the cycle life of the battery without PTA. EMZB-20% Ac also shows a Coulombic efficiency of 90.7% at a high areal capacity of 8 mAh cm^-2 and an energy retention of 83.6% after 1000 cycles at 5 C with an areal capacity of 1 mAh cm^-2. This work provides a promising electrolyte regulation strategy for the design and application of a high-performance EMZB and other energy storage systems.