Enabling Reversible MnO2/Mn2+ Transformation by Al3+ Addition for Aqueous Zn-MnO2 Hybrid Batteries

Electrolyte Regulation toward Cathodes with Enhanced-Performance in Aqueous Zinc Ion Batteries

Enhancing cathodic performance is crucial for aqueous zinc-ion batteries, with the primary focus of research efforts being the regulation of the intrinsic material structure. Electrolyte regulation is also widely used to improve full-cell performance, whose main optimization mechanisms have been extensively discussed only in regard to the metallic anode. Considering that ionic transport begins in the electrolyte, the modulation of the electrolyte must influence the cathodic performance or even the reaction mechanism. Despite its importance, the discussion of the optimization effects of electrolyte regulation on the cathode has not garnered the attention it deserves. To fill this gap and raise awareness of the importance of electrolyte regulation on cathodic reaction mechanisms, this review comprehensively combs the underlying mechanisms of the electrolyte regulation strategies and classifies the regulation mechanisms into three main categories according to their commonalities for the first time, which are ion effect, solvating effect, and interfacial modulation effect, revealing the missing puzzle piece of the mechanisms of electrolyte regulation in optimizing the cathode.

Significant Enhancement in the Thermoelectric Performance of the MnSb2Te4 Topological Insulator through Vacancy Regulation and Lattice-Softening Strategies

The topological insulator MnSb2Te4 shows promising potential in thermoelectric applications due to its intrinsically low lattice thermal conductivity. However, its thermoelectric performance is limited by the high carrier concentration, of which the origin is still unclear. In this work, the carrier concentration is successfully tuned from 2.24 × 1021 cm-3 to as low as 9.1 × 1019 cm-3. Transmission electron microscopy and positron annihilation measurements suggest that large amounts of Mn vacancies exist in the septuple layer of MnSb2Te4, which are responsible for the high carrier concentration. The Mn vacancies are suppressed by the excess Mn element and AgSbTe2 alloying, which not only reduces the carrier concentration but also weakens the carrier scattering and thus improves the mobility. The decrease in carrier concentration also leads to reduced electronic thermal conductivity. The excess Mn atoms introduce a strain field in the Mn layer, which enhances phonon scattering. Furthermore, the substitution of Ag for Mn causes lattice softening by weakening the chemical bonds in MnSb2Te4, which leads to reduced phonon velocity and, therefore, further reduction in lattice thermal conductivity. As a result, an extremely low lattice thermal conductivity of 0.44 W m-1 K-1 was obtained at 300 K and it further decreased to 0.17 W m-1 K-1 at 798 K. Finally, a record zT value of 1.53 at 798 K was achieved in Mn1.06Sb2Te4(AgSbTe2)0.04, and the optimal carrier concentration is about 2 × 1020 cm-3.

Ion-Anchored Strategy for MnO2/Mn2+ Chemistry without "Dead Mn" and Corrosion

The utilization of MnO2/Mn2+ chemistry in near-neutral pH acetate aqueous electrolytes provides an opportunity to achieve a higher energy density (theoretical capacity 616 mA h/g, discharge platform >1.5 V). However, this Zn-MnO2 aqueous battery suffers from inevitable "dead Mn" and proton corrosion. In this study, we discover that the diffusion of the cathode reaction intermediate Mn3+ is intrinsic for the generation of "dead Mn", and the accumulation of "dead Mn" increases the H+ which shuttles to the anode, inducing serious corrosion. A pH-neutral hydrogel ion-anchored strategy is proposed here not only to restrict the diffusion of Mn3+ but also to suppress the proton transference. This hydrogel ion anchor is designed by deprotonating a series of monomers undergoing in situ free radical polymerization at the cathode interface. The anionic monomer with a moderate binding energy to manganese ions is screened to anchor Mn3+, which enhances the reversibility of the MnO2/Mn2+ reaction. Simultaneously, a substantial amount of anionic groups and hydrophilic functional groups in the hydrogel effectively constrains the proton shuttle to corrode the anode. Consequently, the Zn/MnO2 battery achieves exceptional cyclic stability of the MnO2/Mn2+ reaction, sustaining 8500 cycles even at a relatively low current density and discharge current density of 1 mA/cm2. Our findings highlight the importance of anchoring Mn3+ at the cathode interface and offer valuable insights for advancing practical applications of MnO2/Mn2+ reactions.

Manganese-Based Oxide Cathode Materials for Aqueous Zinc-Ion Batteries: Materials, Mechanism, Challenges, and Strategies

Aqueous zinc-ion batteries (AZIBs) have recently attracted worldwide attention due to the natural abundance of Zn, low cost, high safety, and environmental benignity. Up to the present, several kinds of cathode materials have been employed for aqueous zinc-ion batteries, including manganese-based, vanadium-based, organic electrode materials, Prussian Blues, and their analogues, etc. Among all the cathode materials, manganese (Mn)-based oxide cathode materials possess the advantages of low cost, high theoretical specific capacity, and abundance of reserves, making them the most promising cathode materials for commercialization. However, several critical issues, including intrinsically poor conductivity, sluggish diffusion kinetics of Zn2+, Jahn-Teller effect, and Mn dissolution, hinder their practical applications. This Review provides an overview of the development history, research status, and scientific challenges of manganese-based oxide cathode materials for aqueous zinc-ion batteries. In addition, the failure mechanisms of manganese-based oxide materials are also discussed. To address the issues facing manganese-based oxide cathode materials, various strategies, including pre-intercalation, defect engineering, interface modification, morphology regulation, electrolyte optimization, composite construction, and activation of dissolution/deposition mechanism, are summarized. Finally, based on the analysis above, we provide future guidelines for designing Mn-based oxide cathode materials for aqueous zinc-ion batteries.

Ferroelectric-Enhanced cathode kinetics toward High-Performance aqueous Zinc-Ion batteries

Rechargeable aqueous zinc ion batteries (AZIBs) offer promising potential for large-scale energy storage systems due to their high affordability and safety. However, their practical applications are hindered by the undesired rate capability and cycling stability of the used cathode, attributed to sluggish ions kinetics during charge-discharge process. Herein, we propose an electric field balancing strategy to regulate the electrolyte ions behavior by constructing a ferroelectric interface on the cathode surface using a prototypical of MnO2-based cathode. An appropriate thickness coating of ferroelectric materials coating (i.e., β-PVDF) on the MnO2 surface is theoretically and experimentally demonstrated to enhance the ion kinetics due to the optimized electrical distribution during electrochemical operations. Further comprehensive electrochemical mechanism studies reveal that the ferroelectric interface on the MnO2@β-PVDF not only promotes the diffusion of Zn2+ but also reduces the electrochemical overpotential (17.6 mV), resulting in improved electrochemical reversibility and capacity performance. The resultant MnO2@β-PVDF cathode exhibits the highest capacity of 277.6 mAh g-1 (at 0.1 A g-1) and capacity retention of 68.6% after 120 cycles, surpassing both the pristine MnO2 and non-ferroelectric materials coated MnO2 electrodes. This success presents a new approach to enhance the overall electrochemical performance of the cathodes for the practical application of AZIBs.

Recent Progress in High-voltage Aqueous Zinc-based Hybrid Redox Flow Batteries

The energy density of redox flow batteries (RFBs) is generally affected by the standard electrode potential and the solubility of the redox active species. These crucial factors are closely related to the solvent in which the active materials are dissolved. Aqueous RFBs have been widely studied due to their excellent reaction kinetics and high solubility of the redox couple in aqueous media. However, the low voltage of conventional aqueous RFBs has hindered them from being candidates for practical applications. Recently, high-voltage aqueous RFBs are implemented based on the low negative potential of the Zn/[Zn(OH)₄ ]^2- reaction in an alkaline solution. Here, we review recent progress in the design of high energy density RFBs in both aqueous and non-aqueous electrolytes, notably focusing on the Zn/MnO₂ hybrid RFBs in detail. Furthermore, strategies for inhibiting zinc dendritic growth and stabilizing manganese redox couple in the RFBs system are discussed.

The preparation of ultrastable Al3+ doped CeO2 supported Au catalysts: Strong metal-support interaction for superior catalytic activity towards CO oxidation

The classical strong metal-support interaction (SMSI) plays a key role in improving thermal stability for supported Au catalysts. However, it always decreases the catalytic activity because of the encapsulation of Au species by support. Herein, we demonstrate that Al³⁺ is a functional additive which could effectively improve both catalytic activity and sintering resistant property for H₂ pretreated Al³⁺ doped CeO₂ supported Au (AuCeAl) catalyst at high temperature. The physical characterization and in-situ DRIFTS results provide insight that more oxygen vacancies generated by Al³⁺ doping could be as preferential adsorption sites for CO molecules when the encapsulation of Au species occurred, which is certificated by an accelerated formation of bicarbonate species. In the meantime, smaller Au nanoparticles with higher dispersion (2.8 nm, 85.63%) is achieved in AuCeAl catalysts, compared with that in CeO₂ supported Au (AuCe) catalysts (5.1 nm, 36.17%). Additionally, the as-prepared AuCeAl catalysts also have superior catalytic performance even after calcination at 800 °C in air.