Enriching Oxygen Vacancy Defects via Ag-O-Mn Bonds for Enhanced Diffusion Kinetics of δ-MnO2 in Zinc-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).

Advances of Zn Metal-Free "Rocking-Chair"-Type Zinc Ion Batteries: Recent Developments and Future Perspectives

Aqueous zinc ion battery (AZIBs) has attracted the attention of many researchers because of its safety, economy, environmental protection, and high ionic conductivity of electrolytes. However, the battery greatly suffers from zinc dendrite produced by zinc metal anode leading to poor cycle life and even unsafe problems, which limit its further development for various important applications. It is known that the success of the commercialization of lithium-ion batteries (LIBs) is mainly due to replacement of lithium metal anode with graphite, which avoids the formation of Li dendrite. Therefore, it is an important step to develop aqueous zinc ion anode to replace conventional zinc metal one with zinc-metal free anode material. In this review, the working principle and development prospect of "rocking-chair" AZIBs are introduced. The research progress of different types of zinc metal-free anode materials and cathode materials in "rocking-chair" AZIBs is reviewed. Finally, the limitations and challenges of the Zn metal-free "rocking-chair" AZIBs as well as solutions are deeply discussed, aiming to provide new strategies for the development of advanced zinc-ion batteries.

Recent development of manganese dioxide-based materials as zinc-ion battery cathode

The development of advanced cathode materials for zinc-ion batteries (ZIBs) is a critical step in building large-scale green energy conversion and storage systems in the future. Manganese dioxide is one of the most well-studied cathode materials for zinc-ion batteries due to its wide range of crystal forms, cost-effectiveness, and well-established synthesis processes. This review describes the recent research progress of manganese dioxide-based ZIBs, and the reaction mechanism, electrochemical performance, and challenges of manganese dioxide-based ZIBs materials are systematically introduced. Optimization strategies for high-performance manganese dioxide-based materials for ZIBs with different crystal forms, nanostructures, morphologies, and compositions are discussed. Finally, the current challenges and future research directions of manganese dioxide-based cathodes in ZIBs are envisaged.

Oxygen defects engineering and structural strengthening of hydrated vanadium oxide cathode by coating glucose hydrothermal carbon and pre-embedding Mn (II) ion for high-capacity aqueous zinc ion batteries

Vanadium oxide-based cathode with unique layered structure is considered as a candidate for aqueous zinc ion batteries (AZIBs). Unfortunately, considering poor electronic conductivity, sluggish diffusion kinetics, and the destruction of layered structures in the cycling process, the actual capacity and rate capability are constrained. Herein, the glucose hydrothermal carbon (GHC) and transition metal Mn2+ ion have been utilized to incorporate hydrated vanadium oxide (Mn-VOH@GHC). The oxygen vacancies defects of VOH, induced by GHC anchored on surface and Mn2+ inserted between interlayers, provides more active sites, higher electronic conductivity, and faster ion diffusion. In addition, GHC reinforces the integrity of external structure, while Mn2+ ion acts as structural pillars to support the interlayer structure. The Mn-VOH@GHC electrode can produce a high capacity of 530 mAh/g at the current density of 0.2 A/g thanks to these crucial properties, and after 2000 cycles at a high current density of 2 A/g, it can also produce a reversible capacity of 344 mAh/g. The results suggest that the synergistic effect of defect engineering and metal ion pre-insertion provides a new idea in enhancement of the electrochemical performance of AZIBs cathode materials.

Ionic-Liquid-Assisted Synthesis of Mixed-Phase Manganese Oxide Nanorods for a High-Performance Aqueous Zinc-Ion Battery

Aqueous zinc-ion batteries (ZIBs) provide a safer and cost-effective energy storage solution by utilizing nonflammable water-based electrolytes. Although many research efforts are focused on optimizing zinc anode materials, developing suitable cathode materials is still challenging. In this study, one-dimensional, mixed-phase MnO₂ nanorods are synthesized using ionic liquid (IL). Here, the IL acts as a structure-directing agent that modifies MnO₂ morphology and introduces mixed phases, as confirmed by morphological, structural, and X-ray photoelectron spectroscopy (XPS) studies. The MnO₂ nanorods developed by this method are utilized as a cathode material for ZIB application in the coin-cell configuration. As expected, Zn//MnO₂ nanorods show a significant increase in their capacity to 347 Wh kg^-1 at 100 mA g^-1, which is better than bare MnO₂ nanowires (207.1 Wh kg^-1) synthesized by the chemical precipitation method. The battery is highly rechargeable and maintains good retention of 86% of the initial capacity and 99% Coulombic efficiency after 800 cycles at 1000 mA g^-1. The ex situ XPS, X-ray diffraction, and in-depth electrochemical analysis confirm that MnO₆ octahedra experience insertion/extraction of Zn²⁺ with high reversibility. This study suggests the potential use of MnO₂ nanorods to develop high-performance and durable battery electrode materials suitable for large-scale applications.