Hierarchical K‐Birnessite‐MnO₂ Carbon Framework for High‐Energy‐Density and Durable Aqueous Zinc‐Ion Battery

Abstract

widespread interest as promising candidate due to the advantages of high safety, good economy, and the intrinsic merits of Zn with low redox potential (−0.76 V vs standard hydrogen electrode), high theoretical capacity (820 mAh g −1 ), and energy density. [2][3][4][5][6][7][8] To fulfill the application potential of ZIBs, suitable cathode materials are highly critical to pair Zn anode. Hitherto, several types of cathode materials, such as manganese-based oxides, [9][10][11][12] vanadium-based oxides, [10,13] Prussian blue analogs, [14] and Quinone analogs, [15] have entered researchers' spotlight. The investigation yields consensus of MnO 2 as the most prevalent choice thanks to its good economy, low toxicity, high theoretical capacity, and working potential. [5,10,[16][17][18] However, the low electronic/ionic conductivity and non-negligible manganese dissolution of MnO 2 result in the inferior rate performance and fast capacity decay of MnO 2 -based cathodes, hindering the commercialization of ZIBs. [19][20][21] Great endeavors have been dedicated to improve the reaction kinetics and structural stability of MnO 2 -based cathodes in strategies of polymorphs regulation, [16,22] preintercalation, [18,[23][24][25][26][27][28] heteroatom doping, [29,30] compositing with conductive materials, [18,[31][32][33][34][35] and Mn 2+ additives of electrolyte. [9,36] All these strategies have been proven to effectively improve the electrochemical performance of MnO 2 -based cathodes in ZIBs to some extent. It is found that δ-MnO 2 (layered structure, typical with large interlayer spacing of ≈7 Å) could be more theoretically favorable for Zn 2+ insertion/extraction than their tunnel-structured counterparts (e.g., α-MnO 2 with 2 × 2 tunnels and β-MnO 2 with 1 × 1 tunnels). [5,16] Both preintercalation of guest species into MnO 2 and compositing MnO 2 with electrical conductive materials can improve its electrical conductivity, suppress manganese dissolution, and stabilize its structure. [18,21,25,28,34] Moreover, there are also considerable attempts to reveal the charge storage mechanism of aqueous mild Zn-MnO 2 batteries with the aim of further performance optimization. [5] Different energy storage mechanisms, such as Zn 2+ insertion/extraction, [35] H + /Zn 2+ coinsertion, [37] conversion reaction, [9] and dissolution/deposition, [38] have been proposed to explain certain ZIBs systems. With respect to the scientific progress, it is inferred that the significantly enhanced electrochemical performance of MnO 2 -based cathode are highly MnO 2 -based material is one of the most promising cathode candidates of aqueous zinc-ion batteries (ZIBs), but its commercialization is hindered by the sluggish reaction kinetics and poor structural stability. Herein, a hierarchical framework consisting of core-shell structured carbon nanotubes@K-birnessite-MnO 2 enwrapped by graphene/carbon black bicomponent networks (CNT@ KMO@GC) via a simple method for ZIBs is designed and developed. The hierarchical framework characterized with favorable K ...

Synthesis of Nitrogen‐Doped KMn8O16 with Oxygen Vacancy for Stable Zinc‐Ion Batteries

“…[ 31 , 39 , 40 , 41 , 42 ] Some inspiring studies have employed these strategies to boost the zinc ion storage performance of MnO 2 . [ 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 ] However, most researches involve complex multi‐step synthesis methods and more explorations are needed to further optimize the electrochemical performance. Therefore, it is highly desirable to introduce oxygen vacancy and heteroatom doping into MnO 2 simultaneously via a facile and efficient approach.…”

Stability Optimization Strategies of Cathode Materials for Aqueous Zinc Ion Batteries: A Mini Review

“… Structural modification and composite of cathode materials: (A) Crystal structures of bulk MoS 2 and MoS 2 /graphene; (B,C) the corresponding migration energy barriers with the variation of the MoS 2 -to-graphene distance; (D) schematic illustration of freestanding CNT/MnO 2 -PPy; (E) schematic diagram of Zn 2+ (de)intercalating mechanism in O d -HVO/rG; (F) illustration of electron/ion transport and ion diffusions across the electrodes of CNT@KMO@GC. Reproduced with permission ( Zhang et al, 2020a ; Li et al, 2021d ; Huang et al, 2021 ; Wang et al, 2021 ). …”

“…Compared with HVO (capacity retention of 86.5%) and Od-HVO (capacity retention of 93.6%), the O d -HVO/rG cathode expressed scarcely any attenuation after 750 cycles at 5 Ag −1 . Moreover, Li et al obtained a cathode material (CNT@KMO@GC) composed of graphene (G), carbon black (CB), and K-sodium manganite (K x MnO 2 ·yH 2 O, KMO) based on core–shell carbon nanotube (CNT) by hydrothermal and solution treatment ( Wang et al, 2021 ). In Figure 2F , KMO provides the main charge storage due to the interlayer intercalation of K + and H 2 O; CNT provides a conductive framework for the loaded KMO owing to high conductivity and structural stability; G and CB provide the conductive network to reduce the accumulation of active substances.…”

“…The prepared cathode has a capacity retention rate of 65.2% after 10,000 cycles at 5 Ag −1 , which is significantly higher than KMO (39.1% of the initial capacity) and CNT@ (F) illustration of electron/ion transport and ion diffusions across the electrodes of CNT@KMO@GC. Reproduced with permission (Zhang et al, 2020a;Li et al, 2021d;Huang et al, 2021;Wang et al, 2021). KMO (51.5% of initial capacity).…”

Hierarchical Carbon Nanosheet Embedded MnOx Cathode for High‐Performance Aqueous Zinc‐Ion Batteries

“…Besides, the formation of irreversible phase of MnO 2 during long‐term cycling also limits its practical application [14,27,28] . Previous related studies indicated that doping heteroatom into the host materials is an effective approach to enhance its electrical conductivity and suppress dissolution of the manganese(II) ions [29–35] . However, the existing Zn‐MnO 2 batteries are still far from meeting the demand of practical applications.…”