Atomically Coupled 2D MnO₂/MXene Superlattices for Ultrastable and Fast Aqueous Zinc-Ion Batteries

Abstract

The delta manganese dioxide (δ-MnO 2 ) has sparked a great deal of scientific research for application as the cathode in aqueous zinc-ion batteries (AZIBs) owing to its characteristic layered structure. However, further development and commercial application of the δ-MnO 2 cathode are hindered by the low rate performance and poor cycling stability, which are derived from its inherently poor electrical conductivity and structural instability during the charge/ discharge process. Herein, we report the fabrication of the 2D MnO 2 /MXene superlattice by the solution-phase assembly of unilamellar MnO 2 and Ti 3 C 2 T x MXene nanosheets, where the unilamellar MnO 2 nanosheet is separated and stabilized between unilamellar MXene nanosheets. The MXene nanosheets can not only serve as structural stabilizers to isolate the MnO 2 nanosheets and prevent them from aggregating but also act as conductive contributors to strengthen the electrical conductivity, thus maintaining the overall structural stability and realizing the rapid electron transport. Additionally, the regular stacking with a repeating periodicity of the 2D MnO 2 /MXene can lead to highly exposed active sites, promoting ion diffusion. As a consequence, the large specific capacity of 315.1 mAh g −1 at 0.2 A g −1 , prominent rate performance of 149.8 mAh g −1 at 5 A g −1 , and excellent long-term cycling stability after 5000 cycles with 88.1% capacity retention are obtained for the MnO 2 /MXene cathode in AZIBs. Meanwhile, the superior H + /Zn 2+ diffusion kinetics and desirable pseudocapacitive behaviors are elucidated by electrochemical measurements and density functional theory computations. This study provides an advanced perspective for the innovation of manganese oxide-based cathode materials in AZIBs.

Interfacial polymerization of PEDOT sheath on V2O5 nanowires for stable aqueous zinc ion storage

“…Table S2† summarizes the performance of vanadium and manganese-based cathodes. While the V 2 O 5 @PEDOT-50m displays relatively low specific capacity as compared with the V 2 O 5 · n H 2 O/graphene, 25 porous V 2 O 5 microspheres 41 or 3D@V 2 O 5 , 42 its cycling stability is remarkably improved as compared with V 2 O 5 , cationic intercalated vanadium oxides, 43,44 and some MnO 2 -based cathodes 10,45 (Table S2†). In addition to the above outstanding electrochemical stability, the V 2 O 5 @PEDOT-50m electrode exhibits nearly 100% coulombic efficiency at both low and high current densities, suggesting the superior reversibility of the Zn 2+ insertion/extraction within this electrode.…”

“…So far, manganese-based oxides, 10,11 Prussian blue analogues 12,13 and vanadium based compounds [14][15][16][17][18] have been extensively investigated as potential cathodes for ZIBs. Among them, the vanadium oxides have attracted much interest due to their multiple redox reactions and layered or tunnel structure.…”

Oriented Linear Self-Assembly of Colloidal Nanocrystals through Regioselective Formation of Hydrogen-Bonded Supramolecular Bridges

“…The XPS spectra of the NC chains exhibit shifts toward lower binding energies for both Y 3d (Figure b) and Na 1s (Figure c) peaks, in comparison to the spectra of pristine NaYF 4 NCs. These energy shifts imply an electron-donating interaction between PEG (acting as a Lewis base) and the metal atoms on the NC surface . To further understand how PEG facilitates the connection between individual NCs, Fourier-transform infrared (FTIR) spectroscopy is employed (Figure d).…”

Sandwiched MnO2-Fe(CN)64–-Doped PPy-MnO2 Cathodes with Tunable Interlayer Spaces and Dual Redox Active Sites for Enhanced Na Storage

“…The thickness of the MnO 2 is about 0.7 nm as revealed by the atomic force microscopy (AFM) image (Figure 1c), indicating the generation of unilamellar nanosheets. 33 The polymer nanoflakes are obtained through the controllable microfluidic synthesis (Figure S1), in which the K 3 Fe(CN) 6 serves as the oxidant to initiate the polymerization of pyrrole for producing the positively charged Fe(CN) 6 4− doped polypyrrole nanosheets (inset of Figure 1a and Figure S2). 34−36 The redox-active Fe(CN) 6 4− species could electrochemically activate the PPy chains to enhance their ion storage capability.…”