Ultrasmall Mn3O4 nanocrystalline@three-dimensional macroporous honeycomb-like hollow carbon matrix for high-rate and long-lifetime zinc-ion storage

Development of bixbyite microdice fabricated cathode for aqueous rechargeable zinc ion batteries

In this study, an ultrasonic-aided reverse micelle formation, followed by the calcination route, was developed for the synthesis of bixbyite microdice aimed at the fabrication of a cathode for ARZIBs. The prepared product was Mn2O3 having crystallinity and grain size of 65.12% and 25.61 nm, respectively, with a small percentage of other Mn-based oxides within it. The FESEM image showed dice like microsized Mn2O3, revealing the possible formation of a reverse micelle core of approximately 500 nm. XPS narrow spectra revealed the presence of Mn3+ in a mixture of Mn with +2 and +4 oxidation states. The crystal planes from the TEM images matched with XRD results and strengthened the formation of bixbyite Mn2O3 nanoparticles. The optical band gap of 3.21 eV specified the semiconducting property of the prepared Mn2O3, and therefore, the prepared Mn2O3 was used as a cathode material in a CR-2032 coin cell of ARZIBs. CV showed a reversible reaction within the cell, indicating the (de)intercalation of Zn2+ ions between the anode and cathode. The fresh cell showed high conductivity and low resistance compared with the used cell after BCD testing, confirmed by EIS. The cell delivered high specific discharge capacities of 293.59 ± 4.75 and 252.10 ± 4.66 mA h g-1 at applied current densities of 0.1 and 0.3 A g-1, respectively. Consequently, BCD was performed for 1000 cycles at a current density of 0.3 A g-1. Throughout the cycling, the capacity retention and coulombic efficiency were maintained at 90.35 ± 0.30% and 98.44 ± 0.27%, respectively, suggesting the resilient reversibility of charging and discharging.

Enabling Long-cycling Aqueous Zn-Mn3O4 Batteries via Segregated and Interlaced Carbon Frameworks

Mn3O4 is a promising candidate for aqueous zinc ion batteries (ZIBs) due to its high theoretical capacity (468.5 mAh g-1) and environmental friendliness, while its practical application is hindered by slow kinetics and rapid capacity degradation. Herein, a porous Mn3O4 with segregated and interlaced carbon framework (HCF-Mn3O4) is introduced. The in situ hydro-assembled interlaced carbon nanotube (CNT) forms a porous structure enhancing electron conduction and accelerating Zn2+ transport; while the segregated CNT network serves as an encapsulation layer to improve mechanical stability. Together, these features facilitate the simultaneous insertion and transformation of H+/Zn2+ and enhance Zn2+ diffusion kinetics. As a result, HCF-Mn3O4 achieves a high specific capacity of 474 mAh g-1 at 0.05 A g-1, excellent rate performance of 178 mAh g-1 at 1.50 A g-1, and stable cycling over 3000 cycles with minimal capacity decay (≈0.02% per cycle). This design offers new opportunities for developing high-rate, long-lasting ZIBs.

K-Mn3O4-NCs@PANI nanochains for high-rate and stable aqueous zinc-ion batteries: A doping and morphology-tailored synthesis strategy

Aqueous zinc ion batteries (AZIBs) are promising energy storage solutions due to their high energy density and safety. However, developing cathode materials that offer both high energy density and durability for Zn2+ ions storage remains challenging. Manganese (Mn) oxide-based cathodes have been developed for AZIBs due to their high discharge voltage and desirable capacity, but face challenges like poor conductivity, slow reaction kinetics, and dissolution during cycling. Doping, morphology/structure design, and protective layers are effective for enhancing the structure, conductivity, and electronic properties of Mn-based oxides. A synthetic strategy combining these methods for Mn3O4 cathodes is proposed for AZIBs. K+ ions doping in Mn3O4 (K-Mn3O4) can regulate local electronic structure, induce oxygen vacancies, improve conductivity, and provide more active sites for Zn2+ ions diffusion. Additionally, K-Mn3O4 nanochain (K-Mn3O4-NCs), with a unique chain-like nanostructure (NCs) and high aspect ratio, synthesized via Mn2+ ions chelation with nitrilotriacetic acid (NTA) and calcination, show reduced interparticle contact resistance, shorter Zn2+ ions diffusion length, and faster reaction kinetics. Meanwhile, the in-situ polymerized polyaniline (PANI) layer on K-Mn3O4-NCs shields against corrosion (K-Mn3O4-NCs@PANI), connects 1D K-Mn3O4-NCs into a continuous conductive network, suppresses volume expansion, and improves stability. Electrochemical analysis shows that K-Mn3O4-NCs@PANI exhibits higher stability and faster reaction kinetics due to a reduced bandgap, increased oxygen defects, and less coulombic repulsion between Zn2+ ions and Mn oxide hosts. The K-Mn3O4-NCs@PANI cathode achieved a high capacity of 510 mAh/g at 0.1 A/g and excellent rate capacity of 203.2 mAh/g at 5 A/g. After 20,000 cycles, it maintained a capacity of 90.3 mAh/g at 5 A/g, showing exceptional long-term stability with a minimal decay rate of 0.026 ‰ per cycle.

Rice powder template for hausmannite Mn3O4 nanoparticles and its application to aqueous zinc ion battery

In this study, a simple calcination route was adopted to prepare hausmannite Mn3O4 nanoparticles using rice powder as soft bio-template. Prepared Mn3O4 was characterized by Fourier Transform Infra-Red Spectroscopy (FTIR), Field Emission Scanning Electron Microscopy (FESEM), Energy Dispersive X-ray microanalysis (EDX), Powder X-Ray Diffraction (XRD), Transmission Electron Microscopy (TEM), Brunauer-Emmett-Teller (BET) and Solid state UV-Vis spectroscopic techniques. Mn-O stretching in tetrahedral site was confirmed by FTIR and Raman spectra. % of Mn and O content supported Mn3O4 formation. The crystallinity and grain size was found to be 68.76% and 16.43 nm, respectively; tetragonal crystal system was also cleared by XRD. TEM clarified the planes of crystal formed which supported the XRD results and BET demonstrated mesoporous nature of prepared Mn3O4 having low pore volume. Low optical band gap of 3.24 eV of prepared Mn3O4 nanoparticles indicated semiconductor property and was used as cathode material to fabricate CR-2032 coin cell of Aqueous Rechargeable Zinc Ion Battery (ARZIB). A reversible cyclic voltammogram (CV) showed good zinc ion storage performance. Low cell resistance was confirmed by Electrochemical Impedance Spectroscopy (EIS). The coin cell delivered high specific discharge capacity of 240.75 mAhg-1 at 0.1 Ag-1 current density. The coulombic efficiency was found to be 99.98%. It also delivered excellent capacity retention 94.45% and 64.81% after 300 and 1000 charge-discharge cycles, respectively. This work offers a facile and cost effective approach for preparing cathode material of ARZIBs.