Single-Crystal Growth of Layered Birnessite-Type Manganese Oxides and Their Delamination into MnO₂ Nanosheets

Abstract

We have successfully grown hexagonally developed K x MnO2 single crystals (50 μm in lateral size and 10 μm in thickness) by slow cooling from 1273 to 1173 K at a rate of 0.5 K/h using K2MoO4 as a flux source. To obtain large-sized MnO2 nanosheets from these K x MnO2 single crystals, we investigated an appropriate process to suppress cracking in the soft-chemical delamination process. Crystals with fewer cracks were obtained upon reacting K x MnO2 with (NH4)2S2O8. The protonated crystals were found to undergo massive swelling upon contact with a tetramethylammonium hydroxide solution. The swollen crystals were exfoliated into unilamellar MnO2 nanosheets by subsequent treatment with tetrabutylammonium ions. The nanosheets were several micrometers in lateral sizes, larger than those obtained from polycrystalline birnessite samples, and they had a torn texture due to etching defects.

Exploring the Mechanism of Single‐Crystal MnO2 as Cathodes for Zinc Ion Batteries

“…On the other hand, preparing single-crystal structures not only enhances material stability but also optimizes ion transport pathways, increases the effective active surface area, and improves the interface compatibility between the electrode and electrolyte, thereby enhancing battery performance and extending its lifespan. [37][38][39][40][41] Hence, finding an appropriate structure is the key to addressing this challenge. Single-crystal β-MnO 2 preparation has emerged as a pivotal approach to solve this issue.…”

“…Adsorption designs like carbon coating do not offer substantial structural improvements, leading to unsatisfactory outcomes. On the other hand, preparing single‐crystal structures not only enhances material stability but also optimizes ion transport pathways, increases the effective active surface area, and improves the interface compatibility between the electrode and electrolyte, thereby enhancing battery performance and extending its lifespan [37–41] . Hence, finding an appropriate structure is the key to addressing this challenge.…”