Compositional changes associated with the chemical exfoliation of lithium cobalt oxide, a layered transition metal oxide, are discussed. Starting from a layered bulk structure, lithium cobalt oxide can undergo chemical exfoliation through a two‐step method: treatment with a protic acid, then treatment with tetramethylammonium hydroxide (this intercalates the layered structure and yields exfoliated nanosheets). This work provides an in‐depth analysis of compositional and structural changes occurring to the powder upon the first step to exfoliation, treatment with acid, revealing variations in vacancies and valence changes depending on the conditions used. Through coupled analysis of X‐ray photoelectron spectroscopy, X‐ray diffraction, UV‐Vis absorption spectroscopy, and inductively coupled plasma‐optical emission spectroscopy data, we illustrate that both lithium and cobalt ions are diffusing out the structure along with the dissolution of full unit cells. As such, nanosheets accessed from the bulk by this exfoliation process should not be considered simply as divisions of the original unit cell. This work provides fundamental insights on the stability of LiCoO2 and the exfoliation of layered transition metal oxides, beyond the access of individual nanosheets, and is vital to determining structure‐property relationships of chemically exfoliated nanosheets (eg, changes in valency which dictate catalytic activity, magnetic susceptibility, etc).

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Two-dimensional materials have been at the forefront of chemistry and materials science research for the past decade owing to promising applications across many fields. Improvements in exfoliation processes continually give...

Transition metal oxides often possess complex interactions between charge, spin, lattice, and orbital degrees of freedom, resulting in correlated electronic and magnetic phases. Li x CoO2, one of the most commonly used cathode choices in rechargeable batteries, is a prime example of this, evidencing numerous correlated effects evolving as a function of lithium content (x). Due to the strong electrostatic forces that govern the layered nature of this material, however, most investigations of these behaviors have been on bulk forms (>0.1 mm). In the two-dimensional (2D) limit, correlated effects are more easily tuned and studied; therefore, it is of fundamental importance to develop an experimental basis for investigation. Herein, a two-step process is utilized to chemically delithiate and exfoliate LiCoO2 single crystals and study nanoflakes 10–60 nm thick, with 0.37 < x < 0.8. An initial electrical characterization of this new form reflects bulk conduction properties, verifying the reliability of this new technique: temperature-dependent resistance measurements indicate an insulating 2D variable ranging hopping conduction for samples of x > 0.75, and metallic characteristics with a finite residual conductance for x < 0.75. However, these thin flakes also exhibit correlated characteristics less commonly observed and understood in Li x CoO2. An energy barrier upon contact formation is observed for all conditions, independent of lithium concentration and electrode work function, suggesting enhanced correlated effects due to reduced dimensionality. Additionally, charge-ordering phenomena in the temperature-dependent resistance occur under specific preparation conditions. These anomalies are markedly larger in magnitude than previous accounts in bulk systems and are also found in low lithium ranges of x < 0.5, matching theoretical predictions not commonly observed experimentally. This work utilizes a new approach to gain insight behind the complex transport phenomena inherent in Li x CoO2, providing a new opportunity to understand these correlated effects using a 2D, single-crystal form.

for electronic devices. Oxides constitute a broad family of materials with a wide range of potential applications, from catalysis to electronic, photonic, ferroelectric, magnetic and multiferroic functionalities. Understanding structure-property relations in free-standing, supported, and confined two-dimensional ceramics or "ceramic flatlands" has been identified as one of the challenges for future work in ceramics by a recent National Science Foundation workshop. [9] Nonetheless, over the last decade, there have been many reviews on 2D oxides either as the main focus or as a part of a more general nano-materials focused review papers or books. One of the earlier reviews of nanosheets of oxides and hydroxides focused on synthesis, properties -especially photon-induced behavior -and their assembly, was published in 2010 by Ma et al. [11], followed by a second review [12] as a part of a special issue on "2D Nanomaterials beyond Graphene" in 2015. Around the same time (2011) another review by Mas-Balleste et al.[13] also emphasized the importance and variety of 2D oxides. A more recent focused review on 2D oxides can be found in 2019 paper of Hinterding et al.

Two-dimensional materials have gained significant attention across the materials community due to their remarkable physical, chemical, electronic, and optical properties. With many two-dimensional materials discovered each year, investigations into their processing, scalability, and resulting properties are important to fully realize their potential in next-generation technologies. While numerous exfoliation techniques are available for a variety of two-dimensional materials, liquid-phase exfoliation techniques offer many advantages, particularly high throughput and scalability. Herein, we report a liquid-phase exfoliation method to access multilayer cobalt oxide nanosheets in pH-neutral aqueous solutions varying in size, concentration, and application. The size, thickness, and morphology of the multilayer nanosheets were confirmed using atomic force microscopy and transmission electron microscopy. Finally, selected cobalt oxide nanosheets underwent additional analysis of the crystallinity, structure, and cobalt valance.

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22D particle surfactants are attractive for the formation of highly stable emulsions and use as templates to prepare composite structures with performance properties dependent on the composition. Cobalt oxide nanosheets...