Cation deficiency associated with the chemical exfoliation of lithium cobalt oxide. Issue 9 (5th March 2019)

• Record Type: Journal Article
• Authors: Pachuta, Kevin G.; Pentzer, Emily B.; Sehirlioglu, Alp
• Is Part Of: Journal of the American Ceramic Society. Volume 102:Issue 9(2019)
• Page Start: 5603
• Page End: 5612
• Publication Date: 2019-03-05
• Subjects: chemical exfoliation -- defects -- layered transition metal oxides -- lithium cobalt oxide -- two‐dimensional structures; Ceramics -- Periodicals; 620.1405
• DOI: 10.1111/jace.16382
• Languages: English
• ISSNs: 0002-7820

Abstract

Abstract: 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). Abstract : This figure shows the schematic (with representated images below) for the exfoliation process of LiCoO2 by way of a two‐step wet chemical treatment process. In the first step, LiCoO2 undergoes acid treatment causing ionic replacement of Li + with H + . In the second step, the acid treated powder is treated with a bulky hydroxide baring amine causing the particles to swell and exfoliate to atomically thin cobalt oxide nanosheets.