Protonation of Lix(Co,Ni,Mn)O2 compounds in acidic conditions.

The easy intercalation/deintercalation of Li+ ions is the key factor for the functionality of the layered Li x CoO 2 compound as a Li-ion battery cathode material. However, the hexagonal CoO 2 -layer piling in the Li x CoO 2 structure is prone to incorporate not only monopositively-charged lithium ions but also monopositive protons. Here we employ a hydrothermal acid treatment for a gradual (controlled by the treatment time) de-intercalation of Li+ ions and a subsequent intercalation of protons between the CoO 2 layers in Li x CoO 2. We demonstrate that the lithium-for-proton exchange reaction can be monitored by AAS for the Li-content, by XRD for the proton-containing phase formation, and by FTIR and TG for the appearance of specific features indicative of the incorporated protons. With XPS we verify that upon the lithium-for-proton exchange the valence of cobalt remains the same, i.e. the proton incorporation compensates the positive charge loss due to the Li+-ion extraction. Finally, we show that essentially parallel lithium-for-proton exchange reactions occur also for Ni- and Mn-substituted Li(Co,Ni,Mn)O 2 samples, that is, for compounds that are highly relevant in current Li-ion battery technology. In acidic aqueous conditions Li(Co,Ni,Mn)O 2 compounds gradually release lithium ions and incorporate protons; this exchange reaction can be followed by TG and FTIR measurements. Image 1 • Acid treatment of LiCoO 2 releases Li+ cations and incorporates protons. • Ultimately this reaction yields trigonal H y CoO 2. • According to XPS Co valence remains constant upon the Li+-for-H+ exchange. • FTIR and TG can be used to monitor the incorporation of protons. • Similar Li+-for-H+ exchange reaction occurs also for Li(Co,Ni,Mn)O 2. [ABSTRACT FROM AUTHOR]