# What is the reason for decomposition of layered cathode materials?

Articles like this claim oxygen can evolve from layered metal oxide cathode materials when charging the Li-ion battery. Is it the high positive potential given to the cathode while charging pulling the electrons from the chemical bonds of the cathode materials and thus cause the decomposition to evolve oxygen? If not, what is the cause of the evolution of oxygen?

Then, try to be clear in using the word "cathode". A cathode is the electrode where a reduction happens, whatever its working mode (cell or electrolysis). So when recharging a Li-ion battery, the $$\ce{Li+}$$ ion are going to the cathode to be reduced : reduction happens on the Li-graphite electrode (cathode). And no Oxygen can be formed on this electrode. Oxygen may be produced by electrolysis at the other electrode made of Cobalt and Manganese oxides. These oxides are oxidized to a higher number of oxidation. But of course, these oxides are not vrery stable, they may lose part of their oxygen as $$\ce{O2}$$.
To summarize, the Lithium electrode is always the negative pole, whatever its working mode. The Lithium atom works as an anode when the cell is working (producing $$\ce{Li+}$$ ions and electrons), and as a cathode when the cell is being recharged. The other electrode is always the positive pole, whatever its working mode. Its metallic oxides are reduced when the cell is producing current (cathode). When being recharged, this electrode is an anode, as its oxides are oxidized to a higher oxidation number.