Photoelectrochemical behavior of LiCoO2 membrane electrode

We studied the photoresponse of a membrane electrode of stoichiometric LiCoO2 used in lithium ion batteries. The electrode LiCoO2 in contact with dimethyl carbonate, propylene carbonate and LiClO4 presents the behavior of a p-semiconductor/electrolyte junction. The deinsertion of lithium of the LiCoO2 suppresses the photoresponse at 3.9 V versus the lithium potential. The reappearance of the photoresponse after re-intercalation suggests that the alterations in the electronic structure of the LixCoO2 electrode probed by the photoelectrochemical experiments during deinsertion are reversible until x=0.5. The direct band gap energy of the LiCoO2 stoichiometry is 2.5 eV before and after lithium reinsertion. The experiments showed also that a small photo-intercalation current is observed in this cathodic material.