High resolution in situ Li depth profiling of thin films stacked Li ion batteries under charging conditions by means of TERD and RBS techniques with 5 MeV He+2 ion beam

The experimental results are reported on Ni/Si/LiPON/LCO/Pt/Ti and Au/Si/LiPON/LCO/Au batteries prepared on SiN and Al self-supporting films (LiPON = Li3.3PO3.8N0.2, LCO = LiCoO2) which have been in situ measured simultaneously by Transmission ERD and RBS techniques with 5 MeV He+2 ion beam, in order to understand Li transport from positive electrode (LCO) to negative electrode (Si) under charging and over-charging. It has been found on over-charging that for the former battery Li ions over-flowed out of Si reacts with Ni electrode in the follow direction, whereas for the latter battery Li once charged in Si returns back through LiPON to LCO in the counter direction and reacts with Al through intermediate Au. Quite different two transport phenomena of Li on over-charging are discussed in terms of transport process of Li through LiPON, the difference in Fermi energies of the metal electrodes at both sides of LCO/LiPON/Si and in contact potentials of Si with the metal electrodes.