The change of open circuit voltage (OCV) in aging process was surveyed to clarify the relations with the solid electrolyte interface (SEI) layer formation and with the Li ion battery performance. The compositions of absorbing materials were designed by organic compounds (EC, GBL, and FEC) and salts (LiPF6 and LiBF4). The OCV was affected by not only the organic compounds but also the salt contents. It was concluded that the absorbed BF4 anion affected the SEI layer formation, and that the thermal stability was far superior to the other systems. This means that Li ion battery with thermal stability could be also fabricated by the control of the electrochemical absorption in the aging process. (C) 2008 Elsevier B.V. All rights reserved.