Measurement of concentration boundary layer thickness development during lithium electrodeposition onto a lithium metal cathode in propylene carbonate M. Ota a , S. Izuo a , K. Nishikawa a , Y. Fukunaka a, *, E. Kusaka a , R. Ishii a , J.R. Selman b a Department of Energy Science and Technology, Graduate School of Energy Science, Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan b Center for Electrochemical Science and Engineering, Illinois Institute of Technology, Chicago, IL, USA Received 3 May 2003; received in revised form 23 July 2003; accepted 29 August 2003 Abstract Li metal was electrodeposited galvanostatically on aLi metal substrate in propylene carbonate (PC) containing 0.5 M lithium perchlorate (LiClO 4 ). The concentration profile of Li  ion developed with electrodeposition was measured in situ by holographic interferometry. The interference fringe shift at a higher current density indicates that the mass transfer rate of Li  ion along a vertical cathode is primarily governed by natural convection induced by Li metal electrodeposition. This transient natural convection is reasonably described by the boundary layer theory. However, no interference fringe shift was observed in the initial stage of electrodeposition at a lower current density. The incubation period until the interference fringes start to shift was considerably prolonged as the applied current density was decreased. The charge consumed during the incubation period varied from 7 to 30 mC cm 2 . This phenomenon was attributed to the diffusion of residual H 2 O in the PC electrolyte. # 2003 Elsevier B.V. All rights reserved. Keywords: Lithium; Propylene carbonate; Electrodeposition; Dendritic growth; Concentration profile; Natural convection; Holographic interferometer; Incubation period 1. Introduction Rechargeable batteries and lithium secondary bat- teries in particular, are widely used as a power source for electronic devices. Lithium metal is the most attractive candidate for the anode material of these batteries, because the combination of lowest weight and highest negative standard electrode potential results in the highest theoretical specific energy density. However, lithium metal as a negative electrode has many pro- blems, for example, capacity decrease and short-circuit- ing after repeated charge/discharge cycles. It is believed that significant morphology changes of the electrode surface during the repeated charge/discharge cycle process cause these problems. Therefore, to exploit the advantage of the highest theoretical energy power density, good morphological reversibility must be achieved by maintaining a flat electrode surface during many cycles, to guarantee not only the power density but also the safety of these batteries. To assure a longer cycle life, we have to understand lithium electrodeposition and dissolution phenomena physically as well as electrochemically. The electroche- mical reaction of Li  ion at Li metal is mediated by the existence of a passive SEI layer on an active Li metal surface. There are many reports on lithium electrode- position from the surface chemistry point of view [1 /5]. Dendrite formation has been discussed based on the concept of passive layer formation on lithium metal [6,7]. However, dendrite formation has not been corre- lated with the ionic mass transfer rate in non-aqueous electrolyte, although concentration depletion of the reactant ion is known to be an important factor in * Corresponding author. Tel.: /81-75-753-5415; fax: /81-75-753- 4719. E-mail address: fukunaka@energy.kyoto-u.ac.jp (Y. Fukunaka). Journal of Electroanalytical Chemistry 559 (2003) 175 /183 www.elsevier.com/locate/jelechem 0022-0728/03/$ - see front matter # 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.jelechem.2003.08.020