ORIGINAL PAPER K. Nishikawa Æ M. Ota Æ S. Izuo Æ Y. Fukunaka E. Kusaka Æ R. Ishii Æ J. R. Selman Transient natural convection induced by electrodeposition of Li + ions onto a lithium metal vertical cathode in propylene carbonate Received: 18 March 2003 / Accepted: 11 August 2003 / Published online: 7 October 2003 Ó Springer-Verlag 2003 Abstract Transient natural convection caused by Li + electrodeposition at constant current along a vertical Li metal cathode immersed in a 0.5 M LiClO 4 –PC (pro- pylene carbonate) electrolyte was compared with that by Cu 2+ ion electrodeposition in aqueous CuSO 4 solution. The concentration profile of the Li + ions was measured in situ by holographic interferometry. The interference fringes start to shift with time at a higher current den- sity. The concentration boundary layer thickness for Li + ions was successfully determined. With the progress of electrodeposition, the density difference between the electrolyte at the cathode surface and the bulk electro- lyte increased to induce upward natural convection of the electrolyte. The electrolyte velocity was measured by monitoring the movement of tracer particles. The measured transient behavior of the ionic mass and momentum transfer rates normalized with respect to the steady-state value was numerically analyzed. Transient natural convection along a vertical cathode due to Li metal electrodeposition can be reasonably explained by boundary layer theory, similar to the case of Cu elec- trodeposition in aqueous CuSO 4 solution. Keywords Electrodeposition Æ Holographic interferometry Æ Ionic mass transfer Æ Lithium Æ Transient natural convection Introduction Natural convective flow develops along the surface of a vertical plane electrode installed in an unstirred elec- trolyte when current is spontaneously passed. It interacts with the ionic mass transfer rate and the resultant cur- rent density distribution along the vertical direction. Moreover, it starts to couple with the morphological variation of the electrodeposited metal. Most of the theoretical and experimental research thus far has dealt only with steady laminar natural convective flow. The electrodeposition of Cu 2+ ions in aqueous CuSO 4 solution has been used to understand the interaction between electrochemical and transport phenomena since the 1940’s work of Wagner [1] and Brenner [2]. The analysis of transient natural convection is also practi- cally important, e.g. for designing the operational scheduling of unsteady-state industrial electrolysis such as periodic reverse current electrolysis. It is also indis- pensable to interpret certain data measured in cyclic voltammetry, when a vertically oriented plate or foil electrode is employed. Natural convection in a Li deposition system: why? Lithium batteries, like most high-energy-density or high- power-density batteries, are designed such that the electrolyte layer between the electrodes is very thin and therefore presents minimal ohmic resistance. Often the electrolyte is contained within a microporous membrane or diaphragm, which prevents electronic contact (shorting) between the electrodes due to accidental dis- tortion, etc. Therefore, natural convection in lithium batteries is practically excluded. However, the phenom- enological understanding of lithium metal electrode- position and dissolution, and especially the reversibility of the process, can be studied advantageously in a cell that features natural convection. In the literature, there are many reports about lithium electrodeposition from surface chemistry [3, 4, 5, 6, 7]. The important practical J Solid State Eletrochem (2004) 8: 174–181 DOI 10.1007/s10008-003-0447-z K. Nishikawa Æ M. Ota Æ S. Izuo Æ Y. Fukunaka (&) E. Kusaka Æ R. Ishii Department of Energy Science and Technology, Graduate School of Energy Science, Kyoto University, Sakyo-ku, Kyoto, Japan E-mail: fukunaka@energy.kyoto-u.ac.jp Tel.: +81-75-7535415 Fax: +81-75-7534719 J. R. Selman Center for Electrochemical Science and Engineering, Illinois Institute of Technology, Chicago, IL 60616, USA