1. J. Heyrovský Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, Dolejškova 3, CZ-18223 Prague 8, Czech Republic, Laboratory of Photonics and Interfaces, EPFL, Ecublens, CH-1015 Lausanne, Switzerland, and High Power Lithium, Park Scientifique, PSE-B, EPFL, Ecublens, CH-1015 Lausanne, Switzerland