Our results are summarized schematically in Figure . During formation at potentials V > Li + /Li, Figure ,b indicate that a layer promoting Lithium adhesion forms under influence of the H2O additive. Following the discussion above we therefore consider this layer to likely consist of Li2O, LiOH and possibly LiH species (after Li UPD), with HER occurring simultaneously (Figure ). During growth, at potentials V < Li + /Li, growth is directed under influence of the H2O additive through HER (Figure ), such that all these species are likely to be present in the nanorod shell (Figure ). It should be stressed that we consider this to be a highly dynamic process, also illustrated by the fact that the additive concentration has to be balanced with the growth rate (Figure , SI-5), where these species can be converted further after formation (SI-7) .