Silicon nanowires grown on a stainless steel current collector were evaluated as Li ion battery anodes in an ionic liquid consisting of butyl-trimethyl ammonium bis(trifluoromethylsulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide. The electrodes showed good performance in the ionic liquid electrolyte with a stable discharge capacity of similar to 2000 mAh g(-1) and coulombic efficiency of 97% after 50 cycles. However, the large internal stresses caused by the volumetric expansion of the Si during lithiation limits the long-term cycle life of the battery in both ionic and organic electrolytes due in-part to the repeated disruption and reformation of the solid electrolyte interface layer on the Si. In contrast, when the same Si nanowire electrode was cycled at relatively shallow discharges, similar to those of carbon anodes, 320 mAh g(-1), the battery showed better performance with cycle life greater than 650 cycles and coulombic efficiency close to 100% in the ionic liquid electrolyte. Cycling at 1000 mAh g(-1) showed lifetimes in excess of 200 cycles in an organic electrolyte without cell degradation. The effect of Si doping, and amount of electrolyte in contact with the anode on the battery capacity and cycle life are also presented. (C) 2012 Published by Elsevier B.V.