For the first time, the effect of the nanowires diameter in terms of size and distribution on electrochemical properties of SiNWs grown by VLS was investigated. The diameter size was tuned by using three different gold catalyst film thicknesses. The crucial influence of this parameter is evidenced through comparison of the charge–discharge behavior and a study of the rate capability for the three samples. The rechargeable capacity as well as the rate capability is shown to be the best when the smallest diameters (<65nm) are used compared to larger one (<210nm and <490nm). High capacity values of 3500mAhg−1 are obtained for the smallest diameters at C/5 rate but still 2500, 1500 and 500mAhg−1 are recovered at C, 2.5C and 5C. An excellent cycle life over 50 cycles is achieved at 1.3C with a capacity of 2500mAhg−1. This shows that by tailoring the diameter size and distribution, SiNWs can provide high power density anodes in lithium ion batteries.