Recently, Ni3.5Sn4 intermetallic has been reported as an efficient buffering material for Si-containing composite negative electrodes used in Li-ion batteries. In the present work, the electrochemical properties of this Ni-overstoichiometric compound are studied in detail. Micrometric, nanosized and carbon-added nanosized Ni3.5Sn4 have been investigated. For all materials, very good cycle life is obtained over more than 400 cycles. Nanosized Ni3.5Sn4 with crystallite size of 6nm exhibits a reversible capacity of 240mAhg−1, ten times higher than for the micrometric state. Moreover, nanosized Ni3.5Sn4 exhibits high-rate capability with 80% of full discharge capacity at 16C. Carbon addition slows down kinetics but increases the reversible capacity up to 273mAhg−1. The electrochemical properties of nanostructured Ni3.5Sn4 phase make it a promising constituent for composite anodes of Li-ion batteries.