Sn materials offer high theoretical capacities in lithium ion batteries, but they must have good cycling stability and high rate-capability in order to be commercialized. Complex and costly material treatments of Sn have been effective in reducing capacity fade, but conventionally produced bare Sn is desired for reducing cost. One simple method is to form a high-quality solid electrolyte interphase (SEI) on Sn particles with low resistance and high passivation. Fluoroethylene carbonate (FEC) added to the electrolyte forms a protective and less-resistant SEI on Sn particles during the in-situ electrochemical SEI formation cycle. FEC is a good oxidizing agent that removes highly oxidized carbon compounds and makes a SEI thinner during an oxidation process (delithiation) of SEI formation cycle. The high-quality SEI greatly improves the rate-capability and capacity of nano-sized bare Sn electrodes without any treatments: minimal capacity fade (0.014% cycle−1) at 320mAhg−1 (1.3C) for 150 cycles. The mitigating effect of FEC on capacity fade is not seen with electrodes fabricated from micro-scale (0.1~0.2μm) Sn. The long lithium-ion diffusion path makes these micro-sized materials susceptible to decrepitation during repeated volume changes.