When designing nano-Si electrodes for lithium-ion batteries, the detrimental effect of the c-Li₁₅Si₄ phase formed upon full lithiation is often a concern. In this study, Si nanoparticles with controlled particle sizes and morphology were synthesized and the parasitic reactions of the metastable c-Li₁₅Si₄ phase with the non-aqueous electrolyte was investigated. The use of smaller Si nanoparticles (~ 60 nm) as well as the addition of fluoroethylene carbonate additive played decisive roles in the parasitic reaction such that the c-Li₁₅Si₄ phase could disappear at the end of lithiation. This suppression of c-Li₁₅Si₄ improved cycle life of the nano-Si electrodes but with a little loss of its specific capacity. In addition the characteristic c-Li₁₅Si₄ peak in the dQ/dV plots can be used as an early-stage indicator to the cell capacity fade during cycling. Our findings can contribute to the design guidelines of Si electrodes and allow us to quantify another factor to the performance of the Si electrodes.