Solvent dissociation dynamics from solvated lithium ion solvated by ethylene carbonates (EC) have been investigated by means of direct ab-initio molecular dynamics (AIMD) method. The lithium ion was solvated by four EC molecules as the first solvation shell. It was found that the solvation number of lithium ion is drastically changed from 4 to 1 when the solvated lithium ion accepts an excess electron. The binding energy of Li-EC decreased to a one-tenth. Finally, the contact ion pair composed of Li+ and EC− was formed as the product. The mechanism of solvent dissociation was discussed on the basis of theoretical results.