We evaluated (1) thermal and electrochemical stability and (2) ion-dissociation ability of PF6-n(CF3)(n)(-) anions by computational method. The thermal stability order by Delta DeltaE (anion) is PF4(CF3)(2)(-) > PF5(CF3)(-) > PF3(CF3)(3)(-) > PF6-. The ion-dissociation ability order by Delta DeltaE (Li salts) is LiPF3(CF3)(3) > LiPF4(CF3)(2) > LiPF5(CF3) > LiPF6. The conductivity of electrolyte solution with LiPF4(CF3)(2) (3.9 mS/cm) was a little lower than that of LiPF6 (4.4 mS/cm) in 0.1 mol/l Li salt/PC:DME electrolyte, while the oxidation potential of LiPF4(CF3)(2) in PC was higher than that of LiPF6. The LiPF4(CF3)(2)-cell showed better cycle characteristics than LiPF6-cell.