Fusaji Kita

On the characteristics of electrolytes with new lithium imide salts

Abstract In our continuous study on organic lithium salts, we found that the imide salt (RfSO 2 )(R′fSO 2 )NLi shows high conductivity in organic solvents, and that the modification of the imide salts change the anodic oxidation potential and the dissolution potential of aluminum current collector. Lithium imide with long fluoroalkyl groups such as (C 4 F 9 SO 2 )(CF 3 SO 2 )NLi and the new ester-type imide salts, ((CF 3 ) 2 CHOSO 2 ) 2 NLi do not dissolve the aluminum collector up to 4.8 and 4.3 V, respectively. We also examined the polymer analogue of the ester-type imide salt such as (-CH 2 (CF 2 ) 4 CH 2 OSO 2 N(Li)SO 2 O-) 9–10 .

Characteristics of the electrolyte with fluoro organic lithium salts

Some fluoro organic lithium salts have attractive features as organic electrolyte such as solubility, conductivity, and oxidation potentials. The fluoro organic lithium salts with SO 2 groups show higher conductivities than those with CO groups. Methide (CF 3 SO 2 ) 3 CLi and imide (RfSO 2 ) 2 NLi salts show higher conductivities than oxide salts RfSO 2 OLi with only one RfSO 2 group. The lithium salts with long fluoroalkyl groups and two or more RfSO 2 groups show high oxidation potentials and high aluminum corrosion potentials over 4.3 V. The battery performances of modified imide salts such as (C 2 F 5 SO 2 ) 2 NLi, (C 4 F 9 SO 2 )(CF 3 SO 2 )NLi, and ((CF 3 ) 2 CHOSO 2 ) 2 NLi are satisfactory. The cycle characteristics of the imide salt cells are better than those of the LiPF 6 cell. Especially, the ((CF 3 ) 2 CHOSO 2 ) 2 NLi shows the best cycle characteristics. In XPS analysis the anode surfaces of the imide cells are covered with imide salt components.

Electronic structures and electrochemical properties of LiPF6-n(CF3)n

We evaluated (1) thermal and electrochemical stability and (2) ion-dissociation ability of PF 6-n (CF 3 ) n anions by computational method. The thermal stability order by ΔΔE (anion) is PF 4 (CF 3 ) - 2 > PF 5 (CF 3 ) > PF 3 (CF 3 ) - 3 > PF - 6 . The ion-dissociation ability order by ΔΔE (Li salts) is LiPF 3 (CF 3 ) 3 > LiPF 4 (CF 3 ) 2 > LiPF 5 (CF 3 ) > LiPF 6 . The conductivity of electrolyte solution with LiPF 4 (CF 3 ) 2 (3.9 mS/cm) was a little lower than that of LiPF 6 (4.4 mS/cm) in 0.1 mol/l Li salt/PC:DME electrolyte, while the oxidation potential of LiPF 4 (CF 3 ) 2 in PC was higher than that of LiPF 6 . The LiPF 4 (CF 3 ) 2 -cell showed better cycle characteristics than LiPF 6 -cell.