The use of a long chain ionic liquid in an LiMn2O4 based lithium ion cell

• Published in: Electrochimica acta 2012-08, Vol.76, p.179-184
• Main Authors: Sutto, Thomas E., Duncan, Teresa T.
• Format: Article
• Language: English
• Subjects: Ionic liquid; Lithium; Lithium manganese oxide
• ISSN: 0013-4686; 1873-3859
• DOI: 10.1016/j.electacta.2012.04.096

A long chain substituted imidazolium ionic liquid, 1,2-dimethyl-3-octylimidazolium bis(trifluoromethanesulfonyl)imide (MMOITFSI), is used as the electrolyte for reversible intercalation of Li into LiMn2O4. Ionic conductivity measurements indicate that in spite of the longer chain attached to the imidazolium ring, the conductivity for the pure liquid and with 0.5M LiTFSI present, remains above 1mS/cm. Cyclic voltammetry revealed high reversibility of Li+ into LiMn2O4 in this ionic liquid. Charge/discharge experiments indicated reversible capacity of 115mAHr/g at a discharge rate of C/6 for 0.5M Li in MMOITFSI. Higher discharge rates (C/3) resulted in lower capacities (below 100mAHr/g), most likely due to the higher viscosity of the long chain ionic liquid. Improved discharge rates, of 111mAHr/g at a higher discharge rate of C/3, were observed when 10wt% of a short chain ionic liquid, 1,2-dimethyl-3-propylimidazolium bis(trifluoromethanesulfonyl)imide (MMPITFSI), was added to the MMOITFSI. For both the pure MMOITFSI and the ionic liquid blend of MMOITFSI with MMPITFSI, cycle lifetimes showed minimal degradation due to intercalation by the imidazolium cation into the graphite used to enhance the conductivity of the cathode material.