respectively. The plating and stripping peaks characteristic of the
redox reaction of Li+ could be observed (Fig. 4) and the coulombic
efficiencies were estimated to be approximately 83%.
In conclusion, we have developed a new family of very stable
ionic liquids based on the 3-azabicyclo[3.2.2]nonane ring structure
which makes a logical contribution to a set of existing cation
structures. A study of physicochemical properties and a com-
parison with related structures have revealed organic plastic crystal
phases, wide electrochemical windows and highly reversible lithium
metal electrodeposition. These properties will allow ABN1nTf2N–
LiTf2N mixtures to be used in rechargeable lithium-metal batteries,
and also offer the prospect of a solid electrolyte equivalent through
harnessing one of the OPC phases.
Fig. 3 Linear-sweep voltammograms of 3-ABN13Tf2N and PP13Tf2N
obtained on a platinum working electrode; scan rate: 50 mV s21
Notes and references
;
temperature: ambient; reference electrode Ag/AgTf (10 mM in P14Tf2N).
{ We thank James Beavis and Dr Rob Rees for the computational work.
§ We note that the P15 salt of the pyrrolidinium series is a solid at 25 uC.
" This phase transition is observed when 4b is isolated from water.
1 L. S. Wilkes and M. J. Zaworotko, J. Chem. Soc., Chem. Commun.,
1992, 965.
2 L. Fuller, R. T. Carlin, H. C. De Long and D. Haworth, J. Chem. Soc.,
Chem. Commun., 1994, 299.
3 (a) Ionic Liquids in Synthesis, ed. P. Wasserscheid and T. Welton, Wiley-
VCH, Weinheim, Germany, 2003; (b) T. Welton, Coord. Chem. Rev.,
2004, 248, 2459; (c) J. Eßer, P. Wasserscheid and A. Jess, Green Chem.,
2004, 6, 316; (d) P. Wasserscheid and W. Keim, Angew. Chem., Int. Ed.,
2000, 39, 3773; (e) J. D. Holbrey and K. R. Seddon, Clean Prod.
Process, 1999, 1, 223.
4 (a) M. C. Buzzeo, R. G. Evans and R. G. Compton, ChemPhysChem,
2004, 5, 1106; (b) S. Z. El Abedin, E. M. Mustafa, R. Hempelmann,
H. Natter and F. Endres, Electrochem. Commun., 2005, 7, 1111; (c)
P. C. Howlett, D. R. MacFarlane and A. F. Hollenkamp, Electrochem.
Solid-State Lett., 2004, 7, A97–A101; (d) H. Sakaebe and
H. Matsumoto, Electrochem. Commun., 2003, 5, 594; (e) P. Wang,
S. M. Zakeeruddin, P. Comte, I. Exnar and M. Gra¨tzel, J. Am. Chem.
Soc., 2003, 125, 1166.
5 (a) T. Herzig, C. Schreinera, D. Gerhard, P. Wasserscheid and
H. J. Gores, J. Fluorine Chem., 2007, 128, 612; (b) Z. Zhou,
H. Matsumoto and K. Tatsumi, Chem.–Eur. J., 2006, 12, 2196; (c)
H. Matsumoto, H. Sakaebe and K. Tatsumi, J. Power Sources, 2005,
146, 45; (d) D. Gerhard, S. C. Alpaslan, H. J. Gores, M. Uerdingen and
P. Wasserscheid, Chem. Commun., 2005, 5080; (e) D. R. MacFarlane,
P. Meakin, J. Sun, N. Amini and M. Forsyth, J. Phys. Chem. B, 1999,
103, 4164; (f) J. Sun, M. Forsyth and D. R. MacFarlane, J. Phys. Chem.
B, 1998, 102, 8858.
Fig. 4 Cyclic voltammograms of 3-ABN12Tf2N containing 0.4 mol kg21
LiTf2N obtained on a Pt electrode; scan rate: 50 mV s21; reference
electrode Ag/AgTf (10 mM in P14Tf2N); temperature: 80–90 uC.
translational motion of the ring system is more restricted than in
the related but more planar pyrrolidinium and piperidinium
systems. This correlation, which is reflected in the higher viscosities
of the non-planar heterocycles vs. the planar imidazolium systems,
was noted earlier by MacFarlane et al.5e The viscosity of 4c, which
is a liquid at room temperature, was found to be 209 mPa s at
40 uC.
6 D. R. MacFarlane, J. Huang and M. Forsyth, Nature, 1999, 402, 792.
7 N. Matsumi, M. Miyake and H. Ohno, Chem. Commun., 2004, 2852.
8 T. Mukai, M. Yoshio, T. Kato, M. Yoshizawa and H. Ohno, Chem.
Commun., 2005, 1333.
Interestingly, the OPC material 4b, when mixed with LiTf2N
(0.4 mol kg21), showed significant solid state conductivity of
y 6 6 1026 S cm21at 35 uC.6
9 C. Tiyapiboonchaiya, J. M. Pringle, J. Sun, N. Byrne, P. C. Howlett,
D. R. MacFarlane and M. Forsyth, Nat. Mater., 2004, 3, 29.
10 M. Yoshizawa-Fujita, D. R. MacFarlane, P. C. Howlett and
M. Forsyth, Electrochem. Commun., 2006, 8, 445.
The electrochemistry of the new salts was investigated at tem-
peratures above their melting point on a platinum electrode and a
Ag/AgTf (10 mM in P14Tf2N) reference electrode arrangement
developed by our group.16 All compounds have wide electro-
chemical windows, similar to those of the P1n and PP1n systems
(Fig. 3). This is in contrast to the recently reported hetero-bicyclic
compound exhibiting an electrochemical window of 4 V.10
Importantly, the cathodic stability extends beyond the reduction
potential of lithium and the feasibility of reversible electro-
deposition of lithium in these salts was demonstrated for 4b +
0.4 mol kg21 LiTf2N on a platinum and copper electrode
11 (a) V. L. Brown, Jr. and T. E. Stanin, Ind. Eng. Chem. Prod. Res. Dev.,
1965, 4, 40; (b) C. A. Wulff and E. F. Westrum, J. Phys. Chem., 1964,
68, 430.
12 F. F. C. Bazito, Y. Kawano and R. M. Torresi, Electrochim. Acta, 2007,
52, 6427.
13 (a) J. Timmermans, J. Phys. Chem. Solids, 1961, 18, 1; (b) A. J. Hill,
J. Huang, J. Efthimiadis, P. Meakin, M. Forsyth and D. R. MacFarlane,
Solid State Ionics, 2002, 154–155, 119.
14 T. Shimizu, S. Tanaka, N. Onoda-Yamamuro, S. Ishimaru and
R. Ikeda, J. Chem. Soc., Faraday Trans., 1997, 93, 321.
15 E. I. Cooper and C. A. Angell, Solid State Ionics, 1986, 18–19, 570.
16 G. A. Snook, A. S. Best, A. G. Pandolfo and A. F. Hollenkamp,
Electrochem. Commun., 2006, 8, 1405.
5228 | Chem. Commun., 2007, 5226–5228
This journal is ß The Royal Society of Chemistry 2007