Page 114 - Handbook of Battery Materials

80 2 Practical Batteries

[106]. THF-2MeTHF-LiAsF 6 with an additional of 2-methylfuran showed the longest
cycle life [107, 108].
2+
3+
3+
The addition of some metal ions, such as Mg ,Zn ,In ,orGa , and some
2+
organic additives, such as 2-thiophene, 2-methylfuran, or benzene, to PC-LiCIO 4
improved the coulombic efficiency for lithium cycling [109]. Lithium deposition
on a lithium surface covered with a chemically stable, thin, and tight layer which
was formed by the addition of HF to electrolyte can suppress the lithium dendrite
formation in secondary lithium batteries [110].
The dendritic growth of lithium was suppressed on a lithium electrode surface
modified by an ultrathin solid polymer electrolyte prepared from 1,1-difluoroethane
by plasma polymerization [111].
A high rate discharge led to the recombination of isolated lithium which resulted
in an increase in cycle life, and the cycle life decreased with an increase in the
charge current density [112].
While the initial surface species formed on lithium in alkyl carbonates consist
of ROCO 2 Li compounds, these species react with water to form Li 2 CO 3 ,CO 2 ,
and ROH. This reaction gradually changes the composition of the surface films
formed on lithium in these solvents, and Li 2 CO 3 becomes the major component
[113]. A film of Li 2 CO 3 was formed on lithium by the direct reaction of PC with
lithium [114]. Diethyl carbonate was found to react with lithium to form lithium
ethyl carbonate [115]. The main reaction products in the surface film on lithium
were CH 3 OLi in DME, and C 4 H 9 OLi in THF [116]. A surface film which contained
ROLi, ROCO 2 Li, and Li 2 CO, was formed on lithium in 1,3-dioxolane-LiClO 4
[117].
A lithium electrode is reported to show high rechargeability in solutions con-
taining LiAsF 6 . A brown film composed of an (−O–As–O) n polymer and LiF
was formed on lithium in THF-LiAsF 6 [118]; elsewhere, a film on lithium was
determined to be As 2 O 3 and F 2 AsOAsF 2 in THF–LiAsF 6 [119]. Another film had
a probable two-layer structure consisting of Li 2 O covered by an outer Li 2 O–CO 2
adduct in 2MeTHF-LiAsF 6 [120]. A film of reduction product ROCO 2 Li was formed
on lithium in ethylene carbonate-LiAsF 6 or PC-LiAsF 6 [121].
As the cycling efficiency of metallic lithium is always significantly below 100%
(∼99%), the lithium anode has to be over-dimensioned (200–400%) in practical
cells.

References

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logue, Sanyo Electric Co., Ltd. Type Nickel-cadmium Batteries,Sanyo
2. Yano, M. and Nogami, M. (1997) Denki Electric Co., Ltd., Osaka.
Kagaku, 65, 154. 6. Tuck, C.D.S. (1991) Modern Battery
3. Miura, A. (1989) Denki Kagaku, 57 (6), Technology, Sanyo Electric Co., Ltd,
459. Osaka, pp. 244–289.
4. Akazawa, T., Sekiguchi, W., and 7. van Vucht, J.H.N., Kuijpers, F.A., and
Nakagawa, J. (1987) Proceedings of Brunning, H.C.A.M. (1970) Philips Res.
28th Battery Symposium, Tokyo. Rep., 25, 133.