Res. Chem. Intermed.
, Vol. 32, No. 5–6, pp. 453–459 (2006)
Also available online - www.vsppub.com
Suppression mechanism of the self-discharge reaction
in nickel–metal hydride batteries using a sulfonated
, YASUYUKI HARADA, REIZO MAEDA,
HIROSHI NAKAMURA, SHIGEKI MATSUTA, TOSHIYUKI NOHMA and
Mobile Energy Company, Sanyo Electric Co., Ltd., 7-3-2 Ibukidai-higashimachi, Nishi-ku, Kobe,
Hyogo 651-2242, Japan
Received 8 November 2004; accepted 26 November 2004
Abstract—The suppression mechanism of the self-discharge reaction in nickel–metal hydride batter-
ies using a sulfonated polyoleﬁn separator was investigated with sealed-type AA size cells. The exper-
imental results indicate that a sulfonated polyoleﬁn separator effectively suppresses the self-discharge
reaction in nickel–metal hydride batteries by trapping nitrogen-containing redox shuttle substances. It
is also found that a sulfonated polyoleﬁn separator traps the shuttle substances as gaseous ammonia. In
the experiment examining the inﬂuence of the amount of the shuttle substances on the self-discharge,
the starting point of the self-discharge agreed well with the point at which the nitrogen adsorption
capacity of a sulfonated polyoleﬁn separator reached its maximum.
Keywords: Nickel–metal hydride battery; self-discharge; storage characteristics; sulfonated separator;
redox shuttle reaction.
Since nickel–metal hydride (Ni-MH) batteries have a better combination of output
power, capacity, life, reliability and cost, they are employed in almost all com-
mercially available Hybrid Electric Vehicles (HEVs) which are thought to be the
most promising among environmentally-friendly cars [1–6]. Low self-discharge of
Ni-MH batteries is vital for HEVs, since it inﬂuences the start-up of HEVs under
various conditions, especially when HEVs are driven after a long rest. In spite of
many studies on the self-discharge of alkaline storage batteries such as Ni-MH bat-
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