Nauka /Interperiodica

particles, of a large
number of cracks and pores that hindered the free solid-
phase diffusion of lithium ions in the electrode mate-
rial. The increase in the thickness of the passive film at
the surface of the negative carbon electrode as a result
of the electrolyte electroreduction also plays a substan-
tial role in the capacity decrease.
Abraham 
 
et al.
[25] investigated the reasons for the
worsening of characteristics of LIB the size 18650 with
positive electrodes based on LiNi
0.8
Co
0.2
O
2
and nega-
tive electrodes of a mixture of graphite and mesocarbon
microbeads. For the electrolyte they used 1 M LiPF
6
in
a mixture of ethylene carbonate (EC) and diethyl car-
bonate (DEC). The research methods included such
physicochemical methods as gas and liquid chromatog-
raphy, electron microscopy, x-ray photoelectron spec-
troscopy, and impedance. Having compared the results
of a comprehensive analysis of electrodes of freshly
assembled LIB and electrodes extracted out of LIB that
had been stored at a certain voltage (from 3.60 to 3.92 V)
at elevated (
40–70°ë
) temperatures, the authors of [25]
came to the conclusion that the increase in the imped-
ance of LIB is caused mainly by processes on the posi-
tive electrode. The increase in the impedance, which is
controlled by the transport of lithium ions and the
charge transfer at the electrolyte/positive electrode
interface, is accompanied by a change in the surface
film on the electrode and the crystalline structure of the
surface of particles of LiNi
0.8
Co
0.2
O
2
. The negative
electrode also can contribute to the capacity decrease:
the solid-electrolyte film on the surface of this electrode
can undergo destruction and restructuring during high-
temperature storage. The separator and the current
leads, in turn, affect but insignificantly the impedance
of LIB, especially below 
50°ë
.
Amine 
 
et al.
[16] investigated the reasons for the
worsening of electrochemical characteristics of similar
LIB as a result of storage at elevated temperatures.

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4
RUSSIAN JOURNAL OF ELECTROCHEMISTRY
Vol. 41
No. 1
2005
KANEVSKII, DUBASOVA
They stored the batteries at 40, 50, 60, and 
70°ë
and
then discharged them at room temperature and deter-
mined the impedance of the discharged electrodes.
They established that the discharge energy density of
LIB steadily decreases after storage, while the imped-
ance of LIB as steadily increases with increasing tem-
perature. The major increase in the impedance is caused
by the increase in the resistance to the charge transfer
on the positive electrode. To stabilize the characteristics
of LIB, it is necessary to eliminate reactions between
the positive electrode and a nonaqueous solvent [16].
The authors of [49] measured the impedance of
commercial prismatic LIB of a capacity of 650 mA h at
different depths of discharge, as well as before and after
the cycling and after storage at 
50°ë
. Based on an anal-
ysis of the impedance spectra and charge–discharge
characteristics of LIB, they established that the capac-
ity drop was simbatical to an increase in the interfacial
resistance at the positive electrode and to a decrease in
the specific capacity of the negative electrode. The dis-
charge and storage at an elevated temperature lead to an
increase in the interfacial resistance on the positive
electrode.
Below we will consider some specific features of
exploitation of LIB and the changes in them observed
during investigations, which may lead to their instabil-
ity and the worsening of exploitation characteristics
(drop of the discharge voltage, decrease in the dis-
charge capacity, and, as a result, the lowering of the
cycle life of LIB).
THE SELF-DISCHARGE 
OF LIB DURING STORAGE
The self-discharge of LIB, as that of batteries of
other types, is divided into reversible and irreversible.
Naturally, the parameter most important for the charac-
terization of stability of rechargeable power sources is
the irreversible self-discharge, at which it is no longer
possible to restore the initial capacity of the battery.
The authors of [63] reported on the self-discharge of
LIB the size 18650 (Sony) and 17500 (Matsushita) with
positive electrodes based on Li