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L. K. Matkovska et al.
promising candidates for replacement of flammable and potentially dangerous liquid
electrolytes [5].
Solid polymer electrolytes (SPE) have been used in different applications as
the ion conductors in various electrochemical devices such as lithium batteries,
ultracapacitors, fuel cells, solar cells, etc. [6]. Rechargeable lithium and lithiumion batteries play an important role on the market of electrochemical energy storage
devices, since they are widely used for charging of portable electronic devices and
for autonomous controlling devices [2]. Therefore, recently the development of
new solid polymer electrolytes was an important objective, since optimal balance
between high ionic conductivity and technological conditions of material has not
been still achieved [7, 8]. SPE have such properties as good compatibility with
electrodes, low self-discharging rate, easy processing for various shapes and sizes,
lack of leakage, flexibility, and self-sufficiency for form changes during chargedischarge cycles [7–10].
Polyethylene oxide (PEO) [11, 12] is one of the mostly studied oligomers, which
are used for SPE creation due to the effective coordinating of metal ions in it because
of the optimum distance and orientation of ether oxygen atoms in its molecular
chains [12]. The disadvantage of PEO is amorphous-crystalline structure [4, 13, 14]
that leads to the conductivity through the amorphous area of a polymer only [11, 15]
above the glass transition temperature T g [6, 12, 16] and, as a result, PEO has low
ionic conductivity at room temperature because of the presence of high crystalline
phase [4, 14, 17].
Nowadays, as a rule, solid polymer electrolytes include inorganic salts dissolving
in oligomers which, in their turn, form a solid matrix with the ionic conductivity
[10, 12, 18, 19]. Added salt serves as a source of ions and contributes their
movement along the polymer chains, so that plays the crucial role in ions transport
in polymer electrolytes [16]. Hereby, concentration and mobility of ions are
significant parameters affecting the conductivity in polymer electrolytes [14, 17].
Understanding of mechanism of the ion transport in a polymer requires the study of
ion-ion and ion-polymer interactions that is of great interest [10, 14]. Many studies
of ion transport in polymer electrolytes have been conducted using various types
of cations such as Na + , Li + , Ag + , and Mg + [20]. However, the composites based
on lithium salts are preferably studied, because the Li + cations are the smallest and
can easily move in a polymer matrix [17, 20, 21]. Another important characteristic
is thermal stability of ions and their inertness to the cell components [22].
In [23] a model of the mechanism of charge transfer that takes into account
the accuracy of ion association in the PEO-salt (PEO-Li + ) system was proposed.
According to this model, the charge transport through the polymer matrix can occur
in four ways:
• The lithium cation motion along the single polymer chain of PEO
• The lithium cation motion from one to another polymer chain
• The lithium cation motion along the polymer chain of PEO between ion clusters
(cation-anion)
• Cation motion between ion clusters and the polymer chain
L. K. Matkovska et al.
promising candidates for replacement of flammable and potentially dangerous liquid
electrolytes [5].
Solid polymer electrolytes (SPE) have been used in different applications as
the ion conductors in various electrochemical devices such as lithium batteries,
ultracapacitors, fuel cells, solar cells, etc. [6]. Rechargeable lithium and lithiumion batteries play an important role on the market of electrochemical energy storage
devices, since they are widely used for charging of portable electronic devices and
for autonomous controlling devices [2]. Therefore, recently the development of
new solid polymer electrolytes was an important objective, since optimal balance
between high ionic conductivity and technological conditions of material has not
been still achieved [7, 8]. SPE have such properties as good compatibility with
electrodes, low self-discharging rate, easy processing for various shapes and sizes,
lack of leakage, flexibility, and self-sufficiency for form changes during chargedischarge cycles [7–10].
Polyethylene oxide (PEO) [11, 12] is one of the mostly studied oligomers, which
are used for SPE creation due to the effective coordinating of metal ions in it because
of the optimum distance and orientation of ether oxygen atoms in its molecular
chains [12]. The disadvantage of PEO is amorphous-crystalline structure [4, 13, 14]
that leads to the conductivity through the amorphous area of a polymer only [11, 15]
above the glass transition temperature T g [6, 12, 16] and, as a result, PEO has low
ionic conductivity at room temperature because of the presence of high crystalline
phase [4, 14, 17].
Nowadays, as a rule, solid polymer electrolytes include inorganic salts dissolving
in oligomers which, in their turn, form a solid matrix with the ionic conductivity
[10, 12, 18, 19]. Added salt serves as a source of ions and contributes their
movement along the polymer chains, so that plays the crucial role in ions transport
in polymer electrolytes [16]. Hereby, concentration and mobility of ions are
significant parameters affecting the conductivity in polymer electrolytes [14, 17].
Understanding of mechanism of the ion transport in a polymer requires the study of
ion-ion and ion-polymer interactions that is of great interest [10, 14]. Many studies
of ion transport in polymer electrolytes have been conducted using various types
of cations such as Na + , Li + , Ag + , and Mg + [20]. However, the composites based
on lithium salts are preferably studied, because the Li + cations are the smallest and
can easily move in a polymer matrix [17, 20, 21]. Another important characteristic
is thermal stability of ions and their inertness to the cell components [22].
In [23] a model of the mechanism of charge transfer that takes into account
the accuracy of ion association in the PEO-salt (PEO-Li + ) system was proposed.
According to this model, the charge transport through the polymer matrix can occur
in four ways:
• The lithium cation motion along the single polymer chain of PEO
• The lithium cation motion from one to another polymer chain
• The lithium cation motion along the polymer chain of PEO between ion clusters
(cation-anion)
• Cation motion between ion clusters and the polymer chain