113
(Viton) and TiO 2 nanoparticles was formed into a lotus root-like porous structure,
which resulted in high ionic conductivities of up to 1.21 × 10
−3
S cm
−1
at room temperature, with high electrochemical stability potential of 5.52 V (vs. Li/Li+), and a
lithium ion transference number of 0.65 [100]. Carbon nanotubes have also been
used for their tensile strength and high aspect ratios, as discussed previously. As
they are not electrically insulating, they were packaged within insulating clay layers
to form effective 3D nanofillers, increasing the lithium ion conductivity of a PEO
electrolyte by almost two orders of magnitude, while improving the mechanical
properties significantly, even with a very modest 5 wt % loading [101].
Other Ions
Lithium is of limited availability, and the global distribution of lithium is un-even,
appearing in the highest amounts in South America. Sodium ions are considered a
cost-effective alternative as there are no imminent shortages of it [102]. Sodiumbased batteries may be thought of as complementary to lithium ion batteries, rather
than competitive with them as the specific energy is lower than that of lithium ion
batteries, limiting the number of applications. However, in stationary settings, such
as power back-ups in factories or power plants where this is less of an issue, they
could provide a significant, cost-effective alternative. The insertion chemistry of
sodium is similar to lithium, but the electrodes need to be optimized and new electrolytes must be found. To date, only a few solid-state electrolytes have been
reported. In 2010, Kumar and Hashmi reported on a novel sodium ion conducting,
gel polymer electrolyte nanocomposites based on poly (methyl methacrylate)
(PMMA) with dispersed silica nanoparticles at ~4 wt. % [103]. The authors report
that these gel electrolytes have a maximum conductivity of ~3.4 × 10
−3
S cm
−1
at
20 °C, while providing both the expected mechanical improvements, and thermal
and electrochemical stability. Similar to PEO-LiX, a PEO-NaPO 3 has been
described, and subsequently loaded with ceramic BaTiO 3 nanofillers, exhibiting a
two-order of magnitude enhancement vs. the nanofiller-free film, reaching a maximum ionic conductivity of 1.2 × 10
−6
S cm
−1
at 345 K with a cationic transport
number of 0.33 [104].
Most recently, magnesium ion batteries are gaining attention in the secondary
battery arena. With the relatively high abundance of magnesium vs. lithium, the
high energy density of magnesium, and the comparable size of the two ions, magnesium batteries would be highly valued. Additionally, magnesium metal is less
reactive than lithium in a battery. The major obstacle as of now is in developing a
suitable magnesium ion conducting electrolyte. All liquid electrolytes haven proven
too corrosive to the electrodes, and focus has gone directly to the stage of developing solid-state electrolytes. The latest successes have mostly been with all-inorganic
frameworks, such as magnesium scandium selenide spinel structures [91]. However,
reports that utilize similar recipes to the PEO-LiX systems discussed above by
incorporating ceramic nanoparticles are in the literature. For example, in 2017, a
composite polymer electrolyte was reported [105]. The authors demonstrated that a
Polymer Nanocomposites for Ion Transport
(Viton) and TiO 2 nanoparticles was formed into a lotus root-like porous structure,
which resulted in high ionic conductivities of up to 1.21 × 10
−3
S cm
−1
at room temperature, with high electrochemical stability potential of 5.52 V (vs. Li/Li+), and a
lithium ion transference number of 0.65 [100]. Carbon nanotubes have also been
used for their tensile strength and high aspect ratios, as discussed previously. As
they are not electrically insulating, they were packaged within insulating clay layers
to form effective 3D nanofillers, increasing the lithium ion conductivity of a PEO
electrolyte by almost two orders of magnitude, while improving the mechanical
properties significantly, even with a very modest 5 wt % loading [101].
Other Ions
Lithium is of limited availability, and the global distribution of lithium is un-even,
appearing in the highest amounts in South America. Sodium ions are considered a
cost-effective alternative as there are no imminent shortages of it [102]. Sodiumbased batteries may be thought of as complementary to lithium ion batteries, rather
than competitive with them as the specific energy is lower than that of lithium ion
batteries, limiting the number of applications. However, in stationary settings, such
as power back-ups in factories or power plants where this is less of an issue, they
could provide a significant, cost-effective alternative. The insertion chemistry of
sodium is similar to lithium, but the electrodes need to be optimized and new electrolytes must be found. To date, only a few solid-state electrolytes have been
reported. In 2010, Kumar and Hashmi reported on a novel sodium ion conducting,
gel polymer electrolyte nanocomposites based on poly (methyl methacrylate)
(PMMA) with dispersed silica nanoparticles at ~4 wt. % [103]. The authors report
that these gel electrolytes have a maximum conductivity of ~3.4 × 10
−3
S cm
−1
at
20 °C, while providing both the expected mechanical improvements, and thermal
and electrochemical stability. Similar to PEO-LiX, a PEO-NaPO 3 has been
described, and subsequently loaded with ceramic BaTiO 3 nanofillers, exhibiting a
two-order of magnitude enhancement vs. the nanofiller-free film, reaching a maximum ionic conductivity of 1.2 × 10
−6
S cm
−1
at 345 K with a cationic transport
number of 0.33 [104].
Most recently, magnesium ion batteries are gaining attention in the secondary
battery arena. With the relatively high abundance of magnesium vs. lithium, the
high energy density of magnesium, and the comparable size of the two ions, magnesium batteries would be highly valued. Additionally, magnesium metal is less
reactive than lithium in a battery. The major obstacle as of now is in developing a
suitable magnesium ion conducting electrolyte. All liquid electrolytes haven proven
too corrosive to the electrodes, and focus has gone directly to the stage of developing solid-state electrolytes. The latest successes have mostly been with all-inorganic
frameworks, such as magnesium scandium selenide spinel structures [91]. However,
reports that utilize similar recipes to the PEO-LiX systems discussed above by
incorporating ceramic nanoparticles are in the literature. For example, in 2017, a
composite polymer electrolyte was reported [105]. The authors demonstrated that a
Polymer Nanocomposites for Ion Transport