90
used in lithium ion batteries. To date, H
+
, OH
−
, and Li
+
represent the vast majority
of mobile ions studied in hybrid solid ion conductors, and the majority of this
Chapter will focus on these alongside a brief survey of related Na
+
and Mg
2+
-
conducting materials.
2 Polymer Nanocomposites
The use of polymers allows for robustness, safety, and flexibility, yet the freedom of
ion movement can be limited with micro-aggregation or crystallization, leading to
lower-than-ideal conductivities. It is typically necessary for the polymer phase to be
amorphous in order for ions to move (although a report in 2001 showed ion conductivity in a crystalline polymer) [8]. How can the polymers be manipulated to become
more efficient ion conductors? Also, how can modern electrochemical devices take
advantage of the many attractive properties presented by polymers, but reinforce
them mechanically? The answer may lie in an integrated mixture of organic and
inorganic entities. The flexibility afforded by organic polymers and the strength
provided by the inorganic portions allows for benefits of both. Two broad types of
ion conductors that will be discussed here involve (1) mobility through a nanoscale
polymeric composite that is capable of solvating ions or has been functionalized
with anchored moieties that can do so, and (2) mobility along an ion conductor,
organized in particular geometries with polymeric nanomaterials. Advanced strategies are now being applied to maintain an amorphous composition at a range of
temperatures, hence a high conductivity under technologically useful conditions.
2.1 Organic Polymers/Inorganic Nanoparticles
Organic polymers are popular as they have revolutionized much of the world we live
in today, in part due to their relative ease of processing; they can be molded and set
with ease, and can be very chemically and thermally stable [9]. They may also be
tailored to allow for liquid-like behavior within a solid form as advances in polymer
chemistry allow for control of size, organization, and functionality of these materials. Most neutral polymers are poor ionic conductors on their own (σ i < 10
−5
S cm
−1
)
[10] and need to be infiltrated with ionic compounds or salts. Traditionally, high
dielectric (i.e. non-conducting) polymers, such as poly(ethylene) oxide (PEO), that
can coordinate to and solvate ions have been used. However, in their pure form,
PEO matrices often form ordered domains upon addition of salt, reducing the elastomeric qualities of the media and the ion transport performance. Plasticizers have
been used to address this by increasing the disorder and kinetically preventing crystallization, maintaining an amorphous state in the polymer films. However, softening plasticizers (e.g. small molecules or solvents) may result in a reduction of ion
transport and lead to films that are less robust, while increasing the flammability
C. A. Bauer
used in lithium ion batteries. To date, H
+
, OH
−
, and Li
+
represent the vast majority
of mobile ions studied in hybrid solid ion conductors, and the majority of this
Chapter will focus on these alongside a brief survey of related Na
+
and Mg
2+
-
conducting materials.
2 Polymer Nanocomposites
The use of polymers allows for robustness, safety, and flexibility, yet the freedom of
ion movement can be limited with micro-aggregation or crystallization, leading to
lower-than-ideal conductivities. It is typically necessary for the polymer phase to be
amorphous in order for ions to move (although a report in 2001 showed ion conductivity in a crystalline polymer) [8]. How can the polymers be manipulated to become
more efficient ion conductors? Also, how can modern electrochemical devices take
advantage of the many attractive properties presented by polymers, but reinforce
them mechanically? The answer may lie in an integrated mixture of organic and
inorganic entities. The flexibility afforded by organic polymers and the strength
provided by the inorganic portions allows for benefits of both. Two broad types of
ion conductors that will be discussed here involve (1) mobility through a nanoscale
polymeric composite that is capable of solvating ions or has been functionalized
with anchored moieties that can do so, and (2) mobility along an ion conductor,
organized in particular geometries with polymeric nanomaterials. Advanced strategies are now being applied to maintain an amorphous composition at a range of
temperatures, hence a high conductivity under technologically useful conditions.
2.1 Organic Polymers/Inorganic Nanoparticles
Organic polymers are popular as they have revolutionized much of the world we live
in today, in part due to their relative ease of processing; they can be molded and set
with ease, and can be very chemically and thermally stable [9]. They may also be
tailored to allow for liquid-like behavior within a solid form as advances in polymer
chemistry allow for control of size, organization, and functionality of these materials. Most neutral polymers are poor ionic conductors on their own (σ i < 10
−5
S cm
−1
)
[10] and need to be infiltrated with ionic compounds or salts. Traditionally, high
dielectric (i.e. non-conducting) polymers, such as poly(ethylene) oxide (PEO), that
can coordinate to and solvate ions have been used. However, in their pure form,
PEO matrices often form ordered domains upon addition of salt, reducing the elastomeric qualities of the media and the ion transport performance. Plasticizers have
been used to address this by increasing the disorder and kinetically preventing crystallization, maintaining an amorphous state in the polymer films. However, softening plasticizers (e.g. small molecules or solvents) may result in a reduction of ion
transport and lead to films that are less robust, while increasing the flammability
C. A. Bauer