In today’s energy
climate, developing alternatives to gasoline for the transportation industry is
critical. The batteries in today's fully electric and hybrid electric vehicles
(Li ion battery) led to fires in computers and airplanes. Substitution of liquid electrolytes
with polymer electrolytes can open the door to safer batteries that can get
more miles (500 compared to 100) per charge. In order for this to occur, the speed with
which Li ions move needs to increase by a factor of 100. This is a large increase, and can only be
realized by completely changing the way in which these ions move. Currently,
ions move through the polymer electrolyte by leaping from one polymer
configuration to another, a method in which Li motion is coupled to polymer
motion. This project goal is to design an electrolyte in which ions form a
large network capable of conduction without the need for the polymer movement. Focus will be on
Na ion batteries, rather than Li ion batteries, because Na is cheaper and more
abundant than Li, as Li reserves are primarily located in South American.
Three systems will be investigated: one in which the negatively charged ions are on the polymer
backbone, one with linker ions to promote network formation,
and one in which the negatively charged ions are on one polymer and the
positively charged ions are on another polymer.
It is recognized that simply increasing
the ion content in ionomers does not provide a great amount of control over shape
of the aggregates. Physical models of ion aggregates derived from our previous
simulations suggest that ion aggregate sizes will be exponentially distributed
in simple ionomer systems. In the first, we have prior data in which ions form linear
chains, but not a network. Simply increasing ion content may be sufficient to
form a conducting ion network. In the
second, we can use terminating ions and linking ions to control the
characteristics of the network. The third system may allow to probe ion
contents greater than those allowed by the other two systems. We will apply our expertise in neutron
scattering techniques, dielectric spectroscopy, and molecular dynamics
simulations in order to provide a complete picture of the dual benefits of
ionic aggregation. Observables from experimental techniques will be
used to calibrate simulations, which then provide the detailed mechanistic
information to improve future generations of these materials. At the conclusion
of the project, we will demonstrate that a new variable for promoting conductivity - collective motion - that can be tuned through precisely tuned ion aggregation. We
will show how ion aggregation can be controlled through ion content and ion
identity. We will also introduce a new experimental system, PEO-swollen mixed polycation-polyanion
electrolytes, which will primarily conduct through ion aggregates.
