NSF REU Site Renewal: Interfaces and Surfaces
Summer 2015
Faculty Advisor Project Submission
Engineering Thermal Control in Batteries using Adaptive Electrode Interfaces
Faculty Advisor: Prof. Mark Roberts (Department of Chemical & Biomolecular Engineering)
Research Project: Lithium-ion batteries have seen considerable growth in recent years due to
their high energy (150-250 W·hr/kg) and power densities (300 to 1500 W/kg). However, Li-ion
batteries are notorious for serious safety issues related to thermally runaway, and these hazards
are exacerbated in large format systems necessary for application in transportation and
renewable energy generation.[1] Current approaches to alleviating the thermal hazards involve
utilizing gel or solid state electrolytes, which greatly diminishes device performance, or using
separators that melt and prevent ion flow at high temperatures. Even in these systems, the
potential for thermal failure exists. In the proposed research, we seek to investigate responsive
polymer interfaces that can be incorporated in current Li-ion battery technology.
Our group has recently developed thermally-responsive polymer electrolytes in aqueous
systems that enable control of solution conductivity, pH and redox activity with temperature.[2]
While the current system is attractive for manipulating solution properties for a variety of
electrochemical applications, it is not suitable for most Li-ion batteries. The proposed research
will build upon our knowledge of responsive electrolytes to investigate similar approaches for
thermal control in non-aqueous electrolyte systems. Numerous literature reports have already
demonstrated the feasibility of manipulating polymer phase behavior in non-aqueous solutions
using temperature. Copolymers containing benzyl methacrylates dissolved in ionic liquids
undergo a thermal transition above 100C causing the polymer to collapse and phase separate
from solution.[3] The focus of the proposed research is to investigate methods for modifying Li
battery anode and cathode materials using surface-graphed polymers that can phase separate
from solution at high temperatures to create ion-resistive layers that prevent further lithium
reaction, overheating and thermal runaway. Grafted polymer films will be designed to allow ion
transport to the electrode at low temperatures, and then impede ion conduction when polymer
film collapses due to electrode heating beyond a target threshold. Our approach circumvents the
current thermal safety approaches that require either low-performance devices or irreversible
destruction of the battery.
Research Expectations for REU Participant: Proposed research activities consist of polymer
synthesis, surface grafting, and film characterization, thermal analysis and electrochemical
characterization. Initially, copolymers containing the thermally-active polymer, PNIPAm, will be
grafted from graphitic carbon surfaces to determine how the structure and composition of
polymer film affect the electrochemical activity of modified electrodes at various temperatures.
Copolymers containing benzylmethacrylate with Li-ion conducting groups will be synthesized
and evaluated for their thermal response in ionic liquids and polymer aprotic solvents. Select
polymer systems will then be grafted to carbon electrodes using atomic-transfer radical
polymerization methods. These modified electrodes will be evaluated for their electrochemical
activity in lithium salt solutions over a range of temperatures. Specifically, we seek to understand
how the length, density and composition of grafted polymer layers affect the extent to which the
electrochemical properties and ion conductivity can be controlled with temperature in aqueous
solutions, ionic liquids, and polar aprotic solvents.
NSF REU Site Renewal: Interfaces and Surfaces
Summer 2015
Faculty Advisor Project Submission
Figure 1. (A) Surface grafting approach to carbon surfaces using atom-transfer radical
polymerization. (B) Thermal response of poly(benzylmethacrylate) polymers in ionic liquids.[3]
[1]
[2]
[3]
Biensan, P. et al., J. Power Sources 81-82, 906-912 (1999).
J.C. Kelly, M. Pepin, D.L. Huber, B.C. Bunker, M.E. Roberts, Adv. Mater., 2012, 24, 886.
T. Ueki, M. Watanabe, Langmuir, 2007, 23, 988–990.