This CAREER award supports theoretical and computational research, software development, and education efforts on ion-containing polymeric materials. This family of materials has demonstrated great promise for use as a separation component in batteries that power light-weight electronic devices such as cell phones. Energy storage and release in batteries relies on the directed shuttling of positively charged chemical species inside a separation medium or electrolyte. The conventional electrolyte is normally a liquid which conducts ions efficiently. Often the liquid can be too chemically reactive, leading to safety concerns. Polymers are promising replacements. Polymers are large, chain-like molecules from which, for example, plastic bags, fibers, and tires are made. They can be engineered to behave as solids at room temperature and show modest chemical reactivity. In this project, the PI aims to develop theoretical and computational tools to understand the physical and chemical properties of these kind of materials. The PI plans to develop theoretical concepts and computer simulation algorithms to address the critical material science problems underlying the design of polymer electrolytes. At the heart of this problem is an intimate connection among the structure or the architecture of the material at the atomic scale, the morphology or the form of the material, and functionality or how the components interact with each other. To understand the multitude of possible properties, theoretical approaches and computational algorithms will be developed to enable simulation of candidate polymer electrolyte materials across length scales. These efforts will be backed by extensive experimental collaborations, which will provide the fundamental understanding necessary to advance the rational design of these polymeric materials. The broader impacts of the research include training high school students through the Raising Interest in Science and Engineering program of Stanford University. The students will participate in the design of novel simulation algorithms and in the creation of a database of materials properties that will be accessible to the broader scientific community to aid in the design of materials. The PI will work to broaden the diversity of the scientific community by educating leading theoretical researchers to solve tackle challenging questions crucial to quantitative material design. These efforts will be integrated through interaction with a local community college. The developed software package facilitating the experimental screening will be shared with the public.
This award supports a theoretical and computational study and education focused on dielectric properties of ion-containing block copolymers, a particularly promising candidate for use in electrolyte membranes in lithium-ion batteries. The ability of block copolymers to self-assemble into spatially heterogeneous morphologies provides a unique opportunity for engineering the mechanical properties and ion-conductivity simultaneously inside the same material. At the same time, it poses fundamental challenges on studying the electrostatic interaction in structured electrolytes with a low average dielectric permittivity. Low permittivity implies strong correlation inside the materials, and structured electrolytes demand expensive calculations to resolve the electrostatic potential from Poisson's equation.
Four interrelated research objectives are identified that address different aspects of dielectric screening in structured block copolymers with comparatively low permittivity. The first objective develops field theory for heterogeneous polymer electrolytes and a symmetry-adapted software package, based on ionic polymer self-consistent field theory. The second objective identifies the distinct phase behaviors governed by the competing effects of entropy and electrostatic interaction and enables the development of analytical theory near critical points. The third objective examines how strong ionic correlation impacts the miscibility of polymer blends by combining experiments with modeling to generalize the Debye-Huckel theory. The fourth objective aims to extract mesoscale solvation and screening parameters from atomistic simulations, which will reveal the microscopic dielectric screening mechanism in these materials and provide the foundation for continuum field theory. These four objectives, which span theory, simulation, and experiments, are expected to provide a coherent picture of ionic interactions in structured polymer electrolytes. This research represents a fundamental multi-scale study of the electrostatic interactions between ionic species in structured polymer electrolytes. Developing field theories enables efficient screening of the parameter space. Performing atomistic simulations enables the estimation of phenomenological parameters used in field theory, and thus allows assumptions to be tested. Combining these two approaches presents an opportunity to elucidate the fundamental physics which dictate non-local and nonlinear electrostatic interactions in dielectrically heterogeneous media. This serves as a stepping stone for designing coarse-grained simulations to investigate the dynamics and effects of composition fluctuations. The developed methodology will prove useful for the study of other electrostatics-driven self-assembly phenomena at the molecular level.
The broader impacts of the research include training high school students through the Raising Interest in Science and Engineering program of Stanford University. The students will participate in the design of novel simulation algorithms and in the creation of a database of materials properties that will be accessible to the broader scientific community to aid in the design of materials. The PI will work to broaden the diversity of the scientific community by educating leading theoretical researchers to tackle and solve challenging questions crucial to quantitative material design. These efforts will be integrated through interaction with a local community college. The developed software package facilitating the experimental screening will be shared with the public.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
