Date of Award

8-2016

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Chemical Engineering

Major Professor

David J. Keffer

Committee Members

Orlando Rios, Steven Abel, Kenneth Read

Abstract

In today’s world, the demand for novel methods of energy storage is increasing rapidly, particularly with the rise of portable electronic devices, electric vehicles, and the personal consumption and storage of solar energy. While other technologies have arguably improved at a rate that is exponential in accordance with Moore’s law, battery technology has lagged behind largely due to the difficulty in devising new electric storage systems that are simultaneously high performing, inexpensive, and safe.

In order to tackle these challenges, novel Li-ion battery anodes have been developed at Oak Ridge National Laboratory that are made from lignin, a low-cost, renewable resource that is obtained from an abundant supply of biomass. The anodes that result from the lignin manufacturing process exhibit performance comparable to that of conventional graphitic anodes for a fraction of the cost. However, these materials are unusual in that they consist solely of a mixture of amorphous and crystalline carbon, and this complex, hierarchical material is not well understood. This thesis reveals the mechanism behind the structural composition and the performance of these carbon composite anodes.

The anodes are investigated using two distinct approaches: 1) a computational approach, whereby atomistic models of the composite systems are created and simulated using reactive molecular dynamics, and 2) an experimental approach, whereby the small scale structure of the material is elucidated using neutron diffraction.

The computational approach reveals deep insight into the nature of Li-ion localization, and a novel technique (that is highly generalizable) has been developed to understand the local atomic environment that surrounds Li-ions at various binding energies. The experimental approach is used in conjunction with the simulation results to understand the structure of the carbon composites, and how unique structural properties vary as a function of the parameters that are controlled in the manufacturing process. This insight leads to the revelation that a large interfacial surface area between amorphous and crystalline carbon domains is paramount for high-capacity storage of Li-ions.

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