Summary:Lithium-ion (Li-ion) battery technology is of particular interest due to its high energy and power characteristics that are adaptable to meet the needs of existing and emerging applications ranging from electronics to transportation to electrical grid stability. High capacity bulk materials (silicon, germanium), explored to advance beyond the current industry standard (graphite) anode, pose a critical challenge to long battery lifetimes due to large volume changes of the host material as a result of Li insertion/extraction. Without sufficient mechanical robustness of silicon- or germanium- based anodes and without free space available in the electrode for volume expansion, the significant stresses generated during cell operation commonly lead to rapid capacity losses and mechanical degradation of the anode.

Anodes comprised of nanomaterials have been investigated as alternatives to bulk materials since their constrained dimensions may provide increased electrochemical activity and improved mechanical stability.  Several types of nanocomposites materials were found to offer good electrochemical performance but the lack of fundamental understanding of structure-property relationship in these composites limit further developments of high capacity anode technology.

The proposed research considers two anode architectures which can be generally described as a carbon substrate (graphene or vertically aligned carbon nanotubes) coated with combinations of Li ion reactive layers (silicon, germanium, carbon). The anodes are similar in composition but differ in microstructure. These differences allow for further examination of the relationship between material structure, material properties, and anode performance.  This research has already demonstrated that highly structured and tunable composite anodes can be created through vapor deposition techniques with stable performance and specific capacity beyond state-of-the art graphite achieved. Further investigation of the mechanisms that may lead to degradation of these systems are currently being explored to further enhance the anode stability.