Effects of carbon fiber electrode deformation in multifunctional structural lithium ion batteries

Experimentally achieved values of electrochemical cell capacities have been much lower than those theoretically reported, in large part due to a large fraction of inactive materials in the battery cell. One possible way to address this outcome is to repurpose this parasitic mass for another required function of a device in which the electrochemical cell is used to provide energy storage. In this study, we demonstrated a carbon fiber/lithium battery to realize carbon fiber’s mechanical and electrochemical capability in a structural battery system. Coupled mechanical–electrochemical experiments were performed, and we found that the load a carbon fiber battery bore during electrochemical cycling strongly depended on the number of lithium ions intercalated into graphite. We also observed that carbon fibers were reversibly elongated and contracted up to 0.5% in the fiber direction during battery cycling without external loadings. Also, we measured lithium ion diffusivity in carbon fibers to test whether microstructure changes due to external mechanical stresses can alter the diffusion path, resulting in diffusivity changes, and identified no statistically meaningful effect of carbon fiber deformation on battery power performance (diffusion coefficient).