(640c) Lignin Carbon Composites As Renewable Components in Electrochemical Devices: Synthesis, Characterization & Modeling

Lignin is a low-cost, renewable resource that, under controlled processing conditions, can be converted into a nanostructured carbon composite with crystalline and amorphous domains. Features of the nanostructure, including the size of the graphitic nanocrystallites and the volume fraction of the crystalline domain, can be tailored through the choice of processing temperature and lignin feedstock. A collaborative experimental and computational research effort has investigated the processing-structure-property-performance relationship for these materials and their application as anodes in lithium-ion batteries. The atomic structure has been investigated using synchrotron x-ray and neutron scattering, complemented by electron microscopy. Interpretation of the scattering patterns has been accomplished via atomistic Molecular Dynamics (MD) simulation and Hierarchical Decomposition of the Radial Distribution Function (HDRDF). The HDRDF approach decomposes the total RDF into a set of atomistic and mesoscale components, which can be rapidly parameterized in terms of structural descriptors including nanocrystallite size and shape, crystalline volume fraction and total density. MD simulations of lithiated and sodiated systems reveal distinct binding mechanisms and explain variations in charging capacity of composites as a function of processing temperature. Electrochemical performance is measured via evaluation of coin cells under a range of operating conditions. The observation that lignin carbon composites demonstrate storage capacities in excess of the theoretical capacity of graphite anodes is explained in terms of a different binding mechanism in these carbon composites.