Supercapacitors store energy within the electric double layer (EDL) by arranging ions at an electrode-electrolyte interface in response to an applied potential. Among candidate electrode materials, graphene-based supercapacitors are of great interest thanks to their high specific surface area, high conductivity, and relative chemical and electrochemical stability. However, devices based on graphene electrodes also suffer from fundamental charge storage limitations that are connected to the unique electronic structure of graphene. Using ab initio simulations within the effective screening medium (ESM) formalism, we have explored charge storage in pristine and defective graphene to understand the detailed origins of these limitations. In this talk, I will demonstrate ways in which the proper description of the capacitance of graphene-based devices depends not only on the properties of the electrode and electrolyte individually, but also on the nature of their interaction at the charged electrode-electrolyte interface. The resulting changes are difficult to capture using simple models, yet affect performance of graphene-based supercapacitors in often fundamental and nontrivial ways that merit consideration. I will also show how combining first-principles computation with in operando X-ray absorption spectroscopy can give insights into nanoscale chemical changes and mesoscale morphological changes occurring in 3D graphene supercapacitor electrodes during charging. Finally, general strategies for using the fundamental understanding to improve graphene-based supercapacitors will be discussed, based on modifying properties of both the solid electrode and liquid electrolyte.

Ab initio simulations of charged interface effects in graphene-based supercapacitors

251st National Meeting (2016)

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