Abstract
Graphene electrodes are investigated for electrochemical double layer capacitors (EDLCs) with lithium ion electrolyte, the focus being the effect of the pore size distribution (PSD) of electrode with respect to the solvated and desolvated electrolyte ions. Two graphene electrode coatings are examined: a low specific surface area (SSA) xGNP-750 coating and a high SSA coating based on a-MWGO (activated microwave expanded graphene oxide). The study comprises an experimental and a computer modeling part. The experimental part includes fabrication, material characterization and electrochemical testing of an EDLC with xGNP-750 coating electrodes and electrolyte 1M LiPF6 in EC:DMC. The computational part includes simulations of the galvanostatic charge-discharge of each EDLC type, based on a continuum ion transport model taking into account the PSD of electrodes, as well as molecular modeling to determine the parameters of the solvated and desolvated electrolyte ions and their adsorption energies with each type of electrode pore surface material. Predictions, in agreement with the experimental data, yield a specific electrode capacitance of 110 F g−1 for xGNP-750 coating electrodes in electrolyte 1M LiPF6 in EC:DMC, which is three times higher than that of the high SSA a-MWGO coating electrodes in the same lithium ion electrolyte.
Highlights
Electrochemical double layer capacitors (EDLCs) are energy storage devices of high power density, high efficiency and long life time while they may utilize low cost materials [1] but are generally of lower energy density than batteries
Materials of large specific surface area have been favored as electrodes in EDLCs, as it has been thought that they would store a large amount of charge in the form of a monolayer of ions assumed to line their surface according to the Stern layer hypothesis [9,10]
The present study investigates graphene-based electrodes for EDLCs with lithium ion electrolyte with the aim to evaluate the effect of pore size distribution (PSD) of the electrode material on the performance of the EDLC
Summary
Electrochemical double layer capacitors (EDLCs) are energy storage devices of high power density, high efficiency and long life time while they may utilize low cost materials [1] but are generally of lower energy density than batteries. The present study investigates graphene-based electrodes for EDLCs with lithium ion electrolyte with the aim to evaluate the effect of pore size distribution (PSD) of the electrode material on the performance of the EDLC. Computational simulations using the continuum ion transport model [35] applied to a pore size distribution are carried out for the galvanostatic chargedischarge of this EDLC as well as an EDLC with a-MWGO (activated MWGO) coating electrodes of high surface area a-MWGO powder of SSABET,powder = 3100 m2 g−1 [41], with either organic electrolyte 1M TEABF4 in ACN, to compare predictions with experimental data [41], or lithium ion electrolyte. The comparison of the simulation predictions between the two graphene-based electrodes of significantly different SSA (specific surface area) values and PSDs offers an insight into the recommended trends in the design of graphene electrodes in EDLCs with lithium ion electrolyte
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