Effect of pore structures on desolvation of carbon materials as the electrode materials of supercapacitors: A first-principles study

Abstract More and more attention has been paid to the role of the desolvation effect of ions in the electrolyte for supercapacitor in improving its capacitance. We have previously calculated that the complete desolvation size of Li+, Na+, and K+ in the basal plane pore (BPP) is 4.7 A, 4.4 A, and 4.4 A, but the desolvation of the edge plane pore (EPP) is not considered. So in this work, the complete desolvation behaviour of Li+, Na+, and K+ at the EPP in the pore structure of porous carbon materials in the aqueous solution is studied by first-principles calculations. The calculation results show that the solvated Li+ can be completely desolvated when the pore size of EPP is less than 3.61 A, while the solvated Na+ and K+ will not be desolvated under any pore size of EPP. Combining the work of this paper with our previous work, solvated Li+ has desolvation behaviour in both EPP and basal plane pore (BPP). Four models of pores are constructed by the combination of EPP and BPP to discuss the storage of desolvated Li+ in porous carbon materials. The calculation results show that the necking flask like EPP-BPP pore with ∼ 3.61 A outer pore and ∼ 7.4 A inner pore can accommodate more Li+ improving the capacitance of the supercapacitors. The desolvation mechanism of EPP and BPP on the solvated ions has important theoretical guiding significance for designing the pore structure of porous carbon materials.