Electrochemical conversion from hydroxyl to carbonyl groups for improved performance of dual-carbon lithium ion capacitors
ENERGY STORAGE MATERIALS(2024)
摘要
Pseudocapacitance from oxygen functional groups of carbon materials have been taken advantage to improve the capacity of lithium ion capacitors (LICs). However, the Li+ adsorption of hydroxyl groups and the Li+ desorption from lithiated hydroxyl groups remain poorly understood. Herein, density functional theory (DFT) calculations in combination with experimental characterizations of hydroxyl-rich graphene (HRG) cathodes at different lithiated states are performed. The calculation results predict that fully lithiated hydroxyl groups undergo Li+ desorption at a high potential of 4.45 V (vs. Li+/Li), and consequent conversion into carbonyl groups instead of return to hydroxyl groups. Experimental investigations through galvanostatic charge/discharge tests and ex -situ X-ray photoelectron spectra (XPS) analyses of HRG verify the predicted Li+ desorption potential and the conversion. This electrochemical conversion is effective to obtain carbonyl-rich graphene (CRG) with significantly improved specific capacities. The conversion process can be completed in LIC full cells assembled with pre-lithiated HRG cathodes, through which an HRG//N-doped porous carbon (NPC) LIC transforms into a CRG//NPC LIC with improved performance. The dual-carbon CRG//NPC LIC delivers an energy density of 206.2 Wh kg- 1 at a power density of 169.5 W kg- 1, and superior cycling stability.
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关键词
Hydroxyl groups,Oxygen functional groups,Graphene,Cathode,Lithium ion capacitors,Electrochemical conversion
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