LiFePO4/Mesoporous Carbon Hybrid Supercapacitor Based on LiTFSI/Imidazolium Ionic Liquid Electrolyte

This document is the Accepted Manuscript version of a Published Work that appeared in final form inJournal of Physical Chemistry C , copyright © American Chemical Society after peer review. To access the final edited and published work see https://doi.org/10.1021/acs.jpcc.7b09869A hybrid SC prepared with mesoporous carbon as the negative electrode, LiFePO4 as the positive electrode, and a LiTFSI/imidazolium ionic liquid solution as electrolyte is presented. The cell was conceived on the basis that it offers all of the safety features of ionic liquids (IL) and LiFePO4, in addition to the advantages of a high energy density device. Most of the high performance hybrids so far reported in the literature employ aqueous or organic electrolytes, whereas studies of hybrid cells based on IL are still rare. Here, a fundamental study was conducted to understand how the different interfaces and mechanisms operate in a hybrid system based on IL electrolyte and how this affects cell performance. This device was mainly characterized using cyclic chronopotentiometry that allows cell voltage and electrode potentials to be simultaneously recorded. By means of this technique, it was possible to evaluate the overall behavior of the hybrid cell and the faradaic and capacitive electrodes simultaneously and to compare it with the performance of selected standard cells. The results show that the cell is able to attain an energy density of 43.3 W h kg–1 at 0.010 A g–1 (C/5 in relation to LiFePO4), while maintaining a good cycling performance.The authors would like to thank the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) – Brazil for the financial support (PVE 2014, process number 400714/2014-0). Financial support from Ministerio de Economía, Industria y Competitividad (project MAT2016-77114-R) and Principado de Asturias (Fondo Europeo de Desarrollo Regional (GRUPIN 14-118).Peer reviewe