Optimizing the Performance of a Graphitized Carbon Xerogel as Cathode for Sodium Dual‐Ion Batteries

Abstract

The objective of this study is to optimize the performance of a graphitized carbon xerogel doped with graphene oxide (GXGO) as cathode for sodium dual-ion batteries. Carbon xerogels are synthetic materials produced in large amounts, with wellcontrolled chemistry, porosity and structure, by a simple and fast microwave process that has been scaled-up. The intercalation of PF 6 À anions from various NaPF 6 salt-based electrolytes in a GXGO-based cathode is investigated by considering the influence of the upper cut-off voltage (UCOV) and of the electrolyte on the electrochemical parameters. The best results were attained in an electrolyte with a 2.0 M NaPF 6 concentration in EC : EMC carbonate solvent mixture with added FEC, at a UCOV of 5.0 V. GXGO cathode provides a discharge capacity of 47 mAh g À 1 after 2500 cycles with a coulombic efficiency of 97 %. Moreover, it shows great cycling stability and capacity retention of essentially 100 % after the initial cycles.

Analysis of PF6− Anion Intercalation/De‐Intercalation Mechanisms in Graphite Cathodes of Sodium Dual‐Ion Batteries

“…This staged mechanism has been reported in previous works for the intercalation of these anions in graphite and/or graphitic materials from sodium salts in different organic carbonate mixtures. [6,10,23,35] As mentioned in the introduction, through the qualitative analysis of these cyclic voltammetries (CVs), i. e., calculating the b value, the evolution during cycling of diffusion-controlled and pseudo-capacitive intercalation/de-intercalation contributions to the total measured current can be determined. Thus, b parameter values of all anodic and cathodic peaks of the voltammograms for cycles 20, 50, 100, 200 and 300 were determined by plotting the corresponding log i versus log ν at the different scan rates studied from the CVs in Figure 1.…”

“…Regarding to Na-DIBs electrode materials, oil-derived synthetic graphite, [3,9,10,15] and other carbon materials [16][17][18][19][20][21][22][23] such as biogas-derived nanofibers, [16] amorphous mesoporous carbon, [17] expanded graphite [18] and graphitized carbon xerogel [23] have recently investigated as cathodes for the intercalation of several anions, i. e., BF 4 À , ClO 4 À and mainly PF 6 À , from the corresponding sodium salt dissolved in mixtures of organic carbonates, such as ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC). Among them, graphite cathode and PF 6 À anion clearly outperformed the others.…”

Superfast Synthesis of Carbon Xerogels

“…Due to their unique properties, CAs and CXs have obtained great attention in numerous fields that are decisive for the ecological transformation of the global economy. Their potential use was studied for electrochemical applications in fuel cells, , supercapacitors − or batteries, − and for thermal insulation materials, as catalyst supports, , and as highly efficient adsorbents . The high interest in these materials lies in the option to tune the material properties of meso- and microporous carbon for individual applications.…”

“…An alternative to them is CXs, where the RF gel is dried thermally. − Even though the porous structure of the gels deteriorates, CXs still possess extraordinary porous properties. They are thus promising candidates for a large number of applications . The reduction of pore sizes and porosity upon drying can be counterbalanced by the adjustment of synthesis parameters or by using additives. , Therefore, CXs present a greater potential for commercial applications than their CA counterparts.…”

“…They are thus promising candidates for a large number of applications. 9 The reduction of pore sizes and porosity upon drying can be counterbalanced by the adjustment of synthesis parameters or by using additives. 20,21 Therefore, CXs present a greater potential for commercial applications than their CA counterparts.…”