Stabilization and Improvement of Energy Storage Performance of High Mass Loading Cobalt Hydroxide Electrode by Surface Functionalization

Abstract

Nano oxides and hydroxides generate great interest as promising positive electrode materials for the development of high energy density supercapacitors. However, their usually limited ionic and electronic conductivities significantly decrease their energy storage performances when increasing the electrode's mass loading. Here, we report on a sonochemical approach to functionalize the surface of Co(OH)2 nanomaterials by EmimBF4 ionic liquid that greatly improves the stability and the electrochemical performances of high mass loading electrodes (13 mg/cm²). This surface functionalization boosts the transport properties and strongly enhances the capacity as well as the capacity retention at higher current densities compared to basic Co(OH)2 (e.g. 113.5 C/g vs. 59.2 C/g at 1 A/g). Additionally, the protective layer formed by the ionic liquid stabilizes the electrode material upon cycling in KOH aqueous electrolyte and protects the material from oxidation upon open-air storage.

Ionothermal Synthesis of Polyanionic Electrode Material Na3V2(PO4)2FO2 through a Topotactic Reaction

“…However, being sensitive to air moisture and because sulfate precursors decompose at high temperature, conventional synthesis methods are not well adapted, contrary to the ionothermal synthesis approach for which the IL medium prevents air exposure. , Moreover, the nature of the anionic part and the length of the alkyl chain on the cationic counterpart of the ionic liquid used in the ionothermal synthesis can significantly influence the morphology of the as-obtained products . A surface functionalization involving the grafting of ionic liquid molecules onto a material’s surface can also occur during the synthesis step, which can later protect the electrode materials from moisture oxidation and enhance their electrochemical performance upon cycling by improving their ionic transport properties. − …”

“…Then, the presence of a conductive ionic liquid on the surface of NVPFO 2 , as highlighted by IR, could also improve the sodium diffusion at high cycling rates. Indeed, better diffusion kinetics upon cycling has already been observed for Co­(OH) 2 used as positive electrode for hybrid supercapacitors when its surface was functionalized by ILs. , …”

“…Indeed, better diffusion kinetics upon cycling has already been observed for Co(OH) 2 used as positive electrode for hybrid supercapacitors when its surface was functionalized by ILs. 36,39…”

“…32 A surface functionalization involving the grafting of ionic liquid molecules on the materials'surface can also occur during the synthesis step, which can later protect the electrode materials from moisture oxidation, and enhance their electrochemical performance upon cycling by improving their ionic transport properties. [36][37][38][39] In this work, we will investigate the possible use of the ionothermal approach to synthesize the polyanionic compound Na 3 V 2 (PO 4 ) 2 FO 2 (NVPFO 2 ) with an original morphology. The influence of this peculiar morphology on the electrochemical performance of the as-obtained material will also be studied in detail.…”

Controlled Nanostructuration of Cobalt Oxyhydroxide Electrode Material for Hybrid Supercapacitors

“…In addition to the fact that ILs allow controlling the nanoparticles morphology and aggregation, they can also functionalize nanoparticle surfaces during synthesis, and thus, modify or bring new properties [ 31 , 32 , 33 ]. This surface modification is reported to be beneficial for electrode materials due to a synergetic effect between highly ionic conductive IL and inorganic materials that permits easier hydrogen adsorption/desorption processes and enhances transport properties [ 32 , 34 , 35 , 36 ]. However, the influence of the chemical nature of ionic liquids is poorly studied and remains unclear.…”