Promising Nanometric Spinel Cobalt Oxides for Electrochemical Energy Storage: Investigation of Li and H Environments by NMR

Abstract

Spinel-type cobalt oxides with formula H x Li y Co 3−δ O 4 exhibit interesting properties for various electrochemical energy storage applications thanks to their attractive electronic properties, due to the presence of H and Li ions in their structure as well as their nanometric dimensions. The effect of temperature on the H and Li environments is studied by investigating materials heat-treated at temperatures ranging from 25 to 650 °C by means of NMR spectroscopy. Two types of proton are evidenced: one bonded to oxygen atoms belonging to the network (hydroxyl group) and the other one involved in the H 2 O molecule. This configuration is in agreement with IR spectroscopy measurements, revealing the absence of free −OH groups, which mean that protons in the structure are involved in hydrogen bonds. After heat treatments at increasing temperature, NMR confirms that hydrogen is released, which induces first the migration of Li ions beyond 200 °C (probably from the 8a to the 16c sites), followed by a progressive reorganization of the structure with formation of HT-LiCoO 2 beyond 400 °C.

Effect of Temperature on Structure and Electronic Properties of Nanometric Spinel-Type Cobalt Oxides

“…The initial nano-Co 3 O 4 powder was subjected to heat treatments, under air, at temperatures ranging from 100 to 650 °C (100, 150, 200, 250, 300, 400, and 650 °C). These temperatures were determined on the basis of the X-ray diffraction in situ analysis, taking into account that thermal analysis shows a continuous loss of water from room temperature and a decomposition of Co 3 O 4 into CoO after 650 °C, as evidenced elsewhere . The temperature was increased at the rate of 2 °C/min up to the target temperature, held for a 4 h isothermal stage and then decreased down to room temperature at 2 °C/min.…”

Ionic liquids to monitor the nano-structuration and the surface functionalization of material electrodes: a proof of concept applied to cobalt oxyhydroxide

“…[9][10][11] Several metal oxides/(oxy)hydroxides such as RuO 2 , MnO 2 , Co(OH) 2 , Ni(OH) 2 , Co 3 O 4 , HCoO 2 , and NiCoO 2 have been widely investigated and show promising features. [12][13][14][15][16][17][18][19][20][21] However, for all of them, nano-structuration to optimize the electrode-electrolyte interface and a conductive scaffold to improve their electronic conductivity are crucial for maximizing their performances. [22][23][24] Among all these electrode materials, non-stoichiometric layered cobalt oxyhydroxide (HCoO 2 ) offers a two dimensional structure suitable for fast ionic diffusion as well as a good intrinsic electronic conductivity due the high oxidation state of cobalt, which favors electron transportation.…”

High power density aqueous hybrid supercapacitor combining activated carbon and highly conductive spinel cobalt oxide

“…These phases, which were synthesized by oxidizing precipitation of cobalt nitrate in a basic medium (T < 90 C), exhibit a modified spinel -Co 3 O 4 type structure, with protons, lithium and cobalt vacancies, as well as Co 4þ ions in the octahedral trivalent cobalt network [4e6]. Such octahedral tetravalent cobalt ions entail electronic delocalization and very good electronic conductivity properties (5 Â 10 À4 S cm À1 , against 10 À6 S cm À1 for ideal Co 3 O 4 ), which can still be improved by a controlled thermal treatment at a moderate temperature (200 C), while keeping particle size and specific surface area (200 m 2 g À1 ) suitable for electrochemical cycling [5,6].…”