Evolution Mechanism of the Na[sub 0.6]CoO[sub 2] Conductive Additive during Cycling in the Alkaline Electrolyte of Ni–MH Batteries

Abstract

The stability of the normalNa0.6ConormalO2 phase, as intended to be used as a conductive additive at the positive electrode of Ni–MH batteries, was tested in electrochemical cycling conditions, in KOH alkaline electrolyte. Simple aging of normalNa0.6ConormalO2 in the electrolyte entails its spontaneous transformation into a mixture of γ and β(III) cobalt oxyhydroxides. This reaction, occurring within the solid state, is based on an original mechanism, which involves cationic exchange processes and passes through an intermediate interstratified phase. Electrochemical oxidation of normalNa0.6ConormalO2 in the alkaline electrolyte, as well as chemical oxidation, leads to a γ cobalt oxyhydroxide, which can be totally reduced to β(III) , depending on the reduction conditions. It is important to understand such an evolution mechanism of the normalNa0.6ConormalO2 additive because it will have a significant and positive influence on the electrochemical cycling of the positive electrode in specific deep discharge or low potential storage conditions.

Synthesis and Electrochemical Study of New P3 Type Layered Na0.6Ni0.25Mn0.5Co0.25O2 for Sodium‐Ion Batteries

“…The lattice parameter ratio value of a mon / b mon represents the presence of monoclinic distortion. Here, the ratio is 1.732 which represents negligible distortion with the rhombohedral symmetry of present composition as mentioned for previous materials by Delmas group ,. The crystallographic parameters are showed in Table .…”

Nickel-Doped Sodium Cobaltite 2D Nanomaterials: Synthesis and Electrocatalytic Properties

“…Especially, the two-layer form of Na x CoO 2 has been of significant recent interest, as it displays a variety of functional properties, including superconductivity (T C = 4.5 K) in the hydrated phase (x = 0.3), 9 as well as thermoelectric energy conversion with a large thermopower (100 µV/K at 300 K for γ-Na 0.5 CoO 2 ). 10 The three-layer β-Na 0.6 CoO 2 phase has also been scrutinized, especially as conductive additive for nickel-metal hydride batteries 11 with improved cycling stability.…”

Nickel hydroxide electrodes as amperometric detectors for carbohydrates in flow injection analysis and liquid chromatography

“…Nickel hydroxide has been the subject of intense studies, mainly concerning its application in secondary batteries [18][19][20][21]. This material also shows electrochromic properties changing its color from transparent (reduced state) to deep brown (oxidized state, NiOOH) [22,23].…”