Preparation of the electrochemically formed spinel-lithium manganese oxides

Abstract

Electrochemically formed spinel-lithium manganese oxides were synthesized from manganese hydroxides prepared by a cathodic electrochemical precipitation from various concentrations of manganese nitrate solutions. Two types of manganese hydroxides were formed from diluted and concentrated Mn(NO 3) 2 aqueous solutions. Uniform and equi-sized disk shaped Mn(OH) 2 crystals of 0.2–5 μm in diameter were obtained on a Pt substrate after the electrochemical precipitation from lower concentration of ranging from 2 mmol dm −3 to 2 mol dm −3 Mn(NO 3) 2 aq., while the grass blade-like precipitate which is ascribed to manganese hydroxide with 20–80 μm long and 1–5 μm wide were formed from concentrated Mn(NO 3) 2 aq. Both manganese hydroxides gave the electrochemically formed spinel-LiMn 2O 4 onto a Pt sheet, which is ready for electrochemical measurement, after calcination of the Li incorporated precipitate at 750 °C without any additives. While the shape and size of the secondary particle frameworks (aggregates) of the electrochemically formed spinel-LiMn 2O 4 can be controlled by the electrolysis conditions, the nanostructured primary crystals of 200 nm in diameter were obtained in all cases except that the fiber-like nanostructured spinel-LiMn 2O 4 crystals with 200 nm in diameter were obtained from concentrated Mn(NO 3) 2 aq. Though these two types of electrochemically formed spinel-LiMn 2O 4 showed well-shaped CVs even in higher scan rates, it would be suitable for high power density battery applications. These behaviors are assumed to be ascribed to the crystal size and shape of the processed spinel-LiMn 2O 4.