Molten-chlorides assisted rapid preparation and crystallinity-irrelevant properties of nanostructured LiCoO2 as lithium-ion battery cathodes

Abstract

In this paper, the 850 °C molten-chlorides (NaCl-KCl, eutectic point ∼657 °C) assisted reaction of Co3O4 (melting point ∼895 °C) with LiOH⋅H2O (melting point ∼462 °C) is adopted for the precursor shape-replicated construction of nanostructured LiCoO2, focusing on the rapid formation mechanism and crystallization-irrelevant properties of phase-pure LiCoO2 for Li-ion battery (LIB) cathodes. Temperature−/time-dependent crystallization shows that, after the heterogeneous nucleation of LiCoO2 at 660 °C, the complete consumption of Co3O4 occurs at 850 °C within 10 min and the building block of each of the finally resulting 850 °C/8-h LiCoO2 microspheres has been endowed with a (003)-manifest crystal plane. By comparison, it is due to the complete consumption of Li-insulating Co3O4, not to the increase of LiCoO2 crystallinity, that explains the high electrochemical properties of these phase-pure samples. Especially, cycling stabilities of the 850 °C/10-min and 850 °C/8-h LiCoO2 are close to each other, but each of them is much better than those of the chlorides-absent counterparts obtained at the node of 850 °C/8-h. These, together with the approximate rate capabilities of these chlorides-present LiCoO2, implies an applicable approach of the molten-salt method to the rapid construction of nanostructured LiCoO2 for high-performance LIB cathodes.