Rheological phase reaction synthesis of lithium intercalation materials for rechargeable battery

Abstract

Over the past 10 years, there has been a growing interest in rechargeable lithium-ion batteries. The choice of the cathode materials for application are normally LiCoO2 [1], LiNiO2 [2] and LiMn2O4 [3]. The layered oxide LiCoO2 and LiNiO2, when used as cathodes show high specific energy but require a complex and expensive synthesis process. The spinel has been extensively studied due to the low cost and being environmentally benign. However, it has the disadvantage of poor structural instability as a result of the JahnTeller effect caused by Mn3+, which can be suppressed by doping with other ions such as partial replacement of Li by Mn in Li1+x Mn2−x O4. These cathode materials are usually prepared by solid-state reaction consisting of mechanical mixing and extensive heating at high temperature. The prepared powder always shows inhomogeneity of composition, strongly agglomerated state and large grain size, which reduces the capacity and cyclability of the materials. To obtain better electrochemical characteristics, many solgel and related processes have been developed to obtain the lithium intercalation oxides [4–6]. These processes have showed the feasibility for preparing these materials. But they are a little complex and usually expensive, which is not beneficial to large industry producing. In this work, a rheological phase reaction method has been introduced to synthesis the cathode materials of LiCoO2, LiNiO2 and LiMn2O4. The rheological phase reaction method is a process of preparing compounds or materials from solid-liquid rheological mixture. That is, the solid reactants are fully mixed in a proper molar ratio, made up by adding the required amount of water or other solvent to a solid-liquid rheological body in which the solid particles and liquid substance are uniformly distributed. Then after reaction under suitable conditions, the product is obtained. Under the solid-liquid rheological state, many substances have new reaction properties [7–9]. This synthesis method is inexpensive and simple. On the other hand, the resultant powders prepared by this method show perfect crystal structures and excellent electrochemical performance. In this paper, the synthesis of these three lithium intercalation oxides and further electrochemical property studies of the prepared LiMn2O4 powder are presented. The three oxides, LiCoO2, LiNiO2 and LiMn2O4 studied in this work were prepared using lithium nitrate LiNO3 and stoichiometric amounts of cobalt acetate