Overlooked impact of precursor mixing: Implications in the electrochemical performance of battery electrode materials

Abstract

Solid-state reactions are an essential part of the synthesis of various cathode materials for lithium-ion batteries (LIBs). Despite the simplicity and effectiveness for mass production, a subtle variation in synthesis conditions can often give rise to unexpectedly different physical properties, significantly affecting the electrochemical performance of electrode materials. However, this aspect has long been overlooked in the LIB community, which should focus on advancement in understanding the influence of synthesis conditions. As solid-state reactions occur only at the interface of precursor materials, maximizing the interfacial contact area between mixed precursor powders is crucial. Mechanical milling and/or mixing are common practices that have been performed in both academia and industry for this purpose. Unlike the common belief that this pre-treatment before calcination would be of great benefit for the preparation of high-performance LIB materials, we revealed in this work that this practice is not always successful for this goal. In our case study of the preparation of LiCoO2, we demonstrated that mechanical mixing—a routinely implemented process for homogeneous mixing of precursors—can be harmful if it is performed without assuring optimal working conditions for mixing. The underlying reasons for this surprising result are elucidated in this work, and we hope that this new insight can help avoid the potential pitfall of routine implementations performed for LIB materials.