A review on preparing new energy ultrafine powder materials by freeze-drying

Efficient utilization of new energy is important way to reduce carbon emission and achieve sustainable development. High-quality new energy ultrafine powder materials (NEUPMs) play a significant role in improving energy efficiency due to their large specific surface area and high reactivity. Therefore, preparation of NEUPMs has become a key issue. Among numerous preparation methods, freeze-drying is one of the most promising techniques as it can produce ultrafine powders with uniform particle size. Although freeze-drying exhibits many advantages, the control of particle size and homogeneity of powders has not attracted adequate attention of researchers. Therefore, the objective of this paper is to provide a review illustrating the importance of particle size control and its implementation methods from the aspects of the principle, influencing factors, theoretical models, and applications. First, the principle and process of preparing NEUPMs by freeze-drying are analyzed. Then, the factors that influence particle size and homogeneity of powders such as freezing conditions, solution concentration and heat treatment conditions are discussed. Next, the mathematical models of freeze-drying process are summarized. Meanwhile, the application of NEUPMs prepared by freeze-drying in new energy field is discussed. Finally, this review provides some suggestions for further study of the mechanisms involved in freeze-drying.