Application of Layered High Entropy Oxides as Cathode Materials for Li/Na-ion Batteries

With the increasing fossil energy consumptions and environmental concerns, new sustainable energy sources and new energy storage fields are playing increasingly important roles in modern society. A series of energy storage devices such as lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs) have received global attentions from researchers and urgent demands for social developments. In LIBs/SIBs, the cathode material as the main component is critical factor affecting the property of full cells presently. As one of the earliest systems, layered oxide cathode materials have good commercial prospects until to now, therefore, a lot of strategies, such as new materials developing, elemental doping and surface coating, etc., have been explored to improve the electrochemical performance of them. To develop novel electrode materials and inspired by the design concept of high entropy alloys (HEAs), high entropy oxides (HEOs) as a new class of material were developed in recent years and studied as an anode material for LIBs starting in 2018. It shows unexpected reversibility compared to other non-high entropy compositions due to the unique entropy stability property. Subsequently, increasing number of researches have been reported on the use of high entropy materials in energy storage devices. The virtually infinite variety of multi-elemental compositions for a single-phase structure allows the tailoring of their physical properties and enables unprecedented materials design. A series of HEOs were prepared by nebulized spray pyrolysis (NSP) and solid-state reaction in this work. In order to explore the use of HEOs in LIBs/SIBs, the terms of materials design, synthesis method, crystal structure evolutions accompanied with charge compensation and electrochemical performance of HEOs are studied. The transfer of the high entropy concept to electrode materials may provide new strategies and technologies for material design and the preparation of novel compounds with unprecedented properties. Based on these results, it can be expected that the high entropy strategy can open new insights into electronic and structural chemistry for advanced electrode materials