Universal Design Strategy for air-Stable Layered Na-ion Cathodes towards Sustainable Energy Storage.

Na-ion batteries (NIBs) are considered to be sustainable alternatives to the current Li-ion technologies for energy storage systems, and even for electric vehicles, due to the abundant and widely distributed resources. However, the most promising cathode materials of NIBs so far, i.e., O3 layered oxides, are still suffering from serious air instability issue, which not only significantly increases the manufactural cost because of the long-term use of dry rooms in mass production, but also leads to a massive upsurge in energy consumption as well as greenhouse gas emissions, going against the sustainable objective of NIBs. While some feasible strategies have been proposed via case studies, there lacks fundamental understandings in the correlations between air stability and materials' composition, therefore universal design strategies are yet to be established. Herein, we investigate the air degradation origins and mechanisms of O3 cathodes in-depth via combined first-principles and experimental approaches, and propose the Bond Dissociation Energy as an effective descriptor for predicting the air stability. We then validated experimentally in various unary, binary, and ternary O3 cathodes that the air stability can indeed be effectively improved via simple compositional design. Guided by the predictive model, the designed material can be stored in air for over 30 days without structural or electrochemical degradation, therefore confirming the accuracy and universality of our theory. Moreover, based on real-world data, it is calculated that such air-stable cathodes can significantly facilitate reductions in both energy consumption (∼ 4,100,000 kWh) and carbon footprint (∼ 2,200-ton CO 2 ) annually for a 2 GWh Na-ion batteries manufactory. Therefore, the fundamental understandings and universal design strategy presented in this work open up an avenue for rational materials design of NIBs towards both elemental and manufactural sustainability. This article is protected by copyright. All rights reserved.