Towards rechargeable Na-SexSy batteries: From fundamental insights to improvement strategies

Advanced Na-SexSy batteries provide a good chance to take full advantage of rich Na resources in the earth's crust as well as to combine the high capacity of S with the high electronic conductivity of Se, which are expected to become a new high-energy density electrochemical energy storage system. Herein, we offer a comprehensive review of recent advances in advanced Na-SexSy battery system with a focus on fundamental insights into its chemistry, materials design, and potential improvement strategies. Firstly, the electrochemical mechanisms of Na-SexSy batteries are presented to deepen the understanding of electrochemical principle. Then, the main challenges facing such a new system are summarized, encompassing low reactivity of SexSy with a low Se ratio, shuttle effect of intermediates, large volumetric variation, and sodium dendritic growth., Next, we discuss the design strategies of cathode materials for Na-SexSy batteries in detail, involving their synthesis, properties, interactions, and electrochemical performance. More critically, some promising solutions to cope with existing issues of Na-SexSy batteries are discussed. At last, the prospective of the Na-SexSy batteries is evaluated with an aim of guiding future developmental directions.