Towards high-performance cathodes: Concentration gradient structure design for lithium-ion batteries and sodium-ion batteries

Abstract

The concentration gradient structure design shows great potential in addressing the durability and structural integrity issues of cathode materials during Li/Na ions insertion and extraction. Despite notable advancement has been made in its application for Lithium-ion batteries (LIBs) and Sodium-ion batteries (SIBs), the gradient structure design is still in its early stage of development. This review comprehensively summarizes the latest advances in concentration gradient cathode materials for LIBs and SIBs, focusing on the latest research findings in design concepts, synthetic strategies, structural features, characterization techniques and electrochemical properties. It places special emphasis on how the concentration gradient effectively mitigates structural degradation, optimizes stress dissipation, and improves sluggish electrical and ionic conductivity, all of which ultimately boost the specific discharge capacity, rate performance, and cyclic stability. Additionally, the concentration gradient cathode materials are systematically categorized and discussed as phosphate-based materials, layered transition metal oxides, and Prussian blue analogues, with an in-depth discussion of their application in both LIBs and SIBs. Finally, the review delves into the persistent challenges and outlines prospective avenues for future research concerning concentration gradient cathode materials.