Modification Strategy for Mn-based Layered Transition Metal Oxide as Sodium-ion Battery Cathodes

Abstract

Sodium-ion batteries (SIBs) are being touted as the future of energy storage. However, the lackluster performance of current cathode technology is a major roadblock to their widespread use. Among the promising candidates for cathodes, layered sodium manganese oxide stands out due to its low cost and higher energy density. However, its cycling performance is limited due to structural and surface instabilities. To overcome these challenges, researchers are exploring various strategies, such as doping, coating, and heterostructure design, to enhance the performance of manganese-based oxide. Doping involves introducing foreign atoms to enhance structural stability and electrochemical performance. Coating is a surface protection method, while heterostructure design involves developing a composite material composed of different crystal phases of sodium manganese oxide to leverage the intrinsic advantage of each phase. By analyzing the latest research, a novel coating approach of utilizing functionalized polymer (polyamic acid) as an encapsulation layer for P2-Na0.7MnO2 cathode is demonstrated. The polymer is equipped with abundant functional groups such as hydroxyl, carboxyl, amide, fluoromethyl, and aromatic, that endow a high oxidative stability and high toughness, thereby mitigating structural transition and electrolyte decomposition. Additionally, a high percentage of polar groups enable ionic conduction of Na+ through the polymer coating, as well as reducing active material dissolution through a chelation mechanism. Hence, the encapsulated cathode exhibits significant improvement in its cycling performance, maintaining stable discharge capacity for 500 cycles at 1000 mA g-1.