Unlocking Few‐Layered Ternary Chalcogenides for High‐Performance Potassium‐Ion Storage

Potassium‐ion batteries (KIBs) have attracted increasing attention for grid‐scale energy storage due to the abundance of potassium resources, low cost, and competitive energy density. The key challenge for KIBs is to develop high‐performance electrode materials. However, the exploration of high‐capacity and ultrastable electrodes for KIBs remains challenging because of the sluggish diffusion kinetics of K+ ions during the charging/discharging processes. This study reports for the first time a facile ion‐intercalation‐mediated exfoliation method with Mg2+ cations and NO3– anions as ion assistants for the fabrication of expanded few‐layered ternary Ta2NiSe5 (EF‐TNS) flakes with interlayer spacing up to 1.1 nm and abundant Se sites (NiSe4 tetrahedra/TaSe6 octahedra clusters) for superior potassium‐ion storage. The EF‐TNS deliver a high capacity of 315 mAh g–1, excellent rate capability (121 mAh g–1 at a current density of 1000 mA g–1), and ultrastable cycling performance (81.4% capacity retention after 1100 cycles). Detailed theoretical analysis via first‐principles calculations and experimental results elucidate that K+ ions intercalate through the expanded interlayers effectively and prefer to transport along zigzag pathways in layered Ta2NiSe5. This work provides a new avenue for designing novel ternary intercalation/pseudocapacitance‐type KIBs with high capacity, excellent rate capability, and superior long‐term cycling performance.