Combined intercalation and space-charge mechanism enabled high-capacity, ultrafast and long-lifespan sodium-ion storage for chalcogenide anodes†

The increasing demand for advanced battery redox chemistry, surpassing intercalation, conversion, and alloying processes, is pivotal in driving the rapid progress of next-generation rechargeable batteries. Herein, we discover a new ionic storage mechanism combining intercalation and space-charging chemistry in the transition metal dichalcogenides (TMDs) of group IV and V elements (specifically Ti, Nb, and Ta). Taking NbS₂ as an example, a new ternary intercalation compound Cu_0.43DME_0.12NbS₂ is spontaneously formed through a Cu⁺–ether co-intercalation process with Cu current collectors in ether-based electrolytes. Subsequently, Na⁺ ions can reversibly (de)intercalate into Cu_0.43DME_0.12NbS₂ with limited volume expansion, and Na⁺ can adsorb on the surface of in situ electrochemically-induced Cu nanoparticles with fast kinetics and extra storage. Such synergistic processes enable a high specific capacity of 705 mA h g⁻¹, surpassing its theoretical limit, a superior rate capability of 116 mA h g⁻¹ at 75 A g⁻¹, and an impressive cycle longevity of over 1 year. Combined with Na₃V₂(PO₄)₃ (NVP), the full cell demonstrates an exceptional power density of 17 453 W kg⁻¹. The study paves the way for designing functional electrode materials for high-power and long-lifespan batteries.