Reactive-sputtered W–W2N thin films delivering superior cycle stability for energy storage applications

초록

In this work, biphasic W–W2N thin films were synthesized via reactive magnetron sputtering with controlled nitrogen incorporation for hybrid supercapattery applications. Structural and chemical analyses confirmed the coexistence of metallic W, cubic W2N, and a surface oxidative WOₓ layer. The optimized WN-20 sample delivered a high areal capacitance of 44.09 mF cm−2 at 0.5 mA cm−2, along with excellent cycling stability of 97.54% after 8000 cycles. An asymmetric device assembled using the optimized electrode achieved a maximum energy density of 66 Wh kg−1 at a power density of 415 W/kg. Electrochemical analysis revealed a hybrid charge storage mechanism, with b-values in the range of 0.5–0.8 and a transition from diffusion-controlled to capacitive behavior at higher scan rates. The enhanced performance is attributed to the synergistic interaction between metallic W (improved electrical conductivity), W2N (structural and redox-active framework), and the surface WOₓ layer (additional pseudocapacitive contribution), enabling improved charge transfer and ion transport kinetics. These findings highlight the potential of engineered biphasic transition metal nitride thin films for high-performance hybrid energy storage systems.

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